Comparison of Intraocular Pressure Measured by Goldman Applanation Tonometer, Noncontact Tonometer and Trans-palpebral Tonometer

Comparison of Intraocular Pressure Measured by Goldman Applanation Tonometer, Noncontact Tonometer and Trans-palpebral Tonometer | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Comparison of Intraocular Pressure Measured by Goldman Applanation Tonometer, Noncontact Tonometer and Trans-palpebral Tonometer Madhu Thapa, Dr Pragati Gautam Gautam, Dr Saroj GC, Gautam Kumar This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-8612933/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 17 Apr, 2026 Read the published version in BMC Ophthalmology → Version 1 posted 16 You are reading this latest preprint version Abstract Background: To evaluate reliability and agreement of non-contact tonometry (NCT) and trans-palpebral tonometry (TPT) compared with Goldmann-applanation tonometry (GAT). Methods: A total of 224 eyes from 112 patients were included between January and April 2025. Intraocular pressure (IOP) was measured using GAT, NCT, and TPT. Comparison among the three measurement groups were performed using the related-samples Friedman test. Post hoc pairwise comparisons were conducted using the Wilcoxon signed-rank test with Bonferroni correction. Reliability was assessed using Cronbach’s alpha and the intraclass correlation coefficient (ICC). Agreement between methods was evaluated using Bland–Altman plots and Spearman’s rank-order correlation. Results: Median IOP were 14 mmHg for GAT, 14 mmHg for NCT and 15 mmHg for TPT. Friedman's ANOVA showed statistically significant difference among three methods (χ² = 40.652, p < 0.001). TPT readings were significantly different from both GAT and NCT (p < 0.001), the difference between GAT and NCT was not significant (p = 0.024).Cronbach’s alpha was 0.691, indicating acceptable internal consistency. The ICC for average IOP was 0.668 (95% CI: 0.571–0.743, p < 0.001), suggesting moderate- reliability. Spearman’s correlation showed moderate-agreement between GAT and NCT (ρ = 0.586, p < 0.001), weak-agreement between TPT and NCT (ρ = 0.315, p < 0.001), and no correlation between GAT and TPT (ρ = 0.090, p = 0.177). Bland-Altman analysis confirmed good-agreement between GAT and NCT, fair-agreement between NCT and TPT, and poor-agreement between GAT and TPT. Conclusions: GAT and NCT demonstrated moderate agreement, while TPT showed limited agreement with both NCT and GAT. Goldman tonometry Intra ocular pressure Non-contact tonometry Trans-palpebral tonometry Figures Figure 1 Figure 2 Figure 3 Background Glaucoma is a major global cause of blindness with approximately 7.7 million people are either visually impaired or blind due to glaucoma.1 Its projected prevalence is 111.8 million by the year 2040.2 Elevated IOP is the only modifiable risk factor for glaucoma.3 Therefore; accurate IOP measurement is critical for glaucoma diagnosis and monitoring. Post-operative IOP monitoring after glaucoma surgery is essential to assess the success of the surgery.4,5 Goldman applanation tonometry (GAT) is considered as gold standard for IOP measurement.6 The working principle of GAT is based on the Imbert–Fick law, P = F/A, i.e pressure within the thin-walled sphere (P) is equal to the force (F) required to flatten the surface of the sphere divided by the area (A) of the force applied.6,7 It requires touching the cornea with an applanation bi-prism, requiring anesthetizing cornea before procedure. This contact procedure allows the risk of transferring the diseases and is an uncomfortable procedure. Non-contact pnuemotonometer (NCT) uses air to flatten the cornea. The sensor detects the force required to indent the cornea and records the IOP accordingly.6 This is non-contact procedure. literatures have shown a good agreement in IOP reading by GAT and non-contact tonometer.8,9 However, many studies have shown that IOP recorded by NTC is higher than GAT, and this disagreement is more pronounced as the IOP is higher. 10 Trans-palpebral tonometry (TPT) is a technique to measure IOP over the eyelid, minimising the risk of disease transfer and discomfort. Its principle is based on determining the acceleration of a freely falling rod as it rebounds against the tarsal plate of the eyelid through the sclera.6 As per some literatures, IOP measured by this technique is more accurate in patients with thinner corneas after refractive surgery.11 The device is cost-effective, handy, easy to use and non-contact, which makes it an ideal instrument for community screening. Moreover, it can be used for self-measurement of IOP at home.12 Patients who have corneal opacity or scars, this technique can be utilized.13 This study aims to evaluate the reliability and agreement between these 3 methods of IOP measurement. Methods Subjects This is a hospital-based analytical cross-sectional study conducted at the Department of Ophthalmology, B.P. Koirala Lions Centre for Ophthalmic Studies, Maharajgunj Medical Campus, Institute of Medicine, from January to April 2025. Research approval (Ref. no : 363( 6 – 11 ) E2) was obtained from the Institutional Review Committee (IRC) of the Institute of Medicine in accordance with the Declaration of Helsinki. A convenience sampling method was used. 224 eyes of 112 patients over 18 years were included in the study. Patients with glaucoma, any active intraocular or extraocular inflammations and patients with corneal opacity or scar, where applanation was not possible, were excluded. IOP measurements were done using the Eyetone Trans-palpebral digital tonometer. non-contact Pneumotonomter (Pulsair, Keeler) and Goldman applanation tonometer (Haag Streit). NCT and TPT were done by a single trained technical staff, whereas GAT was done by a single Ophthalmologist. NCT was done at first, followed by TPT and GAT was done at the end to avoid any IOP changes that can occur after applanation. IOP were measured three times by each method and an average value was recorded. Statistical analysis Data analysis was performed using SPSS (version 26.0, IBM Corp., Armonk, NY). Descriptive statistics for continuous variables were expressed as mean ± standard deviation (SD) for normally distributed data and median with interquartile range (IQR) for non-normally distributed data. Categorical variables were presented as frequencies and percentages. The normality of the data distributions for CCT, IOP measurements obtained by the GAT, NCT, and TPT was evaluated using the Kolmogorov-Smirnov test. To compare the IOP measurements across the three tonometry methods, the Related-Samples Friedman's Two-Way ANOVA by Ranks was employed due to the non-normal distribution of the data. Post-hoc pairwise comparisons were performed using the Wilcoxon Signed-Rank Test with Bonferroni correction to adjust for multiple testing. The reliability of IOP measurements across the three tonometry methods was evaluated using Cronbach's Alpha and the Intraclass Correlation Coefficient (ICC) (single measures and average measures). The strength and direction of the association between IOP measurements from different tonometers were analysed using Spearman's rank-order correlation. Additionally, correlation analysis was extended to explore the relationship between IOP measurements and CCT. The agreement between the tonometry methods was further assessed using Bland-Altman analysis, which included evaluation of the mean difference (bias) and the 95% limits of agreement (LoA). For non-normally distributed differences, a percentile-based Bland-Altman approach was applied, reporting the median difference and the 2.5th and 97.5th percentile limits of agreement. To assess the impact of CCT on IOP measurements, subgroup analyses were conducted using Spearman's rank-order correlation across three CCT ranges: ≤ 499 µm, 500–529 µm, and ≥ 530 µm. All statistical tests were two-tailed, and a p-value of < 0.05 was considered statistically significant unless otherwise specified. Results 112 participants were included in the study, comprising 43 males (38.39%) and 69 females (61.61%). The participants' ages ranged from 19 to 77 years, with a median age of 44.50 years (Q1: 32.00, Q3: 58.00). IOP measurements obtained by GAT, NCT, and TPT were non-normally distributed (p < 0.001), whereas CCT showed a normal distribution (p = 0.200). The median IOP values for GAT, NCT, and TPT, along with the mean CCT as shown in Table 1. Table 1. Descriptive statistics for IOP measurements and CCT (n= 224) Parameter Median (Q1 – Q3, IOP, non-normal) Mean (CCT, normal) IOP by Goldmann Applanation 14.00 (12.00 – 16.00) mmHg — IOP by Non-contact Tonometer 14.00 (12.00 – 16.00) mmHg — IOP by Trans-palpebral Tonometer 15.00 (14.00 – 16.67) mmHg — Central Corneal Thickness — 536.59 µm Comparative analysis of IOP measurements A Related-Samples Friedman's Two-Way ANOVA by Ranks showed a statistically significant difference in IOP measurements across GAT, NCT, and TPT (χ² = 40.652, df = 2, p < 0.001). Pairwise comparisons using the Wilcoxon Signed-Rank Test with Bonferroni correction revealed that TPT recorded significantly different IOP values compared to both GAT and NCT (adjusted p < 0.001). At the same time, the difference between GAT and NCT was not statistically significant (adjusted p = 0.024) as shown in Table 2. Table 2. Wilcoxon Signed-Rank test for pairwise comparison of IOP measurements Comparison Z-value p-value Adjusted p-value Goldmann vs. Non-contact -2.665 0.008 0.024 Goldmann vs. Trans-palpebral -5.825 <0.001 <0.001 Non-contact vs. Trans-palpebral -5.051 <0.001 <0.001 Reliability analysis To assess the reliability of the tonometry measurements, Cronbach's Alpha and Intra Class Correlation Coefficients (ICC) were calculated. Cronbach's Alpha for the three tonometry methods was 0.691, indicating acceptable internal consistency. The Single Measures ICC of 0.401 (95% CI: 0.307–0.491, p < 0.001) reflects moderate reliability for individual tonometry readings. The Average Measures ICC of 0.668 (95% CI: 0.571–0.743, p < 0.001) indicates good reliability when the average of multiple measurements is considered. Correlation analysis To evaluate the agreement between the three tonometry methods, Spearman's rank-order correlation was performed. Results demonstrated that while GAT and NCT show a moderate level of agreement (ρ = 0.586, p < 0.001). TPT does not correlate well with GAT (ρ = 0.090, p = 0.177) and only weakly with NCT (ρ = 0.315, p < 0.001) as shown in Table 3. Table 3. Spearman's correlation analysis showing strength and direction of the association between IOP measurements from different tonometers Comparison Spearman's ρ p-value Interpretation Goldmann vs. Non-contact 0.586 <0.001 Moderate Correlation Goldmann vs. Trans-palpebral 0.09 0.177 Very Weak Correlation Non-contact vs. Trans-palpebral 0.315 <0.001 Weak Correlation Bland-Altman analysis and limits of agreement (LoA) for the pairwise comparison Of the three intraocular pressure (IOP) measurement differences, only the difference between GAT and TPT was normally distributed (p = 0.200), while the differences between GAT and NCT, and NCT and TPT, were non-normally distributed (both p < 0.001). The mean difference (bias) between GAT and TPT was -1.44 mmHg, with 95% limits of agreement ranging from -8.05 to +5.16 mmHg. The differences were normally distributed (p = 0.200). TPT slightly overestimated IOP compared to GAT on average as shown in Figure 1. The median difference between NCT and TPT was –1.00 mmHg, with 2.5th and 97.5th percentile limits of agreement at –5.79 and +5.12 mmHg, respectively. Differences were non-normally distributed (p < 0.001) as shown in Figure 2. The median difference between GAT and NCT was 0.00 mmHg, with 2.5th and 97.5th percentile limits of agreement at -6.38 and +4.00 mmHg. The differences were non-normally distributed (p < 0.001), with notable variability across measurements as shown in Figure 3. Comparing the GAT with TPT measurement showed the weakest agreement, with a mean bias of -1.44mm Hg, with much wider limits of agreement. GAT underestimated the IOP measurement than TPT. NCT showed good agreement with GAT, with a mean bias close to 0 mmHg, with a limit of agreement narrower. NCT showed a fair agreement with TPT, with a negative bias of 1 mmHg; the limit of agreement was also narrower. Overall, NTC has an agreement with both TPT and GAT, but the bias is less with GAT. TPT showed a poor agreement with GAT, with outliers at higher IOP. Correlation analysis with central corneal thickness Spearman’s rank correlation analysis revealed a statistically significant but weak positive correlation between CCT and IOP measurements obtained using GAT (r = 0.175, p = 0.009) and NCT (r = 0.164, p = 0.014), but did not correlate with TPT. Correlation analysis of IOP measurements within CCT groups Subgroup analysis was conducted to examine the relationship between intraocular pressure (IOP) measurements obtained by different tonometry methods within three CCT categories: ≤ 499 µm, 500–549 µm, and ≥ 500 µm. In the ≤ 499 µm group, a strong positive and significant correlation was observed between GAT and NCT only (r = 0.714, p = 0.006). In the 500–549 µm group, a moderate positive correlation was found between GAT and NCT (r = 0.602, p < 0.001), and a weak but significant correlation between NCT and TPT (r = 0.308, p < 0.001). In the ≥ 550 µm group, GAT and NCT again showed a moderate correlation (r = 0.508, p < 0.001), and TPT demonstrated weak but significant correlations with both GAT (r = 0.299, p = 0.011) and NCT (r = 0.356, p = 0.002) as shown in Table 4. Table 4 Spearman’s rank correlation coefficients and significance levels for intraocular pressure measurements across different Central Corneal CCT Group Tonometry Comparison Correlation Coefficient (r) p-value Interpretation ≤ 499 µm GAT vs. NCT 0.714 0.006 Strong Positive (Significant) GAT vs. TPT –0.400 0.176 Moderate Negative (Non-significant) NCT vs. TPT 0.18 0.555 Very Weak (Non-significant) 500–549 µm GAT vs. NCT 0.602 < 0.001 Moderate Positive (Significant) GAT vs. TPT 0.058 0.493 Very Weak (Non-significant) NCT vs. TPT 0.308 < 0.001 Weak Positive (Significant) ≥ 550 µm GAT vs. NCT 0.508 < 0.001 Moderate Positive (Significant) GAT vs. TPT 0.299 0.011 Weak Positive (Significant) NCT vs. TPT 0.356 0.002 Moderate Positive (Significant) Discussion GAT, gold standard technique, remains the widely used tonometry for IOP measurements due to its low intraobserver and interobserver variability and ease of use.14 GAT is difficult to perform on uncooperative patients, patients with corneal pathologies and children.15,16 TPT measures the IOP by assessing the indentation caused by a certain weight falling over the lids.10 Moreover is not influenced by corneal pathologies and is easy to perform.17 It also offers a non-invasive alternative suitable for home monitoring.18 NCT is also a method with a non-touch technique and no risk of transfer of infection. It utilises the pressurised pulse of air to applanate the cornea. NCT is influenced by central corneal thickness like GAT.19 In this study, the median IOP values measured by GAT and NCT were equal, while TPT recorded slightly higher. There were statistically significant differences in IOP measurements across GAT, NCT, and TPT. TPT recorded significantly different IOP values compared to both GAT and NCT (adjusted p < 0.001). The difference between GAT and NCT was not statistically significant (adjusted p = 0.024) as reported by Gupta et al, as well as by Nadeem at all.15,9 Similarly, other studies have shown that TPT measurement was slightly higher than GAT.14,20 NCT has also been shown to record IOP higher than GAT.8 However, contrary to our findings, some reports have shown lower IOP measurement by TPT as compared to GAT as well.21 Such conflicting results discrepancies may be attributed to variations in study populations, corneal biomechanics, measurement protocols, and device calibration. Reliability analysis The internal consistency among the three tonometry methods, as assessed by Cronbach’s Alpha, was 0.691, indicating questionable reliability. ICC showed a moderate correlation of 0.401 (95% CI: 0.307–0.491, p < 0.001) for single measurements and showed a good reliability, ICC of 0.668 (95% CI: 0.571–0.743, p < 0.001) when the average of all measurements is considered, as shown by Maheshwari et al.22 Similarly, Waisbourd et al and Sander et al have shown good reliability between TPT and GAT (ICC 0.8620).23,20 Correlation analysis A moderate positive correlation between the GAT and the NCT (ρ = 0.586, p < 0.001) was seen, whereas there was a weak positive correlation between the NCT and the TPT (ρ = 0.315, p < 0.001). Likewise, a very weak and non-significant correlation between the GAT and the TPT (ρ = 0.090, p = 0.177).9 Maheshwari et al. have also shown a good correlation between GAT and NCT.23 However, some authors did not find a significant correlation between TPT and GAT.13 Bland-Altman analysis The GAT vs NCT comparison demonstrated the best agreement, with a mean bias close to 0 mmHg and a limits of agreement range of approximately − 6.375 to + 4.0 mmHg. Nadeem et al. also found good reliability of GAT with NCT. 9 In contrast, GAT vs TPT exhibited the weakest agreement, with a mean bias of − 1.444 mmHg and a much wider limits of agreement (− 8.053 to + 5.165 mmHg), indicating significant variability and underestimation by GAT relative to TPT. Waisbourd et al have also showed that showed that TPT has overestimated IOP with fair agreement between GAT and TPT23 where whereas some other reports13 have shown a poor agreement between GAT and TPT, similar to our finding. The NCT vs TPT comparison showed a similar negative bias (− 1.0 mmHg), but with a slightly narrower agreement range (− 5.793 to + 5.123 mmHg), suggesting moderate agreement. Overall, NCT aligns more closely with both GAT and TPT than