Near work-induced transient myopia in Indian subjects.
OBJECTIVE
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.


METHODS
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.


RESULTS
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.


CONCLUSIONS
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.
Elite School of Optometry, Chennai, India.|Department of Vision and Hearing Sciences, Anglia Ruskin University, Cambridge, UK.
Viswanathan
V
Sivaraman
Elite School of Optometry, Chennai, India.
Jameel H
JH
Rizwana
Elite School of Optometry, Chennai, India.
Krishnakumar
K
Ramani
Department of Vision and Hearing Sciences, Anglia Ruskin University, Cambridge, UK.|Vision and Eye Research Unit, Anglia Ruskin University, Cambridge, UK.
Holly
H
Price
Department of Vision and Hearing Sciences, Anglia Ruskin University, Cambridge, UK.|Vision and Eye Research Unit, Anglia Ruskin University, Cambridge, UK.
Richard
R
Calver
Vision and Eye Research Unit, Anglia Ruskin University, Cambridge, UK.
Shahina
S
Pardhan
Midwestern University, Arizona, USA.
Balamurali
B
Vasudevan
Department of Vision and Hearing Sciences, Anglia Ruskin University, Cambridge, UK.|Vision and Eye Research Unit, Anglia Ruskin University, Cambridge, UK.
Peter M
PM
Allen
D000065:Accommodation, Ocular / Q000502:physiology*; D000293:Adolescent; D000328:Adult; D005260:Female; D006801:Humans; D007194:India / Q000453:epidemiology; D008297:Male; D009216:Myopia / Q000453:epidemiology / Q000209:etiology* / Q000503:physiopathology; D011932:Reading; D012029:Refraction, Ocular / Q000502:physiology*; D014787:Vision Tests; D015348:Vision, Binocular / Q000502:physiology*; D055815:Young Adult
decay time constant; myopia; near work-induced transient myopia; target contrast; target size