The functional performance of the Argus II retinal prosthesis

Abstract

Visual prostheses are devices to treat profound vision loss by stimulating nerve cells anywhere along the visual pathway, typically with electrical pulses. The Argus^® II implant, developed by Second Sight Medical Products (SSMP, Sylmar, CA, USA), targets the retina and features 60 electrodes that electrically stimulate the surviving retinal neurons. Of the approximately 20 research groups that are actively developing visual prostheses, SSMP has the longest track record. The Argus II was the first visual prosthesis to become commercially available: it received the European conformity mark in 2011 and FDA approval was granted in early 2013 for humanitarian use in the USA. Meanwhile, the Argus II safety/benefit study has been extended for research purposes, and is still ongoing. In this review, we will discuss the performance of the Argus II in restoring sight to the blind, and we will shed light on its expected developments in the coming years.

Keywords::

• Argus II
• electrical stimulation of the retina
• epiretinal implant
• low vision
• retinal prosthesis
• retinitis pigmentosa
• spatial resolution
• visual acuity
• visual prosthetics
• vision rehabilitation

Acknowledgements

The authors wish to thank J Dorn and B Mech (Second Sight Medical Products Inc., Sylmar, CA, USA) for their invaluable contribution to the Five-year view section, and comments on the manuscript. The authors also wish to thank E Zrenner (University of Tuebingen, Germany) for discussions concerning the publications of his group on alpha-IMS implants. The authors take full responsibility for the contents of their work.

Financial & competing interests disclosure

HC Stronks and G Dagnelie serve as consultants for Second Sight Medical Products, and are designated on a patent regarding the Argus II prosthesis. HC Stronks is currently affiliated with Bionic Vision Australia. The authors have no other relevant affiliations or financial involvement with any organization or entity with a financial interest in, or financial conflict with the subject matter or materials discussed in the manuscript apart from those disclosed.

No writing assistance was utilized in the production of this manuscript.

Key issues

• Performance in relatively simple visual tasks, for example, object localization, improved in nearly 100% of the tested Argus II subjects.

• More complex tasks, for example, detection of motion, improved in approximately 50% of Argus II subjects.

• An orientation and mobility task based on walking toward a high-contrast target, or walking along a high-contrast line on the floor improved significantly when using the implant in a grouped analysis of Argus II subjects.

• The differences between reported visual acuity of Argus II (60 electrodes) and alpha-IMS (1500 electrodes) wearers are small, despite the theoretical eight-times lower resolution of the Argus II device.

• Retinal implant functionality is limited by many factors including physical (e.g., electrode interactions), physiological (e.g., retinal degeneration) and human factors (e.g., the patient’s capability to comprehend prosthetic vision). At present, hardware engineering factors, such as electrode size and electrode density, may be of lesser importance.

• Vision processing strategies, patient screening methods and optimizing the electrode–tissue interface are aspects of implant functionality that can be improved in the future.

• The Argus II device will be continuously improved, including the implementation of advanced vision processing strategies, zooming, eye scanning and color coding.

• Within 5 years from now, Second Sight Medical Products hope to implant more than 2000 Argus II devices worldwide.

• According to current plans, the next-generation devices from Second Sight Medical Products device will be a high-acuity retinal implant with 240 electrodes, and a cortical 60-electrode implant.

Notes