Abstract
The altered sensory experience of profound early onset deafness provokes sometimes large scale neural reorganisations. In particular, auditory-visual cross-modal plasticity occurs, wherein redundant auditory cortex becomes recruited to vision. However, the effect of human deafness on neural structures involved in visual processing prior to the visual cortex has never been investigated, either in humans or animals. We investigated neural changes at the retina and optic nerve head in profoundly deaf (N = 14) and hearing (N = 15) adults using Optical Coherence Tomography (OCT), an in-vivo light interference method of quantifying retinal micro-structure. We compared retinal changes with behavioural results from the same deaf and hearing adults, measuring sensitivity in the peripheral visual field using Goldmann perimetry. Deaf adults had significantly larger neural rim areas, within the optic nerve head in comparison to hearing controls suggesting greater retinal ganglion cell number. Deaf adults also demonstrated significantly larger visual field areas (indicating greater peripheral sensitivity) than controls. Furthermore, neural rim area was significantly correlated with visual field area in both deaf and hearing adults. Deaf adults also showed a significantly different pattern of retinal nerve fibre layer (RNFL) distribution compared to controls. Significant correlations between the depth of the RNFL at the inferior-nasal peripapillary retina and the corresponding far temporal and superior temporal visual field areas (sensitivity) were found. Our results show that cross-modal plasticity after early onset deafness may not be limited to the sensory cortices, noting specific retinal adaptations in early onset deaf adults which are significantly correlated with peripheral vision sensitivity.
Highlights
A lifetime of sensory deprivation, as experienced by profoundly and congenitally deaf individuals can induce sometimes large-scale neural reorganisations within sensory cortices [1]
We investigated such neural plasticity at the retina and optic nerve in deaf and hearing humans using the non-invasive technique of Ocular Coherence Tomography (OCT) to image and quantify retinal microstructure and test whether retinal changes relate to differences in peripheral vision sensitivity
Optic nerve head analyses We conducted optic nerve head analyses using ocular coherence tomography (OCT) on all deaf and hearing participants to address whether the increased neural substrate to vision robustly demonstrated at cortical level, may extend to increased neural substrate within the optic nerve
Summary
A lifetime of sensory deprivation, as experienced by profoundly and congenitally deaf individuals can induce sometimes large-scale neural reorganisations within sensory cortices [1] Such plasticity influences the remaining senses, with visual sensitivity in the congenitally deaf selectively enhanced as a result [2]. Neural reorganisations concerning the sensory cortices of early onset deaf adults are widely reported, the effect of human deafness on neural structure involved in visual processing prior to the visual cortex has not so far been investigated either in humans or animals We investigated such neural plasticity at the retina and optic nerve in deaf and hearing humans using the non-invasive technique of Ocular Coherence Tomography (OCT) to image and quantify retinal microstructure and test whether retinal changes relate to differences in peripheral vision sensitivity. A recent study [9] investigated cross-modal plasticity in deaf and hearing cats and compared results with behavioural changes and found that peripheral vision sensitivity was significantly increased in the deaf cats, and that enhanced abilities could be traced to neural correlates in the deaf auditory cortex and not the visual cortex
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