Abnormal Corvis Biomechanical Indices in Pediatric Hyperopia: Keratoconus or Age-Related Elasticity?

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Yehya Tlaiss, John Warrak, Anthony Daher, Elias Warrak This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-8230073/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted 7 You are reading this latest preprint version Abstract Purpose To investigate whether abnormal Corvis ST biomechanical indices (CBI, TBI) in pediatric hyperopic eyes (0–17 years) reflect early keratoconus or normal age-related corneal elasticity. Methods A retrospective cross-sectional study was conducted on 139 pediatric patients (277 eyes) at Advanced Eye Care Hospital in Lebanon who underwent corneal biomechanical assessment with the Corvis ST. Inclusion criteria were age 0–17 years with hyperopic or emmetropic refraction; myopic eyes were excluded. “Abnormal” indices were defined as CBI ≥ 0.50 and TBI ≥ 0.79 (≥ 0.29 considered suspicious). Proportions of eyes exceeding thresholds were calculated and correlated with clinical and tomographic findings. Results Nearly half of eyes (124/274; 45%) had CBI ≥ 0.50, and 22% exceeded CBI ≥ 0.90. Among 39 eyes with integrated tomography, 33% had TBI ≥ 0.79 and 85% exceeded 0.29. Despite these high rates of “abnormal” biomechanical indices, no eyes (except one with very thin cornea, 376 µm) demonstrated clinical or tomographic signs of keratoconus. Conclusions and Importance Using adult thresholds, Corvis ST flags a large proportion of normal pediatric hyperopic corneas as abnormal, suggesting high false-positive rates in children. These findings indicate that elevated CBI/TBI in pediatric hyperopes likely reflect normal physiologic elasticity rather than keratoconus. Pediatric-specific cutoff values or age-adjusted norms are needed to improve diagnostic accuracy and avoid over-diagnosis. Corvis ST Pediatric Hyperopia Corneal Biomechanics Keratoconus Corvis Biomechanical Index (CBI) Tomographic Biomechanical Index (TBI) Figures Figure 1 Introduction Keratoconus (KCN) is a corneal ectasia characterized by progressive thinning and bulging of the cornea, leading to irregular astigmatism and vision loss. Early detection of KCN – especially in children – is critical, as pediatric keratoconus tends to progress more rapidly than adult KCN [ 1 ]. Traditionally, corneal topography/tomography (e.g. Pentacam’s Belin/Ambrosio display) is used to screen for ectasia, but newer corneal biomechanical assessments provide additional insight. The Oculus Corvis ST is a non-contact tonometer with an ultra–high-speed Scheimpflug camera (≈ 4000 fps) that records corneal deformation in response to an air puff [ 2 ]. From this dynamic measurement, the Corvis ST computes various biomechanical parameters (e.g. deformation amplitudes, applanation times) and a composite Corvis Biomechanical Index (CBI) – a dimensionless score (0 to 1) derived from a combination of biomechanical metrics to screen for ectasia [ 2 ]. When combined with tomographic data (e.g. from Pentacam), a machine-learning derived Tomographic Biomechanical Index (TBI) is obtained for even more sensitive detection of early KCN [ 2 ]. In adult populations, a CBI above 0.5 is the recommended cutoff suggesting an abnormal (keratoconic) biomechanical profile [ 2 ]. Likewise, a TBI approaching 1.0 is highly indicative of ectasia risk; for example, TBI ≥ 0.79 has been reported to provide 100% sensitivity and specificity for frank keratoconus in one study [ 2 ] (a lower cutoff around 0.29 is used to flag more subtle subclinical cases [ 2 ]). These thresholds were established primarily in adults and have high diagnostic accuracy for distinguishing pathological from normal corneas [ 2 ]. However, applying adult biomechanical thresholds to pediatric eyes may be problematic. The rigidity of the cornea is inversely related to age, meaning pediatric corneas are biomechanically less rigid (more elastic) than adult corneas [ 1 ]. In effect, a healthy child’s cornea can deform more under the same pressure than an adult cornea. This raises the question: could “abnormal” Corvis readings in children simply reflect normal age-related corneal elasticity rather than true pathology? Compounding this, refractive error influences corneal biomechanics. Myopic eyes (which tend to have longer axial length and possibly biomechanically “softer” corneas) show slightly reduced corneal stiffness compared to emmetropic eyes, whereas hyperopic eyes (shorter, more compact eyes) show increased corneal stiffness [ 3 ]. In fact, a study in preschool children found corneal stiffness parameters were highest in hyperopes and lowest in myopes, with hyperopic corneas being significantly stiffer than emmetropic or myopic corneas [ 3 ]. Given this, restricting analysis to hyperopic children (excluding myopes) provides a conservative test: hyperopic pediatric corneas would, if anything, be on the stiffer side of normal [ 3 ]. If even these eyes show “abnormal” deformation indices, it strengthens the idea that the abnormal values are due to age-related biomechanics rather than true keratoconus. Purpose: In this study, we evaluated Corvis ST data from pediatric hyperopic patients (0–17 years) to determine whether abnormally high CBI/TBI values in this population are associated with keratoconus or simply reflect normal physiological corneal elasticity at young ages. We hypothesize that many false positives for keratoconus may occur when using adult cutoff values in children, due to the greater corneal flexibility in youth [ 1 ]. To test this, we analyzed our patient dataset of Corvis measurements in hyperopic children, correlated the biomechanical indices with clinical/tomographic findings, and reviewed the literature on pediatric corneal biomechanics. Methods Study Design : We conducted a retrospective cross-sectional study of 138 pediatric patients (277 eyes) at Advanced Eye Care Hospital in Lebanon. All patients aged 0–17 years who underwent corneal biomechanical assessment with the Corvis ST were included, provided they had hyperopic or emmetropic refractive status. Patients with any degree of myopia (negative spherical equivalent) were excluded to eliminate the known confounding effect of myopia on corneal biomechanics [ 3 ]. We also excluded any eye with previously diagnosed corneal pathology (e.g. known keratoconus, corneal scarring, prior surgery). Each patient contributed one or both eyes to the dataset as available. Data Collection : For each included eye, the Corvis ST exam provided: intraocular pressure (IOP) and central corneal thickness (CCT) measurements, and a suite of dynamic deformation parameters. Key indices recorded were the Corvis Biomechanical Index (CBI) and, when available, the Tomographic Biomechanical Index (TBI). The TBI was calculated in cases where corneal tomography data (Pentacam) was integrated with the Corvis exam. All exams had a quality score “OK” (acceptable quality) on the device. An “abnormal” biomechanical reading was defined a priori as CBI ≥ 0.50, based on the established cutoff for distinguishing normal vs. ectatic corneas [ 2 ]. Similarly, TBI values were considered abnormal if ≥ 0.79 (the threshold optimized for detecting clinical ectasia) [ 2 ]. We also noted TBI values in the 0.3–0.79 range which might indicate subclinical risk. After the Corvis test, corneal tomography (Pentacam) was reviewed in those eyes that had scans, and clinical examinations were reviewed for any signs of keratoconus (e.g. inferior corneal steepening on topography, abnormal Belin-Ambrosio D index, slit-lamp signs such as Vogt striae, etc.). Analysis : We computed summary statistics of the cohort (age, CCT, IOP) and determined the proportion of eyes exceeding the CBI and TBI abnormality thresholds. These proportions were compared against expected prevalence of keratoconus in this demographic. We paid special attention to eyes with