Abstract
Purpose :
Retinoscopy is low cost and useful for obtaining objective estimates of refraction in children. Photorefraction (PR) is a similar technique that provides added automatic digital advantage. Previously, we showed that with a Badal optometer, a hand-held PR autorefractor could achieve high sensitivity and accuracy for refraction. This study investigates the degree of accommodation that degrades the refraction measurement in this hand-held tool and whether the induced error could be minimized by simple instruction given to either the testing eye or the fellow eye’s fixation and/or the environment lighting condition.
Methods :
Previously we showed the hand-held autorefractor with an accuracy of 0.1D for the artificial eye and less than 0.25D for human eyes. In this study, we recruited volunteers in the age range of 6 to 60 years. In typical room light conditions, the patient held the autorefractor directly in front of one eye for a sequence of 4 refraction measurements. For each measurement, s/he was told to close the fellow eye (with testing eye looking into the device), open the fellow eye to look at a distant object (at 5m), at mid-distant object (at 1m), or at the far end of the device (at 16cm). Each measurement took about 2 seconds after preparation. The measured results were compared to their clinical subjective eye exam results.
Results :
Different levels of accommodation and stability were observed under different viewing instructions. When the fellow eyes were instructed to view distant objects, the eyes appear to be most relaxed and the measured refraction agree with the clinical results within standard errors of 0.15D for adults and 0.3D for young kids. When the testing eyes were directly looking into the device, about 1.5 to 2 diopters of accommodation and, depending on age, different variation were observed. When accommodation was demanded to the fellow eyes (with targets at 16 cm and 1m), the magnitude of accommodation and its stability largely depend on both the demand level and the patients' ability of accommodation. For presbyopia, the measurement results were well repeatable and able to correctly predict the clinical prescription (+/- 0.15D). The most significant source of error for presbyopia occurs in a bright environment/ viewing target that causes small pupil size and reduces the signal level.
Conclusions :
Accommodation in a hand-held PR autorefractor appears to be manageable by leading the fellow eye relax to a far viewing object.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.