GAT does with TPT, making NCT a potentially more reliable alternative in settings where GAT is unavailable. Gupta et al have also shown the good agreement between NCT and GAT.15 However, none of the methods are interchangeable, especially in cases where accurate IOP measurements are required, as in the case of glaucoma. Correlation with CCT IOP measurement is correlated with CCT.19,24 Spearman’s rank correlation analysis revealed a statistically significant but weak positive correlation between CCT and IOP measurements obtained using GAT and NCT, while TPT showed no significant correlation with CCT. GAT and NCT demonstrated significant correlations across all CCT groups, with a stronger correlation observed in thin corneas. In contrast, GAT and TPT, as well as NCT and TPT, showed no correlation in thinner corneas but weak correlations in corneas with greater thickness. Some other reports have shown good correlation of CCT with GAT as well as TPT.22 However, Kyie et al have shown weak correlation of CCT with NCT but no correlation with GAT.19 Similarly, some literatures have shown that GAT has a significant correlation with corneal resistance and corneal hysteresis.25 Corneal thickness has not shown any correlation with age and refractive status.24 Toker el reported that TPT also has a moderate correlation with CCT.26 This study also has some limitations. This study used a convenience sampling method, which may introduce selection bias, limiting the generalizability of the findings to the broader population. The study was conducted in a single tertiary care centre, which may not reflect variations in patient demographics or clinical practices in other settings. Additionally, the exclusion of patients with glaucoma and corneal abnormalities limits the applicability of results to these important clinical groups. Lastly, the cross-sectional design restricts the ability to assess changes in IOP measurements over time or under different physiological conditions. Conclusions TPT recorded significantly different IOPs than GAT and NCT. GAT and NCT showed a moderate agreement where whereas TPT showed a weak correlation with NCT and no correlation with GAT. All three methods can be used for a screening, but when an accurate measurement of IOP is required, GAT should be preferred. CCT showed to have a weak correlation with GAT and NCT, but no correlation with TPT. Abbreviations IOP: Intraocular pressure GAT: Goldmann applanation tonometry NCT: Non contact tonometry TPT: Transpalpebral tonometry CCT: central corneal thickness Declarations Ethical approval Was obtained from the ethics committee of Institutional Review Committee of Institute of Medicine , Tribhuvan University , Kathmandu, Nepal with the Reference number of 363(6-11) E2. Human ethics/ Consent to Participate: The authors certify that INFORMED CONSENT were obtained from all the patients who participated in the study. Consent for publication: This is not applicable here. Data availability: The data used to support the findings of this study are available from the corresponding author upon a request. Acknowledgements: Not applicable. Competing interests: There is not competing interest in publication of this research. Funding: There is not funding received for this study. 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Cite Share Download PDF Status: Published Journal Publication published 17 Apr, 2026 Read the published version in BMC Ophthalmology → Version 1 posted Editorial decision: Revision requested 05 Mar, 2026 Reviews received at journal 03 Mar, 2026 Reviews received at journal 25 Feb, 2026 Reviews received at journal 22 Feb, 2026 Reviewers agreed at journal 21 Feb, 2026 Reviews received at journal 20 Feb, 2026 Reviewers agreed at journal 20 Feb, 2026 Reviewers agreed at journal 18 Feb, 2026 Reviews received at journal 18 Feb, 2026 Reviewers agreed at journal 13 Feb, 2026 Reviewers agreed at journal 13 Feb, 2026 Reviewers invited by journal 13 Feb, 2026 Editor invited by journal 23 Jan, 2026 Editor assigned by journal 22 Jan, 2026 Submission checks completed at journal 22 Jan, 2026 First submitted to journal 15 Jan, 2026 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-8612933","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":593570557,"identity":"7913e125-8fe7-4106-832a-2aff7b57667a","order_by":0,"name":"Madhu Thapa","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA70lEQVRIiWNgGAWjYDCCA0DM28DAYADifABiNnYitUiAtDDOAGlhJkULMw9IhJAWvtunEz+83XG4zpz97MHPNr+2yfMxMzB++JiDW4vkudzNknPPHJaw7MlLls7tu23YxszALDlzG24tBmd4N0jzth2WMDiQYyCd23ObEaiFjZkXv5bNv8Fazr8x/m3Zc9ueGC3bILbcyDGTZvhxO5GgFkmgFsu5bemSG268S7Psbbid3MbM2IzXL3xAh91422bNb3A+9/CNH39u285vbz744SMeLUgAGCmMbSAGYwNR6iFaGP4Qq3gUjIJRMApGEgAARJVVUBRmxlIAAAAASUVORK5CYII=","orcid":"","institution":"Tribhuvan University","correspondingAuthor":true,"prefix":"","firstName":"Madhu","middleName":"","lastName":"Thapa","suffix":""},{"id":593570559,"identity":"f8ad64d0-af46-4f97-8d7e-7f9992ccfaea","order_by":1,"name":"Dr Pragati Gautam Gautam","email":"","orcid":"","institution":"Tribhuvan University","correspondingAuthor":false,"prefix":"Dr","firstName":"Pragati","middleName":"Gautam","lastName":"Gautam","suffix":""},{"id":593570563,"identity":"0671ec5f-80b5-4130-96ad-0ba82c4df717","order_by":2,"name":"Dr Saroj GC","email":"","orcid":"","institution":"Kakani health care center","correspondingAuthor":false,"prefix":"Dr","firstName":"Saroj","middleName":"","lastName":"GC","suffix":""},{"id":593570569,"identity":"21c2e2fe-461d-4d8c-98b6-82b94ad2dfe4","order_by":3,"name":"Gautam Kumar","email":"","orcid":"","institution":"Tribhuvan University","correspondingAuthor":false,"prefix":"","firstName":"Gautam","middleName":"","lastName":"Kumar","suffix":""}],"badges":[],"createdAt":"2026-01-15 18:08:37","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-8612933/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-8612933/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1186/s12886-026-04821-w","type":"published","date":"2026-04-17T15:57:11+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":103165098,"identity":"e30c8a1f-d94a-4c74-a076-892b541211ea","added_by":"auto","created_at":"2026-02-22 12:25:00","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":75106,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eBland-Altman plot comparing intraocular pressure measurements between Goldmann Applanation Tonometry and Transpalpebral Tonometry.\u003c/strong\u003eThe blue line represents the mean difference in IOP between the two methods (-1.44mm Hg), the red lines indicate the 95% limits of agreement (-8.05 to 5.17 mmHg)\u003c/p\u003e","description":"","filename":"floatimage1.png","url":"https://assets-eu.researchsquare.com/files/rs-8612933/v1/8fd2fb814419e413240aee9a.png"},{"id":103165176,"identity":"e9be580e-ac4a-4ae3-aeee-31c2b905817f","added_by":"auto","created_at":"2026-02-22 12:25:05","extension":"jpeg","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":126756,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003ePercentile-based Bland-Altman plot comparing IOP measurements between Non-Contact Tonometry and Transpalpebral Tonometry.\u003c/strong\u003e The mean difference in IOP was -1.0mm Hg, with 95% limits of agreement from -5.79 to 5.12 mm Hg.\u003c/p\u003e","description":"","filename":"floatimage2.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-8612933/v1/a079118e50e97a260b11ae8b.jpeg"},{"id":103165105,"identity":"9ee9ff4d-cf72-4112-8a7f-200453cfc9d6","added_by":"auto","created_at":"2026-02-22 12:25:01","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":62219,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003ePercentile-based Bland-Altman plot comparing IOP measurements between Goldmann Applanation Tonometry and Non-Contact Tonometry.\u003c/strong\u003eThe mean difference in IOP was 0.0 mmHg, with 95% limits of agreement from -6.8 to 6.38 mm Hg.\u003c/p\u003e","description":"","filename":"floatimage3.png","url":"https://assets-eu.researchsquare.com/files/rs-8612933/v1/70894a732e3c8cd1cc5dfe26.png"},{"id":107350710,"identity":"6b19adde-d262-41b5-ad8b-6f481bfcbd3c","added_by":"auto","created_at":"2026-04-20 16:00:53","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":899841,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-8612933/v1/de0baea9-3434-4603-8345-62099e8531b2.