[Electro-oculopotentiometry].

Primary visual cortex receives visual input from the eyes through the lateral geniculate nuclei, but is not known to receive input from other sensory modalities. Its level of activity, both at rest and during auditory or tactile tasks, is higher in blind subjects than in normal controls, suggesting that it can subserve nonvisual functions; however, a direct effect of non-visual tasks on activation has not been demonstrated. To determine whether the visual cortex receives input from the somatosensory system we used positron emission tomography (PET) to measure activation during tactile discrimination tasks in normal subjects and in Braille readers blinded in early life. Blind subjects showed activation of primary and secondary visual cortical areas during tactile tasks, whereas normal controls showed deactivation. A simple tactile stimulus that did not require discrimination produced no activation of visual areas in either group. Thus in blind subjects, cortical areas normally reserved for vision may be activated by other sensory modalities.

Blindness↗

PubMed1996

Reading-evoked visual dimming.

PURPOSE: To carry out a neuroradiologic investigation in a monocular 49-year-old patient who during the past five years described symptoms of dimming of central vision in his left eye, which was provoked only by reading. METHODS: Computed tomography and magnetic resonance imaging were performed. RESULTS: An orbital apex intraconal tumor situated laterally to and above the optic nerve was found. CONCLUSIONS: Reading-evoked visual dimming can be a variant of gaze-evoked amaurosis. The optic nerve displaced laterally and superiorly, and stretched by the act of reading, may be compressed between the tumor above and the contracted inferior rectus muscle inferiorly.

Blindness↗