Design and Construction of a Corneal Topography Examination Device

Abstract

In this work, a corneal topographic study system was designed and built based on the principle of the Placido disk, which depends on capturing the reflection image of the concentric rings separated by fixed distances and illuminated by a white photodiode on the tear layer on the surface of the cornea.

The built device was calibrated using three glass balls of different radii by calculating the average distances between the reflected rings from the three balls, to find a relationship between the distance between the reflected rings and the radius of curvature to be used in measuring the radius of curvature of the eye for multiple points.

Photographs of the reflection of the illuminated pattern were taken from the eyes of a patients for the purpose of analysis. By means of a gradient of gray level and using the ImageJ program, and matching the curves, the positions of the peaks were determined for eight radial axes from the center of the pupil, with separating of 45 degrees.

The radius of curvature of the cornea was calculated at several points using the interstitial distances, and then the average was found for three regions within radii of 3, 5, and 7 mm. The keratometric values of these points were calculated, and then the color distribution of these values was drawn, which is represented by the curvature map and the keratometric map, using Origin software.

The device showed the possibility of analyzing the color distribution of the maps by consulting a specialist doctor to determine the type of refractive error that the patient suffers from, which was determined as asymmetrical astigmatism due to a slight deformity in the cornea.