Variations in Ocular Biometry and Refraction in Pakistani Adults – Results of the Pakistan National Blindness and Visual Impairment Survey

Abstract

Purpose: : To describe variation in ocular biometry and refractive error among adults examined in The Pakistan National Blindness and Visual Impairment Survey.

Methods: : This study was a nationwide population–based cross–sectional survey of adults aged 30 years and older. Axial ocular dimensions including axial length (AL), anterior chamber depth (ACD), lens thickness (LT), and vitreous chamber depth (VCD) were measured using an A–scan ultrasound device. Corneal curvature (CC) and noncycloplegic refraction were measured with an autorefractor. Lens nuclear opacity (NO) was graded clinically using the Lens Opacity Classification System (LOCS III).

Results: : 16,507 adults were examined (95.5% response rate) in the survey. Biometric and refraction data were available for 13697 (82.9%) phakic subjects. AL, ACD, LT, VCD and CC values were 22.8 +/– 0.83 mm, 3.08 +/– 0.59 mm, 3.72 +/– 0.77 mm, 16.00 +/– 1.34 mm and 7.68 +/– 0.31 mm (mean +/– SD), respectively. On average, people aged 30 to 49, when compared to those aged 50 or older, had longer ALs (mean difference, +0.05 mm), deeper ACDs (+0.15 mm), greater CC (+ 0.05 mm), but thinner lenses (–0.06 mm). VCDs did not vary significantly with age. After controlling for age, women had shorter ALs and VCDs, shallower ACDs and thinner lenses and steeper CCs than men. Taller people had longer ALs, yet women had shorter ALs even after adjustment for height. The variation in noncycloplegic refraction with age was nonlinear. Among people aged 30 to 49 years, a higher prevalence of hyperopia was seen in older compared with younger persons explained principally by shorter AL (and VCD) in older persons. Among those aged 50 years and older, a higher prevalence of myopia was seen in older compared with younger persons, due to increasing LT and increasing NO in the older age groups (despite shorter AL in older persons).

Conclusions: : Ocular dimensions vary with age and gender in Pakistani adults. The variation in noncycloplegic refraction in people 30 years and older may be explained by differences in axial lengths between older and younger persons, and from 50 years onwards, differences in lens thickness and nuclear opacification.

Keywords: myopia • hyperopia • refraction