Normative assessment of corneal thickness and iridocorneal angle parameters in guinea pigs (Cavia porcellus) using spectral-domain optical coherence tomography

Normative assessment of corneal thickness and iridocorneal angle parameters in guinea pigs (Cavia porcellus) using spectral-domain optical coherence tomography | 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 Short Report Normative assessment of corneal thickness and iridocorneal angle parameters in guinea pigs (Cavia porcellus) using spectral-domain optical coherence tomography Fábio L. C. Brito, Maria F. X. Rocha, Jéssica N. Voitena, Eric C. Ledbetter, and 1 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-9383399/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted 8 You are reading this latest preprint version Abstract Guinea pigs ( Cavia porcellus ) are valuable models for ophthalmic research due to their ocular similarities to humans. Optical coherence tomography (OCT) provides a non-invasive, high-resolution method for detailed, cross-sectional imaging of the ocular structures across species. This study aimed to establish normative biometric parameters of the cornea and iridocorneal angle in guinea pigs using spectral-domain optical coherence tomography (SD-OCT). Twenty eyes from ten clinically healthy adults underwent complete ophthalmic examination followed by anterior segment SD-OCT imaging without sedation. Central corneal thickness (CCT), central epithelial thickness (CET), iridocorneal angle (ICA), and angle opening distance at 500 µm from the scleral spur (AOD500) were quantified. Data distribution was assessed using the Shapiro–Wilk test, and parametric or non-parametric analyses were applied accordingly. The mean (± SD) CCT was 234.45 ± 16.53 µm, with the inferior quadrant being the thickest and the central region the thinnest. CET averaged 50.35 ± 5.81 µm, representing 21.54 ± 2.58% of CCT, with no significant correlation between CET and CCT (r = 0.24, p = 0.31). ICA and AOD500 averaged 39.2 ± 10.1° and 435.6 ± 111.3 µm, respectively, displaying a strong positive correlation (r = 0.89, p 0.05). The present results provide the first SD-OCT–based references for corneal and angle biometry in guinea pigs, facilitating their use as a translational model in ophthalmic research and aiding in the diagnosis and monitoring of anterior segment diseases in exotic pet medicine. anterior segment corneal thickness guinea pig iridocorneal angle optical coherence tomography Figures Figure 1 Figure 2 Figure 3 1. Introduction The guinea pig ( Cavia porcellus ) is increasingly recognized as a relevant animal model in comparative ophthalmic research and translational medicine due to its ocular anatomical and physiological similarities to humans, particularly the structure of the anterior segment and retina (van der Woerdt 2012 ; Guo et al. 2022 ). However, comprehensive in vivo imaging data of ocular structures in guinea pigs remain scarce, limiting the translational, experimental, and clinical applications of these techniques in laboratory animal ophthalmology. Optical coherence tomography (OCT) is a non-invasive, high-resolution imaging modality that allows cross-sectional visualization of the retina, optic nerve, cornea, and iridocorneal angle in a non-contact, real-time fashion (Huang et al. 1991 ). In small exotic mammals such as guinea pigs, OCT imaging poses specific and unique challenges, including the small globe size, positioning constraints, and corneal curvature, which may affect image acquisition and segmentation accuracy (Di et al. 2020). Nevertheless, recent studies in rodents, including mice and rats, have demonstrated the feasibility of retinal and anterior segment imaging using customized positioning techniques and appropriate sedation protocols (Batista et al. 2023 ). Few studies have addressed normative OCT parameters in guinea pigs. Most available data are derived from histological sections or indirect measurements, which do not offer the resolution or reproducibility of in vivo OCT-based methods (Jnawali et al. 2018 ). Establishing species-specific normative values for corneal thickness, epithelial thickness, and iridocorneal angle width using SD-OCT would greatly enhance the diagnostic and research utility of this model. Furthermore, such data would facilitate longitudinal studies in ocular toxicology, pharmacology, and gene therapy targeting anterior segment, retinal, and optic nerve diseases. This study aims to report and validate the use of spectral-domain OCT for quantitative evaluation of the anterior segments in guinea pigs, establishing normative biometric parameters for central corneal thickness (CCT), central epithilium thickness (CET), iridocorneal angle (ICA), and angle opening distance (AOD). By providing detailed imaging protocols and reproducible measurements, this study contributes to the growing body of veterinary ophthalmic imaging in non-traditional species and supports the use of guinea pigs in translational vision science and clinical disease evaluation. 2. Materials and Methods This prospective, cross-sectional study was conducted in accordance with Guidelines for Ethical Research in Veterinary Ophthalmology (GERVO). The study included 10 clinically healthy adult guinea pigs ( Cavia porcellus ) of both sexes, weighing between 700 and 1200 g with informed consent from their owners. All animals underwent a complete ophthalmic examination to confirm the absence of ocular abnormalities prior to inclusion. The guinea pigs were evaluated in an Ophthalmology Service. Routine ophthalmic evaluation included slit-lamp biomicroscopy for anterior segment inspection, applanation tonometry using a Tono-Pen Vet® to measure intraocular pressure (IOP), and fluorescein staining to assess corneal integrity. Indirect fundus examination and color retinography were performed using a Volk Pictor Plus® portable retinal camera. 2.1 Spectral-domain optical coherence tomography 2.1.1 Image Acquisition Spectral-domain optical coherence tomography (SD-OCT) imaging was performed without sedation using an anterior segment module, with animals gently restrained in a horizontal position. The corneal surface was regularly irrigated to maintain optical clarity, and pachymetry scans were obtained along the visual axis at five predefined corneal regions. Only high-quality scans (Scan Quality Index ≥ 27), free from motion artifacts and with adequate structural delineation, were included. All measurements were conducted by a single board-certified veterinary ophthalmologist to ensure consistency and eliminate interobserver variability. 