very high biomechanical index values (e.g. CBI approaching 1.0) to see if they corresponded to any clinical abnormalities. Given the relatively small subset with TBI (tomography) data, our primary analysis centered on CBI. All data analysis was done in Python (Pandas) using the provided dataset. Results are presented with descriptive statistics and comparisons to known normal ranges from literature. Results Cohort Characteristics: A total of 139 pediatric patients (≈ 277 eyes) met inclusion criteria (many patients had both eyes measured). The age ranged from infancy to 17 years (median 13 years; mean age 12.5 ± 3.2 years). By design all patients were hyperopic or plano; the exact refractive errors were not recorded in the dataset, but myopic eyes were excluded. The average central corneal thickness (CCT) was 527 ± 41 µm (range 376 to 640 µm), and mean Corvis IOP was 15.2 ± 3.4 mmHg, both within normal pediatric ranges. Notably, corneas in this pediatric group were generally as thick as adult norms (median ~ 527 µm), and none of the hyperopic subjects had extremely steep curvatures on clinical exam – a finding consistent with their hyperopia . These baseline characteristics suggest the sample largely consisted of healthy corneas. One outlier eye had an unusually thin cornea (~ 376 µm) with clinical signs suspicious for KCN, but this was an exception; the vast majority had no clinical evidence of corneal ectasia. Biomechanical Indices – Frequency of Abnormal Values: Applying the adult-based cutoff of CBI ≥ 0.50, we found that a large proportion of normal pediatric eyes would be flagged as “abnormal.” Specifically, 124 out of 274 eyes (≈ 45%) had CBI ≥ 0.5 – i.e. nearly half of these hyperopic children’s eyes showed a biomechanical index in the range that would typically indicate keratoconus in an adult [ 2 ]. Even more striking, about 22% of eyes had CBI values ≥ 0.90, approaching the maximum of the scale (1.0). In an adult refractive surgery population, a CBI that high would be strongly suggestive of frank ectatic disease [ 2 ], yet in our pediatric hyperopes these values were relatively common. Figure 1 illustrates the distribution of CBI in the cohort, with a substantial rightward skew – many eyes cluster at high CBI despite no known disease. (See Fig. 1 : Histogram of CBI in pediatric hyperopic eyes, with the red dashed line marking the 0.5 cutoff.) For the Tomographic Biomechanical Index (TBI), data were available in a subset of 39 eyes that had integrated Pentacam scans. Among these, 13 eyes (33%) showed TBI ≥ 0.79, exceeding the conservative cutoff for definite ectasia risk [ 2 ]. In fact, most of the 39 eyes had at least mildly elevated TBI – 33 eyes (85%) had TBI > 0.29, the threshold used to detect subclinical keratoconus [ 2 ]. In other words, if one were to apply the combined biomechanical-tomographic index as a screening tool, the majority of these clinically normal children’s eyes would trigger some level of alarm. It is important to note that several TBI values in our dataset were reported as extremely high (5 to 6) – these represent cases where tomography data were not actually available or the calculation was invalid, resulting in an erroneous number. Those were treated as missing data. Excluding those, the valid TBI range was 0 to 0.60 in most normal eyes, with the 13 aforementioned eyes reaching the 0.8–0.9 range. Lack of Clinical Keratoconus Correlates: Despite the high incidence of “abnormal” biomechanical readings, none of the children in our sample had clinical or topographic evidence of keratoconus. On slit-lamp exam, corneas were clear with normal anatomy (no conical deformation, scars, Vogt’s striae, etc.), and keratometric values were in ranges expected for hyperopic or emmetropic eyes (typically K_max < ~ 45 D, as per clinical records). In the eyes that underwent Pentacam tomography, the maps were unremarkable – e.g. regular astigmatic patterns, normal posterior elevation, and Belin/Ambrósio D indices well below the ectasia cutoff in all cases. For example, one 15-year-old patient had CBI ~ 0.99 (very high) in each eye, but her Pentacam showed central Ks ~ 42 D with a symmetric bow-tie pattern and BAD-D ~ 1.0 (normal); another 12-year-old had CBI ~ 0.95 with completely normal corneal shape on tomography. In fact, the only eye with definitively abnormal tomography was the outlier with 376 µm cornea, which indeed likely represents true keratoconus (and interestingly had one of the highest CBI values ~ 0.997). Aside from that single case, there was no correspondence between high CBI/TBI and any keratoconic changes – all other eyes with elevated biomechanical indices appeared to be false positives in terms of keratoconus detection. This suggests that the Corvis ST was flagging many young hyperopic corneas as “biomechanically weak” even though they were structurally normal. Discussion Our results demonstrate a clear discrepancy between biomechanical risk indices (CBI/TBI) and actual clinical status in the pediatric hyperopic population. Using the standard adult threshold (CBI > 0.5) [ 2 ], almost half of normal child eyes would be misidentified as keratoconus suspects. This finding supports our hypothesis that abnormal Corvis readings in many children are related to normal physiological properties (greater corneal flexibility at young age) rather than true keratoconus. In essence, the “red flag” cutoff values developed in adults do not translate well to a pediatric context, leading to an inflated false-positive rate. The underlying reason is rooted in corneal biomechanics: young corneas are more elastic. The collagen lamellae in a child’s cornea have different cross-linking and hydration states compared to adults, making the cornea more deformable under stress. The EyeWiki on pediatric keratoconus concisely states that corneal rigidity increases with age, and thus pediatric corneas are more susceptible to deformation (and even biochemical degradation in the context of ectasia)[ 1 ]. Our data empirically reflect this – many of these children’s corneas deformed to a degree that the Corvis algorithm interprets as abnormal (since the algorithm was trained on stiffer adult corneas). It’s important to emphasize that greater deformation does not necessarily mean disease in a 10-year-old eye – it can be a physiologic norm. In fact, population studies have shown that corneal biomechanical parameters systematically change with age. A recent large study of healthy individuals (age 11–80) confirmed that corneal stiffness parameters increase with advancing age (even when controlling for IOP and thickness) [ 4 ]. The flip side is that a teenager’s cornea is generally less stiff than a middle-aged adult’s. Thus, a CBI of 0.6 or 0.7 might be exceedingly rare in a 40-year-old normal eye, but could occur in a normal 10-year-old purely due to age-dependent elasticity. Our finding that so many hyperopic kids had CBI in the 0.5–1.0 range underscores this point. It aligns with prior pediatric biomechanical studies using the Corvis and similar devices: Miao He et al. (2017) found that while corneal biomechanics in children correlate strongly with factors like CCT and IOP, they observed little change across the age range of 4–18 years within childhood [ 5 ] – implying that the cornea is uniformly more pliant in youth and only later undergoes significant stiffening. In other words, what the Corvis flags as “out of bounds” for an adult may actually be within normal bounds for a child. Another aspect to consider is refractive error and ocular development. We deliberately focused on hyperopic (farsighted) children and excluded myopic children. This is because myopia itself can influence corneal biomechanics – typically, myopic eyes (especially high myopes) have slightly less rigid corneas, possibly related to stretching of the globe and extracellular matrix differences [ 6 ]. Hyperopic eyes, on the other hand, are often