Evaluation of clinical techniques to measure tonic accommodation

Previous studies have advocated the use of a degraded accommodative stimulus to assess the value of tonic accommodation (TA) under clinical conditions. This study has attempted to determine the efficacy of two such clinically applicable techniques, i.e., viewing a low spatial frequency (approximately 0.1 cpd) difference of Gaussian (DOG) grating or a retinoscope beam in an otherwise dark room. Additionally the accommodative response (AR) was measured in darkness. The data indicate that these clinical techniques did provide a degraded stimulus to accommodation. However, measures of AR recorded when fixating the clinical targets did not correlate with the values of AR obtained in darkness. This lack of correlation suggests that the responses obtained when viewing either the DOG target or retinoscope beam may not represent a veridical measure of TA.