Automatic infrared refractors--a comparative study.

In order to determine the performance of seven automatic infrared (IR) eye refractors, measurements have been conducted on a model eye as well as on normal subjects and patients under standardized conditions. Concerning the model eye, a range of measurement slightly smaller than specified and linearity errors have been detected on several instruments. Using a group of 55 normal ametropic subjects, the results of the automatic refraction were compared to the results of a conventional subjective examination. The spherical equivalent differed by less than 0.51 D in more than 80% of all cases on all instruments. The error of the cylinder power was smaller than 0.51 D in more than 90% of all cases. Larger errors were found on patients with intra ocular lenses, aphakic eyes, or scattering eye media. In each of these groups the automatic refraction was at times either impossible or yielded a wrong result.