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Comparison of Intraocular Pressure Measured by Goldman Applanation Tonometer, Noncontact Tonometer and Trans-palpebral Tonometer","fulltext":[{"header":"Background","content":"\u003cp\u003eGlaucoma is a major global cause of blindness with approximately 7.7\u0026nbsp;million people are either visually impaired or blind due to glaucoma.1 Its projected prevalence is 111.8\u0026nbsp;million by the year 2040.2 Elevated IOP is the only modifiable risk factor for glaucoma.3 Therefore; accurate IOP measurement is critical for glaucoma diagnosis and monitoring. Post-operative IOP monitoring after glaucoma surgery is essential to assess the success of the surgery.4,5\u003c/p\u003e \u003cp\u003eGoldman applanation tonometry (GAT) is considered as gold standard for IOP measurement.6 The working principle of GAT is based on the Imbert\u0026ndash;Fick law, P\u0026thinsp;=\u0026thinsp;F/A, i.e pressure within the thin-walled sphere (P) is equal to the force (F) required to flatten the surface of the sphere divided by the area (A) of the force applied.6,7 It requires touching the cornea with an applanation bi-prism, requiring anesthetizing cornea before procedure. This contact procedure allows the risk of transferring the diseases and is an uncomfortable procedure.\u003c/p\u003e \u003cp\u003eNon-contact pnuemotonometer (NCT) uses air to flatten the cornea. The sensor detects the force required to indent the cornea and records the IOP accordingly.6 This is non-contact procedure. literatures have shown a good agreement in IOP reading by GAT and non-contact tonometer.8,9 However, many studies have shown that IOP recorded by NTC is higher than GAT, and this disagreement is more pronounced as the IOP is higher. 10\u003c/p\u003e \u003cp\u003eTrans-palpebral tonometry (TPT) is a technique to measure IOP over the eyelid, minimising the risk of disease transfer and discomfort. Its principle is based on determining the acceleration of a freely falling rod as it rebounds against the tarsal plate of the eyelid through the sclera.6 As per some literatures, IOP measured by this technique is more accurate in patients with thinner corneas after refractive surgery.11 The device is cost-effective, handy, easy to use and non-contact, which makes it an ideal instrument for community screening. Moreover, it can be used for self-measurement of IOP at home.12 Patients who have corneal opacity or scars, this technique can be utilized.13\u003c/p\u003e \u003cp\u003eThis study aims to evaluate the reliability and agreement between these 3 methods of IOP measurement.\u003c/p\u003e"},{"header":"Methods","content":"\u003cp\u003eSubjects\u003c/p\u003e \u003cp\u003eThis is a hospital-based analytical cross-sectional study conducted at the Department of Ophthalmology, B.P. Koirala Lions Centre for Ophthalmic Studies, Maharajgunj Medical Campus, Institute of Medicine, from January to April 2025. Research approval (Ref. no : 363(\u003cspan additionalcitationids=\"CR7 CR8 CR9 CR10\" citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e) E2) was obtained from the Institutional Review Committee (IRC) of the Institute of Medicine in accordance with the Declaration of Helsinki. A convenience sampling method was used. 224 eyes of 112 patients over 18 years were included in the study. Patients with glaucoma, any active intraocular or extraocular inflammations and patients with corneal opacity or scar, where applanation was not possible, were excluded.\u003c/p\u003e \u003cp\u003eIOP measurements were done using the Eyetone Trans-palpebral digital tonometer. non-contact Pneumotonomter (Pulsair, Keeler) and Goldman applanation tonometer (Haag Streit). NCT and TPT were done by a single trained technical staff, whereas GAT was done by a single Ophthalmologist. NCT was done at first, followed by TPT and GAT was done at the end to avoid any IOP changes that can occur after applanation. IOP were measured three times by each method and an average value was recorded.\u003c/p\u003e \u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003eStatistical analysis\u003c/h2\u003e \u003cp\u003eData analysis was performed using SPSS (version 26.0, IBM Corp., Armonk, NY). Descriptive statistics for continuous variables were expressed as mean\u0026thinsp;\u0026plusmn;\u0026thinsp;standard deviation (SD) for normally distributed data and median with interquartile range (IQR) for non-normally distributed data. Categorical variables were presented as frequencies and percentages. The normality of the data distributions for CCT, IOP measurements obtained by the GAT, NCT, and TPT was evaluated using the Kolmogorov-Smirnov test.\u003c/p\u003e \u003cp\u003eTo compare the IOP measurements across the three tonometry methods, the Related-Samples Friedman's Two-Way ANOVA by Ranks was employed due to the non-normal distribution of the data. Post-hoc pairwise comparisons were performed using the Wilcoxon Signed-Rank Test with Bonferroni correction to adjust for multiple testing. The reliability of IOP measurements across the three tonometry methods was evaluated using Cronbach's Alpha and the Intraclass Correlation Coefficient (ICC) (single measures and average measures). The strength and direction of the association between IOP measurements from different tonometers were analysed using Spearman's rank-order correlation. Additionally, correlation analysis was extended to explore the relationship between IOP measurements and CCT. The agreement between the tonometry methods was further assessed using Bland-Altman analysis, which included evaluation of the mean difference (bias) and the 95% limits of agreement (LoA). For non-normally distributed differences, a percentile-based Bland-Altman approach was applied, reporting the median difference and the 2.5th and 97.5th percentile limits of agreement. To assess the impact of CCT on IOP measurements, subgroup analyses were conducted using Spearman's rank-order correlation across three CCT ranges: \u0026le; 499 \u0026micro;m, 500\u0026ndash;529 \u0026micro;m, and \u0026ge;\u0026thinsp;530 \u0026micro;m.\u003c/p\u003e \u003cp\u003eAll statistical tests were two-tailed, and a p-value of \u0026lt;\u0026thinsp;0.05 was considered statistically significant unless otherwise specified.\u003c/p\u003e \u003c/div\u003e"},{"header":"Results","content":"\u003cp\u003e112 participants were included in the study, comprising 43 males (38.39%) and 69 females (61.61%). The participants\u0026apos; ages ranged from 19 to 77 years, with a median age of 44.50 years (Q1: 32.00, Q3: 58.00).\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eIOP measurements obtained by GAT, NCT, and TPT were non-normally distributed (p \u0026lt; 0.001), whereas CCT showed a normal distribution (p = 0.200). The median IOP values for GAT, NCT, and TPT, along with the mean CCT as shown in Table 1.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eTable 1. Descriptive statistics for IOP measurements and CCT (n= 224)\u003c/strong\u003e\u003c/p\u003e\n\u003ctable border=\"0\" cellspacing=\"0\" cellpadding=\"0\" align=\"left\" width=\"100%\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 37px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eParameter\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 38px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eMedian (Q1 \u0026ndash; Q3, IOP, non-normal)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 23px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eMean (CCT, normal)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 37px;\"\u003e\n \u003cp\u003eIOP by Goldmann Applanation\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 38px;\"\u003e\n \u003cp\u003e14.00 (12.00 \u0026ndash; 16.00) mmHg\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 23px;\"\u003e\n \u003cp\u003e\u0026mdash;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 37px;\"\u003e\n \u003cp\u003eIOP by Non-contact Tonometer\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 38px;\"\u003e\n \u003cp\u003e14.00 (12.00 \u0026ndash; 16.00) mmHg\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 23px;\"\u003e\n \u003cp\u003e\u0026mdash;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 37px;\"\u003e\n \u003cp\u003eIOP by Trans-palpebral Tonometer\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 38px;\"\u003e\n \u003cp\u003e15.00 (14.00 \u0026ndash; 16.67) mmHg\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 23px;\"\u003e\n \u003cp\u003e\u0026mdash;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 37px;\"\u003e\n \u003cp\u003eCentral Corneal Thickness\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 38px;\"\u003e\n \u003cp\u003e\u0026mdash;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 23px;\"\u003e\n \u003cp\u003e536.59 \u0026micro;m\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003e\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eComparative analysis of IOP measurements\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eA Related-Samples Friedman\u0026apos;s Two-Way ANOVA by Ranks showed a statistically significant difference in IOP measurements across GAT, NCT, and TPT (\u0026chi;\u0026sup2; = 40.652, df = 2, p \u0026lt; 0.001). Pairwise comparisons using the Wilcoxon Signed-Rank Test with Bonferroni correction revealed that TPT recorded significantly different IOP values compared to both GAT and NCT (adjusted p \u0026lt; 0.001). At the same time, the difference between GAT and NCT was not statistically significant (adjusted p = 0.024) as shown in Table 2.