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M. Arunthavaraja, K. J. Ciuffreda, B. Vasudevan; Nitm Following Marked Sustained Accommodation at Near. Invest. Ophthalmol. Vis. Sci. 2009;50(13):2893.
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It has been speculated that NITM (accommodatively-based nearwork-induced transient myopia) is myopigenic in nature. Thus, the purpose of the present investigation was to determine objectively the initial magnitude of NITM, and its potential additivity, following successive but interrupted periods of marked, sustained accommodation at near in asymptomatic young adult myopic subjects.
Fifteen visually normal, asymptomatic young adults (ages 18 - 28 years) were tested with full distance refractive correction. They included 9 early-onset (EOM) and 6 late-onset (LOM) myopic subjects. Accommodation was assessed objectively with a Canon R-1, open-field infrared auto-refractor under monocular viewing conditions (RE). The distance refractive state was measured immediately before and after each of the 3 ten minute periods of focusing upon a moderate contrast (50%), near target (12 cm; 8D) subtending 6 degrees. The task was repeated twice with a 5-minute inter-task rest period of imposed far viewing. NITM was defined as the post-task minus pre-task change in distance refractive state immediately following each task.
Significant amounts of NITM were generated following each trial. These ranged from 0.11 to 0.71D, with a mean of 0.31D. The group mean NITM was 0.32, 0.29, and 0.31D for trials 1, 2, and 3, respectively. For the EOMs subgroup, NITM was 0.28, 0.30, and 0.34D, while for the LOMs subgroup, it was 0.38, 0.29, and 0.26D, for for trials 1, 2, and 3, respectively. However, additivity of NITM was not found following the sequence of interrupted near tasks.
There was no evidence of NITM additivity following a marked and sustained, but interrupted, near task. Although NITM has been reported to be additive following long periods of sustained reading (Vasudevan & Ciuffreda, 2008), providing rest periods between near task trials appears to prevent a cumulative effect. These findings support the idea of far viewing being protective in nature from myopia development.
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