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Jean Delbeke, Delphine Pins, Géraldine Michaux, Marie-Chantal Wanet-Defalque, Simone Parrini, Claude Veraart; Electrical Stimulation of Anterior Visual Pathways in Retinitis Pigmentosa. Invest. Ophthalmol. Vis. Sci. 2001;42(1):291-297.
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purpose. To explore electrically induced phosphenes in blind patients with
retinitis pigmentosa (RP) in comparison with healthy subjects and to
develop a screening test for candidates for an optic nerve visual
methods. Phosphenes are obtained by charge balanced biphasic pulse stimulations
through a surface cathode over the closed eyelids and an anode near the
opposite ear. The resulting strength–duration relationship for
somatosensory, phosphene, and pain threshold has been recorded in five
RP patients as well as in 10 healthy volunteers.
results. In sighted subjects, the average rheobase and chronaxy for
phosphene perception are 0.28 mA and 3.07 msec, respectively. For pulse
durations longer than 2 msec, phosphenes are usually obtained at
current strengths below the level giving rise to any other electrically
generated sensation. In RP patients, however, phosphenes are not so
easily obtained. One in five had no visual response at all. Another
patient reported a flash perception for the longest pulse durations
only. Spontaneous phosphenes interfered heavily with the stimulation in
a third person. Finally, despite the higher threshold, two patients
displayed normally shaped strength–duration curves.
conclusions. The surface stimulation has proven harmless, adequate, and very helpful
to ascertain that the optic nerve can be electrically activated in
completely blind individuals. Long-duration stimulation pulses yield
very low phosphene thresholds in healthy subjects. Anterior visual
pathways activation requires higher currents in RP
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