Retinal nerve fibre layer thickness of black and Indian myopic students at the University of KwaZulu-Natal

Abstract

Aim: To compare retinal nerve fibre layer (RNFL) thickness in black and Indian myopic students at the University of KwaZulu-Natal.

Method: Eighty (40 black and 40 Indian) participants of both genders and aged between 19 and 24 years (mean and standard deviation: 21 ± 1.7 years) were included in the study. Refractive errors were assessed with the Nidek AR-310A auto-refractor and via subjective refraction. RNFL thicknesses were then measured using the iVue-100 optical coherence tomography device. Axial lengths were measured with the Nidek US-500 A-scan ultrasound device. Data were analysed by descriptive statistics, t-tests, Pearson’s correlation coefficients and regression analysis.

Results: The mean myopic spherical equivalent was significantly more negative amongst the Indian (-2.42 D ± 2.22 D) than amongst the black (-1.48 D ± 1.13 D) (p = 0.02) participants.The mean axial length was greater amongst the black (23.35 mm ± 0.74 mm) than amongst the Indian (23.18 mm ± 0.87 mm) participants but the difference was not significant. In the total sample (n = 80), the average global RNFL thickness ranged from 87 μm to 123 μm (105 μm ±9 μm). Mean global RNFL thickness was slightly greater amongst black (108 μm ± 7 μm) than amongst Indian (102 μm ± 9 μm) (p = 0.00) participants. Mean global RNFL thickness was similar for male (106 μm ± 7 μm) and female (105 μm ± 10 μm) (p = 0.79) participants.A positive and significant association between myopic spherical equivalent and global RNFL thickness was found for the total sample (r = 0.36, p = 0.00) and for Indians (r = 0.33, p = 0.04)but not for the black (r = 0.25, p = 0.13) participants. There was a negative and significant correlation between axial length and global RNFL thickness amongst the Indian participants (r = -0.34, p = 0.03) but not amongst the total sample (r = -0.12, p = 0.30) or the black (r = 0.06, p = 0.73) participants.

Conclusion: The findings suggest that racial differences in RNFL thickness need to be considered in the clinical examination and screening for glaucoma and other optic nerve pathologies amongst black and Indian people. Additionally, the possible influences ofrefractive error and axial length should be considered when evaluating RNFL thickness.