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S. Plainis, D. Petratou, T. Giannakopoulou, D. A. Atchison, M. K. Tsilimbaris; Binocularity Improves Performance to Defocus-Induced Blur. Invest. Ophthalmol. Vis. Sci. 2010;51(13):3936.
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© ARVO (1962-2015); The Authors (2016-present)
To evaluate the advantage of binocular vision over monocular vision under blurred conditions using visual acuity measures and pattern Visual Evoked Potential (VEP) recordings.
There were thirteen subjects (age: 28±5 years) with decimal visual acuities better than 1.0 in both eyes. All measurements were performed monocularly (dominant eye) and binocularly at 1m viewing distance with best spectacle sphero-cylindrical correction and natural pupils. Blur was induced using positive powered lenses up to +3.50 D. Visual acuity was measured with the LogMAR 2000 "new ETDRS" charts (Precision Vision, USA). VEPs were elicited using reversing 10 arcmin checks at a rate of 4 reversals per second with square wave modulation. The stimulus was displayed on a Sony GDM F-520 CRT monitor by means of a VSG 2/5 stimulus generator card (Cambridge Research Systems Ltd, UK). The stimulus subtended a circular field of 7 degrees with 100% contrast, and a mean luminance of 30 cd/m2. Each VEP trace was the average of 64 epochs of 1 sec duration each.
With binocular stimulation the amplitude and the implicit time of the P100 component of the VEPs were greater and shorter, respectively, in all cases than for monocular stimulation. Specifically, the mean (± standard deviation) of the binocular enhancement ratio in the P100 amplitude was 1.8 (±0.6) at 0.0D defocus, increasing linearly with defocus to be 2.9 at +3.50 D. The mean peak latency was 1.4 ms (±3.5) shorter at 0.0D defocus with binocular than for monocular stimulation, with the difference increasing exponentially with defocus to 12.3 ms (± 11.7) at +3.00 D. Similar to the effects for the VEP amplitude, visual acuity was always better with binocular than with monocular vision, with the difference being greater the higher the defocus.
Both subjective and objective results show that binocular vision ameliorates the effect of defocus blur, especially for higher levels of defocus. The binocular facilitation may be due to the increased cortical activity corresponding to the fovea.
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