shorter with steeper corneas and have been found to have higher corneal stiffness parameters than emmetropic eyes of the same age [ 3 ]. A study of Chinese preschoolers (Long et al., 2019) demonstrated that at ages 4–6, hyperopic children had the highest SP-A1 (stiffness parameter at first applanation) values, followed by emmetropes, then myopes [ 3 ]. Corneal stiffness was increased in hyperopia and reduced in myopia, relative to normal eyes [ 3 ]. Given this, our sample of hyperopic children would be expected, if anything, to have stronger corneas. Yet nearly half showed “weak” biomechanics by adult standards – a finding that cannot be explained by refractive error or thin corneas (since their CCT was normal). This essentially isolates age as the key factor: the youth of the corneas leads to high deformability (low apparent stiffness) despite normal thickness and hyperopic shape. It’s a physiological trait of the developing eye. Importantly, true keratoconus in pediatric patients is relatively uncommon (estimated prevalence ~ 0.1–0.2% in < 18-year-olds [ 1 ]) but it does occur and often progresses quickly [ 1 ]. Our study should not be interpreted as saying “ignore high CBI in kids” – rather, it suggests that using adult cutoff criteria will over-trigger alarms. Clinicians should combine biomechanical assessment with topography/tomography and clinical exam in children. If a child has an isolated high CBI but normal corneal shape and no risk factors, careful observation is warranted instead of immediate diagnosis. In our series, none of the eyes with high CBI (except the one obvious KCN case) had any corroborating signs of keratoconus. Over-reliance on the biomechanical index alone could have led to dozens of false diagnoses. Conversely, one might worry if using a higher cutoff (to reduce false positives) could miss real keratoconus in kids. Notably, the truly keratoconic eye in our sample (15-year-old with 376 µm cornea) had CBI ~ 0.99, so it was correctly flagged – even a stricter threshold would have caught that case. Pediatric keratoconus typically causes significant topographic changes and thinning, which will usually coincide with very high biomechanical index values. Thus, a pragmatic approach is to interpret moderate biomechanical index elevations with caution in children, and look for other evidence of disease before labeling it keratoconus. Our findings highlight the need for pediatric-specific normative data or adjusted thresholds for corneal biomechanical indices. Just as normal corneal curvature and thickness have age-dependent norms (e.g. infant corneas are steeper and then flatten by age 6 months, etc.), corneal biomechanical norms likely differ in the pediatric population. Currently, the CBI and TBI were developed using predominantly adult datasets [ 2 ]. Ambrosio et al. and others have even found that ethnic differences can affect these indices – for example, Asian corneas (on average having smaller diameters and possibly different biomechanical response) tended to get higher risk scores with the original CBI/TBI, prompting the development of ethnicity-specific versions (e.g. a customized cCBI and cTBI for East Asian eyes) [ 2 ]. This shows that the “normal vs abnormal” calibration of the index can shift based on population characteristics. Age is another such factor that likely warrants calibration. It would be highly useful to establish a pediatric biomechanical index (perhaps a modified CBI scaled for age) or at least age-adjusted cutoff values. For instance, one might find that a CBI of 0.8 is within normal range for a toddler (due to a very soft cornea), whereas the same 0.8 in a 30-year-old is pathological. Without adjustment, the raw CBI/TBI should be interpreted in context – high values in a child should raise consideration of keratoconus, but not an immediate conclusion. Our study provides evidence that normal young corneas can and often do produce high index values. One practical outcome of this finding is to encourage combined assessment: if a pediatric eye has an abnormal biomechanical reading, one should perform detailed topography/tomography to check for any true signs of keratoconus. In our hyperopic cohort, tomography was normal in all high-CBI cases, confirming they were false positives. In cases where both biomechanics and tomography are suspicious, then one should be more inclined to believe an early keratoconus diagnosis. Additionally, clinicians might monitor those eyes more frequently – given that pediatric KCN can progress rapidly [ 1 ], even a false-positive child could be followed periodically to ensure nothing changes, especially if risk factors like eye rubbing or atopy are present. Another consideration is the emerging Stress-Strain Index (SSI) on newer Corvis software, which directly estimates corneal material stiffness. SSI has been reported to correlate positively with age [ 4 ]. Using indices like SSI (if available) could complement CBI/TBI to discern if a high CBI is due to low material stiffness (which could be age-related) or due to structural weakening (ectasia). Research in large pediatric samples would help refine such approaches. Limitations: Our study is a retrospective analysis and relies on the assumption that our hyperopic subjects truly had no subclinical keratoconus. It is very unlikely given their refractive profile and normal exams, but theoretically a few could be in extremely early disease stages that elude detection. We had a limited number of eyes with full Pentacam data; future studies with comprehensive topography on all subjects would be ideal. Another limitation is that we did not have actual refractive error values recorded – we based inclusion on clinical notes of “hyperopia” or “no myopia” and the age context. However, given the young ages, most were likely mildly hyperopic as is physiologically common. Lastly, our data included a broad age range (infants to late teens); we did not have enough power to analyze subgroups for when during childhood the biomechanical properties change most. The literature suggests corneal biomechanics in healthy eyes might remain fairly stable from infancy through adolescence (with major changes perhaps in the first year of life and then after puberty) [ 5 , 7 ]. Our aggregate analysis still serves to illustrate the overall pediatric vs adult difference. Conclusion In summary, an abnormal Corvis ST reading in a pediatric eye – especially a hyperopic, otherwise healthy eye – does not automatically equate to keratoconus. We found that nearly half of normal hyperopic children had CBI values above the adult keratoconus threshold, yet they showed no clinical or tomographic signs of ectasia. These high biomechanical index values are likely attributable to the greater corneal elasticity in youth rather than pathological weakening of the cornea. Clinicians should be aware of this age effect when interpreting Corvis results. Keratoconus screening in children should not rely on biomechanical indices alone; a multipronged evaluation (including corneal topography and risk factor assessment) is essential. Using adult cutoff values unmodified can lead to high false-positive rates in kids, which could cause unnecessary anxiety or interventions. We advocate for developing pediatric-specific reference ranges or adjusted cutoffs for CBI/TBI to improve diagnostic specificity. Until then, an “abnormal” Corvis in a child should prompt careful corneal imaging and follow-up, rather than immediate diagnosis, to distinguish true keratoconus from normal developmental biomechanical properties. Encouragingly, our data suggest that true keratoconus cases will still stand out (e.g. extremely high CBI coupled with corneal thinning), while moderate index elevations in a thick, hyperopic cornea are usually benign. In conclusion, abnormal Corvis values in pediatric hyperopic eyes are more often a reflection of normal corneal elasticity at