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I. Vedamurthy, W. Harrison, M. Liu, I. Cox, C. M. Schor; The Influence of Short Term Near-Spectacle-Correction on Accommodation, Refractive State, and Eye Alignment in Adults. Invest. Ophthalmol. Vis. Sci. 2008;49(13):4556.
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A pilot study evaluated the effect of short-term first-near-spectacle correction on the accommodative-stimulus response (ASR) function, accommodative amplitude (AA), AC/A and CA/C ratios in two adult age groups and determined if changes in these functions recovered after discontinuing the use of near spectacles for two months.
Twenty-four normal subjects in two age groups (21-30 years [n =12] and 38-43 years [n = 12]) completed the study. There were 5 emmetropes, 6 myopes and 1 hyperope in both groups. A Badal optometer and Wheatstone-mirror haploscope were used to measure the ASR function, AA, response AC/A and stimulus CA/C ratios before and two months after wearing single-vision reading spectacles for near tasks, and a third time, two months after discontinuing the use of reading spectacles.
AC/A and CA/C ratios and the linear slope of the ASR function did not change significantly after wearing near spectacles (p > 0.05). AA, defined as the difference between the near-point of accommodation (NPA) and the far point (distance refractive state), did not change significantly with treatment (p > 0.05). However, there was a hyperopic shift of the ASR function that significantly reduced the NPA (p<0.05), and lowered the y-intercept of the ASR (far-point refraction). There was no significant difference between changes observed for myopes and emmetropes. These changes did not recover after 2 months of discontinuing the use of near spectacles.
The NPA may normally be enhanced by a tonic bias of accommodation that elevates the entire ASR function and produces a myopic refraction bias. When this bias relaxes after wearing near spectacles, there is a hyperopic shift of the refractive state, and a reduction of the NPA, specified from optical infinity, but the AA specified from the far-point refraction is unaffected. In practical terms, our results suggest that the prescription of near corrections for incipient presbyopia should be based on patient symptoms and not solely on patient age.
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