Corneal asphericity and its related factors

Proper correction of spherical aberration using intraocular lenses requires precise selection of the sphericity of intraocular lens surfaces based on individual biometric data and corneal asphericity coefficient (Q value). This study aimed to determine and analyze the corneal Q value and its related factors among Saudi participants.

In this cross-sectional study, normal right eyes of healthy Saudi participants aged 17 - 58 years who visited Al-Kahhal Medical Complex, Dammam, Saudi Arabia, were included. The Pentacam rotating Scheimpflug camera was used to determine the average Q value at 6-mm diameter. Q values were obtained from each quadrant (superior, nasal, inferior, and temporal) and two meridians (horizontal and vertical). Mean Q values of the anterior and posterior corneal surfaces were also obtained. Other factors including age, sex, refractive error, and central corneal radius were documented.

Five hundred right eyes from 500 participants were included. The mean (standard deviation [SD]) (range) age was 27.2 (7.1) (18 - 58) years. The mean (SD) (range) Q value of 500 eyes was - 0.24 (0.10) (- 0.71 to + 0.09) anteriorly and - 0.16 (0.14) (- 0.70 to + 0.23) posteriorly, being significantly more prolate anteriorly (P < 0.05). The corneas were significantly more prolate in the nasal than in the temporal quadrant, in the superior than in the inferior quadrant, and in the horizontal than in the vertical meridian (all P < 0.05). There were statistically significant differences in anterior, nasal, temporal, inferior, horizontal, and vertical Q values among age groups (all P < 0.05) but not in the superior or posterior Q values (both P > 0.05). The corneas became less prolate with increasing age (P < 0.05). However, Q values were comparable between the sexes (all P > 0.05). There was no significant correlation between anterior (r = + 0.08; P = 0.095) or posterior (r = - 0.08; P = 0.092) Q value and spherical equivalent, but a significant trend was detected toward more prolate shape with increasing myopia in the temporal and inferior quadrants (r = + 0.19; P < 0.001, r = + 0.10; P = 0.022, respectively). There was a significant negligible correlation between the posterior Q value and central corneal radius (r = - 0.18; P < 0.001) but no significant correlation between the anterior Q value and central corneal radius (r = + 0.02; P = 0.673).

Most corneas in this Saudi population were prolate in contour. Anterior corneal asphericity was positively correlated with age and was not significantly related to sex, refractive error, or central corneal radius. Further studies are needed to verify our preliminary findings.