Comparative Evaluation of Peripapillary Retinal Nerve Fiber Layer Thickness in Myopes and Emmetropes in a Tertiary Hospital in Nigeria

Abstract

PRÉCIS: This comparative cross-sectional study in an indigenous black population demonstrated that high myopic eyes have a significantly thinner retinal nerve fiber layer when compared with emmetropic and other myopic subgroups. PURPOSE: To compare the peripapillary retinal nerve fiber layer (RNFL) thickness in myopes and emmetropes and determine the relationship between age and sex and RNFL thickness in myopes and emmetropes in an African population. METHODS: This was a hospital-based observational cross-sectional study in which both myopic and emmetropic subjects were recruited. Myopic subjects were classified into low [-0.5D to -3.0 diopters (D)], moderate (>-3.0D to -5.0D), and high myopia (>-5.0D) based on spherical equivalent. Myopic and emmetropic groups were further subdivided into subgroups based on age as follows: 20-29, 30-39, 40-49, and 50-59 to recruit subjects across the age groups. Consecutive subjects presenting to the eye clinic that met the eligibility criteria were recruited into the study until the sample size in each group was completed. All participants underwent full ophthalmic examination, refraction, visual fields analysis, and A-scan biometry. The peripapillary RNFL thickness of the retina was measured using the Optovue iScan Spectral Domain Optical Coherence Tomography (SD-OCT). Measurements from one eye (right) of participants were used for analysis. Quantitative data were descriptively summarized and compared using t test, ANOVA, and ANCOVA. RESULTS: A total of 116 participants were recruited, 28 (24.1%) subjects were emmetropes, while 33 (28.5%) had low myopia, 27 (23.3%) moderate myopia, and 28 (24.1%) high myopia. The mean age of all subjects was 36.0±11.4 years. All subgroups of myopia had thinner RNFL [Low=103.8±8.6 µm ( P =0.582); Moderate=101±6.5 µm ( P =0.171); High=94.4±7.9 µm ( P =<0.001)] compared with emmetropes (105.2±10.7 µm). There was a decrease in the mean global RNFL thickness with increasing myopia. RNFL thickness was negatively correlated with age ( r = -0.303). The rate of reduction per year was higher in emmetropes (0.66 µm) compared with myopes (0.25 µm). The rate of decline of RNFL per year is associated with thicker mean global RNFL thickness seen in emmetropes as compared with myopes. CONCLUSION: High myopes in this population have thinner peripapillary RNFL values compared with emmetropes, low and moderate myopes. RNFL thickness was negatively correlated with age in both emmetropes and myopes.