Subretinal Microelectrode Arrays Allow Blind Retinitis Pigmentosa Patients to Recognize Letters and Combine them to Words

Eleven patients received subretinal implants, powered and controlled via a subdermal cable ending in a thin intraocular foil, placed transsclerally between the retinal pigment epithelium and the neuroretina. The tip of this foil carries two distinct arrays, a Multiphotodiode Array (MPDA) with 1500 electrodes, each electrode being controlled by an adjacent photodiode and an amplifier within a 3times3times0.1 mm chip, as well as a second array with 16 electrodes, for direct stimulation (DS). Subretinal multielectrode implants with currents close to recognition threshold (10 to 27 nC/electrode) produce retinotopically correct patterns that allow for the first time recognition of individual letters (8 cm high, viewed in appr. 62 cm distance) even at low luminance levels. Stripe patterns of moderate luminance can be resolved up to 0.35 cycles/deg via the subretinal chip. This clearly supports the feasibility of light sensitive subretinal multielectrode devices for restoration of useful visual percepts in blind patients.