2.1.2 Central Corneal Thickness and Corneal Epithelium Thickness Central corneal thickness and epithelial thickness were assessed using standardized acquisition protocols. Proper centration of the pupil was ensured, and poorly centered scans were excluded. A pachymetric map consisting of 17 zones over a 6-mm diameter was automatically generated based on multiple radial and horizontal scans, allowing precise evaluation of corneal thickness across regions. 2.1.3 Iridocorneal angle analysis and angle opening distance (AOD) measurement Iridocorneal angle (ICA) and angle opening distance (AOD) measurements were obtained under controlled lighting conditions to minimize pupillary variation. Measurements were performed at specific temporal and nasal quadrants to optimize visualization of the limbal region. The AOD500 was defined as the perpendicular distance between the posterior corneal surface and anterior iris surface, measured 500 µm anterior to the scleral spur. Each parameter was measured three times, and mean values were used for statistical analysis, with efforts made to minimize motion artifacts and ensure reproducibility. 2.2 Statistical analysis All statistical analyses were conducted using GraphPad Prism (version 10.5.0), with a significance level set at p < 0.05. Sample size calculation, based on a 95% confidence level, an expected standard deviation of 16.1 µm, and a maximum allowable error of 12 µm, indicated a minimum requirement of seven eyes. Thus, the inclusion of 20 eyes from 10 guinea pigs was considered statistically sufficient. Data normality was assessed using the Shapiro–Wilk test for all continuous variables, including central corneal thickness (CCT), central epithelial thickness (CET), iridocorneal angle (ICA), and angle opening distance (AOD). Most variables followed a normal distribution, except for superior corneal thickness, which was analyzed using non-parametric methods. Normally distributed data were expressed as mean ± standard deviation and analyzed using parametric tests such as one-way ANOVA and Pearson’s correlation, whereas non-normally distributed data were expressed as median and interquartile range and analyzed using Kruskal–Wallis tests with Dunn’s post hoc comparisons and Spearman’s rank correlation. Comparisons between independent groups were performed using the Mann–Whitney U test when appropriate. Regional comparisons among the five corneal areas were conducted using either one-way ANOVA or Kruskal–Wallis tests, depending on data distribution. Associations between ocular parameters were evaluated using Pearson’s or Spearman’s correlation tests accordingly. The CET/CCT ratio was calculated and expressed as a percentage for each eye. Interocular comparisons between right and left eyes were performed using paired statistical tests, including the paired t-test for normally distributed variables and the Wilcoxon signed-rank test for non-normal data. 3. Results A total of 20 eyes from 10 clinically healthy guinea pigs (were evaluated using SD-OCT. There were no statistically significant differences between right and left eyes for any of the parameters assessed (p > 0.05 for all comparisons, paired t-test or Wilcoxon signed-rank test), allowing for the combination of both eyes in further analyses. Descriptive statistics for each parameter are presented in Table 1 . Most parameters showed normal distribution, except for superior corneal thickness, which was analyzed using non-parametric methods. The CCT averaged 234.4 ± 16.1 µm (Fig. 1 ). The thickest region was inferior (256.9 ± 23.2 µm), while the thinnest was central. The CET averaged was 50.35 ± 5.81 µm (Fig. 1 ). Table 1 Summarizes the descriptive statistics for the parameters evaluated: Parameter Distribution Descriptive Statistic CCT Normal 234.4 ± 16.1 CCT_Nasal Normal 239.6 ± 24.6 CCT_Temporal Normal 240.6 ± 24.8 CCT_Superior No normal 240.5 [29.2] CCT_Inferior Normal 256.9 ± 23.2 CET Normal 50.35 ± 5.81 ICA Normal 40.8 ± 11.3 AOD Normal 451.5 ± 132.1 Legend: CCT = central corneal thickness; CCT_Nasal = nasal corneal thickness; CCT_Temporal = temporal corneal thickness; CCT_Superior = superior corneal thickness; CCT_Inferior = inferior corneal thickness. Variables with normal distribution were described as mean ± standard deviation and analyzed using the Student’s t-test. Non-normally distributed variables were described as median [interquartile range] and analyzed using the Mann–Whitney U test In the present study, the mean central epithelial thickness (CET) was 50.35 ± 5.81 µm, while the mean central corneal thickness (CCT) was 234.45 ± 16.53 µm. The Shapiro–Wilk test confirmed a normal distribution for both variables (p > 0.05). Given the normality of the data, Pearson’s correlation test was applied, revealing a weak and non-significant positive correlation between CET and CCT (r = 0.24, p = 0.306) (Fig. 2 ). On average, the CET represented 21.54% ± 2.58% of the total corneal thickness. These findings indicate that, although CET contributes substantially to CCT, its proportion remains relatively consistent and is not strongly correlated with overall corneal thickness. The mean angle of drainage (ICA) and angle opening distance (AOD) were 39.2 ± 10.1° and 435.6 ± 111.3 µm (Fig. 1 ), respectively. Both the drainage angle (°) and the angle opening distance (µm) exhibited normal distribution according to the Shapiro–Wilk test (p > 0.05). A Pearson correlation analysis demonstrated a strong and statistically significant positive correlation between these two parameters (r = 0.89, p = 2.03 × 10⁻⁷) (Fig. 3 ), indicating that increases in the drainage angle are closely associated with wider angle openings in this cohort. 4. Discussion To our knowledge, this is one of the first studies to provide detailed in vivo normative biometric data of the cornea and iridocorneal angle in guinea pigs using SD-OCT. The successful acquisition of high-quality images without the need for sedation confirms the feasibility of anterior segment imaging in this species and establishes a foundation for future diagnostic and experimental applications. The mean CCT found in our study (234.45 ± 16.53 µm) is consistent with previous descriptions in small mammals, although comparative data specific to guinea pigs and related animal species remain sparse. For instance, studies in rabbits—another lagomorph often used in ophthalmic research—report CCT values ranging from 280 to 350 µm depending on strain and methodology, typically measured using ultrasound pachymetry or anterior segment OCT (Chan et al. 1983 ; Wang et al. 2013). The relatively thinner cornea in guinea pigs may reflect species-specific adaptations, potentially influenced by characteristics such as eye size, corneal hydration, or various environmental factors such as ambient light exposure. The regional thickness profile revealed a classical pattern, with the inferior quadrant