A comparison of two methods of measuring dark adaptation

Abstract

<h2>Summary</h2> The results of dark adaptation tests obtained with the biophotometer and with the Hecht-Schlaer adaptometer on the same subject have been compared. It was found that the biophotometer does not use a bright enough bleach light to bleach the cones, so that cone adaptation is absent from the biophotometer curve. When the intensity of the bleach light is increased, however, the cone adaptation may be measured with the biophotometer. Within the limits of error, the rod adaptation as measured with the biophotometer and the Hecht-Schlaer adaptometer is identical. The first reading obtained after the bleach period with the biophotometer is felt to represent the final cone threshold as determined with the Hecht-Schlaer instrument. Consequently, it is, felt that the continued use of the biophotometerin the study of vitamin A deficiency is valid, giving a true picture of dark adaptation. It is suggested that measurements of dark adaptation be continued for fifteen or twenty minutes following the bleach period in the biophotometer test.