\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eTable 2. Wilcoxon Signed-Rank test for pairwise comparison of IOP measurements\u003c/strong\u003e\u003c/p\u003e\n\u003ctable border=\"0\" cellspacing=\"0\" cellpadding=\"0\" width=\"539\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 254px;\"\u003e\n \u003cp\u003e\u003cem\u003eComparison\u003c/em\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 72px;\"\u003e\n \u003cp\u003e\u003cem\u003eZ-value\u003c/em\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 72px;\"\u003e\n \u003cp\u003e\u003cem\u003ep-value\u003c/em\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 141px;\"\u003e\n \u003cp\u003e\u003cem\u003eAdjusted p-value\u003c/em\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 254px;\"\u003e\n \u003cp\u003eGoldmann vs. Non-contact\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 72px;\"\u003e\n \u003cp\u003e-2.665\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 72px;\"\u003e\n \u003cp\u003e0.008\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 141px;\"\u003e\n \u003cp\u003e0.024\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 254px;\"\u003e\n \u003cp\u003eGoldmann vs. Trans-palpebral\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 72px;\"\u003e\n \u003cp\u003e-5.825\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 72px;\"\u003e\n \u003cp\u003e\u0026lt;0.001\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 141px;\"\u003e\n \u003cp\u003e\u0026lt;0.001\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 254px;\"\u003e\n \u003cp\u003eNon-contact vs. Trans-palpebral\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 72px;\"\u003e\n \u003cp\u003e-5.051\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 72px;\"\u003e\n \u003cp\u003e\u0026lt;0.001\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 141px;\"\u003e\n \u003cp\u003e\u0026lt;0.001\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003e\u003cstrong\u003eReliability analysis\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eTo assess the reliability of the tonometry measurements, Cronbach\u0026apos;s Alpha and Intra Class Correlation Coefficients (ICC) were calculated. Cronbach\u0026apos;s Alpha for the three tonometry methods was 0.691, indicating acceptable internal consistency. The Single Measures ICC of 0.401 (95% CI: 0.307\u0026ndash;0.491, p \u0026lt; 0.001) reflects moderate reliability for individual tonometry readings. The Average Measures ICC of 0.668 (95% CI: 0.571\u0026ndash;0.743, p \u0026lt; 0.001) indicates good reliability when the average of multiple measurements is considered.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCorrelation analysis\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eTo evaluate the agreement between the three tonometry methods, Spearman\u0026apos;s rank-order correlation was performed. Results demonstrated that while GAT and NCT show a moderate level of agreement (\u0026rho; = 0.586, p \u0026lt; 0.001). TPT does not correlate well with GAT (\u0026rho; = 0.090, p = 0.177) and only weakly with NCT (\u0026rho; = 0.315, p \u0026lt; 0.001) as shown in Table 3.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eTable 3. Spearman\u0026apos;s correlation analysis showing strength and direction of the association between IOP measurements from different tonometers\u003c/strong\u003e\u003c/p\u003e\n\u003ctable border=\"0\" cellspacing=\"0\" cellpadding=\"0\" width=\"100%\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 39px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eComparison\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 18px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eSpearman\u0026apos;s \u0026rho;\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 14px;\"\u003e\n \u003cp\u003e\u003cstrong\u003ep-value\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 27px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eInterpretation\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 39px;\"\u003e\n \u003cp\u003eGoldmann vs. Non-contact\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 18px;\"\u003e\n \u003cp\u003e0.586\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 14px;\"\u003e\n \u003cp\u003e\u0026lt;0.001\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 27px;\"\u003e\n \u003cp\u003eModerate Correlation\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 39px;\"\u003e\n \u003cp\u003eGoldmann vs. Trans-palpebral\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 18px;\"\u003e\n \u003cp\u003e0.09\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 14px;\"\u003e\n \u003cp\u003e0.177\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 27px;\"\u003e\n \u003cp\u003eVery Weak Correlation\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 39px;\"\u003e\n \u003cp\u003eNon-contact vs. Trans-palpebral\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 18px;\"\u003e\n \u003cp\u003e0.315\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 14px;\"\u003e\n \u003cp\u003e\u0026lt;0.001\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 27px;\"\u003e\n \u003cp\u003eWeak Correlation\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003e\u003cstrong\u003eBland-Altman analysis and limits of agreement (LoA) for the pairwise comparison\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eOf the three intraocular pressure (IOP) measurement differences, only the difference between GAT and TPT was normally distributed (p = 0.200), while the differences between GAT and NCT, and NCT and TPT, were non-normally distributed (both p \u0026lt; 0.001).\u003c/p\u003e\n\u003cp\u003eThe mean difference (bias) between GAT and TPT was -1.44 mmHg, with 95% limits of agreement ranging from -8.05 to +5.16 mmHg. The differences were normally distributed (p = 0.200). TPT slightly overestimated IOP compared to GAT on average as shown in Figure 1.\u003c/p\u003e\n\u003cp\u003eThe median difference between NCT and TPT was \u0026ndash;1.00 mmHg, with 2.5th and 97.5th percentile limits of agreement at \u0026ndash;5.79 and +5.12 mmHg, respectively. Differences were non-normally distributed (p \u0026lt; 0.001) as shown in Figure 2.\u003c/p\u003e\n\u003cp\u003eThe median difference between GAT and NCT was 0.00 mmHg, with 2.5th and 97.5th percentile limits of agreement at -6.38 and +4.00 mmHg. The differences were non-normally distributed (p \u0026lt; 0.001), with notable variability across measurements as shown in Figure 3.\u003c/p\u003e\n\u003cp\u003eComparing the GAT with TPT measurement showed the weakest agreement, with a mean bias of -1.44mm Hg, with much wider limits of agreement. GAT underestimated the IOP measurement than TPT. NCT showed good agreement with GAT, with a mean bias close to 0 mmHg, with a limit of agreement narrower. NCT showed a fair agreement with TPT, with a negative bias of 1 mmHg; the limit of agreement was also narrower. Overall, NTC has an agreement with both TPT and GAT, but the bias is less with GAT. TPT showed a poor agreement with GAT, with outliers at higher IOP.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCorrelation analysis with central corneal thickness\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eSpearman\u0026rsquo;s rank correlation analysis revealed a statistically significant but weak positive correlation between CCT and IOP measurements obtained using GAT (r = 0.175, p = 0.009) and NCT (r = 0.164, p = 0.014), but did not correlate with TPT.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCorrelation analysis of IOP measurements within CCT groups\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eSubgroup analysis was conducted to examine the relationship between intraocular pressure (IOP) measurements obtained by different tonometry methods within three CCT categories: \u0026le; 499 \u0026micro;m, 500\u0026ndash;549 \u0026micro;m, and \u0026ge; 500 \u0026micro;m. In the \u0026le; 499 \u0026micro;m group, a strong positive and significant correlation was observed between GAT and NCT only (r = 0.714, p = 0.006). In the 500\u0026ndash;549 \u0026micro;m group, a moderate positive correlation was found between GAT and NCT (r = 0.602, p \u0026lt; 0.001), and a weak but significant correlation between NCT and TPT (r = 0.308, p \u0026lt; 0.001). In the \u0026ge; 550 \u0026micro;m group, GAT and NCT again showed a moderate correlation (r = 0.508, p \u0026lt; 0.001), and TPT demonstrated weak but significant correlations with both GAT (r = 0.299, p = 0.011) and NCT (r = 0.356, p = 0.002) as shown in Table 4.