being the thickest and the central region the thinnest. This finding mirrors the corneal topography observed in other animals, where the peripheral inferior region tends to be more hydrated or structurally thicker (Chan et al. 1983 ; Wang and Wu 2013 ; Alario et al. 2014; Hoehn et al. 2018 ; Khan 2019 ). In the other guinea pig study using portable ultrasound pachymeter, the corneal thickness measured at the central and peripheral regions (upper and temporal) showed similar results. The values were 227.85 ± 14.09, 226.60 ± 12.50, and 225.70 ± 14.40 µm, respectively (Cafaro et al. 2009 ). This pattern is consistent with the values observed in our study. The thickness of the whole cornea and of the different layers was also performed by histological measurements such distribution may be physiologically linked to eyelid dynamics or gravity-mediated tear pooling. The mean CET of 50.35 ± 5.81 µm in guinea pigs is proportionally comparable to that described in dogs, where CET often represents 20–25% of the CCT (Reiser et al. 2005 ; Cafaro et al. 2009 ; Jeong et al. 2023 ). A similar CET/CCT ration was observed in the present study (21.54 ± 2.58%), suggesting that guinea pigs may maintain a consistent epithelial contribution to overall corneal architecture, despite interspecies differences in absolute corneal thickness. The lack of significant correlation between CET and CCT (r = 0.24, p = 0.31) reinforces the idea that epithelial thickness may be regulated independently of stromal components, as previously suggested in canine and human studies (Maltsev et al. 2018 ; Jeong et al. 2023 ). The evaluation of the iridocorneal angle (ICA) and angle opening distance (AOD) provides valuable insight into anterior segment anatomy in guinea pigs, especially considering the growing interest in this species for translational ophthalmic models. In our study, both ICA and AOD demonstrated normal distributions and exhibited a strong positive correlation (r = 0.89, p < 0.001), suggesting a predictable geometric relationship between angular width and anterior chamber conformation. The mean ICA observed in the current study (39.2 ± 10.1°) is broadly similar to values reported in dogs using SDOCT, which range from 30° to 45°, depending on breed and quadrant assessed (Shim et al. 2022 ). The AOD value of 435.6 ± 111.3 µm is also within the range reported for mesocephalic canine breeds and is indicative of a relatively open angle configuration in healthy guinea pigs. In dogs, narrowing of the ICA and reduction in AOD are typically associated with goniodysgenesis or glaucoma (Kim et al. 2023 ). Although spontaneous glaucoma is uncommon in guinea pigs, these baseline values may serve as a comparative reference for future pharmacological or genetic studies. The strong correlation between ICA and AOD supports the notion that these two metrics can be jointly interpreted when evaluating angle morphology. Similar findings have been reported in human and veterinary studies, reinforcing the utility of AOD as a surrogate for angle openness when complete gonioscopic imaging is not feasible (Shim et al. 2022 ; Kim et al. 2023 ). Given the small globe size of guinea pigs, SD-OCT proved to be an effective, non-invasive tool to capture high-resolution images of the iridocorneal angle region, overcoming the limitations posed by traditional gonioscopy in small species. The study demonstrates strengths such as a standardized imaging protocol, non-sedated manual restraint, and inclusion of both sexes. Limitations include a small sample size and potential variability from positioning and anatomical differences. Despite this, the findings establish important normative corneal reference values in guinea pigs. Further studies are needed to evaluate variations related to age, sex, and disease. In summary, this investigation provides the first SD-OCT–based normative data for CCT, CET, ICA, and AOD in guinea pigs. These results contribute to the understanding of anterior segment architecture in this species and support the application of guinea pigs as translational models in anterior segment research, including glaucoma and corneal disease. Declarations Conflict of interest The authors state that there is no conflict of interest. Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third-party material in this article are included in the article’s Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/ . Author Contribution F.L.C.B. collected the data, wrote the manuscript, conceptualized the idea, and reviewed the manuscript. M.F.X.R. collected the data and wrote the manuscript. J.N.V. reviewed the manuscript E.C.L. reviewed the manuscript F.M.F. conceptualized the idea and the statistical analysis. References Alario AF, Pirie CG (2014) Central corneal thickness measurements in normal dogs: a comparison between ultrasound pachymetry and optical coherence tomography. 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Sci Rep. ;12(1):873. Published 2022 Jan 18. 10.1038/s41598-022-04911-x Hoehn AL, Thomasy SM, Kass PH et al (2018) Comparison of ultrasonic pachymetry and Fourier-domain optical coherence tomography for measurement of corneal thickness in dogs with and without corneal disease. Vet J 242:59–66. 10.1016/j.tvjl.2018.10.008 Huang D, Swanson EA, Lin CP et al (1991) Optical coherence tomography. Science 254(5035):1178–1181. 10.1126/science.1957169 Jeong Y, Kang S, Ahn J et al (2023) Assessment of corneal and limbal epithelial thickness by spectral-domain optical coherence tomography in brachycephalic and non-brachycephalic dogs. Vet Ophthalmol 26(Suppl 1):89–97. 10.1111/vop.13016 Jnawali A, Beach KM, Ostrin LA (2018) In Vivo Imaging of the Retina, Choroid, and Optic Nerve Head in Guinea Pigs. Curr Eye Res 43(8):1006–1018. 10.1080/02713683.2018.1464195 Khan MA (2019) Jul Distribution and measurement of corneal thickness in rabbits. ARVO Annu Meet Abstr Kim H, Jeong Y, Lee E, Seo K, Kang S (2023) Treatment of immune-mediated keratitis (IMMK) in dogs with immunosuppressants observed with spectral domain optical coherence tomography (SD-OCT). J Vet Sci 24(5):e66. 10.4142/jvs.23059 Kim SA, Shim J, Kang S, Seo K (2023) Inter-device agreement between spectral domain optical coherence tomography, ultrasound biomicroscopy, and gonioscopy in evaluating the iridocorneal angle in normotensive dogs. J Vet Sci 24(4):e34. 10.4142/jvs.22241 Maltsev DS, Kudryashova EV, Kulikov AN, Mareichev AY (2018) Relationship Between Central Epithelial Thickness and Central Corneal Thickness in Healthy Eyes and Eyes After Laser In Situ Keratomileusis. Cornea 37(8):1053–1057. 10.1097/ICO.0000000000001568 Reiser BJ, Ignacio TS, Wang Y et al (2005) In vitro measurement of rabbit corneal epithelial thickness using ultrahigh resolution optical coherence tomography. 