Artificial Eyes 4

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It captures an outside image, processes it, and transmits it to implanted electrodes through wires or wirelessly. Upon reaching the implant, the signal it decoded to analogue, and electrical currents stimulate individual electrodes

Light Detection, Camera based system, disadvantages

A camera-based system may exhibit considerable mismatch when the eye's direction differs from that of the head-mounted camera. This discrepancy can result in misdirection, causing patients to reach for incorrect positions when trying to locate an object.

Light Detection, Photodiodes

The image is projected onto the retina using incident light, with photodiodes converting the signal into electrical stimulation. The light source can be natural or manipulated using infrared wavelengths.

This system accommodates natural eye movements, aligning the eyes with the stimulated image within the field-of-view

What is the best system for light detection

a combination of the two approaches camera-based system and photodiodes (epiretinal prostheses-approved devices, suprachoroidal prostheses, subretinal prostheses)

What is one consider regarding optimising the retinal electrode array

electrodes

• Platinum electrodes

• Photodetectors:

  • Photodiodes

  • Photovoltaics

Platinum electrodes

• Compared to AgCl, platinum is biocompatible making it ideal for invasive electrodes and implants

• Connected to a percutaneous connector via a helical lead wire for direct stimulation behind the ear

• Suprachoroidal implant prototype in Bionic Vision Study

Photodiodes

A photodiode is a PN-junction diode that consumes light energy to produce an electric current.

When are silicon photodiodes used

Silicon photodiodes are semiconductor devices used for the detection of light in ultra-violet, visible and infrared spectral regions.

What are the features of the subretinal implant

(A) The subretinal implant features a silicon photodiode (green), an inner electrode (gray), an outer grounded electrode (gray), and an insulating layer (yellow) between the photodiode's sides and the outer electrode. Current generated in the photodiode produces a voltage difference between the inner and outer electrodes which extracellularly stimulates bipolar neurons (pink).

(B) The conventional inner electrode is square shaped.

(C) Some works consider a fractal design based on a repeating H pattern.

Why the H pattern

The sidewalls of the repeating branches generate a large surface area, while the gaps between the branches allow the light to pass through

Photovoltaics

A photovoltaic (PV) cell is a semiconductor device that converts light directly into electricity. When photons interact with a PV cell, they can either bounce off, penetrate, or get absorbed by the semiconductor material. Only the absorbed photons contribute energy for electricity generation. When the semiconductor material absorbs a sufficient amount of light, electrons are liberated from the atoms within the material.

What happens to a photovoltaics under illumination

Under illumination, photocurrent flows into the central active elcetrode, through the series-connected diode, and flows out of the concentric return electrode

What are the challenges in establishing a Stable Electrode Retina Interface

Curved Retina vs. Planar Electrode Technology

• Retina natural curvature

• Microelectrode technology typically produces planar structures

• Mismatch between the two

Variability in Eye Curvature

• Eye curvature differs from person to person

• Mechanical Compression Risk:

  • Curvature mismatch may lead to mechanical compression of the retina

• Increased Current Requirement:

  • Curvature mismatch may result in electrode separation, necessitating higher current levels and potential current spreading over a larger retinal area.

What are the ideal characteristics of a Retinal Stimulating Electrode

Flexibility for Curvature Matching

Electrode Materials

• Platinum: Most commonly used electrode material

• Alternatives and novel versions of platinum

  • Platinum grey (high surface area platinum)

  • Iridium oxide Better charge injection properties than smooth platinum

Why is Hermetic Packaging important

- Active electronic circuits in the body require protection from water and ions.

- Even simple electrodes with wire leads need proper insulation.

What are the two types of hermetic packaging

Enclosure and Encapsulation

Enclosure Hermetic Packaging

Enclosure: Traditional sealed package (e.g., close-fitting titanium). - Enclosure offers long-term reliability.

Argus II uses an enclosure and has been functioning in some users for over 10 years.

Encapsulation Hermetic Packaging

Encapsulation: Conformal coating forming a protective layer around electronics.- A thin layer on a silicon chip is significantly smaller than a metal case. - Essential for allowing light to reach photodiodes in photosensitive chips.

- Alpha-AMS and PRIMA use encapsulants.- First-generation Alpha-IMS experienced encapsulation failure.- Alpha AMS design improvements addressed this issue.- PRIMA is undergoing long-term reliability testing in clinical trials

What is needed to achieve measurable vision outcomes from retinal prostheses

there are several engineering and image processing aspects that need to be considered in device design and system implementation.

What is needed to enable real-time image processing for retinal prostheses

Utilizing External Camera and Processing Unit

• Enhance and simplify low-resolution retinal prostheses images

Key Requirements

• Real-time image processing

• Portability for user convenience

• Potential use of off-the-shelf hardware, such as augmented reality headsets

What is needed for Image Processing Methods for Retinal Prostheses

Image Processing Methods for Retinal Prostheses

• Fundamental Image Processing Functions

  • Adapt visual data from the sensor to perceptual parameters for stimulation

• Categorization of Image Processing Methods

  • General methods for all activities and scenes

  • Specialized methods for specific activities and scenarios

What are methods used for image processing

• General methods for all activities and scenes: focus on downsampling from high resolution input to low resolution retinal prosthesis display

• Specialized methods for specific activities and scenarios: regional averaging, gaussian filtering, edge detection, contrast enhancement, difference of gaussian

Explain the concept of down sampling in image processing

Downsampling refers to reducing the resolution of an image by discarding some of its pixels to create a lower-resolution version. This should be done to adapt visual data from the sensor to perceptual parameters for stimulation

Examples of actual image processing in eye prostheses

user controlled zooming and image processing

contrast enhancement

edge extraction

blurring

thresholding

low-pass filter

interpolation

How should u explain for a task-specific improvement

Focus on Task-Specific Improvement

Emphasis on enhancing performance for specific tasks Aiming to enhance the quality of life

Example: Face Detection

Utilizing a standard computer vision face detection algorithm Identifying areas in the image containing a face

Activation of phosphenes in that region to signal the presence of a face