The Appearance of Phosphenes Elicited Using a Suprachoroidal Retinal Prosthesis

Sinclair, Nicholas C; Shivdasani, Mohit N.; Perera, Thushara; Gillespie, Lisa N; McDermott, Hugh J.; Ayton, Lauren N; Blamey, Peter J.

doi:10.1167/iovs.15-18991

Cited by 56 publications

(94 citation statements)

References 49 publications

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“…Our group, through the Bionic Vision Australia program, has been working on placing an electrode array between the sclera and the choroid, thus using a suprachoroidal approach. [2][3][4][5] While each anatomical location provides unique advantages, the potential benefits of using the suprachoroidal location are the ease of surgical implantation of the electrode array, mechanical stability in situ over the long term, the ability to cover a large area of the visual field, and minimal risk of retinal trauma. event.…”

Section: Purposementioning

confidence: 99%

“…event. 2 Reliable phosphene thresholds could be measured in all patients, and the most effective stimulus parameters 3 and individual phosphene characteristics 5 were determined through extensive psychophysical studies using single-electrode stimulation. Using a camera-based semiportable system along with head scanning, patients were able to recognize simple shapes and objects, and data from one patient showed that the implant was capable of providing measureable visual acuity on an optotype acuity task.…”

Section: Purposementioning

confidence: 99%

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Identification of Characters and Localization of Images Using Direct Multiple-Electrode Stimulation With a Suprachoroidal Retinal Prosthesis

Shivdasani

Sinclair

Gillespie

et al. 2017

Invest. Ophthalmol. Vis. Sci.

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Citation: Shivdasani MN, Sinclair NC, Gillespie LN, et al.; for the Bionic Vision Australia Consortium. Identification of characters and localization of images using direct multiple-electrode stimulation with a suprachoroidal retinal prosthesis. Invest Ophthalmol Vis Sci. 2017;58:3962-3974. DOI: 10.1167/iovs.16-21311 PURPOSE. Retinal prostheses provide vision to blind patients by eliciting phosphenes through electrical stimulation. This study explored whether character identification and image localization could be achieved through direct multiple-electrode stimulation with a suprachoroidal retinal prosthesis.METHODS. Two of three retinitis pigmentosa patients implanted with a suprachoroidal electrode array were tested on three psychophysical tasks. Electrode patterns were stimulated to elicit perception of simple characters, following which percept localization was tested using either static or dynamic images. Eye tracking was used to assess the association between accuracy and eye movements.RESULTS. In the character identification task, accuracy ranged from 2.7% to 93.3%, depending on the patient and character. In the static image localization task, accuracy decreased from near perfect to <20% with decreasing contrast (patient 1). Patient 2 scored up to 70% at 100% contrast. In the dynamic image localization task, patient 1 recognized the trajectory of the image up to speeds of 64 deg/s, whereas patient 2 scored just above chance. The degree of eye movement in both patients was related to accuracy and, to some extent, stimulus direction.CONCLUSIONS. The ability to identify characters and localize percepts demonstrates the capacity of the suprachoroidal device to provide meaningful information to blind patients. The variation in scores across all tasks highlights the importance of using spatial cues from phosphenes, which becomes more difficult at low contrast. The use of spatial information from multiple electrodes and eye-movement compensation is expected to improve performance outcomes during real-world prosthesis use in a camera-based system. (ClinicalTrials.gov number, NCT01603576.) Keywords: retinal prostheses, suprachoroidal, psychophysics, retinitis pigmentosa, electrical stimulation O ver the last decade, retinal prostheses have emerged as the only regulatory approved technology to provide artificial vision to patients with profound vision loss due to photoreceptor dystrophies such as retinitis pigmentosa. 1 These devices work by electrically stimulating surviving second-and thirdorder retinal neurons via an implanted array of electrodes to elicit the perception of light flashes termed phosphenes. Multiple electrodes can be stimulated to induce the perception of an image, usually captured by a video camera. While there have been over 20 groups worldwide trying to develop such a device, only three devices have achieved commercialization so far. The Argus II epiretinal (i.e., electrode array attached directly to the inner surface of the retina) prosthesis from Second Sight Medical Products, Inc. (Sy...

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Section: Purposementioning

confidence: 99%

Section: Purposementioning

confidence: 99%

Identification of Characters and Localization of Images Using Direct Multiple-Electrode Stimulation With a Suprachoroidal Retinal Prosthesis

Shivdasani

Sinclair

Gillespie

et al. 2017

Invest. Ophthalmol. Vis. Sci.

