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B. Vasudevan, IV, K. J. Ciuffreda; Nearwork-Induced Changes in Lenticular - Thickness in Different Refractive Groups. Invest. Ophthalmol. Vis. Sci. 2008;49(13):3578.
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Previous investigations have assumed that transient myopic changes in the distance accommodative response (i.e., nearwork-induced transient myopia; NITM) immediately following nearwork were solely lenticular in origin. However, correlated changes in central lens thickness and related dioptric power have never been measured directly. Thus, the purpose of the present study was to determine the lenticular contribution to the overall optically-based nearwork-induced transient myopia (NITM), following 1 and 2 hours of nearwork.
35 subjects comprised of 12 early-onset myopes, 11 late-onset myopes, and 12 emmetropes were tested. Ages ranged from 22 to 27 years, and they were free of any ocular abnormalities. Lenticular thickness was measured in the right eye using high resolution A-scan ultrasonography prior to, and immediately following, 1 and 2 hours of reading. The overall optically-based NITM change was also assessed using an objective autorefractor in a prior session.
Group mean (±SE) changes in lenticular thickness from baseline after the 1st and 2nd hours of reading were 0.025±0.002 and 0.035±0.003mm, respectively. The group mean increase in lenticular thickness after the 2nd hour (mean=0.035mm) was significantly larger than after the 1st hour (mean=0.025mm). When the subjects were categorized as early-onset myopes, late-onset myopes, and emmetropes, lenticular thickness was significantly greater after the 2nd hour only in the myopes. When converted to diopters, this increase in central lenticular thickness approximated the optically-assessed NITM with individual subject variability evident.
NITM was primarily attributed to the change in central lenticular thickness. Increases in lenticular thickness following nearwork were additive in nature, but only in the myopes. The individual variability may be attributed to fluctuations in the ocular aberrations.
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