Stability of measures of the dark focus of accomodation

Without visual stimulation, the eye tends to assume an individually-determined intermediate state of accommodation (the "dark focus"). The present study examined the stability of these individual dark focus values over time. Two sets of measurements were obtained with a laser-Badal optometer for each of 39 college-age subjects. For 19 subjects the second test occurred during the same experimental session as the first; for 20 subjects the retest was conducted in a separate session 1 week later. Eye dominance was determined by a pointing task. High correlations between test-retest values were found for both immediate and delayed retest. The average change between the tests was less than +/- 0.3 diopter, even when the retest was a week later. These results indicate a definite stability in individual dark focus values. Eye dominance and subject's sex were both irrelevant.