Subject instructions and methods of target presentation in accommodation research.

PURPOSE: The authors investigated the potential of subject instructions to alter the static accommodative stimulus-response function. They also investigated whether the reduced cue environment of the Badal optical system leads to accommodative responses different from those that occur for targets presented in real space.
METHODS: Static accommodative responses with three focusing instructions were compared to baselines obtained with minimal instruction to stabilize gaze. Static accommodative responses were recorded for targets presented in real space and in a Badal optical system.
RESULTS: Individuals differ widely in their responses to Instruction 1 (" ... make no special effort ... "), although some adopt a relatively fixed position of focus. Responses with Instruction 2 (" ... look at the words naturally ... ") and Instruction 3 (" ... carefully focus ... ") are not significantly different from each other, but differ slightly from the responses with the baseline instruction ("pick a word in the middle of the block of text and look at it"). In a sample including most subjects, mean responses for Badal and real space targets are identical. However, it appears that some subjects have difficulty accommodating for Badal targets.
CONCLUSIONS: The authors recommend the use of Instructions 2 and 3 for investigation of the static accommodative response, with a number of provisos. Accommodative responses to Badal and real space targets are generally equivalent, but researchers should take care to identify those persons who have difficulties accommodating for Badal targets.