Near work-induced transient myopia in Indian subjects

• Published in: Clinical and experimental optometry Vol. 98; no. 6; pp. 541 - 546
• Main Authors: Sivaraman, Viswanathan, Rizwana, Jameel H, Ramani, Krishnakumar, Price, Holly, Calver, Richard, Pardhan, Shahina, Vasudevan, Balamurali, Allen, Peter M
• Format: Journal Article
• Language: English
• Published: Australia Taylor & Francis 01.11.2015
• Subjects: Accommodation, Ocular - physiology; Adolescent; Adult; decay time constant; Female; Humans; India - epidemiology; Male; myopia; Myopia - epidemiology; Myopia - etiology; Myopia - physiopathology; near work-induced transient myopia; Reading; Refraction, Ocular - physiology; target contrast; target size; Vision Tests; Vision, Binocular - physiology; Young Adult; myopia; near work-induced transient myopia; decay time constant; target contrast; target size
• ISSN: 0816-4622; 1444-0938
• DOI: 10.1111/cxo.12306

The aim was to determine the characteristics of near work-induced transient myopia (NITM) in asymptomatic Indian subjects and the influence of target size and contrast. Two studies were conducted: First, 24 myopes and 24 emmetropes viewed four targets (N8 and N12 with 50 and 90 per cent contrasts) placed at 0.2-m for five minutes. The refractive status was assessed objectively, before and after carrying out the near task, with the Grand Seiko WAM-5500 open-field autorefractor under monocular viewing conditions. Second, a different group of 24 myopes and 24 emmetropes viewed a N12 target with 90 per cent contrast for 60-minutes with pre- and post-refractive state measurements repeated as above. NITM was defined as the difference between pre-task and post-task distance refraction. In the first study, myopes demonstrated an initial post-task myopic shift of 0.21 D, whereas emmetropes demonstrated a small hyperopic shift of 0.07 D (p < 0.001). The myopes demonstrated a decay time constant of 6.07-seconds. There was no effect of target size or contrast on the magnitude of the NITM or the decay time constant (p > 0.05). In the second study, myopes showed a NITM of 0.31 D, which was significantly greater than emmetropes (p < 0.001). The myopes demonstrated a decay time constant of 8.16-seconds. The magnitude of the NITM was higher in myopes compared to emmetropes for both five minute and 60-minute viewing time. The NITM decayed slightly faster than that found in previous literature for some other ethnic groups. Potential reasons for these findings are discussed.