Investigation of accommodative tracking under monochromatic conditions

The purpose of this reseach was to examine the role of chromatic aberration in supplying accommodative information to the brain. This was accomplished by measuring the latency and the initial directional errors of accommodation under different stimulus conditions. An automated infrared optometer was designed and built to monitor monocular changes of accommodation dynamically with a sensitivity of +- 0.1 D over a range of about 10 D. Three interference filters (500 nm, 570 nm, 640 nm) were used to minimize chromatic aberration; accommodative responses to these essentially monochromatic stimuli were compared to responses to purple (peaks at 435 nm and >700 nm) and white light with and without an achromatizing lens. The results from nine subjects show that in most cases accommodative latencies and initial errors increased under monochromatic conditions. When the stimulus to decrease accommodation was presented some subjects showed initial accommodative directional errors of 30% to 50% for monochromatic sources and fewer than 10% for white light. When the stimulus to increase accommodation was presented, most subjects showed fewer initial accommodative errors in both monochromatic and white light, suggesting that the accommodative system may have a natural bias toward increasing accommodation. This was verified by a supplementary experiment. A relationship was found between latencies and initial errors. The longer latencies associated with more directional errors. In total these results imply that when other directional accommodative cues are eliminated, chromatic aberration may provide information to the brain as to the appropriate direction the accommodation should take,i.e. increase or decrease.