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K.L. Schmid, K.S. Hilmer, R.A. Lawrence, S. Loh, L.J. Morrish, B. Brown; The Effect of Text Size and Contrast on Nearwork-Induced Transient Myopia in Progressing and Non-Progressing Adult Myopes . Invest. Ophthalmol. Vis. Sci. 2003;44(13):4782.
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Purpose: Focussing errors that occur while reading and nearwork-induced transient myopia (NITM) that occurs following reading have been implicated in the development and progression of myopia. This study investigated the effects of two print variables, size and contrast, on accommodation accuracy during the near task and subsequent NITM and its decay. Methods: Young adult subjects (18 to 25 years) were classified into three groups based on their refractive errors and refractive history: emmetropes (n=20), non-progressing myopes (n=18) and progressing myopes (n=18). Three print sizes (N4, N6, N8) and two print contrasts (90%, 60%) were used to give six different text targets. Targets were presented in random order at 25 cm (4 D demand) and the text read for comprehension for 3 minutes. Subjects' refractive errors were contact lens corrected. For each target, accommodation accuracy during reading, and NITM and its decay to pre-task refractive levels were measured using the Shin-Nippon SRW-5000 free space autorefractor. Results: We found a significant effect of target size on accommodation accuracy (Multivariate ANOVA, F2,49= 3.896, P=0.027), however differences were small and unlikely to be clinically relevant (lags of accommodation, mean±SD, N4: 0.28±0.21D, N6: 0.30±0.20D, N8: 0.30±0.21D). Accommodation accuracy was not affected by the reduction in contrast. NITM and its decay were similar for all 6 print modifications (eg NITM N4: 0.27±0.21D, N6: 0.33±0.24D, N8: 0.32±0.20D, Multivariate ANOVA, F2,49=1.826 , P=0.173). Like previous studies we found significant differences in NITM and decay time between emmetropes and myopes, however these were not affected by the size and contrast changes to the reading task; myopes had larger NITM values and longer decay times to baseline than emmetropes (eg NITM myopes: 0.37±0.14D cf emmetropes: 0.19±0.17D P=0.005, decay time myopes: 15.12±6.58 sec cf emmetropes 7.10±4.82 sec, P=0.0045). Conclusions: Our data do not support the suggestion that reductions in size or contrast of reading material (as might occur when students photocopy study materials) cause greater accommodation inaccuracy and greater nearwork induced adaptation effects that would exacerbate myopia development in young adults.
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