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N. Ragge, H. Bridge, I. Alexander, A. Rao, K. Watkins, R. Collin, A. Cowey; Investigating Developmental Plasticity in Human Anophthalmia. Invest. Ophthalmol. Vis. Sci. 2008;49(13):4501.
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To investigate if the visual cortex of individuals with congenital bilateral anophthalmia, who have therefore never experienced light input, can be reorganised to respond to other sensory modalities, for instance touch or hearing. Evidence from anophthalmic mice suggests that auditory stimulation may allow activation of the visual cortex and there is some anatomical evidence for a direct connection between the inferior colliculus and the occipital cortex.
After ethics approval was obtained (Oxford REC 05/Q1605/143), we recruited 5 individuals with bilateral anophthalmia from Moorfields Eye Hospital age 18-31 y (mean 24.2+/-5.2) together with 4 age-matched controls with normal vision. Subjects participated in structural MRI, diffusion imaging to investigate connectivity, proton density scanning to identify the presence of the lateral geniculate nucleus (3 anophthalmic), language fMRI (2 anophthalmic), transcranial magnetic stimulation (TMS) over the occipital cortex area, and event related potentials (EEG/ERP) recordings in response to various sounds.
All anophthalmic subjects failed to show any significant optic nerves and chiasm on MRI, and using proton density imaging, it was not possible to demonstrate a lateral geniculate nucleus, although it was seen in controls. The visual cortex appeared normal on MRI. However, diffusion imaging demonstrated a significant reduction in white matter integrity of optic radiation. TMS studies demonstrated that none of the anophthalmic subjects perceived light on stimulation over the visual cortex, but instead 3 subjects experienced a somatosensory response and one an auditory buzz. Early activations (ERP) of the visual cortex were recorded in response to sound.
There is preliminary evidence for cross-modal developmental plasticity in the visual cortex of anophthalmic individuals.
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