Variation in normal corneal shape and the influence of eyelid morphometry

Purpose. To investigate variation in normal corneal shape and the influence of eyelid morphometry on corneal shape in primary gaze. Methods. Corneal topography (Medmont E300) and external eye photographs (Nikon D5000 SLR camera) were captured in primary gaze from 32 East Asians (13 male and 19 female subjects, 18 to 37 years) and 32 nonYEast Asians (10 male and 22 female subjects, 18 to 30 years). Participants with refractive error within T6.00 DS and up to 1.50 DC corneal toricity were enrolled. A custom MATLAB program was used to determine hemi-meridional and sectorial corneal asphericity. A separate MATLAB program (i-Metrics) was used to determine the dimensions of anterior eyelid parameters. Sectorial corneal asphericity and eyelid morphometry dimensions were compared between ethnic groups. The interactions between sectorial asphericity and eyelid morphometry were also investigated. Results. There was no significant difference in the sectorial corneal asphericity variation between ethnicities (p = 0.231). Eyelid features including horizontal palpebral fissure width; vertical palpebral fissure height; palpebral fissure slant; upper eyelid position, slope, and curvature; and lower eyelid slope and tilt were significantly different (all p < 0.05) between ethnicities. Analysis from the combined data revealed that horizontal palpebral fissure width correlated negatively with corneal spherical equivalent M (r = j0.369, p = 0.003). Upper eyelid curvature correlated negatively with corneal M (r = j0.377, p < 0.001), with differences between ethnicities. Lower eyelid slope was significantly associated with corneal power vector J45 (r = 0.262, p = 0.037). Only lower eyelid curvature showed interaction with inferotemporal (r =j0.351, p = 0.004) and inferonasal (r = j0.250, p = 0.047) mean corneal asphericity. Conclusions. Sectorial variation is present in normal corneal shape and this variation is not significantly different between East and nonYEast Asian eyes. Several eyelid features appear to influence corneal shape in primary gaze