Journey of Visual Prosthesis with Progressive Development of Electrode Design Techniques and Experience with CMOS Image Sensors: A Review

Abstract

ABSTRACTThe objective of visual prosthesis is to develop techniques which can functionally replace the degenerated photoreceptors either by inserting the clinical aid inside the eye or by providing external means. Except AIDS and Cancer, there is hardly any disease than blindness which creates more fear in human's mind. Age-related macular degeneration (AMD) and retinitis pigmentosa (RP) were found to be main cause of vision loss followed by cataract and glaucoma. This paper addresses the journey of visual prosthesis by first highlighting the initial challenges and technical advancement later. We have tactically analyzed the conception of visualization, phosphenes detection and modeling of retina through electrodes which had been the focus of researchers before 1990s. Afterwards with the technological improvement, techniques which could enhance the safety, longevity, biocompatibility, resolution and feasibility were targeted. Categorically visual prosthesis is divided into visual cortex, optic nerve and retinal implantation techniques for restoration of vision in blinds. After analyzing the advantages and shortcomings of all these techniques it is concluded that, retinal implants have been the popular method and adopted as potential way for yielding the artificial vision. Key areas of safety standards, use of new biomaterials for improved resolution and durability, power requirements, image processing techniques, new stimulation methods such as biphasic stimulation, and impact of stimulation current/heat on retinal nerves behavior are also addressed in this paper. With low-cost, lower power consumption and integration technology of CMOS devices, nowadays the CMOS active pixel sensor (CMOS-APS) is the new hope for researchers and clinicians. Analysis of electrode design techniques with microphotodiodes, CCD and now with CMOS-APS suggests that the focus of future research will be in developing the high dynamic range (HDR) pixel that can be directly attached to retina for greater efficiency and resolution.