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Nisha Singh; Evaluation of three distinct parameters for visual fatigue assessment. Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):4309.
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© ARVO (1962-2015); The Authors (2016-present)
Various studies have measured accommodative microfluctuations (AM) and Critical Flicker Fusion Frequency (CFFF) for visual fatigue assessment. Also, several products are available these days claiming relief from eyestrain mostly either by relaxing accommodation or enhancing contrast. Apart from AM, either CFFF or contrast measurements are not well established for visual fatigue assessment. Therefore, this study aims to measure three distinct parameters: AM, Contrast Sensitivity (CS) and CFFF in one study; to compare their efficacy for the assessment of visual fatigue.
30 non-symptomatic & non-presbyopic emmetropes (age 19-42 years) performed 30 min of visual search task displayed on a LCD monitor placed 40 cm away from the eye. During the task, fixation target was displayed for 1 min at the beginning and end of the task. AM were analyzed from refraction recorded using PowerRef II during fixations that is, before and after task. CS using Functional Acuity Contrast Test (FACT) and CFFF with a Visual fatigue detector (developed by a local company in China) was also measured before and after the task. To obtain AM, Low frequency component (LFC) <1Hz and High frequency component (HFC) 1.0Hz-2.5Hz were acquired using FFT. In addition, subjective measurement of visual fatigue was done using a questionnaire before and after the task.
Subjective measurement of visual fatigue showed significant increase after task (Wilcoxon signed rank test; p<0.05). Before and after measurements were compared using paired t-test. Only LFC of AM increased significantly (p<0.05) while CS (p >0.05 for all measured spatial frequencies), CFFF (p =0.53) did not change after the task.
Out of 3 parameters measured, only AM changed significantly after performing 30 minutes of visually taxing task which is in coherence with subjective measurement. Thus, reinforces that AM is an effective indicator for visual fatigue assessment. As induced visual fatigue could cause changes in the microfluctuations of accommodation of non-symptomatic people implies that symptomatic visual fatigue people would probably have exhausted & fragile accommodative system and needs to be taken care of in the management of visual fatigue.
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