Cortical Visual Field Maps of a Patient With Tunnel Vision (Retinitis Pigmentosa)

Abstract

Abstract: : Purpose: To elucidate whether there is reorganization in the visual cortex of a patient with tunnel vision, we performed functional MR imaging experiments in a patient with retinitis pigmentosa. Methods: First we measured the visual field of the patient in the MR scanner. Second we measured retinotopic maps using functional MR imaging with conventional expanding ring and rotating wedge stimuli that extended somewhat beyond the patient's visual field. The entire occipital lobe was measured using a 3T GE MR scanner with spiral sequence. Third we measured normal controls using the same stimuli. We measured and compared the surface areas of several retinotopic maps in the patient and controls. We identified the retinotopic maps on flattened views of cortex, and we measured the surface area on the folded cortical surface (mm2) of V1v, V1d, V2v, V2d, V3v and V3d within the visual field from 2–12 degrees (mrVista software). Results: The surface area values of the retinotopic maps in normal subjects were consistent with measured values in a previous report (1), and the surface area of the patient's retinotopic maps were also within the normal range. However, we observed a tendency for the dorsal visual areas to have slightly larger surface area than the ventral visual areas in most normals. Surprisingly, the visual areas of the patients with retinitis pigmentosa showed the opposite trend, that is, the dorsal regions (upper retinotopic maps) were markedly smaller than the ventral regions. Conclusions: We did not find evidence that the total surface area of the functional portion of the visual field extended into the portion of cortex that receives no input. In this sense, we did not find significant reorganization of functional visual cortex. However, the relatively large ventral regions may imply some reorganization visual cortex. The data are consistent with either a slight increase in the dorsal regions or a small degeneration of the ventral regions in patients with a constricted visual field. Reference: 1) Dougherty RF, et al. J Vision, 2003.

Keywords: plasticity • visual cortex • neuro-ophthalmology: cortical function/rehabilitation