EXTENT AND EFFECT OF SURFACE TILT ON THE DATA DISPLAY OF THE EYESYS VIDEOKERATOSCOPE

Aims - This study examined the occurrence, magnitude, and the conseque nces of a possible tilt between the corneal surface and optical axis o f the EyeSys videokeratoscope. Methods - Initially, a theoretical mode l was developed to calculate the angle of tilt. The predictions of the model were verified empirically using a convex conicoid surface and w ere found to predict the tilt to within 0.5 degrees of the actual tilt . The likely effects of the tilt on the corneal power were also examin ed. The angle of tilt was then measured on the human cornea and the ef fect of neutralising the tilt on the videokeratoscopic data display wa s observed. Results - The angle of tilt was found to lie between 1 deg rees and 6 degrees in a temporal direction. Conclusion - When the corn eal tilt on the human subjects was neutralised, then a reduction in th e nasal/temporal asymmetry was observed.