OPTICAL ZONE CENTRATION IN KERATOREFRACTIVE SURGERY - ENTRANCE PUPIL CENTER, VISUAL AXIS, COAXIALLY SIGHTED CORNEAL REFLEX, OR GEOMETRIC CORNEAL CENTER

Purpose. To study the differences in optical zone marking using the ge ometric corneal center, entrance pupil center, visual axis, and the co axially sighted corneal reflex as centration points. Methods: A modifi ed autokeratometer was used to photograph the cornea in 50 volunteers under standardized levels of illumination, with the subject fixing on the keratometer target. These photographs enabled us to mark the above -mentioned centration points and measure the direction and degree of d ecentration. Results: From the corneal intercept of the visual axis, t he entrance pupil center was found up to 0.75 mm (mean, 0.34 mm) tempo rally, the corneal reflex was found up to 0.62 mm (mean, 0.02 mm) nasa lly, and the geometric corneal center was found up to 1.06 mm (mean, 0 .55 mm) temporally. Conclusion: The ideal physiologic centration point is the corneal intercept of the visual axis. The decentration from th e visual axis was least if the coaxially sighted corneal reflex was us ed for centration.