Axial length/corneal radius of curvature ratio and refractive status in an adult Nigerian population.

Abstract

Associations between axial length (AL) to corneal radius of curvature (CR) ratio and refractive status in a healthy Nigerian adult population were studied. Healthy students and members of staff of Obafemi Awolowo Teaching Hospitals Complex, Ile-Ife, South West Nigeria, free of obvious ocular diseases except possible refractive errors were recruited. Consecutive consenting volunteers were recruited by simple random sampling and a proportionate sample of each population based on its representative fraction in the hospital community was recruited. The study was conducted between June and August 2011. Noncycloplegic objective refraction was done and spherical equivalent refraction (SER) of the right eyes was used for calculation. The AL, CR, and keratometric readings were measured with the IOL Master. The AL/CR ratio was calculated. The data were analyzed with statistical software package STATA 13. Three hundred and fifty volunteers aged 18-60 years were studied. The mean ± standard deviation of AL/CR and SER were 3.04 ± 0.10 and -0.38 ± 1.42D, respectively. AL in myopia was significantly higher than in emmetropia and hypermetropia. There were no significant differences between CR in the refraction groups. Myopes had significantly higher AL/CR than nonmyopes. On controlling for age and gender, 1 mm increase in AL increased SER by -0.77D (95% confidence interval [CI] -0.91--0.64D) while a unit increase in AL/CR increased SER by -8.89D (95% CI -10.00--7.78D). Whereas AL accounts for 39% of variability in SER (P < 0.001), AL/CR accounts for 51% of the variability observed in SER (P < 0.001). This study has further confirmed that the AL remains a strong determinant of refraction, but a derived factor AL/CR accounts for more variation in final refractive status than AL in isolation.