. Purpose:  To determine the threshold charges needed for eliciting visual perceptions through acute electrical stimulation of the human retina in patients suffering from retinitis pigmentosa, using an epiretinal microelectrode array. Methods:  In a multicentre study, 20 patients (average age 55 years) with visual acuities ranging from 4/200 to no light perception were included. The stimulation procedure was performed during a pars plana vitrectomy, for a maximum of 45 min, by using a microcontact film with IrOx electrodes connected by cable to a current generator. After repeated stimulation and threshold charge determination, the microelectrode array was removed. Results:  Nineteen of 20 patients stated in the postoperative interviews that they experienced one or more visual perceptions with close time correlation to single stimulation events. Minimum threshold charges needed to generate visual perceptions could be measured and verified in 15 patients. The charge level ranged from 20 to 768 nC with single or multiple electrodes. One patient suffered a retinal detachment during the procedure; this patient’s retina was successfully reattached. There were no further adverse reactions observed during the 3‐month follow‐up. Conclusion:  Acute epiretinal stimulation of the human retina, using a microelectrode array, can elicit visual perceptions in blind patients with retinitis pigmentosa.

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This paper reports on methods and technical equipment to investigate the epiretinal stimulation of the retina in blind human subjects in acute trials. Current is applied to the retina through a thin, flexible microcontact film (microelectrode array) with electrode diameters ranging from 50 to 360 microm. The film is mounted in a custom-designed surgical tool that is hand-held by the surgeon during stimulation. The eventual goal of the work is the development of a chronically implantable retinal prosthesis to restore a useful level of vision to patients who are blind with outer retinal degenerations, specifically retinitis pigmentosa and macular degeneration.

ABSTRACT.Purpose: Ophthalmic features of neurofibromatosis 2 (NF2) include juvenile cataract, retinal hamartomas and tumours of the cranial nerves. We hypothesize that these tumours lead to strabismological and neuro-ophthalmological symptoms, including palsies of cranial nerves III, IV and VI, nystagmus and gaze palsies. Methods: We carried out a retrospective review of 73 patients with known genotype. They underwent ophthalmic, neuro-ophthalmological and strabismological examination. Statistical analysis was performed by calculating odds ratios and their 95% confidence intervals. Results: Mean best corrected visual acuity was 0.85. Strabismus was found in 38 of 73 patients (52%). A deviation based on a cranial nerve palsy was found in 16 patients (22%) and three had supranuclear palsies. Eleven of 73 patients had a nystagmus, mostly caused by peripheral-vestibular disturbance. Binocular single vision was normal in 41 (58%), subnormal in six (8%) and not present in 24 (34%) patients. The average refractive error was ) 0.57 D. Myopia of ‡ 0.5 D was present in 47 (33%) eyes and hyperopia of ‡ 2.0 D was measured in 11 (8%) eyes. In the subgroup analysis of NF2 mutation types, the relative risk for cranial nerve palsies and negative stereopsis was statistically significantly increased for the nonsense mutation group. The mosaicism group had a statistically significant decreased relative risk for concomitant squint, as did patients with unfound mutations for strabismus and poor stereopsis. Conclusions: The present study is, to our knowledge, the first to examine a larger collection of NF2 patients for strabismological and neuro-ophthalmological lesions. Compared with the normal population, our sample showed a higher amount of strabismus, refractive errors and an increased incidence of vestibular nystagmus.