Distribution of corneal spherical aberration in a Tanzanian population

Abstract

Purpose : In recent cataract surgery, aspherical intraocular lenses has been widely inserted so as to reduce the whole ocular spherical aberration (SA) and lead to an improvement in visual function. However, the distribution of corneal SA in sub-Saharan African people has not yet been reported. In this study, we aimed to investigate the distribution of corneal SA in Tanzanian people, and examine the correlation between corneal SA and ocular parameters so as to determine whether corneal SA can be estimated by common preoperative measurements.

Methods : This study was performed as a part of a cross-sectional population-based study. Residents aged 40 years and older in three villages in the Mkuranga district in Tanzania were enlisted as study participants. Corneal higher-order aberrations (HOAs) for the right eye were measured with a wavefront analyzer (KR-1W, Topcon) and calculated for the central 6.0-mm zone. Corneal curvature radius (CR), corneal astigmatism, anterior chamber depth (ACD), and axial length (AL) were also measured and their correlation with corneal SA was assessed.

Results : The right eyes of 657 participants were analyzed. The mean age of the subjects was 57.2 ± 10.3 years (mean ± SD; range: 40 to 91 years). The mean corneal SA (Zernike spherical aberration coefficient C₄⁰) of this study population was 0.19 ± 0.10 μm (-0.24 to 0.61). The SAs in about three-quarters of all subjects were between 0.10 and 0.30 μm. The root mean squares of total corneal HOAs and the third- and fourth-order aberrations were 0.63 ± 0.25 μm, 0.54 ± 0.24 μm, and 0.27 ± 0.11 μm, respectively. In univariate analysis, corneal SA showed weak but significant correlations with CR (Pearson’s correlation coefficient, r = -0.13, p < 0.01), corneal astigmatism (r = -0.16, p < 0.001), ACD (r = 0.18, p < 0.001), AL (r = -0.11, p < 0.01), and age (r = -0.08, p < 0.05). In multiple linear regression analysis, the SA was correlated with ACD (p < 0.001), AL (p < 0.001), and corneal astigmatism (p < 0.01) with a squared multiple correlation coefficient (Adjusted R²) of 0.08.

Conclusions : The mean corneal SA in Tanzanian individuals was smaller than that in Caucasian and Middle-Eastern individuals. IOLs with milder asphericity may be suitable to Tanzanian population. It was difficult to predict corneal SA from other ocular biometry measurements.

This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.