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Cite Share Download PDF Status: Under Review Version 1 posted Editorial decision: Revision requested 16 May, 2026 Reviewers agreed at journal 28 Apr, 2026 Reviews received at journal 27 Apr, 2026 Reviewers agreed at journal 22 Apr, 2026 Reviewers invited by journal 22 Apr, 2026 Editor assigned by journal 21 Apr, 2026 Submission checks completed at journal 21 Apr, 2026 First submitted to journal 10 Apr, 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. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. 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-9383399","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Short Report","associatedPublications":[],"authors":[{"id":631355241,"identity":"67280fbe-6d06-455c-936a-75f0f088c70a","order_by":0,"name":"Fábio L. C. 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Ledbetter","email":"","orcid":"","institution":"Cornell University","correspondingAuthor":false,"prefix":"","firstName":"Eric","middleName":"C.","lastName":"Ledbetter","suffix":""},{"id":631355246,"identity":"99f95343-9c88-4864-a4bb-e3fa80e7868e","order_by":4,"name":"Fabiano Montiani-Ferreira","email":"","orcid":"","institution":"Federal University of Paraná","correspondingAuthor":false,"prefix":"","firstName":"Fabiano","middleName":"","lastName":"Montiani-Ferreira","suffix":""}],"badges":[],"createdAt":"2026-04-10 23:23:03","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-9383399/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-9383399/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":108401894,"identity":"45025665-7cf5-44b2-9e42-69ad6f8d6103","added_by":"auto","created_at":"2026-05-04 09:07:41","extension":"jpeg","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":1860752,"visible":true,"origin":"","legend":"\u003cp\u003eSpectral-domain optical coherence tomography (SD-OCT) of a clinically healthy guinea pig (\u003cem\u003eCavia porcellus\u003c/em\u003e) \u003cstrong\u003eA\u003c/strong\u003e. Corneal pachymetry map. The central corneal thickness (CCT) measured 239 µm, with peripheral values ranging from 215 µm (inferotemporal) to 283 µm (superior). \u003cstrong\u003eB.\u003c/strong\u003e The epithelial thickness (corneal epithelial thickness, CET) was measured at 59 µm. Corneal layers are clearly delineated, and no signs of structural irregularities or opacification are present. This image exemplifies the normal epithelial profile in this species and supports the use of OCT for high-resolution corneal biometry in small mammals. \u003cstrong\u003eC. \u003c/strong\u003eImage of the anterior segment illustrating the iridocorneal angle (ICA). The angle opening distance (AOD) was measured at 299 µm, and the drainage angle was 24.39°, indicating an open-angle configuration. The corneal and anterior iris contours appear normal, with no evidence of peripheral anterior synechiae or angle closure. This morphometric assessment aids in characterizing baseline anterior chamber anatomy in this species.\u003c/p\u003e","description":"","filename":"floatimage1.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-9383399/v1/78f1df0d78c49637de79219d.jpeg"},{"id":108492693,"identity":"64e1a40d-1485-4f1e-920e-702b6db1322d","added_by":"auto","created_at":"2026-05-05 09:58:20","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":186928,"visible":true,"origin":"","legend":"\u003cp\u003eHistogram distribution of corneal epithelial thickness (CET, left) and central corneal thickness (CCT, center) in guinea pigs, and scatter plot with regression line showing the correlation between both parameters (right). Although both variables showed normal distribution (Shapiro–Wilk p \u0026gt; 0.05), the correlation between CET and CCT was not statistically significant (Pearson’s r = 0.24, p = 0.306). Each data point represents an individual eye measurement. CET: corneal epithelial thickness; CCT: central corneal thickness.\u003c/p\u003e","description":"","filename":"floatimage2.png","url":"https://assets-eu.researchsquare.com/files/rs-9383399/v1/330b539050d337d3f9bac6de.png"},{"id":108401896,"identity":"29882f08-407a-4f58-a1ee-361c4a8e0dff","added_by":"auto","created_at":"2026-05-04 09:07:41","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":210966,"visible":true,"origin":"","legend":"\u003cp\u003eHistogram distribution of drainage angle (left) and angle opening (center) in guinea pigs, and scatter plot with regression line showing the correlation between both parameters (right). Both variables showed normal distribution (Shapiro–Wilk p \u0026gt; 0.05), and a strong, statistically significant positive correlation was found (Pearson’s r = 0.89, p \u0026lt; 0.0001).\u003c/p\u003e","description":"","filename":"floatimage3.png","url":"https://assets-eu.researchsquare.com/files/rs-9383399/v1/d0af9e92eb7fe4f17c6f7523.png"},{"id":108803693,"identity":"e03e7c02-4ba0-46fa-b11f-c6adee6f2aae","added_by":"auto","created_at":"2026-05-08 15:03:57","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":2408867,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-9383399/v1/4cea832a-fef0-4cb5-b62b-1be2f754b57a.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Normative assessment of corneal thickness and iridocorneal angle parameters in guinea pigs (Cavia porcellus) using spectral-domain optical coherence tomography","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eThe guinea pig (\u003cem\u003eCavia porcellus\u003c/em\u003e) is increasingly recognized as a relevant animal model in comparative ophthalmic research and translational medicine due to its ocular anatomical and physiological similarities to humans, particularly the structure of the anterior segment and retina (van der Woerdt \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e2012\u003c/span\u003e; Guo et al. \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). However, comprehensive in vivo imaging data of ocular structures in guinea pigs remain scarce, limiting the translational, experimental, and clinical applications of these techniques in laboratory animal ophthalmology.