LIGHT ADAPTATION AT THE FOVEA FOR NORMAL EYES

Abstract

As a result of experiments on the foveal adaptation process by the method of binocular matching' 2 it seemed likely that data obtained from observers with defective vision might lead to further knowledge of the retinal processes and of certain diseases of the eye and might in some cases assist in their diagnosis. Before this possibility could be tested, it was essential to determine the differences that might exist among apparently normal eyes, for without this information the significance of variations from the normal could not be assessed. The results given below are therefore, in a sense, preliminar-y observations, but they have proved to be of considerable interest in themselves, apart from their value in connection with any subsequent investigation. The earlier work quoted above was carried out using an elaborate trichromatic colorimeter with which both intensity and colour changes induced by various adapting conditions, were recorded. To avoid prolonging the investigation unduly, the number of observers had to be strictly limited and in practice nearly all the observations were made by the author. In order that a much greater number of observers might be tested, it was necessary to restrict the scope of the observations and to simplify them as far as possible, both to save time and to ensure that those not familiar with visual observations would have the minimum of difficulty in carrying out the tests. For this purpose a subjective photometer3 was -constructed with which tests could be carried out using a single adapting radiation and recording intensity changes alone. With this instrument, over 100 observers have been tested and it is with the analysis of these results that this papei is concerned.