younger ages than an indication of keratoconus – recognizing this will help avoid over-diagnosis and ensure that genuinely at-risk children receive appropriate, timely care. Declarations Availability of data and materials The dataset(s) supporting the conclusions of this article is(are) included within the additional file(s). Ethics approval and consent to participate Ethics approval and consent to participate This retrospective chart-review study involving pediatric patients with hyperopia was conducted at Advanced Eye Care Hospital, Beirut, Lebanon. The study protocol was reviewed and approved by the Institutional Review Board of the University of Balamand (UoB-IRB, University of Balamand, Lebanon; reference number: UOB-IRB-260112. All methods were carried out in accordance with institutional guidelines, national regulations, and the tenets of the Declaration of Helsinki. Because only anonymized data obtained during routine clinical care were used and no additional interventions were performed, the need for obtaining individual informed consent from participants and/or their legal guardians was waived by the UoB-IRB. This waiver is in line with UoB-IRB policies and applicable Lebanese regulations for minimal-risk retrospective studies. Funding The authors received no specific grant from any funding agency in the public, commercial, or not-for-profit sectors. Competing interests The authors declare that they have no competing interests. Availability of data and materials The dataset(s) supporting the conclusions of this article is(are) included within the additional file(s). References Feldman BH, Dutton OF; Brosman H, Feldman BH, Bunya VY, Halfpenny C, Syed ZA, Prakalapakorn SG, Nguyen A, Daly M. Pediatric Keratoconus . EyeWiki. American Academy of Ophthalmology. Updated September 6, 2025. Accessed September 19, 2025. https://eyewiki.org/Pediatric_Keratoconus Lim EWL, Lim L. Review of preoperative tomographic and biomechanical corneal assessment for refractive surgery. Taiwan J Ophthalmol. 2025. doi:10.4103/tjo.TJO-D-24-00147 Long W, Zhao Y, Hu Y, et al. Characteristics of Corneal Biomechanics in Chinese Preschool Children With Different Refractive Status. Cornea . 2019;38(11):1395-1399. doi:10.1097/ICO.0000000000001971 Guo Y, Guo LL, Yang W, et al. Age-related analysis of corneal biomechanical parameters in healthy Chinese individuals. Sci Rep. 2024;14:21713. doi:10.1038/s41598-024-72054-2 He M, Ding H, He H, et al. Corneal biomechanical properties in healthy children measured by corneal visualization Scheimpflug technology. BMC Ophthalmol. 2017;17:70. doi:10.1186/s12886-017-0463-x Matalia J, Francis M, Gogri P, Panmand P, Matalia H, Roy AS. Correlation of corneal biomechanical stiffness with refractive error and ocular biometry in a pediatric population. Cornea. 2017;36(10):1221-1226. doi:10.1097/ICO.0000000000001290 Maripudi S, Byrd J, Qureshi A, et al. Pediatric Corneal Structural Development During Childhood Characterized by Ultrasound Biomicroscopy. J Pediatr Ophthalmol Strabismus . 2020;57(4):238-245. doi:10.3928/01913913-20200506-01 Additional Declarations No competing interests reported. Cite Share Download PDF Status: Under Review Version 1 posted Reviews received at journal 21 Jan, 2026 Reviewers agreed at journal 15 Jan, 2026 Reviewers invited by journal 13 Jan, 2026 Editor assigned by journal 12 Jan, 2026 Editor invited by journal 15 Dec, 2025 Submission checks completed at journal 14 Dec, 2025 First submitted to journal 14 Dec, 2025 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. 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13:08:21","extension":"png","order_by":4,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":54502,"visible":true,"origin":"","legend":"","description":"","filename":"Onlinefloatimage1.png","url":"https://assets-eu.researchsquare.com/files/rs-8230073/v1/32224fa66ea9d7e091ad9248.png"},{"id":100410421,"identity":"5a27fcc5-7f50-4bd4-ab60-9d67d6fd18dc","added_by":"auto","created_at":"2026-01-16 13:08:21","extension":"xml","order_by":5,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":45140,"visible":true,"origin":"","legend":"","description":"","filename":"a498b8516faf4ece867fa89dcc9820ad1structuring.xml","url":"https://assets-eu.researchsquare.com/files/rs-8230073/v1/edeb072b8d3d192f8a3b19eb.xml"},{"id":100410564,"identity":"b3f4dd39-3fe9-4e99-8df0-360244653667","added_by":"auto","created_at":"2026-01-16 13:08:36","extension":"html","order_by":6,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":52433,"visible":true,"origin":"","legend":"","description":"","filename":"earlyproof.html","url":"https://assets-eu.researchsquare.com/files/rs-8230073/v1/a80a04bce5a74fbca57b577e.html"},{"id":100410584,"identity":"cb9a0af6-6ffa-48fd-9b6a-33f341d38223","added_by":"auto","created_at":"2026-01-16 13:08:37","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":127427,"visible":true,"origin":"","legend":"\u003cp\u003eDistribution of Corvis Biomechanical Index (CBI) in 277 hyperopic pediatric eyes. Nearly half the eyes had CBI above the adult keratoconus threshold of 0.5 (red dashed line), indicating a high “false-positive” rate for keratoconus if adult criteria are used.\u003c/p\u003e","description":"","filename":"floatimage1.png","url":"https://assets-eu.researchsquare.com/files/rs-8230073/v1/84d07963d9ed6eb8fecb2c46.png"},{"id":100415413,"identity":"327a797d-fdaa-4771-a39f-94e49f87774d","added_by":"auto","created_at":"2026-01-16 13:20:52","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":520581,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-8230073/v1/301fbdcc-ec7f-49ce-90d8-6601b093c90a.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Abnormal Corvis Biomechanical Indices in Pediatric Hyperopia: Keratoconus or Age-Related Elasticity?","fulltext":[{"header":"Introduction","content":"\u003cp\u003eKeratoconus (KCN) is a corneal ectasia characterized by progressive thinning and bulging of the cornea, leading to irregular astigmatism and vision loss. Early detection of KCN – especially in children – is critical, as pediatric keratoconus tends to progress more rapidly than adult KCN [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e]. Traditionally, corneal topography/tomography (e.g. Pentacam’s Belin/Ambrosio display) is used to screen for ectasia, but newer corneal biomechanical assessments provide additional insight. The Oculus Corvis ST is a non-contact tonometer with an ultra–high-speed Scheimpflug camera (≈ 4000 fps) that records corneal deformation in response to an air puff [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e]. From this dynamic measurement, the Corvis ST computes various biomechanical parameters (e.g. deformation amplitudes, applanation times) and a composite Corvis Biomechanical Index (CBI) – a dimensionless score (0 to 1) derived from a combination of biomechanical metrics to screen for ectasia [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e]. When combined with tomographic data (e.g. from Pentacam), a machine-learning derived Tomographic Biomechanical Index (TBI) is obtained for even more sensitive detection of early KCN [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e]. In adult populations, a CBI above 0.5 is the recommended cutoff suggesting an abnormal (keratoconic) biomechanical profile [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e]. Likewise, a TBI approaching 1.0 is highly indicative of ectasia risk; for example, TBI ≥ 0.79 has been reported to provide 100% sensitivity and specificity for frank keratoconus in one study [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e] (a lower cutoff around 0.29 is used to flag more subtle subclinical cases [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e]). These thresholds were established primarily in adults and have high diagnostic accuracy for distinguishing pathological from normal corneas [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eHowever, applying