Catoptric properties of eyes with misaligned surfaces studied by exact ray tracing.

PURPOSE Historically, Purkinje images have been used to calculate ocular surface curvature and misalignment. The purpose of this report is to introduce an exact ray-tracing program that can be used to examine the influence of ocular component variations on the size and position of Purkinje images I, III, and IV. METHODS Ray tracing was carried out on Le Grand's four-surfaced schematic eye to demonstrate the main features of the program. Any location may be chosen for the point light source and the observer. Ocular component dimensions, eye rotation, and crystalline lens decentering and rotation are fully adjustable. The program computes the coordinates of the Purkinje images in three-dimensional space from the point of view of the observer. It also offers the option of exhibiting Purkinje images seen through standard and telecentric imaging devices. Both options yield Purkinje image positions in relation to the rotating center of the limbus, observed clinically. RESULTS The resulting program compared favorably with current ray-tracing software and with data from the literature. CONCLUSIONS The program has many research and teaching applications. For example, our requirement was to calculate a series of linear coefficients that closely approximate Purkinje-image behavior in any given eye. These coefficients may be used to measure misalignment of intraocular components in phakic and pseudophakic eyes.