Axial Length to Corneal Radius of Curvature Ratio and Refractive Errors

Purpose: to determine the distribution of axial length (al) to corneal radius of curvature (crc) ratio and to evaluate its association with refractive errors in an iranian population. methods: in this cross sectional study, multistage cluster sampling was used to select subjects 40-64 years of age residing in shahroud, northern iran. all subjects underwent manifest and cycloplegic refraction, and biometry using the allegro biograph (wavelight ag, erlangen, germany). individuals with a history of intraocular surgery, extensive pterygia and ocular trauma were excluded. results: of a total of 6,311 patients, 5190 (82.2%) participated in the study. we excluded 247 patients to adhere with study criteria and 132 patients due to missing data. mean al/crc was 3.034 [95% confidence interval (ci), 3.031–3.037]. al/crc was 3.028 and 3.042 in female and male subjects, respectively (p<0.001). the r2 coefficients between spherical equivalent (se) refractive error and al/crc, al, crc, lens thickness, and anterior chamber depth were 0.607, 0.351, 0.012, 0.038, and 0.091, respectively. linear regression showed a 12.1 diopter (d) shift towards myopia with every 1 unit increase in al/crc (p<0.001). mean al/crc was 3.472 among myopes with se less than -5.0d; this value decreased linearly and was as low as 2.690 among hyperopes with se more than 5.0d. r2 coefficients for al/crc with spherical and cylindrical power were 0.560 and 0.071, respectively. conclusions: minimal changes in al/crc lead to large changes in refractive error. the correlation between refractive errors was significantly stronger with the al/crc ratio than with al and crc alone.