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Mei Ying Boon, Catherine Suttle, Harry Leung, Stephen Hing, Tiong Peng Yap, Chi Luu; Binocular summation of luminance and chromatic contrast stimuli in children with unilateral or bilateral amblyopia. Invest. Ophthalmol. Vis. Sci. 2013;54(15):3997. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
The binocular contrast summation ratio (BCSR) provides an indication of the extent to which binocular signals are used to enhance vision in this viewing condition compared with monocular viewing. To date, the development of binocular summation for luminance contrast thresholds is not well understood, and has not been investigated for chromatic thresholds. Hence the aim of the study is to investigate BCSR in response to luminance and chromatic contrast stimuli in children with normal vision and in those with bilateral or unilateral amblyopia.
Luminance (black-white) and isoluminant chromatic (red-green) contrast thresholds were measured monocularly (RE, LE) and binocularly in 5-12 year old children with normal vision (n=10), unilateral anisometropic amblyopia (n=10) and bilateral refractive amblyopia (n=17). Stimuli were 1 cycle per degree sinewave gratings in a gabor envelope against a background of the same mean luminance and chromaticity. A spatial 2 alternative forced choice staircase was used to estimate threshold using the mean of 4 reversals. Each stimulus was presented pattern onset-offset (on 100 ms, off 400 ms) 10 times before the child was required to respond. The order of measurement of monocular and binocular thresholds was varied randomly to cancel out practice or fatigue effects across participants.
In the children with normal vision (VA 0.01±0.05 logMAR), average luminance and chromatic BCSRs were 1.63±0.5 and 1.13±0.2 respectively. In children with unilateral amblyopia (amblyopic eye VA 0.33±0.2), these values were 1.44±0.4 and 1.23±0.5 respectively and in children with bilateral amblyopia (VA 0.29±0.1), 1.90±1.1 and 1.87±0.84 respectively. In the latter group, chromatic BCSR was higher than controls (p=0.01). In the latter group, chromatic BCSR was higher than controls (p=0.01). In unilateral amblyopes, amblyopic>fellow eye BCSR for luminance (p=0.02) thresholds.
Binocular summation ratios beyond probability levels in children with normal vision as well as those with amblyopia suggest that neural summation occurs in the developing visual system and that development of summation does not depend on binocular stimulation. The higher than age-normal values of BCSR in children with bilateral amblyopia may reflect a difference in development of binocular function in that subgroup.
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