Axial Length/Corneal Radius Ratio: Association with Refractive State and Role on Myopia Detection Combined with Visual Acuity in Chinese Schoolchildren

Abstract

PurposeTo evaluate the association between the AL/CR ratio and refractive state and explore the effectiveness of this ratio in the assessment of myopia, especially when combined with uncorrected visual acuity in schoolchildren among whom myopia is common.MethodsCross sectional study. 4686 children from 6 primary schools, aged from 6 to 12 years were selected using the clustered-stratified random sampling method. Uncorrected visual acuity (UCVA), axial length (AL), corneal radius of curvature (CR), and cycloplegic refraction were tested. Refraction was measured as the spherical equivalent (SE).Results3922 children were included in the analysis. The mean AL/CR ratio was 2.973±0.002, increased with age, and different in gender. The coefficients of correlations of the SE with the AL/CR ratio, AL, and CR were -0.811, -0.657, and 0.095, respectively. Linear regression showed a 10.72 D shift towards myopia with every 1 unit increase in the AL/CR ratio (P<0.001, r2 = 66.4%). The estimated SE values obtained by substituting the AL/CR ratio and gender back to the regression model that were within a difference of ±0.50 D in ATE/LER (allowable total error and limits for erroneous results) zones compared to the actual measured values was 51%. The area under the ROC curve of the AL/CR ratio, AL, and UCVA for myopia detection were 0.910, 0.822, and 0.889, respectively, and the differences between each pair were statistically significant (P<0.01). At a specificity of 90%, the sensitivities were 72.98%, 50.50%, 71.99%, and 82.96%, respectively, for the AL/CR ratio, AL, UCVA, and the combination of the AL/CR ratio and UCVA.ConclusionsThe AL/CR ratio was found to explain the total variance in SE better than AL alone. The effectiveness of the AL/CR ratio was statistically significantly better than UCVA for detecting myopia in children, and combining the two produced increased sensitivity without significantly decreasing specificity.

Ratio of Axial Length to Corneal Radius in Japanese Patients and Accuracy of Intraocular Lens Power Calculation Based on Biometric Data

“…AL/CR RATIO AND RELATIONSHIPS AMONG THE SE AND AL, CR, AND AL/CR RATIO: The distributions of the AL/CR ratio have been reported in different populations and age groups 31,[34][35][36][37][38][39][40][41] and the AL/CR ratios for myopia were between 2.9 and 3.1 and less than 2.9 for emmetropia and hyperopia. 26,27,[42][43][44][45][46] Table 4 summarizes the other studies. In the current report, the CR was approximately the same as that in those previous reports, and women had significantly steeper corneal curvature values, 43 whereas the current AL was longer than those reported previously.…”

“…The AL/CR ratio then was found to be related more closely to refraction than the AL or CR alone. [26][27][28][29][30][31][32] He and colleagues 26 reported that the AL/CR ratio generally can determine the refractive status of the human eye and described the shape of the globe. Therefore, this study hypothesized that the AL and the AL/CR ratio may play important roles in the inaccuracy of the IOL power calculations.…”

Effect of cycloplegia on the measurement of refractive error in Chinese children

“…The enrolled children were allocated into three groups according to M: myopia, emmetropia, and hyperopia. Myopia was defined as M ≤ −0.50 D, emmetropia as −0.50 D < M < +0.50 D, and hyperopia as M ≥ +0.50 D . The distribution of the refraction was further analysed by stratifying the study children by three age groups: four to six years (preschool children), seven to 11 years (primary school children), and 12 to 16 years (junior middle school children).…”

“…Briefly, auto‐refraction was performed for each child by the same study optometrist without and with cycloplegia. First, non‐cycloplegic refraction was performed using a Desktop Auto‐refractor (RK‐F1; Canon Inc.) with a measurement range of −20.00 to +20.00 D. Cycloplegia was achieved by topical application of four drops of 0.5 per cent tropicamide (Bausch & Lomb Pharmaceutical Co., Ltd, Shandong, China) at five‐minute intervals . Auto‐refraction was then performed again using the same equipment by the same optometrist 30 minutes after the last eye drop was administered.…”

Comparison of noncycloplegic and cycloplegic autorefraction in categorizing refractive error data in children

“…Also, axial length/corneal curvature ratio was considered a better predictor than UCVA for the refractive state of the eye (He et al. ). Therefore, axial length and corneal topography were also included in the analysis.…”