Preliminary tests and construction of a computerized quantitative surgicalkeratometer

Purpose: To construct a simple, computer-based. quantitative surgical kerat ometer to measure a 3.0 to 4.0 mm central region of the corneal surface. Setting: Laboratorio de Optica Oftalmica, Institute de Fisica de Sao Carlos (IFSC-USP), Sao Paulo, Brazil. Methods: A high-intensity fiber-optic-illuminated ring pattern (Placido dis k) is projected on the cornea. Reflected images are captured by a charge-co upled device camera mounted on a Zeiss microscope beam splitter and then di gitized by a frame grabber installed on an IBM-compatible personal computer . Simple algorithms based on image-processing techniques were implemented f or border detection. A calibrating curve based on 4 spherical surfaces was used to calculate diopter values at 360 points at each examination. Results were plotted on the computer monitor using diopter value versus angle (I t hrough 360 degrees) graphs. Preliminary measurements of 14 healthy corneas were compared with the equivalent radial distance points measured on an Eye Sys corneal topographer. Results: Mean deviation was 0.05 mm for radius of curvature, 0.24 diopter f or power, and 5 degrees for cylinder. Conclusion: The keratometer provided precise measurements for corneal shape control during surgery. J Cataract Refract Surg 1999; 25:821-826 (C) 1999 ASCRS and ESCRS.