Long-term Repeatability and Reproducibility of Phosphene Characteristics in Chronically Implanted Argus® II Retinal Prosthesis Subjects

• Published in: American journal of ophthalmology Vol. 170; pp. 100 - 109
• Main Authors: Luo, Yvonne H-L, Zhong, Joe Jiangjian, Clemo, Monica, da Cruz, Lyndon
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 01.10.2016; Elsevier Limited
• Subjects: Aged; Electrodes; Electrodes, Implanted; Humans; Medical research; Middle Aged; Ophthalmology; Phosphenes - physiology; Prostheses; Reproducibility of Results; Retinitis Pigmentosa - physiopathology; Retinitis Pigmentosa - rehabilitation; Retrospective Studies; Vision Disorders - physiopathology; Vision Disorders - rehabilitation; Visual Perception - physiology; Visual Prosthesis
• ISSN: 0002-9394; 1879-1891
• DOI: 10.1016/j.ajo.2016.07.021

Abstract Purpose Previously published literatures of acute studies on few subjects have shown contradictory evidences on the reproducibility and characteristics of the elicited phosphenes, despite using the same stimulating parameters with epiretinal electrode arrays. In this study, we set out to investigate the long-term repeatilibity and reproducibility of phosphenes in subjects chronically implanted with the Argus® II retinal prosthesis. Design Retrospective interventional case series and reliability study Methods Six Argus® II subjects of >5 years implantation from a single site participated. The 4-electrode cluster (“quad”) closest to fovea was stimulated in each subject with a fixed biphasic current. Perceived phosphenes were depicted relative to subjective visual field center. The stimulus was applied at reducing time intervals from 20min to 1second. Two sets of stimulations were performed on the same day and 2 further sets repeated on a separate visit >1 week apart. Results Phosphene Features Each subject depicted phosphenes of consistent shapes and sizes, and reported seeing the same colors with the fixed stimulating parameters, irrespective of the inter-stimuli intervals. However there is a wide inter-subject variation in the phosphene characteristics. Retinotopic Agreement Four subjects drew phosphenes in the same visual field quadrant as predicted by the quad-fovea location. Two subjects depicted phosphenes in the same hemi-field as the expected locations. Conclusion Phosphenes for each subject were consistently reproducible in all our chronically implanted subjects. This has important implication in the development of long-term pixelated prosthetic vision for future devices.