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Niraj Barot, Rebecca McLean, Irene Gottlob, Frank A. Proudlock; Optimising Reading in Infantile Nystagmus Syndrome: Effect of Font Size and Coloured Overlays. Invest. Ophthalmol. Vis. Sci. 2012;53(14):4904.
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© ARVO (1962-2015); The Authors (2016-present)
Infantile nystagmus syndrome (INS) is an involuntary oscillation of the eyes occurring in infancy, which may be: (i) idiopathic or (ii) associated with foveal abnormalities such as albinism. Reading has been poorly investigated in INS. The aim of this study was to investigate (i) the effects of font size on reading speed using the Radner reading chart, and (ii) the effect of coloured overlays on reading in INS using the Radner reading chart to assess performance.
In experiment 1, 73 INS volunteers (34 albinism, 39 IIN) were administered the Radner reading chart to investigate the effect font size on reading speed. Reading parameters included reading acuity (RA, minimum font size read <20secs), maximum reading speed (MRS), critical print size (CPS, font at which reading speed falls below 80% of maximum), and suboptimal reading range (SORR, MRS - CPS). In experiment 2, these parameters were calculated in 45 volunteers with INS (25 albinism, 20 IIN) with and without the aid of coloured overlays. For experiments 1 and 2 a group of healthy controls (n=19) was also compared.
In experiment 1, change in RS with font size in INS resembled previously described patterns consisting of a plateau with a drop off in reading speed below a particular font size (the critical print size). RA and CPS were significantly worse in albinism compared to IIN with both groups being significantly worse than controls. In contrast MRS and SORR were not significantly different between albinism and IIN groups although both groups were significantly worse than controls. RA was strongly correlated to visual acuity (VA) in INS although gradients of <1 indicated that patients with poorer VA could read at font sizes smaller than the VA limit. In contrast, MRS was not correlated to VA in albinism. In experiment 2, coloured overlays did not significantly improve any of the objective measures of reading, although 56% of INS volunteers perceived a benefit. Yellow was the most popular choice of filter.
Individuals with nystagmus not only show reduced RA and MRS but also show larger SORR indicating that reading speeds in INS are sub-optimal over a wider range of font sizes compared to controls. Individuals with poor VA typically read text which is smaller than their VA limit possibly because of more reliance on parafoveal vision. Use of coloured overlays resulted in no change in objective measures of reading performance although INS subjects perceived a benefit.
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