adult biomechanical thresholds to pediatric eyes may be problematic. The rigidity of the cornea is inversely related to age, meaning pediatric corneas are biomechanically less rigid (more elastic) than adult corneas [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e]. In effect, a healthy child’s cornea can deform more under the same pressure than an adult cornea. This raises the question: could “abnormal” Corvis readings in children simply reflect normal age-related corneal elasticity rather than true pathology? Compounding this, refractive error influences corneal biomechanics. Myopic eyes (which tend to have longer axial length and possibly biomechanically “softer” corneas) show slightly reduced corneal stiffness compared to emmetropic eyes, whereas hyperopic eyes (shorter, more compact eyes) show increased corneal stiffness [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e]. In fact, a study in preschool children found corneal stiffness parameters were highest in hyperopes and lowest in myopes, with hyperopic corneas being significantly stiffer than emmetropic or myopic corneas [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e]. Given this, restricting analysis to hyperopic children (excluding myopes) provides a conservative test: hyperopic pediatric corneas would, if anything, be on the stiffer side of normal [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e]. If even these eyes show “abnormal” deformation indices, it strengthens the idea that the abnormal values are due to age-related biomechanics rather than true keratoconus.\u003c/p\u003e \u003cp\u003ePurpose: In this study, we evaluated Corvis ST data from pediatric hyperopic patients (0–17 years) to determine whether abnormally high CBI/TBI values in this population are associated with keratoconus or simply reflect normal physiological corneal elasticity at young ages. We hypothesize that many false positives for keratoconus may occur when using adult cutoff values in children, due to the greater corneal flexibility in youth [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e]. To test this, we analyzed our patient dataset of Corvis measurements in hyperopic children, correlated the biomechanical indices with clinical/tomographic findings, and reviewed the literature on pediatric corneal biomechanics.\u003c/p\u003e \u003cp\u003e\u003c/p\u003e\u003cp\u003e\u003c/p\u003e"},{"header":"Methods","content":"\u003cul\u003e\u003cli\u003e\u003cp\u003e\u003cb\u003eStudy Design\u003c/b\u003e: We conducted a retrospective cross-sectional study of 138 pediatric patients (277 eyes) at Advanced Eye Care Hospital in Lebanon. All patients aged 0–17 years who underwent corneal biomechanical assessment with the Corvis ST were included, provided they had hyperopic or emmetropic refractive status. Patients with any degree of myopia (negative spherical equivalent) were excluded to eliminate the known confounding effect of myopia on corneal biomechanics [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e]. We also excluded any eye with previously diagnosed corneal pathology (e.g. known keratoconus, corneal scarring, prior surgery). Each patient contributed one or both eyes to the dataset as available.\u003c/p\u003e\u003c/li\u003e\u003cli\u003e\u003cp\u003e\u003cb\u003eData Collection\u003c/b\u003e: For each included eye, the Corvis ST exam provided: intraocular pressure (IOP) and central corneal thickness (CCT) measurements, and a suite of dynamic deformation parameters. Key indices recorded were the Corvis Biomechanical Index (CBI) and, when available, the Tomographic Biomechanical Index (TBI). The TBI was calculated in cases where corneal tomography data (Pentacam) was integrated with the Corvis exam. All exams had a quality score “OK” (acceptable quality) on the device. An “abnormal” biomechanical reading was defined a priori as CBI ≥ 0.50, based on the established cutoff for distinguishing normal vs. ectatic corneas [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e]. Similarly, TBI values were considered abnormal if ≥ 0.79 (the threshold optimized for detecting clinical ectasia) [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e]. We also noted TBI values in the 0.3–0.79 range which might indicate subclinical risk. After the Corvis test, corneal tomography (Pentacam) was reviewed in those eyes that had scans, and clinical examinations were reviewed for any signs of keratoconus (e.g. inferior corneal steepening on topography, abnormal Belin-Ambrosio D index, slit-lamp signs such as Vogt striae, etc.).\u003c/p\u003e\u003c/li\u003e\u003cli\u003e\u003cp\u003e\u003cb\u003eAnalysis\u003c/b\u003e: We computed summary statistics of the cohort (age, CCT, IOP) and determined the proportion of eyes exceeding the CBI and TBI abnormality thresholds. These proportions were compared against expected prevalence of keratoconus in this demographic. We paid special attention to eyes with very high biomechanical index values (e.g. CBI approaching 1.0) to see if they corresponded to any clinical abnormalities. Given the relatively small subset with TBI (tomography) data, our primary analysis centered on CBI. All data analysis was done in Python (Pandas) using the provided dataset. Results are presented with descriptive statistics and comparisons to known normal ranges from literature.\u003c/p\u003e\u003c/li\u003e\u003c/ul\u003e"},{"header":"Results","content":"\u003cp\u003eCohort Characteristics: A total of 139 pediatric patients (\u0026asymp;\u0026thinsp;277 eyes) met inclusion criteria (many patients had both eyes measured). The age ranged from infancy to 17 years (median 13 years; mean age 12.5\u0026thinsp;\u0026plusmn;\u0026thinsp;3.2 years). By design all patients were hyperopic or plano; the exact refractive errors were not recorded in the dataset, but myopic eyes were excluded. The average central corneal thickness (CCT) was 527\u0026thinsp;\u0026plusmn;\u0026thinsp;41 \u0026micro;m (range 376 to 640 \u0026micro;m), and mean Corvis IOP was 15.2\u0026thinsp;\u0026plusmn;\u0026thinsp;3.4 mmHg, both within normal pediatric ranges. Notably, corneas in this pediatric group were generally as thick as adult norms (median\u0026thinsp;~\u0026thinsp;527 \u0026micro;m), and none of the hyperopic subjects had extremely steep curvatures on clinical exam \u0026ndash; \u003cem\u003ea finding consistent with their hyperopia\u003c/em\u003e. These baseline characteristics suggest the sample largely consisted of healthy corneas. One outlier eye had an unusually thin cornea (~\u0026thinsp;376 \u0026micro;m) with clinical signs suspicious for KCN, but this was an exception; the vast majority had no clinical evidence of corneal ectasia.\u003c/p\u003e \u003cp\u003eBiomechanical Indices \u0026ndash; Frequency of Abnormal Values: Applying the adult-based cutoff of CBI\u0026thinsp;\u0026ge;\u0026thinsp;0.50, we found that a large proportion of normal pediatric eyes would be flagged as \u0026ldquo;abnormal.\u0026rdquo; Specifically, 124 out of 274 eyes (\u0026asymp;\u0026thinsp;45%) had CBI\u0026thinsp;\u0026ge;\u0026thinsp;0.5 \u0026ndash; i.e. nearly half of these hyperopic children\u0026rsquo;s eyes showed a biomechanical index in the range that would typically indicate keratoconus in an adult [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e]. Even more striking, about 22% of eyes had CBI values\u0026thinsp;\u0026ge;\u0026thinsp;0.90, approaching the maximum of the scale (1.0). In an adult refractive surgery population, a CBI that high would be strongly suggestive of frank ectatic disease [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e], yet in our pediatric hyperopes these values were relatively common. Figure\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e illustrates the distribution of CBI in the cohort, with a substantial rightward skew \u0026ndash; many eyes cluster at high CBI despite no known disease. \u003cem\u003e(See\u003c/em\u003e Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e: \u003cem\u003eHistogram of CBI in pediatric hyperopic eyes, with the red dashed line marking the 0.5 cutoff.)