\u003c/p\u003e \u003cp\u003eOptical coherence tomography (OCT) is a non-invasive, high-resolution imaging modality that allows cross-sectional visualization of the retina, optic nerve, cornea, and iridocorneal angle in a non-contact, real-time fashion (Huang et al. \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e1991\u003c/span\u003e). In small exotic mammals such as guinea pigs, OCT imaging poses specific and unique challenges, including the small globe size, positioning constraints, and corneal curvature, which may affect image acquisition and segmentation accuracy (Di et al. 2020). Nevertheless, recent studies in rodents, including mice and rats, have demonstrated the feasibility of retinal and anterior segment imaging using customized positioning techniques and appropriate sedation protocols (Batista et al. \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2023\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eFew studies have addressed normative OCT parameters in guinea pigs. Most available data are derived from histological sections or indirect measurements, which do not offer the resolution or reproducibility of in vivo OCT-based methods (Jnawali et al. \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2018\u003c/span\u003e). Establishing species-specific normative values for corneal thickness, epithelial thickness, and iridocorneal angle width using SD-OCT would greatly enhance the diagnostic and research utility of this model. Furthermore, such data would facilitate longitudinal studies in ocular toxicology, pharmacology, and gene therapy targeting anterior segment, retinal, and optic nerve diseases.\u003c/p\u003e \u003cp\u003eThis study aims to report and validate the use of spectral-domain OCT for quantitative evaluation of the anterior segments in guinea pigs, establishing normative biometric parameters for central corneal thickness (CCT), central epithilium thickness (CET), iridocorneal angle (ICA), and angle opening distance (AOD). By providing detailed imaging protocols and reproducible measurements, this study contributes to the growing body of veterinary ophthalmic imaging in non-traditional species and supports the use of guinea pigs in translational vision science and clinical disease evaluation.\u003c/p\u003e"},{"header":"2. Materials and Methods","content":"\u003cp\u003e This prospective, cross-sectional study was conducted in accordance with Guidelines for Ethical Research in Veterinary Ophthalmology (GERVO). The study included 10 clinically healthy adult guinea pigs (\u003cem\u003eCavia porcellus\u003c/em\u003e) of both sexes, weighing between 700 and 1200 g with informed consent from their owners. All animals underwent a complete ophthalmic examination to confirm the absence of ocular abnormalities prior to inclusion. The guinea pigs were evaluated in an Ophthalmology Service. Routine ophthalmic evaluation included slit-lamp biomicroscopy for anterior segment inspection, applanation tonometry using a Tono-Pen Vet\u0026reg; to measure intraocular pressure (IOP), and fluorescein staining to assess corneal integrity. Indirect fundus examination and color retinography were performed using a Volk Pictor Plus\u0026reg; portable retinal camera.\u003c/p\u003e \u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003e2.1 Spectral-domain optical coherence tomography\u003c/h2\u003e \u003cdiv id=\"Sec4\" class=\"Section3\"\u003e \u003ch2\u003e2.1.1 Image Acquisition\u003c/h2\u003e \u003cp\u003eSpectral-domain optical coherence tomography (SD-OCT) imaging was performed without sedation using an anterior segment module, with animals gently restrained in a horizontal position. The corneal surface was regularly irrigated to maintain optical clarity, and pachymetry scans were obtained along the visual axis at five predefined corneal regions. Only high-quality scans (Scan Quality Index\u0026thinsp;\u0026ge;\u0026thinsp;27), free from motion artifacts and with adequate structural delineation, were included. All measurements were conducted by a single board-certified veterinary ophthalmologist to ensure consistency and eliminate interobserver variability.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec5\" class=\"Section3\"\u003e \u003ch2\u003e2.1.2 Central Corneal Thickness and Corneal Epithelium Thickness\u003c/h2\u003e \u003cp\u003eCentral corneal thickness and epithelial thickness were assessed using standardized acquisition protocols. Proper centration of the pupil was ensured, and poorly centered scans were excluded. A pachymetric map consisting of 17 zones over a 6-mm diameter was automatically generated based on multiple radial and horizontal scans, allowing precise evaluation of corneal thickness across regions.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec6\" class=\"Section3\"\u003e \u003ch2\u003e2.1.3 Iridocorneal angle analysis and angle opening distance (AOD) measurement\u003c/h2\u003e \u003cp\u003e Iridocorneal angle (ICA) and angle opening distance (AOD) measurements were obtained under controlled lighting conditions to minimize pupillary variation. Measurements were performed at specific temporal and nasal quadrants to optimize visualization of the limbal region. The AOD500 was defined as the perpendicular distance between the posterior corneal surface and anterior iris surface, measured 500 \u0026micro;m anterior to the scleral spur. Each parameter was measured three times, and mean values were used for statistical analysis, with efforts made to minimize motion artifacts and ensure reproducibility.\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv id=\"Sec7\" class=\"Section2\"\u003e \u003ch2\u003e2.2 Statistical analysis\u003c/h2\u003e \u003cp\u003eAll statistical analyses were conducted using GraphPad Prism (version 10.5.0), with a significance level set at p\u0026thinsp;\u0026lt;\u0026thinsp;0.05. Sample size calculation, based on a 95% confidence level, an expected standard deviation of 16.1 \u0026micro;m, and a maximum allowable error of 12 \u0026micro;m, indicated a minimum requirement of seven eyes. Thus, the inclusion of 20 eyes from 10 guinea pigs was considered statistically sufficient.\u003c/p\u003e \u003cp\u003eData normality was assessed using the Shapiro\u0026ndash;Wilk test for all continuous variables, including central corneal thickness (CCT), central epithelial thickness (CET), iridocorneal angle (ICA), and angle opening distance (AOD). Most variables followed a normal distribution, except for superior corneal thickness, which was analyzed using non-parametric methods. Normally distributed data were expressed as mean\u0026thinsp;\u0026plusmn;\u0026thinsp;standard deviation and analyzed using parametric tests such as one-way ANOVA and Pearson\u0026rsquo;s correlation, whereas non-normally distributed data were expressed as median and interquartile range and analyzed using Kruskal\u0026ndash;Wallis tests with Dunn\u0026rsquo;s post hoc comparisons and Spearman\u0026rsquo;s rank correlation.\u003c/p\u003e \u003cp\u003eComparisons between independent groups were performed using the Mann\u0026ndash;Whitney U test when appropriate. Regional comparisons among the five corneal areas were conducted using either one-way ANOVA or Kruskal\u0026ndash;Wallis tests, depending on data distribution. Associations between ocular parameters were evaluated using Pearson\u0026rsquo;s or Spearman\u0026rsquo;s correlation tests accordingly. The CET/CCT ratio was calculated and expressed as a percentage for each eye. Interocular comparisons between right and left eyes were performed using paired statistical tests, including the paired t-test for normally distributed variables and the Wilcoxon signed-rank test for non-normal data.