Comparison of laser and infrared techniques for measurement of the resting focus of accommodation: mean differences and long-term variability.

The resting focus of accommodation was measured in the same subjects with both a laser optometer and a high-speed infrared optometer. Although i.r. optometer and laser optometer measures produce similar estimates of the mean resting-focus level in some subjects, others were found to have different levels of resting focus with the two techniques. Control studies demonstrated that these differences were not due to the temporal sampling characteristics of the laser optometer, but resulted instead from making judgments about the direction of speckle motion during the laser optometer procedure. The temporal stability of the resting focus of accommodation was also investigated with i.r. measures obtained several minutes, 1 day, and 1 and 2 weeks apart. Results indicated long-term variability similar to that previously reported with the laser optometer.