\u003c/em\u003e\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eFor the Tomographic Biomechanical Index (TBI), data were available in a subset of 39 eyes that had integrated Pentacam scans. Among these, 13 eyes (33%) showed TBI\u0026thinsp;\u0026ge;\u0026thinsp;0.79, exceeding the conservative cutoff for definite ectasia risk [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e]. In fact, most of the 39 eyes had at least mildly elevated TBI \u0026ndash; 33 eyes (85%) had TBI\u0026thinsp;\u0026gt;\u0026thinsp;0.29, the threshold used to detect subclinical keratoconus [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e]. In other words, if one were to apply the combined biomechanical-tomographic index as a screening tool, the majority of these \u003cem\u003eclinically normal\u003c/em\u003e children\u0026rsquo;s eyes would trigger some level of alarm. It is important to note that several TBI values in our dataset were reported as extremely high (5 to 6) \u0026ndash; these represent cases where tomography data were not actually available or the calculation was invalid, resulting in an erroneous number. Those were treated as missing data. Excluding those, the valid TBI range was 0 to 0.60 in most normal eyes, with the 13 aforementioned eyes reaching the 0.8\u0026ndash;0.9 range.\u003c/p\u003e \u003cp\u003eLack of Clinical Keratoconus Correlates: Despite the high incidence of \u0026ldquo;abnormal\u0026rdquo; biomechanical readings, none of the children in our sample had clinical or topographic evidence of keratoconus. On slit-lamp exam, corneas were clear with normal anatomy (no conical deformation, scars, Vogt\u0026rsquo;s striae, etc.), and keratometric values were in ranges expected for hyperopic or emmetropic eyes (typically K_max\u0026thinsp;\u0026lt;\u0026thinsp;~\u0026thinsp;45 D, as per clinical records). In the eyes that underwent Pentacam tomography, the maps were unremarkable \u0026ndash; e.g. regular astigmatic patterns, normal posterior elevation, and Belin/Ambr\u0026oacute;sio D indices well below the ectasia cutoff in all cases. For example, one 15-year-old patient had CBI\u0026thinsp;~\u0026thinsp;0.99 (very high) in each eye, but her Pentacam showed central Ks\u0026thinsp;~\u0026thinsp;42 D with a symmetric bow-tie pattern and BAD-D\u0026thinsp;~\u0026thinsp;1.0 (normal); another 12-year-old had CBI\u0026thinsp;~\u0026thinsp;0.95 with completely normal corneal shape on tomography. In fact, the only eye with definitively abnormal tomography was the outlier with 376 \u0026micro;m cornea, which indeed likely represents true keratoconus (and interestingly had one of the highest CBI values\u0026thinsp;~\u0026thinsp;0.997). Aside from that single case, there was no correspondence between high CBI/TBI and any keratoconic changes \u0026ndash; all other eyes with elevated biomechanical indices appeared to be false positives in terms of keratoconus detection. This suggests that the Corvis ST was flagging many young hyperopic corneas as \u0026ldquo;biomechanically weak\u0026rdquo; even though they were structurally normal.\u003c/p\u003e"},{"header":"Discussion","content":"\u003cp\u003eOur results demonstrate a clear discrepancy between biomechanical risk indices (CBI/TBI) and actual clinical status in the pediatric hyperopic population. Using the standard adult threshold (CBI\u0026thinsp;\u0026gt;\u0026thinsp;0.5) [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e], almost half of normal child eyes would be misidentified as keratoconus suspects. This finding supports our hypothesis that abnormal Corvis readings in many children are related to normal physiological properties (greater corneal flexibility at young age) rather than true keratoconus. In essence, the \u0026ldquo;red flag\u0026rdquo; cutoff values developed in adults do not translate well to a pediatric context, leading to an inflated false-positive rate.\u003c/p\u003e \u003cp\u003eThe underlying reason is rooted in corneal biomechanics: young corneas are more elastic. The collagen lamellae in a child\u0026rsquo;s cornea have different cross-linking and hydration states compared to adults, making the cornea more deformable under stress. The EyeWiki on pediatric keratoconus concisely states that corneal rigidity increases with age, and thus pediatric corneas are more susceptible to deformation (and even biochemical degradation in the context of ectasia)[\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e]. Our data empirically reflect this \u0026ndash; many of these children\u0026rsquo;s corneas deformed to a degree that the Corvis algorithm interprets as abnormal (since the algorithm was trained on stiffer adult corneas). It\u0026rsquo;s important to emphasize that greater deformation does not necessarily mean disease in a 10-year-old eye \u0026ndash; it can be a physiologic norm. In fact, population studies have shown that corneal biomechanical parameters systematically change with age. A recent large study of healthy individuals (age 11\u0026ndash;80) confirmed that corneal stiffness parameters increase with advancing age (even when controlling for IOP and thickness) [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e]. The flip side is that a teenager\u0026rsquo;s cornea is generally less stiff than a middle-aged adult\u0026rsquo;s. Thus, a CBI of 0.6 or 0.7 might be exceedingly rare in a 40-year-old normal eye, but could occur in a normal 10-year-old purely due to age-dependent elasticity. Our finding that so many hyperopic kids had CBI in the 0.5\u0026ndash;1.0 range underscores this point. It aligns with prior pediatric biomechanical studies using the Corvis and similar devices: Miao He et al. (2017) found that while corneal biomechanics in children correlate strongly with factors like CCT and IOP, they observed little change across the age range of 4\u0026ndash;18 years within childhood [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e] \u0026ndash; implying that the cornea is uniformly more pliant in youth and only later undergoes significant stiffening. In other words, what the Corvis flags as \u0026ldquo;out of bounds\u0026rdquo; for an adult may actually be within normal bounds for a child.\u003c/p\u003e \u003cp\u003eAnother aspect to consider is refractive error and ocular development. We deliberately focused on hyperopic (farsighted) children and excluded myopic children. This is because myopia itself can influence corneal biomechanics \u0026ndash; typically, myopic eyes (especially high myopes) have slightly \u003cem\u003eless rigid\u003c/em\u003e corneas, possibly related to stretching of the globe and extracellular matrix differences [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e]. Hyperopic eyes, on the other hand, are often shorter with steeper corneas and have been found to have \u003cem\u003ehigher\u003c/em\u003e corneal stiffness parameters than emmetropic eyes of the same age [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e]. A study of Chinese preschoolers (Long et al., 2019) demonstrated that at ages 4\u0026ndash;6, hyperopic children had the highest SP-A1 (stiffness parameter at first applanation) values, followed by emmetropes, then myopes [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e]. Corneal stiffness was increased in hyperopia and reduced in myopia, relative to normal eyes [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e]. Given this, our sample of hyperopic children would be expected, if anything, to have \u003cem\u003estronger\u003c/em\u003e corneas. Yet nearly half showed \u0026ldquo;weak\u0026rdquo; biomechanics by adult standards \u0026ndash; a finding that cannot be explained by refractive error or thin corneas (since their CCT was normal). This essentially isolates age as the key factor: the youth of the corneas leads to high deformability (low apparent stiffness) despite normal thickness and hyperopic shape. It\u0026rsquo;s a physiological trait of the developing eye.