\u003c/p\u003e \u003c/div\u003e"},{"header":"3. Results","content":"\u003cp\u003eA total of 20 eyes from 10 clinically healthy guinea pigs (were evaluated using SD-OCT. There were no statistically significant differences between right and left eyes for any of the parameters assessed (p\u0026thinsp;\u0026gt;\u0026thinsp;0.05 for all comparisons, paired t-test or Wilcoxon signed-rank test), allowing for the combination of both eyes in further analyses.\u003c/p\u003e \u003cp\u003eDescriptive statistics for each parameter are presented in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e. Most parameters showed normal distribution, except for superior corneal thickness, which was analyzed using non-parametric methods. The CCT averaged 234.4\u0026thinsp;\u0026plusmn;\u0026thinsp;16.1 \u0026micro;m (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). The thickest region was inferior (256.9\u0026thinsp;\u0026plusmn;\u0026thinsp;23.2 \u0026micro;m), while the thinnest was central. The CET averaged was 50.35\u0026thinsp;\u0026plusmn;\u0026thinsp;5.81 \u0026micro;m (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eSummarizes the descriptive statistics for the parameters evaluated:\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"3\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eParameter\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eDistribution\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eDescriptive Statistic\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCCT\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eNormal\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e234.4\u0026thinsp;\u0026plusmn;\u0026thinsp;16.1\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCCT_Nasal\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eNormal\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e239.6\u0026thinsp;\u0026plusmn;\u0026thinsp;24.6\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCCT_Temporal\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eNormal\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e240.6\u0026thinsp;\u0026plusmn;\u0026thinsp;24.8\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCCT_Superior\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eNo normal\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e240.5 [29.2]\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCCT_Inferior\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eNormal\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e256.9\u0026thinsp;\u0026plusmn;\u0026thinsp;23.2\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCET\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eNormal\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e50.35\u0026thinsp;\u0026plusmn;\u0026thinsp;5.81\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eICA\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eNormal\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e40.8\u0026thinsp;\u0026plusmn;\u0026thinsp;11.3\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eAOD\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eNormal\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e451.5\u0026thinsp;\u0026plusmn;\u0026thinsp;132.1\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003ctfoot\u003e \u003ctr\u003e\u003ctd colspan=\"3\"\u003eLegend: CCT\u0026thinsp;=\u0026thinsp;central corneal thickness; CCT_Nasal\u0026thinsp;=\u0026thinsp;nasal corneal thickness; CCT_Temporal\u0026thinsp;=\u0026thinsp;temporal corneal thickness; CCT_Superior\u0026thinsp;=\u0026thinsp;superior corneal thickness; CCT_Inferior\u0026thinsp;=\u0026thinsp;inferior corneal thickness. Variables with normal distribution were described as mean\u0026thinsp;\u0026plusmn;\u0026thinsp;standard deviation and analyzed using the Student\u0026rsquo;s t-test. Non-normally distributed variables were described as median [interquartile range] and analyzed using the Mann\u0026ndash;Whitney U test\u003c/td\u003e\u003c/tr\u003e \u003c/tfoot\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eIn the present study, the mean central epithelial thickness (CET) was 50.35\u0026thinsp;\u0026plusmn;\u0026thinsp;5.81 \u0026micro;m, while the mean central corneal thickness (CCT) was 234.45\u0026thinsp;\u0026plusmn;\u0026thinsp;16.53 \u0026micro;m. The Shapiro\u0026ndash;Wilk test confirmed a normal distribution for both variables (p\u0026thinsp;\u0026gt;\u0026thinsp;0.05). Given the normality of the data, Pearson\u0026rsquo;s correlation test was applied, revealing a weak and non-significant positive correlation between CET and CCT (r\u0026thinsp;=\u0026thinsp;0.24, p\u0026thinsp;=\u0026thinsp;0.306) (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). On average, the CET represented 21.54% \u0026plusmn; 2.58% of the total corneal thickness. These findings indicate that, although CET contributes substantially to CCT, its proportion remains relatively consistent and is not strongly correlated with overall corneal thickness.\u003c/p\u003e \u003cp\u003eThe mean angle of drainage (ICA) and angle opening distance (AOD) were 39.2\u0026thinsp;\u0026plusmn;\u0026thinsp;10.1\u0026deg; and 435.6\u0026thinsp;\u0026plusmn;\u0026thinsp;111.3 \u0026micro;m (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e), respectively. Both the drainage angle (\u0026deg;) and the angle opening distance (\u0026micro;m) exhibited normal distribution according to the Shapiro\u0026ndash;Wilk test (p\u0026thinsp;\u0026gt;\u0026thinsp;0.05). A Pearson correlation analysis demonstrated a strong and statistically significant positive correlation between these two parameters (r\u0026thinsp;=\u0026thinsp;0.89, p\u0026thinsp;=\u0026thinsp;2.03 \u0026times; 10⁻⁷) (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e), indicating that increases in the drainage angle are closely associated with wider angle openings in this cohort.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e"},{"header":"4. Discussion","content":"\u003cp\u003eTo our knowledge, this is one of the first studies to provide detailed in vivo normative biometric data of the cornea and iridocorneal angle in guinea pigs using SD-OCT. The successful acquisition of high-quality images without the need for sedation confirms the feasibility of anterior segment imaging in this species and establishes a foundation for future diagnostic and experimental applications.