Nearwork-induced transient myopia (NITM) following marked and sustained, but interrupted, accommodation at near Mathangi Arunthavaraja 1 , Balamurali Vasudevan 2 and Kenneth J. Ciuffreda 1 1 Department of Vision Sciences, SUNY College of Optometry, 33 West 42nd Street, NY and 2 School of Optometry, MidWestern University, Glendale, AZ, USA Abstract Purpose: The purpose of the present investigation was to determine objectively the initial magnitude and decay of nearwork-induced transient myopia (NITM), and its potential additivity, following successive but interrupted periods of marked, sustained accommodation at near in asymptomatic young-adult myopic subjects. Methods: Fifteen visually-normal, asymptomatic young adults (ages 18–28 years) were tested with full distance refractive correction. They included nine early-onset (EOM) and six 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 a 10 min period of focusing upon a moderate contrast (50%), very near target (12 cm; 8 D) subtending a visual angle of 1°. The task was repeated twice with a 5-min inter- trial rest period of imposed far viewing. NITM was defined as the post-task minus pre-task change in distance refractive state and was determined for each of the three trials. Results: Significant amounts of NITM were generated following nearly each trial in each subject. These ranged from 0.11 to 0.71 D, with a mean of 0.31 D. The group mean NITM was 0.32, 0.29, and 0.31 D for trials 1, 2, and 3, respectively. For the EOMs subgroup, NITM was 0.28, 0.30, and 0.34 D, while for the LOMs subgroup, it was 0.38, 0.29, and 0.26 D, for trials 1, 2, and 3, respectively. Decay of NITM was prolonged in many of the subjects (67%). However, additivity of NITM was not found following the sequences of interrupted near tasks. Conclusions: 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 uninterrupted and sustained reading at lower dioptric levels, providing rest periods between each near task trial appears to prevent a cumulative effect (i.e. additivity effect). Keywords: accommodation, myopia, nearwork, nearwork-induced transient myopia (NITM), refractive error development Introduction Nearwork-induced transient myopia (NITM) refers to the closed-loop accommodative after-effect at distance following a sustained near task (Ciuffreda and Vasud- evan, 2008). That is, the accommodative response at far exhibits an initial slight over-accommodation with respect to the pre-task baseline level, with a typical exponential decay of approximately 30 s (Rosenfield et al., 1992) back to the pre-task baseline refractive state. Study of what has become known as ÔNITMÕ dates back to 1914 (Lancaster and Williams, 1914). They found NITM to be as large as 1.30 D under extreme monocular near viewing conditions for 45 min in young adults, with a decay to baseline lasting up to 15 min. Following longer sustained periods of nearwork (60 min), NITM may remain significantly elevated for at least 1 h (Ehrlich, 1987). However, NITM in visually-normal individuals has been typically found to range from approximately Received: 21 December 2009 Revised form: 24 July 2010 Accepted: 27 July 2010 Correspondence and reprint requests to: Kenneth J. Ciuffreda. Tel.: 212-938-5765; Fax: 212-938-5760. E-mail address: kciuffreda@sunyopt.edu Ophthal. Physiol. Opt. 2010 30: 766–775 doi: 10.1111/j.1475-1313.2010.00787.x ª 2010 The Authors. Ophthalmic and Physiological Optics ª 2010 The College of Optometrists