Variations in Corneal Asphericity (Q Value) Between African-Americans and Whites

Abstract

Corneal asphericity as represented by mean Q value varies significantly between African-Americans and whites. The greatest differences are evident in opposing quadrants and appear to be little influenced by age, gender, or SE.

Variation in Normal Corneal Shape and the Influence of Eyelid Morphometry

“…Sheridan and Douthwaite 5 assessed asphericity in terms of shape factor in nasal and temporal hemi-meridians and showed that the nasal cornea flattened at a faster rate than the temporal cornea with respect to geometric center. Recent studies that investigated hemi-meridional Q values in different ethnicities have also showed a similar trend, 8,13 where the corneal asphericity in the nasal and superior hemi-meridians was more prolate than the temporal and inferior hemi-meridians, respectively.…”

“…Previous studies have limited their investigation to only a few meridians 4,7 or hemi-meridians. 2,5,8,13 The current study gives a much broader view of corneal shape as it has investigated corneal shape in sectors encompassing the entire cornea over the central 8-mm zone. This study has shown that for eyes with up to 1.50 diopters of corneal toricity, the corneal shape is not uniform in terms of asphericity in different corneal sectors.…”

“…11 Because the cornea is an elastic structure, its shape can be influenced by various external factors. These factors include age, 12 ethnicity, 13 eyelid position, 14 and eyelid shape, 15 with the eyelid having considerable influence because of its apposition and proximity to the corneal surface. Read et al 15 reported a number of associations between eyelid shape and parameters of normal corneal shape, although no association was reported between eyelid shape parameters and corneal asphericity.…”

Analysis of age, refractive error and gender related changes of the cornea and the anterior segment of the eye with Scheimpflug imaging

“…Myopes were more oblate and hyperopes were more prolate [20,21]. Contrasting these results, some studies show no significant correlation between corneal surface asphericity and spherical equivalence [22,23].…”

Retrospective Analysis Comparing the Preoperative and Postoperative “Q” Values for 2 Different Lasers in Refractive Surgery

“…In our population, the SD in the preoperative Q value was 0.12, which closely models reported values from other studies. 19 The reported difference in DQ/D between both lasers was only 0.02, which is unlikely to be clinically significant. Additionally, because we have no data for the Allegretto laser beyond 25.00 D, it is difficult to conclude whether the VISX laser has a smaller for treatments beyond 24.05 D. For this reason, we report the population average DQ/D as most representative of the data gathered.…”