Effect of Induced Visual Fatigue on Sensory Ocular Dominance and the Effect of Colored Filters on the Levels of Visual Fatigue in Dyslexic Adults with MIS

Abstract

The aim of the current research was to investigate the effect of visual fatigue induced with different clinical test stimuli on the sensory ocular dominance in dyslexic adults with Mearles-Irlen syndrome (MIS) and examine the role of colored filters. Nine female participants with dyslexia plus MIS aged between 18 and 36 years were recruited. Sensory ocular dominance and binocular vision functions were measured before and after induction of visual fatigue was induced. Measurements were conducted with participants wearing their habitual colored filters and without the filters and in two different sessions. Constant and continuous (static) test stimuli were used to create binocular rivalry. To induce visual fatigue, participants were asked to read, copy, and search for thirty minutes; the participants performed each tasks for ten minutes, while wearing their habitual near spectacle lens. No breaks were allowed between tasks. The calculated visual discomfort score (VDCS) for each test condition was analyzed. In sessions one and two respectively, VDCS was increased from 0.67 ± 1.00 to 1.44 ± 0.53 (<i>p</i> = 0.07) and 0.22 ± 0.44 to 1.56 ± 0.73 (<i>p</i> = 0.001), in adults with dyslexia and MIS after assessment of binocular vision function. Similarly, the VDCS was significantly increased to 2.56 ± 0.73 (<i>p</i> = 0.002) in session one and 2.11 ± 0.93 (<i>p</i> = 0.001) in session two, after visual fatigue was induced in these participants. There were no differences between both eyes’ sensory ocular dominance in dyslexic adults with MIS irrespective of the test stimuli used to induce the binocular rivalry. Induction of visual fatigue was followed by disruptions in the sensory ocular dominance that persisted with participants wearing their habitual colored overlays during the fatigue duration. This finding was also not influenced by the test slides used in these participants. Optometric investigations such as binocular vision testing, performed in dyslexic adults with MIS using certain stimuli could induce visual discomfort, but the discomfort induced by stressful visual testing was significantly greater. Moreover, the use of certain test stimuli was shown to disrupt the sensory ocular dominance of this group of participants suggesting that researchers should consider using the appropriate stimuli when examining patients with dyslexia and/or MIS and those experiencing reading difficulties.