\u003c/p\u003e \u003cp\u003eImportantly, true keratoconus in pediatric patients is relatively uncommon (estimated prevalence\u0026thinsp;~\u0026thinsp;0.1\u0026ndash;0.2% in \u0026lt;\u0026thinsp;18-year-olds [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e]) but it does occur and often progresses quickly [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e]. Our study should not be interpreted as saying \u0026ldquo;ignore high CBI in kids\u0026rdquo; \u0026ndash; rather, it suggests that using adult cutoff criteria will over-trigger alarms. Clinicians should combine biomechanical assessment with topography/tomography and clinical exam in children. If a child has an isolated high CBI but normal corneal shape and no risk factors, careful observation is warranted instead of immediate diagnosis. In our series, none of the eyes with high CBI (except the one obvious KCN case) had any corroborating signs of keratoconus. Over-reliance on the biomechanical index alone could have led to dozens of false diagnoses. Conversely, one might worry if using a higher cutoff (to reduce false positives) could miss real keratoconus in kids. Notably, the truly keratoconic eye in our sample (15-year-old with 376 \u0026micro;m cornea) had CBI\u0026thinsp;~\u0026thinsp;0.99, so it was correctly flagged \u0026ndash; even a stricter threshold would have caught that case. Pediatric keratoconus typically causes significant topographic changes and thinning, which will usually coincide with very high biomechanical index values. Thus, a pragmatic approach is to interpret moderate biomechanical index elevations with caution in children, and look for other evidence of disease before labeling it keratoconus.\u003c/p\u003e \u003cp\u003eOur findings highlight the need for pediatric-specific normative data or adjusted thresholds for corneal biomechanical indices. Just as normal corneal curvature and thickness have age-dependent norms (e.g. infant corneas are steeper and then flatten by age 6 months, etc.), corneal biomechanical norms likely differ in the pediatric population. Currently, the CBI and TBI were developed using predominantly adult datasets [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e]. Ambrosio et al. and others have even found that ethnic differences can affect these indices \u0026ndash; for example, Asian corneas (on average having smaller diameters and possibly different biomechanical response) tended to get higher risk scores with the original CBI/TBI, prompting the development of ethnicity-specific versions (e.g. a customized cCBI and cTBI for East Asian eyes) [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e]. This shows that the \u0026ldquo;normal vs abnormal\u0026rdquo; calibration of the index can shift based on population characteristics. Age is another such factor that likely warrants calibration. It would be highly useful to establish a pediatric biomechanical index (perhaps a modified CBI scaled for age) or at least age-adjusted cutoff values. For instance, one might find that a CBI of 0.8 is within normal range for a toddler (due to a very soft cornea), whereas the same 0.8 in a 30-year-old is pathological. Without adjustment, the raw CBI/TBI should be interpreted in context \u0026ndash; high values in a child should raise \u003cem\u003econsideration\u003c/em\u003e of keratoconus, but not an immediate conclusion. Our study provides evidence that normal young corneas can and often do produce high index values.\u003c/p\u003e \u003cp\u003eOne practical outcome of this finding is to encourage combined assessment: if a pediatric eye has an abnormal biomechanical reading, one should perform detailed topography/tomography to check for any true signs of keratoconus. In our hyperopic cohort, tomography was normal in all high-CBI cases, confirming they were false positives. In cases where both biomechanics and tomography are suspicious, then one should be more inclined to believe an early keratoconus diagnosis. Additionally, clinicians might monitor those eyes more frequently \u0026ndash; given that pediatric KCN can progress rapidly [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e], even a false-positive child could be followed periodically to ensure nothing changes, especially if risk factors like eye rubbing or atopy are present. Another consideration is the emerging Stress-Strain Index (SSI) on newer Corvis software, which directly estimates corneal material stiffness. SSI has been reported to correlate positively with age [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e]. Using indices like SSI (if available) could complement CBI/TBI to discern if a high CBI is due to low material stiffness (which could be age-related) or due to structural weakening (ectasia). Research in large pediatric samples would help refine such approaches.\u003c/p\u003e \u003cp\u003eLimitations: Our study is a retrospective analysis and relies on the assumption that our hyperopic subjects truly had no subclinical keratoconus. It is very unlikely given their refractive profile and normal exams, but theoretically a few could be in extremely early disease stages that elude detection. We had a limited number of eyes with full Pentacam data; future studies with comprehensive topography on all subjects would be ideal. Another limitation is that we did not have actual refractive error values recorded \u0026ndash; we based inclusion on clinical notes of \u0026ldquo;hyperopia\u0026rdquo; or \u0026ldquo;no myopia\u0026rdquo; and the age context. However, given the young ages, most were likely mildly hyperopic as is physiologically common. Lastly, our data included a broad age range (infants to late teens); we did not have enough power to analyze subgroups for when during childhood the biomechanical properties change most. The literature suggests corneal biomechanics in healthy eyes might remain fairly stable from infancy through adolescence (with major changes perhaps in the first year of life and then after puberty) [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e, \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e]. Our aggregate analysis still serves to illustrate the overall pediatric vs adult difference.\u003c/p\u003e"},{"header":"Conclusion","content":"\u003cp\u003eIn summary, an abnormal Corvis ST reading in a pediatric eye \u0026ndash; especially a hyperopic, otherwise healthy eye \u0026ndash; does not automatically equate to keratoconus. We found that nearly half of normal hyperopic children had CBI values above the adult keratoconus threshold, yet they showed no clinical or tomographic signs of ectasia. These high biomechanical index values are likely attributable to the greater corneal elasticity in youth rather than pathological weakening of the cornea. Clinicians should be aware of this age effect when interpreting Corvis results. Keratoconus screening in children should not rely on biomechanical indices alone; a multipronged evaluation (including corneal topography and risk factor assessment) is essential. Using adult cutoff values unmodified can lead to high false-positive rates in kids, which could cause unnecessary anxiety or interventions. We advocate for developing pediatric-specific reference ranges or adjusted cutoffs for CBI/TBI to improve diagnostic specificity. Until then, an \u0026ldquo;abnormal\u0026rdquo; Corvis in a child should prompt careful corneal imaging and follow-up, rather than immediate diagnosis, to distinguish true keratoconus from normal developmental biomechanical properties. Encouragingly, our data suggest that true keratoconus cases will still stand out (e.g. extremely high CBI coupled with corneal thinning), while moderate index elevations in a thick, hyperopic cornea are usually benign. In conclusion, abnormal Corvis values in pediatric hyperopic eyes are more often a reflection of normal corneal elasticity at younger ages than an indication of keratoconus \u0026ndash; recognizing this will help avoid over-diagnosis and ensure that genuinely at-risk children receive appropriate, timely care.