Accuracy and repeatablity of a hand-held video keratoscope in a population with a high prevalence of astigmatism

Purpose. A hand-held video keratoscope (HVK) has been developed to allow measurement of corneal astigmatism in infants and young children. Some Native American tribes have a high prevalence of astigmatism, but its longitudinal development is not known. Accuracy was evaluated by comparing HVK and Javal-Schiotz (J-S) measurements in a population of adults with a high prevalence of astigmatism. Repeatability was determined from the two measurements of HVK corneal power. Methods. The HVK uses an 8-mm camcorder and 200 mm diameter ring of 12 LEDs, with a 180 mm working distance. The right eye of 40 adults was measured twice with the HVK and once with J-S. Accuracy was correlation of HVK mean values and J-S measurements. As only two measurements were made, repeatability was one-half the dioptric difference between the two measures, using vector methods (Harris, 1988). Results. Astigmatism ranged from 0 to 5 diopters. HVK and J-S astigmatism correlation was 0.92 (p<0.0001). HVK measurement repeatability was 0.36 +/-0.30 D (mean +/- SD). Conclusions. The HVK provides accuracy and repeatability comparable to conventional keratometry (Zadnik, 1992).