[Measurement of ocular position using Purkinje images. Part 1. A new measurement system]

I developed a new system of measuring ocular position using the first and fourth Purkinje images. This method used two images which were reflected from the front surface of the cornea and the back surface of the lens. I got a cross line from the first Purkinje image by putting a cross lens filter in front of the infrared camera. When I superimposed the vertical line upon the fourth image, I could get the optic axis of the eye. In order to measure the ocular position, I measured the angle of the optic axis. The accuracy of this system was +/- 0.1 degrees and the maximum error was smaller than +/- 0.5 degrees. Measurements with this system were easily obtained from squint patients and correlated well with results from the prism cover test (R2: 0.941). This measurement system was more useful than the prism cover test because I was able to measure horizontal deviations more precisely.