Purpose: Since 2000, several groups have initiated chronic studies, implanting electronic retinal prostheses into the blind eyes of patients with retinitis pigmentosa to produce formed vision.
Design: A review and comparison of their techniques and results.
Methods: The 4 groups reviewed comprise 2 epiretinal and 2 subretinal groups. Visual function results reported in their publications during approximately the past 2 years are compared.
Results: Serious adverse effects occurred in both epiretinal groups but none in the 2 subretinal groups. Phosphenes with some similarity to the multielectrode stimulation pattern were induced by 1 group (EpiRet GmbH), and a somewhat higher phosphene pattern was created by another group (Second Sight). In 1 subretinal group (Retina Implant AG), an even higher phosphene pattern allowed recognition of letters and objects such as a cup or saucer. In the second subretinal group (Optobionics), besides perceived phosphenes, a neurotrophic rescue of visual function produced a marked improvement of visual acuity, color and contrast perception, visual field size, and improved darkness perception. In some subjects, recognition of facial features and household objects was restored.
Conclusions: Both epiretinal and subretinal prostheses created phosphene-type patterned vision in some subjects. The phosphene resolution of Retina Implant AG's subretinal device was substantially greater than both epiretinal devices. Of the 4 groups, only Optobionic's paracentrally placed subretinal Artificial Silicon Retina implant induced an unexpected neurotrophic rescue and return of lost visual function resulting in the greatest return of visual acuity, color and contrast perception, visual field enlargement, and darkness perception.