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Purpose : Visual stimulus control, versus chemical, of the state of accommodation is desirable in several situations, such as refraction. A method for controlling the accommodative state was explored in an investigative clinical trial.

Development / Ideas

Methods : An exploratory study in 20 young subjects hypothesized that a visual stimulus to control the accommodation of the subjects exists. The characteristics of such stimulus were investigated and their effect on the level and duration of accommodation control was assessed. These included: stimulus field of view, color, contrast, brightness, size, shape, stereoscopic appearances and dynamics. As accommodation is perception triggered, cognitive aspects of the stimulus were included.
The experimental setup is shown in Figure 1.
The main systems in the apparatus are a continuous auto-refractor, used to monitor the instantaneous refraction of the subjects, and a haploscope, for presenting binocular stimuli.

Results : The average range of accommodation was 13.48D with a standard deviation of 3.13D. Analysis of the investigated parameter space shows that there are significant similarities between subjects as to the effectiveness of specific visual stimuli in controlling the accommodation state.
Figure 2.a. shows a representative accommodation control of an effective visual stimulus. The stimulus was dynamic and is shown in Figure 2.b. The subject was given a task to align two moving crosses. Results show that the starting accommodative state of the subject was about -4.5D. As the visual stimulus progressed with both contextual as well as stereoscopic (vergence) cues, the accommodative state became closer to infinity leading the subject to 0D as the crosses were aligned.

Conclusions : It is possible to control accommodation by visual stimulus. The stimulus needs to maintain perception of the distance for the duration of the control period. Cognitive tasks associated with attention focus are critical in sustaining the desired accommodation level. Leading to the state of accommodation gradually, presenting dynamic and interesting stimulus, and providing appropriate color contrast are required for successful accommodation control. Size contrast should be avoided to prevent perceptual disparity. Lastly, the level of detail should be as low as possible while maintaining realism.

This is a 2020 ARVO Annual Meeting abstract.