Corneal power, axial length-to-corneal radius ratio, and myopia status prior to corneal refractive surgery: a cross-study analysis

We examined the interplay among corneal refractive power, the axial-length-to-corneal radius of curvature ratio (AL/CR), and myopia severity in patients before corneal refractive surgery. We included 1208 myopic patients with a median age of 22 years (P25 = 19, P75 = 27) and a preoperative spherical equivalent (SE) of - 4.88 D (P25 =  - 6.50, P75 =  - 3.50). Myopia status was classified using the spherical equivalent refraction into low, moderate and severe myopia. Key measurements included corneal curvature radius (CR), flat (K1) and steep (K2) corneal curvatures, anterior corneal surface astigmatism (ΔK), central corneal thickness (CCT), axial length (AL), and AL/CR. Severe myopic patients were slightly older than other cases. CR was smaller in severe myopia. Significant differences were observed in K2 and ΔK between severe and less severe myopic patients, but not in K1 and CCT. Female patients exhibited a lower AL than male patients, but AL/CR differences were only significant in the mild myopia group. A linear relationship was found between increasing AL/CR and decreasing SE. Multivariate analysis adjusted for age and sex revealed that each 1 mm increase in AL resulted in a 1.98 D decrease in SE, while a 1 mm increase in CR led to a 5.00 D increase in SE. A 0.1 unit increase in AL/CR corresponded to a 1.48 D decrease in SE. Severe myopia was associated with steeper corneal curvature, particularly in the steep axis. AL/CR did not differ between genders in moderate and severe myopia, suggesting its reliability as an index for assessing myopic refractive state.