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eTable 4 Spearman\u0026rsquo;s rank correlation coefficients and significance levels for intraocular pressure measurements across different Central Corneal\u003c/strong\u003e\u003c/p\u003e\n\u003ctable border=\"1\" cellspacing=\"0\" cellpadding=\"0\" align=\"\" width=\"100%\" class=\"fr-table-selection-hover\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 12px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eCCT Group\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 22px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eTonometry Comparison\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 23px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eCorrelation Coefficient (r)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 10px;\"\u003e\n \u003cp\u003e\u003cstrong\u003ep-value\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 30px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eInterpretation\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd rowspan=\"3\" valign=\"top\" style=\"width: 12px;\"\u003e\n \u003cp\u003e\u0026le; 499 \u0026micro;m\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 22px;\"\u003e\n \u003cp\u003eGAT vs. NCT\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 23px;\"\u003e\n \u003cp\u003e0.714\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 10px;\"\u003e\n \u003cp\u003e0.006\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 30px;\"\u003e\n \u003cp\u003eStrong Positive (Significant)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 22px;\"\u003e\n \u003cp\u003eGAT vs. TPT\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 23px;\"\u003e\n \u003cp\u003e\u0026ndash;0.400\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 10px;\"\u003e\n \u003cp\u003e0.176\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 30px;\"\u003e\n \u003cp\u003eModerate Negative (Non-significant)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 22px;\"\u003e\n \u003cp\u003eNCT vs. TPT\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 23px;\"\u003e\n \u003cp\u003e0.18\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 10px;\"\u003e\n \u003cp\u003e0.555\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 30px;\"\u003e\n \u003cp\u003eVery Weak (Non-significant)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd rowspan=\"3\" valign=\"top\" style=\"width: 12px;\"\u003e\n \u003cp\u003e500\u0026ndash;549 \u0026micro;m\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 22px;\"\u003e\n \u003cp\u003eGAT vs. NCT\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 23px;\"\u003e\n \u003cp\u003e0.602\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 10px;\"\u003e\n \u003cp\u003e\u0026lt; 0.001\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 30px;\"\u003e\n \u003cp\u003eModerate Positive (Significant)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 22px;\"\u003e\n \u003cp\u003eGAT vs. TPT\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 23px;\"\u003e\n \u003cp\u003e0.058\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 10px;\"\u003e\n \u003cp\u003e0.493\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 30px;\"\u003e\n \u003cp\u003eVery Weak (Non-significant)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 22px;\"\u003e\n \u003cp\u003eNCT vs. TPT\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 23px;\"\u003e\n \u003cp\u003e0.308\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 10px;\"\u003e\n \u003cp\u003e\u0026lt; 0.001\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 30px;\"\u003e\n \u003cp\u003eWeak Positive (Significant)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd rowspan=\"3\" valign=\"top\" style=\"width: 12px;\"\u003e\n \u003cp\u003e\u0026ge; 550 \u0026micro;m\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 22px;\"\u003e\n \u003cp\u003eGAT vs. NCT\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 23px;\"\u003e\n \u003cp\u003e0.508\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 10px;\"\u003e\n \u003cp\u003e\u0026lt; 0.001\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 30px;\"\u003e\n \u003cp\u003eModerate Positive (Significant)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 22px;\"\u003e\n \u003cp\u003eGAT vs. TPT\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 23px;\"\u003e\n \u003cp\u003e0.299\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 10px;\"\u003e\n \u003cp\u003e0.011\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 30px;\"\u003e\n \u003cp\u003eWeak Positive (Significant)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 22px;\"\u003e\n \u003cp\u003eNCT vs. TPT\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 23px;\"\u003e\n \u003cp\u003e0.356\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 10px;\"\u003e\n \u003cp\u003e0.002\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 30px;\"\u003e\n \u003cp\u003eModerate Positive (Significant)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003e\u003cbr\u003e\u003c/p\u003e"},{"header":"Discussion","content":"\u003cp\u003eGAT, gold standard technique, remains the widely used tonometry for IOP measurements due to its low intraobserver and interobserver variability and ease of use.14 GAT is difficult to perform on uncooperative patients, patients with corneal pathologies and children.15,16 TPT measures the IOP by assessing the indentation caused by a certain weight falling over the lids.10 Moreover is not influenced by corneal pathologies and is easy to perform.17 It also offers a non-invasive alternative suitable for home monitoring.18 NCT is also a method with a non-touch technique and no risk of transfer of infection. It utilises the pressurised pulse of air to applanate the cornea. NCT is influenced by central corneal thickness like GAT.19\u003c/p\u003e \u003cp\u003eIn this study, the median IOP values measured by GAT and NCT were equal, while TPT recorded slightly higher. There were statistically significant differences in IOP measurements across GAT, NCT, and TPT. TPT recorded significantly different IOP values compared to both GAT and NCT (adjusted p\u0026thinsp;\u0026lt;\u0026thinsp;0.001). The difference between GAT and NCT was not statistically significant (adjusted p\u0026thinsp;=\u0026thinsp;0.024) as reported by Gupta et al, as well as by Nadeem at all.15,9 Similarly, other studies have shown that TPT measurement was slightly higher than GAT.14,20 NCT has also been shown to record IOP higher than GAT.8 However, contrary to our findings, some reports have shown lower IOP measurement by TPT as compared to GAT as well.21 Such conflicting results discrepancies may be attributed to variations in study populations, corneal biomechanics, measurement protocols, and device calibration.\u003c/p\u003e \u003cdiv id=\"Sec12\" class=\"Section2\"\u003e \u003ch2\u003eReliability analysis\u003c/h2\u003e \u003cp\u003eThe internal consistency among the three tonometry methods, as assessed by Cronbach\u0026rsquo;s Alpha, was 0.691, indicating questionable reliability. ICC showed a moderate correlation of 0.401 (95% CI: 0.307\u0026ndash;0.491, p\u0026thinsp;\u0026lt;\u0026thinsp;0.001) for single measurements and showed a good reliability, ICC of 0.668 (95% CI: 0.571\u0026ndash;0.743, p\u0026thinsp;\u0026lt;\u0026thinsp;0.001) when the average of all measurements is considered, as shown by Maheshwari et al.22 Similarly, Waisbourd et al and Sander et al have shown good reliability between TPT and GAT (ICC 0.8620).23,20\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec13\" class=\"Section2\"\u003e \u003ch2\u003eCorrelation analysis\u003c/h2\u003e \u003cp\u003eA moderate positive correlation between the GAT and the NCT (ρ\u0026thinsp;=\u0026thinsp;0.586, p\u0026thinsp;\u0026lt;\u0026thinsp;0.001) was seen, whereas there was a weak positive correlation between the NCT and the TPT (ρ\u0026thinsp;=\u0026thinsp;0.315, p\u0026thinsp;\u0026lt;\u0026thinsp;0.001). Likewise, a very weak and non-significant correlation between the GAT and the TPT (ρ\u0026thinsp;=\u0026thinsp;0.090, p\u0026thinsp;=\u0026thinsp;0.177).9 Maheshwari et al. have also shown a good correlation between GAT and NCT.23 However, some authors did not find a significant correlation between TPT and GAT.13\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec14\" class=\"Section2\"\u003e \u003ch2\u003eBland-Altman analysis\u003c/h2\u003e \u003cp\u003eThe GAT vs NCT comparison demonstrated the best agreement, with a mean bias close to 0 mmHg and a limits of agreement range of approximately \u0026minus;\u0026thinsp;6.375 to +\u0026thinsp;4.0 mmHg. Nadeem et al. also found good reliability of GAT with NCT. 9 In contrast, GAT vs TPT exhibited the weakest agreement, with a mean bias of \u0026minus;\u0026thinsp;1.444 mmHg and a much wider limits of agreement (\u0026minus;\u0026thinsp;8.053 to +\u0026thinsp;5.165 mmHg), indicating significant variability and underestimation by GAT relative to TPT. Waisbourd et al have also showed that showed that TPT has overestimated IOP with fair agreement between GAT and TPT23 where whereas some other reports13 have shown a poor agreement between GAT and TPT, similar to our finding. The NCT vs TPT comparison showed a similar negative bias (\u0026minus;\u0026thinsp;1.0 mmHg), but with a slightly narrower agreement range (\u0026minus;\u0026thinsp;5.793 to +\u0026thinsp;5.123 mmHg), suggesting moderate agreement. Overall, NCT aligns more closely with both GAT and TPT than GAT does with TPT, making NCT a potentially more reliable alternative in settings where GAT is unavailable. Gupta et al have also shown the good agreement between NCT and GAT.15 However, none of the methods are interchangeable, especially in cases where accurate IOP measurements are required, as in the case of glaucoma.