One factor to be controlled in dark adaptation testing is that of fixation so that the region of the retina under investigation is known and constant. To control the orientation of the line of sight of the nonfixating eye, which is undergoing the test while the other eye is fixating, it is necessary to hold accommodative convergence constant and to provide a compensatory correction for the relative deviation of the two eyes under dissociation. A bio-photometer was modified to measure the dark adaptation of one eye while its orientation was controlled by the fixation of the other eye. Preliminary testing over a 10 minute range on a small sample of subjects suggests that relatively good reliability is attainable, and that the test-retest reliability reaches a maximum at about the sixth minute following the end of the bleach period. Reports of the subject indicate that the visibility judgments are remarkably easier to make by this technique.
Abstract