\u003c/p\u003e \u003cp\u003eThe mean CCT found in our study (234.45\u0026thinsp;\u0026plusmn;\u0026thinsp;16.53 \u0026micro;m) is consistent with previous descriptions in small mammals, although comparative data specific to guinea pigs and related animal species remain sparse. For instance, studies in rabbits\u0026mdash;another lagomorph often used in ophthalmic research\u0026mdash;report CCT values ranging from 280 to 350 \u0026micro;m depending on strain and methodology, typically measured using ultrasound pachymetry or anterior segment OCT (Chan et al. \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e1983\u003c/span\u003e; Wang et al. 2013). The relatively thinner cornea in guinea pigs may reflect species-specific adaptations, potentially influenced by characteristics such as eye size, corneal hydration, or various environmental factors such as ambient light exposure.\u003c/p\u003e \u003cp\u003eThe regional thickness profile revealed a classical pattern, with the inferior quadrant being the thickest and the central region the thinnest. This finding mirrors the corneal topography observed in other animals, where the peripheral inferior region tends to be more hydrated or structurally thicker (Chan et al. \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e1983\u003c/span\u003e; Wang and Wu \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e2013\u003c/span\u003e; Alario et al. 2014; Hoehn et al. \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e2018\u003c/span\u003e; Khan \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). In the other guinea pig study using portable ultrasound pachymeter, the corneal thickness measured at the central and peripheral regions (upper and temporal) showed similar results. The values were 227.85\u0026thinsp;\u0026plusmn;\u0026thinsp;14.09, 226.60\u0026thinsp;\u0026plusmn;\u0026thinsp;12.50, and 225.70\u0026thinsp;\u0026plusmn;\u0026thinsp;14.40 \u0026micro;m, respectively (Cafaro et al. \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e2009\u003c/span\u003e). This pattern is consistent with the values observed in our study. The thickness of the whole cornea and of the different layers was also performed by histological measurements such distribution may be physiologically linked to eyelid dynamics or gravity-mediated tear pooling.\u003c/p\u003e \u003cp\u003eThe mean CET of 50.35\u0026thinsp;\u0026plusmn;\u0026thinsp;5.81 \u0026micro;m in guinea pigs is proportionally comparable to that described in dogs, where CET often represents 20\u0026ndash;25% of the CCT (Reiser et al. \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e2005\u003c/span\u003e; Cafaro et al. \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e2009\u003c/span\u003e; Jeong et al. \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). A similar CET/CCT ration was observed in the present study (21.54\u0026thinsp;\u0026plusmn;\u0026thinsp;2.58%), suggesting that guinea pigs may maintain a consistent epithelial contribution to overall corneal architecture, despite interspecies differences in absolute corneal thickness. The lack of significant correlation between CET and CCT (r\u0026thinsp;=\u0026thinsp;0.24, p\u0026thinsp;=\u0026thinsp;0.31) reinforces the idea that epithelial thickness may be regulated independently of stromal components, as previously suggested in canine and human studies (Maltsev et al. \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e2018\u003c/span\u003e; Jeong et al. \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2023\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eThe evaluation of the iridocorneal angle (ICA) and angle opening distance (AOD) provides valuable insight into anterior segment anatomy in guinea pigs, especially considering the growing interest in this species for translational ophthalmic models. In our study, both ICA and AOD demonstrated normal distributions and exhibited a strong positive correlation (r\u0026thinsp;=\u0026thinsp;0.89, p\u0026thinsp;\u0026lt;\u0026thinsp;0.001), suggesting a predictable geometric relationship between angular width and anterior chamber conformation.\u003c/p\u003e \u003cp\u003eThe mean ICA observed in the current study (39.2\u0026thinsp;\u0026plusmn;\u0026thinsp;10.1\u0026deg;) is broadly similar to values reported in dogs using SDOCT, which range from 30\u0026deg; to 45\u0026deg;, depending on breed and quadrant assessed (Shim et al. \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). The AOD value of 435.6\u0026thinsp;\u0026plusmn;\u0026thinsp;111.3 \u0026micro;m is also within the range reported for mesocephalic canine breeds and is indicative of a relatively open angle configuration in healthy guinea pigs. In dogs, narrowing of the ICA and reduction in AOD are typically associated with goniodysgenesis or glaucoma (Kim et al. \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). Although spontaneous glaucoma is uncommon in guinea pigs, these baseline values may serve as a comparative reference for future pharmacological or genetic studies.\u003c/p\u003e \u003cp\u003eThe strong correlation between ICA and AOD supports the notion that these two metrics can be jointly interpreted when evaluating angle morphology. Similar findings have been reported in human and veterinary studies, reinforcing the utility of AOD as a surrogate for angle openness when complete gonioscopic imaging is not feasible (Shim et al. \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e2022\u003c/span\u003e; Kim et al. \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). Given the small globe size of guinea pigs, SD-OCT proved to be an effective, non-invasive tool to capture high-resolution images of the iridocorneal angle region, overcoming the limitations posed by traditional gonioscopy in small species.\u003c/p\u003e \u003cp\u003eThe study demonstrates strengths such as a standardized imaging protocol, non-sedated manual restraint, and inclusion of both sexes. Limitations include a small sample size and potential variability from positioning and anatomical differences. Despite this, the findings establish important normative corneal reference values in guinea pigs.\u003c/p\u003e \u003cp\u003eFurther studies are needed to evaluate variations related to age, sex, and disease. In summary, this investigation provides the first SD-OCT\u0026ndash;based normative data for CCT, CET, ICA, and AOD in guinea pigs. These results contribute to the understanding of anterior segment architecture in this species and support the application of guinea pigs as translational models in anterior segment research, including glaucoma and corneal disease.\u003c/p\u003e"},{"header":"Declarations","content":"\u003ch2\u003e\u003cstrong\u003eConflict of interest\u003c/strong\u003e\u003c/h2\u003e\n\u003cp\u003eThe authors state that there is no conflict of interest.