Abstract
Retinal prostheses are devices used to restore visual sensation in patients suffering from photoreceptor degeneration, such as retinitis pigmentosa. Suprachoroidal–transretinal stimulation (STS) is a prosthesis with retinal electrodes located in the sclera. STS has the advantage that it is safer than epiretinal or subretinal prostheses, as the implant is not directly attached to the retinal tissue. We have previously reported feasibility of STS with animal experiments and clinical trials. However, functional evaluation with neurophysiological experiments is still largely missing. To estimate the spatial resolution of STS, single-unit activities in response to STS were recorded from relay cells in the dorsal lateral geniculate nucleus of cats, and the response probability of the units was analyzed in relation to the distance between the stimulus location and the receptive field of each recorded unit. A platinum electrode was attached to the sclera after lamellar resection, and the return electrode was placed in the vitreous. The stimulating current, which ranged from 50 to 500 μA, was applied between these electrodes, and the probability of spike responses occurring just after retinal stimulation was measured. The distance at half-maximum of response was determined from the collected response probabilities as a function of stimulus intensity for all units characterized by their distances from the receptive field center to the stimulation point. As the stimulation became weaker, this distance decreased to 1.8° at 150 and 100 μA. As another estimation, the radius of 25% response probability was 1.4° at 100 μA. The diameter of the stimulated cat retinal area, 3.6° or 2.8°, corresponds to human visual acuity of 0.005 or 0.007, or finger counting. Considering the lower hazard to the retina of STS and its potentially large visual field coverage, STS is an attractive method for retinal prosthetic device development.
Highlights
Retinitis pigmentosa (RP) is the leading cause of blindness and is characterized by the degeneration of photoreceptors (Marmor et al, 1983; Pagon, 1988)
The responses to Suprachoroidal–transretinal stimulation (STS) in the single-unit activity of dorsal lateral geniculate nucleus (dLGN) were observed as several bursts, which repeated periodically up to approximately 200 ms after stimulus
A similar burst response to retinal electrical stimulation has been reported for retinal ganglion cell (RGC) with epiretinal stimulation (Jensen et al, 2005b; Fried et al, 2006; Freeman and Fried, 2011), and transretinal stimulation (Crapper and Noell, 1963; Li et al, 2005)
Summary
Retinitis pigmentosa (RP) is the leading cause of blindness and is characterized by the degeneration of photoreceptors (Marmor et al, 1983; Pagon, 1988). Two types of retinal prostheses have been developed far: epiretinal stimulation (Humayun et al, 1994; Majji et al, 1999; Nadig, 1999; Walter and Heimann, 2000) and subretinal stimulation (Chow and Chow, 1997; Zrenner et al, 1999; Schwahn et al, 2001; Chow et al, 2002), named according to the location of the electrode array implantation. Both approaches have a common disadvantage, in that, the stimulating electrode array is invasive for the neural retina because it is directly attached to the retina. Improvements in surgical and electronic technology may solve some of the problems associated with these types of retinal prostheses, the potential risk of damage to the eye after intraocularly inserting an electrode is still debatable
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