A multicenter study of interocular symmetry of corneal biometrics in Chinese myopic patients

Abstract

It is essential to know the normal range of the interocular symmetry of the cornea (ISC) for keratoconus diagnosis and corneal substitutes design. In the present study we investigated the interocular symmetry of corneal biometrics in 6,644 Chinese myopic patients from multiple ophthalmic centers. Corneal biometrics of both eyes were exported from the Pentacam instrument. Interocular symmetry of the corneal biometrics was analyzed by Spearman’s correlation test, intraclass correlation coefficient (ICC) analysis and Bland–Altman plot. Significantly strong interocular correlations were found in anterior and posterior corneal curvatures, corneal diameter, corneal thickness, corneal volume, corneal eccentricity, and corneal asphericity (r = 0.87–0.98, all P < 0.001). Moderate interocular correlations were observed in whole corneal astigmatism (r = 0.78) and posterior corneal astigmatism (r = 0.73). ICC between the right and left eyes was 0.94–0.98 for anterior and posterior corneal curvatures, corneal diameter, corneal thickness and corneal volume, 0.80–0.88 for corneal eccentricity and asphericity, and 0.73–0.79 for corneal astigmatism (all P < 0.001). Bland–Altman plot showed that the 95% limit of agreement between both eyes was narrow and symmetric in most of the corneal biometrics, suggesting strong interocular agreements in these corneal biometrics. In conclusion, significant interocular symmetry of corneal biometrics is observed in Chinese myopia patients. Extra attention should be paid to patients with interocular corneal asymmetry.

Distribution of White-to-White Corneal Diameter and Anterior Chamber Depth in Chinese Myopic Patients

“…The study was approved by the Institutional Review Board (IRB) of every hospital (GZ, SY, CD, WH, and HK) and conducted in agreement with the Declaration of Helsinki. The IRBs waived the need of informed consent as the study only involved review and analysis of medical records and no individual patient could be identified from the data ( 15 , 16 ). Inclusion criteria were myopic patients with a spherical equivalent (SE) ≤ −0.50 D and good quality Scheimpflug scans.…”

“…Only the right eyes of the patients were included for analysis. Exclusion criteria were coexisting corneal diseases, keratoconus, forme fruste keratoconus, severe dry eye, non-axial myopia (such as those caused by spherophakia), previous ocular trauma or surgery, uveitis, glaucoma, wearing contact lenses within the previous 2 weeks, age younger than 18 years (unstable refraction) or older than 40 years (to reduce the effects of the crystal lens on anterior chamber depth measurement) ( 15 , 16 ).…”

“…The WTW and ACD were measured with Pentacam by experienced technicians under dim light condition according to the standard procedures of the manufacturer (Oculus GmbH, Wetzlar, Germany) as previously described ( 15 , 16 ). The fixation target was set to a viewing distance of +1.00 to 0.00 D (far vision) ( 17 ).…”

“…Repeated measurement was taken when Pentacam scans did not pass the quality check. Quality control and data retrieving of Pentacam examination were previously described ( 15 , 16 ).…”

Interocular Symmetry Analysis of Corneal Elevation Using the Fellow Eye as the Reference Surface and Machine Learning

“…Since there is wide variation in the normal population that define their reference ranges, they have shown suboptimal performance in discriminating normal corneas from subclinical forms of disorders [ 14 ]. This is while measures of normal fellow corneas are strongly correlated [ 15 , 16 , 17 ], contralateral eyes are highly symmetric [ 18 , 19 , 20 , 21 , 22 ], and there is consensus that lack of symmetry should be interpreted as a red flag warranting reevaluation or further testing [ 20 , 23 , 24 , 25 , 26 , 27 ]. Nonetheless, our understanding of corneal symmetry is limited to single-point metrics (e.g., elevation at the apex, corneal thickness at the thinnest point) and local indices (e.g., simulated keratometry in the steep and flat axes); the color-coded patterns have not been classified or described, and no multi-feature or global indices have been developed yet.…”