An experimental study on the objective measurement of accommodative amplitude under binocular and natural viewing conditions.

A high resolution optometer makes it possible to measure changes in refractive power objectively using reflected light from the fundus of the eye. There are limitations in that the subject has to see the target monocularly through a hole in the instrument. In the present study, we attempted to measure the accommodation and pupillary response with a newly developed device as a means to measure these factors in both binocular and natural viewing conditions. We compared the subjective accommodative amplitude levels obtained from the near-point distance with those of objective accommodative amplitude obtained in earlier studies using a monocular internal target. The amplitude of accommodation of the cases with binocular, natural viewing conditions was approximately 0.7 D larger than with monocular, internal target gazing. In previous studies, the difference between the subjective amplitude of accommodation and the results of the objective measurements, had been reported to be approximately 2 D, and was explained by the depth of focus. However, the difference between the subjective and objective amplitude of accommodation under binocular, natural viewing was smaller than that between the subjective and objective measurements (under monocular internal target gazing) from previous studies. This leads us to believe that besides the depth of the focus, we should consider the fact that the advantageous conditions inherent in binocular, natural viewing may increase the amplitude of accommodation. In the measurement of accommodative amplitude, the use of objective measuring methods are not affected by the subjects' subjective judgement.