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec15\" class=\"Section2\"\u003e \u003ch2\u003eCorrelation with CCT\u003c/h2\u003e \u003cp\u003eIOP measurement is correlated with CCT.19,24 Spearman\u0026rsquo;s rank correlation analysis revealed a statistically significant but weak positive correlation between CCT and IOP measurements obtained using GAT and NCT, while TPT showed no significant correlation with CCT. GAT and NCT demonstrated significant correlations across all CCT groups, with a stronger correlation observed in thin corneas. In contrast, GAT and TPT, as well as NCT and TPT, showed no correlation in thinner corneas but weak correlations in corneas with greater thickness. Some other reports have shown good correlation of CCT with GAT as well as TPT.22 However, Kyie et al have shown weak correlation of CCT with NCT but no correlation with GAT.19 Similarly, some literatures have shown that GAT has a significant correlation with corneal resistance and corneal hysteresis.25 Corneal thickness has not shown any correlation with age and refractive status.24 Toker el reported that TPT also has a moderate correlation with CCT.26\u003c/p\u003e \u003cp\u003eThis study also has some limitations. This study used a convenience sampling method, which may introduce selection bias, limiting the generalizability of the findings to the broader population. The study was conducted in a single tertiary care centre, which may not reflect variations in patient demographics or clinical practices in other settings. Additionally, the exclusion of patients with glaucoma and corneal abnormalities limits the applicability of results to these important clinical groups. Lastly, the cross-sectional design restricts the ability to assess changes in IOP measurements over time or under different physiological conditions.\u003c/p\u003e \u003c/div\u003e"},{"header":"Conclusions","content":"\u003cp\u003eTPT recorded significantly different IOPs than GAT and NCT. GAT and NCT showed a moderate agreement where whereas TPT showed a weak correlation with NCT and no correlation with GAT. All three methods can be used for a screening, but when an accurate measurement of IOP is required, GAT should be preferred. CCT showed to have a weak correlation with GAT and NCT, but no correlation with TPT.\u003c/p\u003e"},{"header":"Abbreviations","content":"\u003cp\u003eIOP: Intraocular pressure\u003c/p\u003e\n\u003cp\u003eGAT: Goldmann applanation tonometry\u003c/p\u003e\n\u003cp\u003eNCT: Non contact tonometry\u003c/p\u003e\n\u003cp\u003eTPT: Transpalpebral tonometry\u003c/p\u003e\n\u003cp\u003eCCT: central corneal thickness\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eEthical approval\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eWas obtained from the ethics committee of \u003cstrong\u003eInstitutional Review Committee of Institute of Medicine\u003c/strong\u003e, \u003cstrong\u003eTribhuvan University\u003c/strong\u003e, Kathmandu, Nepal with the Reference number of 363(6-11) E2.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eHuman ethics/ Consent to Participate:\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors certify that INFORMED CONSENT were obtained from all the patients who participated in the study.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConsent for publication:\u0026nbsp;\u003c/strong\u003eThis is not applicable here.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eData availability:\u0026nbsp;\u003c/strong\u003eThe data used to support the findings of this study are available from the corresponding author upon a request.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAcknowledgements:\u0026nbsp;\u003c/strong\u003e Not applicable.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCompeting interests:\u0026nbsp;\u003c/strong\u003eThere is not competing interest in publication of this research.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding:\u0026nbsp;\u003c/strong\u003eThere is not funding received for this study.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthors\u0026apos; contributions:\u0026nbsp;\u003c/strong\u003eMT wrote the main manuscript, GK collected data and SGC did statistical analysis and prepared the figures and tables, MT and PGA reviewed the manuscript\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eWorld Health Organization. Vision impairment and blindness [Internet]. Geneva: WHO; 2023 [cited 2024 Dec 19]. Available from: https://www.who.int/news-room/fact-sheets/detail/blindness-and-visual-impairment\u003c/li\u003e\n\u003cli\u003eTham YC, Li X, Wong TY, Quigley HA, Aung T, Cheng CY. Global prevalence of glaucoma and projections of glaucoma burden through 2040: a systematic review and meta-analysis. Ophthalmology. 2014;121(11):2081\u0026ndash;90.\u003c/li\u003e\n\u003cli\u003eThe AGIS Investigators. The Advanced Glaucoma Intervention Study (AGIS): 7. The relationship between control of intraocular pressure and visual field deterioration. Am J Ophthalmol. 2000;130(4):429\u0026ndash;40.\u003c/li\u003e\n\u003cli\u003eAmerican Academy of Ophthalmology. Management of hypotony after glaucoma surgery [Internet]. San Francisco: AAO; 2021 [cited 2025 Jun 8]. Available from: https://www.aao.org/eyenet/article/management-of-hypotony-after-glaucoma-surgery\u003c/li\u003e\n\u003cli\u003eLiebmann JM, Ritch R, DiSclafani M, Stock L. Early intraocular pressure rise after trabeculectomy. Arch Ophthalmol. 1990;108(11):1549\u0026ndash;52.\u003c/li\u003e\n\u003cli\u003eBrusini P, Salvetat ML, Zeppieri M. How to measure intraocular pressure: an updated review of various tonometers. J Clin Med [Internet]. 2021;10(17):3860. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8456330/\u003c/li\u003e\n\u003cli\u003eScienceDirect Topics. Goldmann applanation tonometer [Internet]. Available from: https://www.sciencedirect.com/topics/nursing-and-health-professions/goldmann-applanation-tonometer\u003c/li\u003e\n\u003cli\u003eBasuony R, Orouk W, Soliman T, Attia T. Comparison of intraocular pressure (IOP) measured by non-contact (air-puff) tonometer compared with Goldmann applanation tonometer. Benha Med J [Internet]. 2021. Available from: https://bmfj.journals.ekb.eg/article_191408.html\u003c/li\u003e\n\u003cli\u003eNadeem S, Naeem B ud din, Tahira R, Khalid S, Pak A. Comparison of Goldmann applanation, Diaton transpalpebral and air puff tonometers. Pak J Ophthalmol. 2015;31:1\u0026ndash;6.\u003c/li\u003e\n\u003cli\u003eSharma H, Nainiwal SK, Sarraf A, Porwal R, Sharma V. Intraocular pressure measurement techniques: current concepts and a review. Indian J Clin Exp Ophthalmol [Internet]. 2020;6(3):315\u0026ndash;23. Available from: https://www.ijceo.org/article-details/12296\u003c/li\u003e\n\u003cli\u003eAlzuhairy S. Transpalpebral intraocular pressure measurement by Diaton compared to Goldmann applanation tonometer in myopic eyes before and after transepithelial photorefractive keratectomy in Saudi Arabia. Int J Ophthalmol [Internet]. 2023;16(3):375\u0026ndash;81. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC10009589/\u003c/li\u003e\n\u003cli\u003eKobashi H. Evaluation of a new transpalpebral tonometer for self-measuring intraocular pressure. PLOS One [Internet]. 2024;19(5):e0302568. Available from: https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0302568\u003c/li\u003e\n\u003cli\u003eL\u0026ouml;sch A, Scheuerle A, Rupp V, Auffarth G, Becker M. Transpalpebral measurement of intraocular pressure using the TGDc-01 tonometer versus standard Goldmann applanation tonometry. Graefes Arch Clin Exp Ophthalmol. 2005;243(4):313\u0026ndash;6.\u003c/li\u003e\n\u003cli\u003eYildiz MB, Kose AO, Celik G, Kizilay O, Imamoglu S, Yildiz E. Agreement among Goldmann applanation tonometer, Easyton transpalpebral tonometer, Tono-Pen, and iCare in patients with keratoconus. Beyoglu Eye J [Internet]. 2023;8(3):170\u0026ndash;6. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC10521132/\u003c/li\u003e\n\u003cli\u003eGupta V, Sony P, Agarwal HC, Sihota R, Sharma A. Inter-instrument agreement and influence of central corneal thickness on measurements with Goldmann, pneumotonometer and noncontact tonometer in glaucomatous eyes. Indian J Ophthalmol [Internet]. 2006;54(4):261\u0026ndash;5. Available from: https://journals.lww.com/ijo/fulltext/2006/54040/Inter_instrument_agreement_and_influence_of.8.aspx\u003c/li\u003e\n\u003cli\u003eBhan A, Browning AC, Shah S, Hamilton R, Dave D, Dua HS. Effect of corneal thickness on intraocular pressure measurements with the pneumotonometer, Goldmann applanation tonometer, and Tono-Pen. Invest Ophthalmol Vis Sci. 2002;43(5):1389\u0026ndash;92.