\u003c/p\u003e\n\u003ch2\u003eOpen Access\u003c/h2\u003e\n\u003cp\u003eThis article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third-party material in this article are included in the article\u0026rsquo;s Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article\u0026rsquo;s Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttp://creativecommons.org/licenses/by/4.0/\u003c/span\u003e\u003c/span\u003e.\u003c/p\u003e\n\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\n\u003cp\u003eF.L.C.B. collected the data, wrote the manuscript, conceptualized the idea, and reviewed the manuscript. M.F.X.R. collected the data and wrote the manuscript. J.N.V. reviewed the manuscript E.C.L. reviewed the manuscript F.M.F. conceptualized the idea and the statistical analysis.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eAlario AF, Pirie CG (2014) Central corneal thickness measurements in normal dogs: a comparison between ultrasound pachymetry and optical coherence tomography. Vet Ophthalmol 17(3):207\u0026ndash;211. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1111/vop.12074\u003c/span\u003e\u003cspan address=\"10.1111/vop.12074\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eBatista A, Guimar\u0026atilde;es P, Martins J et al (2023) Normative mice retinal thickness: 16-month longitudinal characterization of wild-type mice and changes in a model of Alzheimer's disease. 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Vet Ophthalmol 16(2):130\u0026ndash;134. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1111/j.1463-5224.2012.01041.x\u003c/span\u003e\u003cspan address=\"10.1111/j.1463-5224.2012.01041.x\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"veterinary-research-communications","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"verc","sideBox":"Learn more about [Veterinary Research Communications](https://www.springer.com/journal/11259)","snPcode":"11259","submissionUrl":"https://submission.nature.com/new-submission/11259/3","title":"Veterinary Research Communications","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"anterior segment, corneal thickness, guinea pig, iridocorneal angle, optical coherence tomography","lastPublishedDoi":"10.21203/rs.3.rs-9383399/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-9383399/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eGuinea pigs (\u003cem\u003eCavia porcellus\u003c/em\u003e) are valuable models for ophthalmic research due to their ocular similarities to humans. Optical coherence tomography (OCT) provides a non-invasive, high-resolution method for detailed, cross-sectional imaging of the ocular structures across species. This study aimed to establish normative biometric parameters of the cornea and iridocorneal angle in guinea pigs using spectral-domain optical coherence tomography (SD-OCT). Twenty eyes from ten clinically healthy adults underwent complete ophthalmic examination followed by anterior segment SD-OCT imaging without sedation. Central corneal thickness (CCT), central epithelial thickness (CET), iridocorneal angle (ICA), and angle opening distance at 500 \u0026micro;m from the scleral spur (AOD500) were quantified. Data distribution was assessed using the Shapiro\u0026ndash;Wilk test, and parametric or non-parametric analyses were applied accordingly. The mean (\u0026plusmn;\u0026thinsp;SD) CCT was 234.45\u0026thinsp;\u0026plusmn;\u0026thinsp;16.53 \u0026micro;m, with the inferior quadrant being the thickest and the central region the thinnest. CET averaged 50.35\u0026thinsp;\u0026plusmn;\u0026thinsp;5.81 \u0026micro;m, representing 21.54\u0026thinsp;\u0026plusmn;\u0026thinsp;2.58% of CCT, with no significant correlation between CET and CCT (r\u0026thinsp;=\u0026thinsp;0.24, p\u0026thinsp;=\u0026thinsp;0.31). ICA and AOD500 averaged 39.2\u0026thinsp;\u0026plusmn;\u0026thinsp;10.1\u0026deg; and 435.6\u0026thinsp;\u0026plusmn;\u0026thinsp;111.3 \u0026micro;m, respectively, displaying a strong positive correlation (r\u0026thinsp;=\u0026thinsp;0.89, p\u0026thinsp;\u0026lt;\u0026thinsp;0.001). No significant interocular differences were observed for any parameter (p\u0026thinsp;\u0026gt;\u0026thinsp;0.05). The present results provide the first SD-OCT\u0026ndash;based references for corneal and angle biometry in guinea pigs, facilitating their use as a translational model in ophthalmic research and aiding in the diagnosis and monitoring of anterior segment diseases in exotic pet medicine.\u003c/p\u003e","manuscriptTitle":"Normative assessment of corneal thickness and iridocorneal angle parameters in guinea pigs (Cavia porcellus) using spectral-domain optical coherence tomography","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2026-05-04 09:07:37","doi":"10.21203/rs.3.rs-9383399/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2026-05-16T07:43:03+00:00","index":"","fulltext":""},{"type":"reviewerAgreed","content":"113918572168929441419672274095471630905","date":"2026-04-28T22:57:04+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2026-04-27T15:02:51+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"263905447946995851208232401431269706527","date":"2026-04-22T09:16:50+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2026-04-22T06:29:00+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2026-04-21T17:25:28+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2026-04-21T17:24:29+00:00","index":"","fulltext":""},{"type":"submitted","content":"Veterinary Research Communications","date":"2026-04-10T23:05:44+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"veterinary-research-communications","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"verc","sideBox":"Learn more about [Veterinary Research Communications](https://www.springer.com/journal/11259)","snPcode":"11259","submissionUrl":"https://submission.nature.com/new-submission/11259/3","title":"Veterinary Research Communications","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"6f1e70f2-e029-4b08-a552-23b8d98378a7","owner":[],"postedDate":"May 4th, 2026","published":true,"recentEditorialEvents":[{"type":"decision","content":"Revision requested","date":"2026-05-16T07:43:03+00:00","index":"","fulltext":""},{"type":"reviewerAgreed","content":"113918572168929441419672274095471630905","date":"2026-04-28T22:57:04+00:00","index":46,"fulltext":""}],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[],"tags":[],"updatedAt":"2026-05-18T17:08:06+00:00","versionOfRecord":[],"versionCreatedAt":"2026-05-04 09:07:37","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-9383399","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-9383399","identity":"rs-9383399","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}