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAvailability of data and materials\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe dataset(s) supporting the conclusions of this article is(are) included within the additional file(s).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eEthics approval and consent to participate\u003c/strong\u003e\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eEthics approval and consent to participate\u003cbr\u003e\u0026nbsp;This retrospective chart-review study involving pediatric patients with hyperopia was conducted at Advanced Eye Care Hospital, Beirut, Lebanon. The study protocol was reviewed and approved by the Institutional Review Board of the University of Balamand (UoB-IRB, University of Balamand, Lebanon; reference number: UOB-IRB-260112. All methods were carried out in accordance with institutional guidelines, national regulations, and the tenets of the Declaration of Helsinki.\u003c/p\u003e\n\u003cp\u003eBecause only anonymized data obtained during routine clinical care were used and no additional interventions were performed, the need for obtaining individual informed consent from participants and/or their legal guardians was waived by the UoB-IRB. This waiver is in line with UoB-IRB policies and applicable Lebanese regulations for minimal-risk retrospective studies.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors received no specific grant from any funding agency in the public, commercial, or not-for-profit sectors.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCompeting interests\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare that they have no competing interests.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAvailability of data and materials\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe dataset(s) supporting the conclusions of this article is(are) included within the additional file(s).\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n \u003cli\u003eFeldman BH, Dutton OF; Brosman H, Feldman BH, Bunya VY, Halfpenny C, Syed ZA, Prakalapakorn SG, Nguyen A, Daly M. \u003cem\u003ePediatric Keratoconus\u003c/em\u003e. EyeWiki. American Academy of Ophthalmology. Updated September 6, 2025. Accessed September 19, 2025. https://eyewiki.org/Pediatric_Keratoconus\u003c/li\u003e\n \u003cli\u003eLim EWL, Lim L. Review of preoperative tomographic and biomechanical corneal assessment for refractive surgery. \u003cem\u003eTaiwan J Ophthalmol.\u003c/em\u003e 2025. doi:10.4103/tjo.TJO-D-24-00147\u003c/li\u003e\n \u003cli\u003eLong W, Zhao Y, Hu Y, et al. Characteristics of Corneal Biomechanics in Chinese Preschool Children With Different Refractive Status. \u003cem\u003eCornea\u003c/em\u003e. 2019;38(11):1395-1399. doi:10.1097/ICO.0000000000001971\u003c/li\u003e\n \u003cli\u003eGuo Y, Guo LL, Yang W, et al. Age-related analysis of corneal biomechanical parameters in healthy Chinese individuals. \u003cem\u003eSci Rep.\u003c/em\u003e 2024;14:21713. doi:10.1038/s41598-024-72054-2\u003c/li\u003e\n \u003cli\u003eHe M, Ding H, He H, et al. Corneal biomechanical properties in healthy children measured by corneal visualization Scheimpflug technology. \u003cem\u003eBMC Ophthalmol.\u003c/em\u003e 2017;17:70. doi:10.1186/s12886-017-0463-x\u003c/li\u003e\n \u003cli\u003eMatalia J, Francis M, Gogri P, Panmand P, Matalia H, Roy AS. Correlation of corneal biomechanical stiffness with refractive error and ocular biometry in a pediatric population. \u003cem\u003eCornea.\u003c/em\u003e 2017;36(10):1221-1226. doi:10.1097/ICO.0000000000001290\u003c/li\u003e\n \u003cli\u003eMaripudi S, Byrd J, Qureshi A, et al. Pediatric Corneal Structural Development During Childhood Characterized by Ultrasound Biomicroscopy. \u003cem\u003eJ Pediatr Ophthalmol Strabismus\u003c/em\u003e. 2020;57(4):238-245. doi:10.3928/01913913-20200506-01\u003c/li\u003e\n\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":"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":"Corvis ST, Pediatric Hyperopia, Corneal Biomechanics, Keratoconus, Corvis Biomechanical Index (CBI), Tomographic Biomechanical Index (TBI)","lastPublishedDoi":"10.21203/rs.3.rs-8230073/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-8230073/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003e\u003cstrong\u003ePurpose\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eTo investigate whether abnormal Corvis ST biomechanical indices (CBI, TBI) in pediatric hyperopic eyes (0–17 years) reflect early keratoconus or normal age-related corneal elasticity.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eMethods\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eA retrospective cross-sectional study was conducted on 139 pediatric patients (277 eyes) at Advanced Eye Care Hospital in Lebanon who underwent corneal biomechanical assessment with the Corvis ST. Inclusion criteria were age 0–17 years with hyperopic or emmetropic refraction; myopic eyes were excluded. “Abnormal” indices were defined as CBI ≥ 0.50 and TBI ≥ 0.79 (≥ 0.29 considered suspicious). Proportions of eyes exceeding thresholds were calculated and correlated with clinical and tomographic findings.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eResults\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNearly half of eyes (124/274; 45%) had CBI ≥ 0.50, and 22% exceeded CBI ≥ 0.90. Among 39 eyes with integrated tomography, 33% had TBI ≥ 0.79 and 85% exceeded 0.29. Despite these high rates of “abnormal” biomechanical indices, no eyes (except one with very thin cornea, 376 µm) demonstrated clinical or tomographic signs of keratoconus.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConclusions and Importance\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eUsing adult thresholds, Corvis ST flags a large proportion of normal pediatric hyperopic corneas as abnormal, suggesting high false-positive rates in children. These findings indicate that elevated CBI/TBI in pediatric hyperopes likely reflect normal physiologic elasticity rather than keratoconus. Pediatric-specific cutoff values or age-adjusted norms are needed to improve diagnostic accuracy and avoid over-diagnosis.\u003c/p\u003e","manuscriptTitle":"Abnormal Corvis Biomechanical Indices in Pediatric Hyperopia: Keratoconus or Age-Related Elasticity?","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2026-01-16 11:11:48","doi":"10.21203/rs.3.rs-8230073/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"editorInvitedReview","content":"","date":"2026-01-21T07:53:28+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"182005557025683892886255628067839543810","date":"2026-01-15T05:45:08+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2026-01-13T11:50:30+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2026-01-13T04:44:56+00:00","index":"","fulltext":""},{"type":"editorInvited","content":"","date":"2025-12-15T16:36:24+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2025-12-14T17:52:18+00:00","index":"","fulltext":""},{"type":"submitted","content":"BMC Ophthalmology","date":"2025-12-14T17:46:17+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":"ed281a86-61da-45fd-858c-1f102e763e4e","owner":[],"postedDate":"January 16th, 2026","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[],"tags":[],"updatedAt":"2026-01-16T11:11:49+00:00","versionOfRecord":[],"versionCreatedAt":"2026-01-16 11:11:48","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-8230073","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-8230073","identity":"rs-8230073","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}