RELIABILITY AND VALIDITY STUDIES OF A NEW COMPUTER-ASSISTED CROSSED-CYLINDER ABERROSCOPE

Purpose. We assessed the reliability and validity of a new computer-as sisted crossed-cylinder aberroscope technique which measures the monoc hromatic optical aberrations of the human eye. Methods. Intra-image va riability, the variability occurring when the same image is repeatedly measured, and inter-image variability, the variability occurring when different images collected from the same eye are measured, were asses sed using 10 repeated measures on each of 10 different subjects. We co mpared the measurements made using the computer-assisted technique wit h manual measurements made when a human operator performed all the abe rroscope grid intersection location tasks. Results. One-way repeated m easures analyses of variance (ANOVA) on the inter-image and intra-imag e variability showed that the mean of the measurements made was statis tically independent of the occasion on which a group of subjects was m easured, and inter-image variability was larger than intra-image varia bility. A two-way repeated measures ANOVA comparing computer-assisted results with manual results showed that the means of the measurements made with the two methods are not statistically different from one ano ther. The manual results showed greater variability than computer-assi sted measurements. Conclusions. The technique is reliable and valid co mpared to earlier objective crossed-cylinder aberroscopic techniques.