\u003c/li\u003e\n\u003cli\u003eJerrome S, Joseph S, Niranjana B, Vidya S, Kumaragurupari T, Balagiri S, et al. Evaluation of the agreement and reliability of transpalpebral tonometers compared with Goldmann applanation tonometer: a systematic review and meta-analysis protocol. Indian J Ophthalmol [Internet]. 2023 ;71(5):2225\u0026ndash;9. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC10391437/\u003c/li\u003e\n\u003cli\u003eChakraborty AK, Majumder M, Sen S. Comparison of transpalpebral tonometer with Goldmann applanation tonometer. Taiwan J Ophthalmol [Internet]. 2014 [cited 2025 Jun 5];4(3):110\u0026ndash;5. Available from: https://www.sciencedirect.com/science/article/pii/S2211505614000234\u003c/li\u003e\n\u003cli\u003eKyei S, Assiamah F, Kwarteng MA, Gboglu CP. The association of central corneal thickness and intraocular pressure measures by non-contact tonometry and Goldmann applanation tonometry among glaucoma patients. Ethiop J Health Sci [Internet]. 2020;30(6). Available from: https://www.ajol.info/index.php/ejhs/article/view/201972\u003c/li\u003e\n\u003cli\u003eSandner D, B\u0026ouml;hm A, Kostov S, Pillunat L. Measurement of the intraocular pressure with the transpalpebral tonometer TGDc-01 in comparison with applanation tonometry. Graefes Arch Clin Exp Ophthalmol. 2005;243(6):563\u0026ndash;9.\u003c/li\u003e\n\u003cli\u003eLi Y, Shi J, Duan X, Fan F. Transpalpebral measurement of intraocular pressure using the Diaton tonometer versus standard Goldmann applanation tonometry. Graefes Arch Clin Exp Ophthalmol. 2010;248(12):1765\u0026ndash;70.\u003c/li\u003e\n\u003cli\u003eMaheshwari D, Drishti C, Rajagopal S, Pillai MR, Ramakrishnan R. Intervariability in IOP measurement by using GAT, rebound tonometer and NCT in glaucoma patients. TNOA J Ophthalmic Sci Res [Internet]. 2023;61(2):177\u0026ndash;82. Available from: https://journals.lww.com/tnoa/fulltext/2023/61020/intervariability_in_iop_measurement_by_using_gat,.7.aspx\u003c/li\u003e\n\u003cli\u003eWaisbourd M, Shemesh G, Top LB, Lazar M, Loewenstein A. Comparison of the transpalpebral tonometer TGDc-01 with Goldmann applanation tonometry. Eur J Ophthalmol. 2010;20(5):902\u0026ndash;6.\u003c/li\u003e\n\u003cli\u003eLle\u0026oacute; A, Marcos A, Calatayud M, Alonso L, Ranhal SM, Sanchis-Gimeno JA. The relationship between central corneal thickness and Goldmann applanation tonometry. Clin Exp Optom [Internet]. 2003;86(2):104\u0026ndash;8. Available from: https://onlinelibrary.wiley.com/doi/abs/10.1111/j.1444-0938.2003.tb03068.x\u003c/li\u003e\n\u003cli\u003eBilge\u0026ccedil; MD, Atalay E, S\u0026ouml;zer \u0026Ouml;, G\u0026uuml;rsoy H, Bilgin M, Yıldırım N. The influence of corneal geometrical and biomechanical properties on tonometry readings in keratoconic eyes. Int Ophthalmol [Internet]. 2020;40(4):849\u0026ndash;57. Available from: https://doi.org/10.1007/s10792-019-01248-9\u003c/li\u003e\n\u003cli\u003eToker MI, Vural A, Erdogan H, Topalkara A, Arici MK. Central corneal thickness and Diaton transpalpebral tonometry. Graefes Arch Clin Exp Ophthalmol. 2008;246(6):881\u0026ndash;9.\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"bmc-ophthalmology","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"boph","sideBox":"Learn more about [BMC Ophthalmology](http://bmcophthalmol.biomedcentral.com/)","snPcode":"","submissionUrl":"https://www.editorialmanager.com/boph","title":"BMC Ophthalmology","twitterHandle":"BMC_series","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"em","reportingPortfolio":"BMC Series","inReviewEnabled":true,"inReviewRevisionsEnabled":true},"keywords":"Goldman tonometry, Intra ocular pressure, Non-contact tonometry, Trans-palpebral tonometry","lastPublishedDoi":"10.21203/rs.3.rs-8612933/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-8612933/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003e\u003cstrong\u003eBackground:\u003c/strong\u003e To evaluate reliability and agreement of non-contact tonometry (NCT) and trans-palpebral tonometry (TPT) compared with Goldmann-applanation tonometry (GAT).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eMethods:\u003c/strong\u003e A total of 224 eyes from 112 patients were included between January and April 2025. Intraocular pressure (IOP) was measured using GAT, NCT, and TPT. Comparison among the three measurement groups were performed using the related-samples Friedman test. Post hoc pairwise comparisons were conducted using the Wilcoxon signed-rank test with Bonferroni correction. Reliability was assessed using Cronbach’s alpha and the intraclass correlation coefficient (ICC). Agreement between methods was evaluated using Bland–Altman plots and Spearman’s rank-order correlation.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eResults:\u003c/strong\u003e Median IOP were 14 mmHg for GAT, 14 mmHg for NCT and 15 mmHg for TPT. Friedman's ANOVA showed statistically significant difference among three methods (χ² = 40.652, p \u0026lt; 0.001). TPT readings were significantly different from both GAT and NCT (p \u0026lt; 0.001), the difference between GAT and NCT was not significant (p = 0.024).Cronbach’s alpha was 0.691, indicating acceptable internal consistency. The ICC for average IOP was 0.668 (95% CI: 0.571–0.743, p \u0026lt; 0.001), suggesting moderate- reliability. Spearman’s correlation showed moderate-agreement between GAT and NCT (ρ = 0.586, p \u0026lt; 0.001), weak-agreement between TPT and NCT (ρ = 0.315, p \u0026lt; 0.001), and no correlation between GAT and TPT (ρ = 0.090, p = 0.177). Bland-Altman analysis confirmed good-agreement between GAT and NCT, fair-agreement between NCT and TPT, and poor-agreement between GAT and TPT.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConclusions:\u003c/strong\u003e GAT and NCT demonstrated moderate agreement, while TPT showed limited agreement with both NCT and GAT.\u003c/p\u003e","manuscriptTitle":"Comparison of Intraocular Pressure Measured by Goldman Applanation Tonometer, Noncontact Tonometer and Trans-palpebral Tonometer","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2026-02-22 12:24:41","doi":"10.21203/rs.3.rs-8612933/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2026-03-05T06:20:01+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2026-03-03T22:05:57+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2026-02-25T09:22:55+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2026-02-22T09:02:14+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"119089484671347077192620560031355839397","date":"2026-02-21T17:30:44+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2026-02-20T18:02:37+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"148411024139232940797444295516321154895","date":"2026-02-20T11:33:14+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"7173774579593904839712968934388119406","date":"2026-02-18T23:05:33+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2026-02-18T11:43:09+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"202240398920407947220497616215087075352","date":"2026-02-14T04:55:01+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"121146312654499001570019836712977168951","date":"2026-02-13T13:39:37+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2026-02-13T13:17:35+00:00","index":"","fulltext":""},{"type":"editorInvited","content":"","date":"2026-01-23T05:44:58+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2026-01-22T07:32:52+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2026-01-22T07:27:28+00:00","index":"","fulltext":""},{"type":"submitted","content":"BMC Ophthalmology","date":"2026-01-15T17:59:03+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"bmc-ophthalmology","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"boph","sideBox":"Learn more about [BMC Ophthalmology](http://bmcophthalmol.biomedcentral.com/)","snPcode":"","submissionUrl":"https://www.editorialmanager.com/boph","title":"BMC Ophthalmology","twitterHandle":"BMC_series","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"em","reportingPortfolio":"BMC Series","inReviewEnabled":true,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"f065d6f3-b4dc-464d-bf88-a0d5c50ba8b4","owner":[],"postedDate":"February 22nd, 2026","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[],"tags":[],"updatedAt":"2026-04-20T16:00:23+00:00","versionOfRecord":{"articleIdentity":"rs-8612933","link":"https://doi.org/10.1186/s12886-026-04821-w","journal":{"identity":"bmc-ophthalmology","isVorOnly":false,"title":"BMC Ophthalmology"},"publishedOn":"2026-04-17 15:57:11","publishedOnDateReadable":"April 17th, 2026"},"versionCreatedAt":"2026-02-22 12:24:41","video":"","vorDoi":"10.1186/s12886-026-04821-w","vorDoiUrl":"https://doi.org/10.1186/s12886-026-04821-w","workflowStages":[]},"version":"v1","identity":"rs-8612933","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-8612933","identity":"rs-8612933","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}