Enantiomorphism is a common finding in the human body (ears, hands, feet). Overall symmetry of the right and left corneas, however, has only been sporadically studied, using different methodologies. Boote et al.
12 mapped in detail the distribution and orientation of the collagen fibrils across the corneas of a pair of mate eye bank eyes using wide-angle x-ray scattering. Although structurally distinct, the right and left corneas showed midline symmetry. Smolek et al.,
13 Wang et al.,
14 and Lombardo et al.
15 observed a moderate to high degree of mirror symmetry between the higher-order aberrations of the right and left corneas, with significant intersubject variability. Corneal optical aberrations are known to be closely linked to corneal shape.
16
A few other groups have studied symmetry between right and left corneas based on keratometry and/or corneal topography parameters, using subjective or objective and qualitative or quantitative methodologies.
17–22 Although we could not find other studies similar to ours, our findings are in accordance with these reports. Dingeldein and Klyce
18 subjectively observed a high degree of mirror symmetry in shape between the right and left corneas, based on the first corneal topography analyses in 1989 (LSU Eye Center corneal analysis system; Louisiana State University, New Orleans, LA, USA). A few studies subsequently reported quantitative comparisons of right and left eye corneal topographies, using the Orbscan
17,20,22 or the Pentacam system (Oculus, Inc., Arlington, WA, USA).
19 With variable methodologies and relatively small sample sizes (50 to 275 subjects), these groups found evidence of corneal symmetry based on small differences between eyes, with or without statistical analyses, and sometimes using correlations to assess proportionality between eyes. The studied parameters varied, including anterior and posterior surface shape parameters, such as simulated keratometry, steepest keratometry, central radius of curvature, apex elevation, and BFS radius, corneal volumes within central zones of given diameters, as well as central corneal thicknesses.
17,19,20,22
A few other studies used a decrease in interocular symmetry as a useful tool to detect keratoconus.
23–26 Although of significant interest in the context of preoperative screening before refractive surgery, this type of assessment based on specific topographical parameters is not meant to guide the production of corneal substitutes, as it informs only a little about global corneal shape, volume, and symmetry.