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“…Retinal prostheses are based on this principle. Retinal prostheses are classified into four types, depending on the position of the electrode array: (1) epiretinal (placed on the retina from the vitreous side), (5) (2) subretinal (placed between the choroid and the retina), (7) (3) placed between the choroid and retinal pigment epithelium, (8) and (4) placed in the sclera. (9) We have been developing a retinal prosthesis based on suprachoroidal transretinal stimulation (STS) in which the electrode array is placed in a scleral pocket created by making a half-layer incision.…”

Section: Introductionmentioning

confidence: 99%

“…For example, biphasic rectangular current pulses are used in epiretinal, (5) suprachoroidal, (8) and STS prostheses. (9,11) Charge-balanced biphasic pulses can carry out electrical stimulation safely without causing damage to tissues.…”

Section: Introductionmentioning

confidence: 99%

Sinusoidal Electrical Pulse More Efficiently Evokes Retinal Excitation than Rectangular Electrical Pulse in Retinal Prostheses

Nakano

Terasawa

Kanda

et al. 2017

Sensors and Materials

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Retinal prostheses for blindness due to retinal photoreceptor degeneration stimulate the retina electrically to evoke a pseudolight sensation (phosphenes). Although rectangular pulses of electrical stimulation are commonly used in retinal prostheses, it remains unclear whether nonrectangular pulses are effective in evoking this response. Here, we conducted in vivo electrophysiological experiments to compare the effectiveness of sinusoidal and rectangular pulses. Biphasic sinusoidal pulses (cathodic-first) applied suprachoroidally and transretinally to the rat eye elicited larger field responses in the superior colliculus than did rectangular pulses. The threshold charge for the evoked response of the sinusoidal pulse was significantly lower than that of the rectangular pulse, suggesting that a sinusoidal pulse is more effective than a rectangular pulse in our retinal prosthesis. Because a sinusoidal pulse can evoke phosphenes with a small charge magnitude even if the electrode area is reduced, the charge density does not increase; thus, the pulse can stimulate the retina without causing tissue injury. Because the sinusoidal pulse allows us to reduce the electrode area, it is possible that phosphenes can be localized to a smaller area by limiting the range of stimulated retinal ganglion cells. Therefore, high resolution of retinal prostheses using the sinusoidal pulse can be expected.

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“…It is therefore entirely plausible that results achieved in the retina may not fully translate into perceptual outcomes as some of the perceptual distortion of phosphenes could be caused by central mechanisms and plasticity associated with long-term blindness (24). Finally, the perceptual benefits achieved with long phase durations may only apply to patients implanted with an epiretinal prosthesis, as perceptual distortions shown to be a result of axonal activation has not primarily been observed with subretinal (2) or suprachoroidal (25,26) stimulation.…”

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confidence: 99%

Are long stimulus pulse durations the answer to improving spatial resolution in retinal prostheses?

Petoe

Shivdasani

2016

Ann. Transl. Med.

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Retinal prostheses can provide artificial vision to patients with degenerate retinae by electrically stimulating the remaining inner retinal neurons. The evoked perception is generally adequate for light localization, but of limited spatial resolution owing to the indiscriminate activation of multiple retinal cell types, leading to distortions in the perceived image. Here we present a perspective on a recent work by Weitz and colleagues who demonstrate a focal confinement of retinal ganglion cell (RGC) activation when using extended pulse durations in the stimulation waveform. Using real-time calcium imaging, they provide evidence that long pulse durations selectively stimulate inner retinal neurons, whilst avoiding unwanted axonal activations. The application of this stimulation technique may provide enhanced spatial resolution for retinal prosthesis users. These experiments provide a robust analysis of the effects of increasing pulse duration and introduce the potential for alternative stimulation paradigms in retinal prostheses.

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The Appearance of Phosphenes Elicited Using a Suprachoroidal Retinal Prosthesis

Cited by 56 publications

References 49 publications

Identification of Characters and Localization of Images Using Direct Multiple-Electrode Stimulation With a Suprachoroidal Retinal Prosthesis

Identification of Characters and Localization of Images Using Direct Multiple-Electrode Stimulation With a Suprachoroidal Retinal Prosthesis

Sinusoidal Electrical Pulse More Efficiently Evokes Retinal Excitation than Rectangular Electrical Pulse in Retinal Prostheses

Are long stimulus pulse durations the answer to improving spatial resolution in retinal prostheses?

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