Variations in Accommodation and Convergence Responses in a Naturalistic Setting

Horwood AM, Turner JE, Houston SE, Riddell PM.. Optometry & Visual Science 2001, 78, 791-804

Accommodation is better when binocular
The accommodation of naïve adults frequently drops dramatically when occluded, especially if the task does not demand detailed vision

Purpose

A remote haploscopic photorefractor, designed for assessment of accommodation and convergence in infants and clinical groups, was used to determine heterophoria accommodative convergence/accommodation (AC/A) ratios in normal naive adults. These were compared with conventional clinical measures.

Methods

Twenty-one naive subjects were used to compare occluded and unoccluded prism cover test responses with the remote haploscopic photorefractor using a text and picture target.

Results

Although luminance was generally low for both targets, binocular vergences were appropriate for target demand in both studies. Binocular accommodation showed greater lag for the highest target accommodative demand and the less demanding target. Occlusion not only reduced vergence response, but also frequently caused a marked reduction in accommodation, especially to the picture target. Normal mean AC/A values were found, but with wide variations between individual subjects.

Conclusions

Although mean accommodation, vergence, and AC/A values were comparable with published data, we suggest that in these conditions using naive subjects, accommodation is frequently inaccurate, especially on occlusion, without concomitant loss of vergence, at least at low light levels. Accommodative convergence may play a less important part in, and other cues contribute more to, the near reflex than has been previously suggested.