The response AC/A ratio: differences between inducing and relaxing accommodation at different distances of fixation

To determine if there is a difference between the response AC/A ratios when measured using the gradient method at near and distance fixation with plus and minus lenses respectively in young adults with normal binocular single vision.

A repeated measures design was used. The accommodative response of the right eye was measured objectively using the Shin-Nippon SRW-5000 autorefractor (Grand Seiko Company, Fukuyama, Japan) (open view) at 33 cm with and without plus lenses (2DS or 3DS) and at 3.8 m with and without minus lenses (2DS or 3DS) dependent on the participants' ability to obtain subjectively "clear" vision. The angle of deviation was measured using the alternate prism cover test at 33 cm and 3.8m fixing with the right eye with the participant sat at the autorefractor. LogMAR 0.0 (6/6) was used for fixation. Response AC/A ratios were calculated.

Twenty-five participants were examined; mean and standard deviation of their ages were 21.2 ± 4.04 years. The mean and standard deviation of the near response AC/A ratios was 4.73 ± 2.34/1 and at distance was 3.05 ± 1.71/1. Pearson's Product Moment Correlation Coefficient showed no correlation between the 2 sets of data. Paired t-test showed that there was a statistically significant difference between the near and distance response AC/A ratios (t = 3.30, p = 0.003). The difference was found to be greater in participants who were non-orthoptic students.

The response AC/A ratio was found to be slightly higher at 33 cm with plus lenses than at 3.8 m with minus lenses. No reason was identified for this difference but adaptation and perceptual effects could be further explored.