2. Outline of Today’s Presentation:
• Anatomy of the Eye
• Hereditary Retinal Diseases
• Macular Degeneration (AMD)
• Retinitis Pigmentosa (RP)
• History of Visual Prosthesis
• Introduction
• Types of Visual Prostheses
• Research behind Alpha-IMS
• Introduction and Hypothesis
• Methods
• Results
• Conclusions of Study
• Conclusions and Future Outlook
3. Anatomy of the Eye
Sclera – white of eye
Optic nerve – transmits
visual information from
retina to brain
Retina – photoreceptor
cells arranged in several
layers
Fovea – provides
sharpest images
4. Macular Degeneration (AMD)
Results in gradual destruction of
the macula among people age 50+
Causes:
Loss of vision, but not complete
blindness
Can still see using peripheral
vision
Image is there, but detail is lost
Two types:
Dry
Wet
Detected by:
Visual acuity test
Dilated eye exam
5. Retinitis Pigmentosa (RP)
Results in loss of photoreceptors
during childhood or late 40s to
early 50s
Causes:
Difficulty seeing at night or in
dim lighting
Gradual loss of peripheral
vision
Loss of central vision (in
advanced cases)
Incurable blindness
Detected by:
Dilated eye exam
Electroretinography (ERG) test
6. History of Visual Prosthesis
1929: German neurologist, Otfrid Foerster, discovered
electrically stimulating occipital lobe caused patients to see
phosphenes
1931: Fedor Krause and Heinrich Schum performed same
experiment on a patient who had been blind for 8 years
1956: Australian, Graham Tassicker, described how a
photosensitive cell placed behind retina of a blind patient
resulted in phosphenes
1960s and 1970s: Giles Brindley and William Dobelle
established Field of Visual Prosthesis by implanting electrodes
into visual cortex and demonstrating their ability to induce
consistent phosphenes
1990s to Present: Advances in biomaterials, electronics, and
retinal surgery have led to a cascade of developments in the field
7. Introduction
Blindness affects over 40 million people around the world with 15
million suffering from blindness due to a hereditary retinal disease
Looking to restore visual function, Field of Visual Prosthesis began
All visual prostheses must perform these steps:
1. Detect and capture ‘light-based’ images
2. Transduce images into electrical stimuli
3. Deliver stimuli to axons of ganglion cells within optic nerve
4. Evoke a response in visual cortex to induce phosphenes
There are a variety of prostheses:
Cortical prosthesis
Optic nerve prosthesis
Retinal prosthesis
With advancement in surgical techniques and bioengineering,
retinal prosthesis is the most advanced visual prosthesis
8. Cortical Prosthesis
First device to artificially induce phosphenes
However, because electrode arrays were situated on
the cortex it caused:
Poor spatial resolution
Discomfort from stimulation
Focal epileptic activity
The Utah Electrode Array (UEA) was developed to
counteract these side effects
Main advantage is that they are the only therapeutic
treatment for individuals with non-functioning
retina or optic nerves
9. Optic Nerve Prosthesis
Used for blind patients with functional
retinal ganglion cells
Multiple electrodes are inserted onto optic
nerve
Stimulation of electrodes in acute settings have
produced phosphenes
Achieving focal stimulation and retinotopic
distribution are challenging
10. Retinal Prosthesis
Replace photoreceptors by producing small, localized currents that alter
membrane potential of adjacent retinal neurons
Energy required by device is derived from:
External power source
Incident light acting through a photoelectric cell
Subjects utilizing this device have been subjected to tests demonstrating:
Improvements in mobility
Motion detection
Object localization and recognition
Grating identification
Retinal ganglion cells and visual pathways need to be viable for device to
function
Two types categorized according to site of implantation:
Epiretinal prosthesis
Subretinal prosthesis
11. Epiretinal Prostheses
Implanted on inner surface of retina
Consists of three main components:
External camera for capturing images
Component that transforms images into electrical stimuli
Component that stimulates remaining cells in inner retina
Examples of devices in advanced stages of development:
Argus II:
Multielectrode array powered by externally worn battery pack
Images are captured by camera mounted on glassestranslated into
pixilated images by visual processing unitdelivered via transscleral cables
to implant
12. Epiretinal Prostheses Continued
EPI-RET3:
Consists of an array of 25 electrodes apposed to ganglion cells
Images are captured by mounted camera on glassestransferred
wirelessly to receiver unit placed in anterior chambersignal is
transmitted via micro cable to implant
13. Subretinal Prostheses
Implanted between retina
Alpha-IMS:
Consists of microphotodiode array (MPDA) with 1500
microelectrodes and a direct stimulation (DS) test field
Consists of three parts:
Subretinal: MPDA implant
Extraocular: foil strip carrying connection lanes to external
connection and reference electrode
Subdermal: silicone cable that leads from implant to behind
the ear where it penetrates skin and ends in a plug
14.
15. Epiretinal Prostheses
Advantages Disadvantages
Easy surgical insertion
Minimal disruption to retina
Location of implant allows
for heat dissipation
Easy upgrades can be made
without further surgery
Camera is capable of zooming
Long-term stability
Decoded electrical signal is
sent directly to ganglion cells
Only stimulates ganglion cells
Eliminates use of natural eye
movements
More sophisticated processing
is required
16. Subretinal Prosthesis
Advantages Disadvantages
Stimulates bipolar and
amacrine cells
Location helps keep
electrodes in close proximity
to viable retinal cells
Uses natural eye movements
Confined space limits size of
device
Possible chance of thermal
injury
Long surgery time (6-8 hours)
18. Introduction and Hypothesis
Hypothesis:
If it is possible to replace photoreceptive function
using a technical device, then there may be a
treatment for hereditary retinal diseases.
Purpose of Study:
Restore visual function in patients by means of a
subretinaly implanted microelectronic device
Uses light-sensitive detector arrays and amplifiers
Converts light into signals that can stimulate bipolar
cell neurons via tiny metal electrodes
19. Methods:
The subretinal alpha-IMS visual implant
Characteristics of implant:
9 mm2 in size consisting of 1500 pixels
Each pixel contains a:
Photodiode
Amplification circuit
Electrode for charge transfer to adjacent retinal layers
Records images at different frequencies
Offers bipolar cells with a point-by-point electrical image
Provides a diamond-shaped visual field of 10° × 10°
Energy is provided by an external coil from a battery pack
20. Methods Continued:
The Patients
Characteristics of participants:
Four females
Five males
Between ages 35–62 years
Eight patients had RP
One patient had Cone-rod dystrophy
Received subretinal implant in eye with worst vision
Written informed consent was obtained prior to
inclusion in study
21. Methods Continued:
Efficacy Testing
The following efficacy tests were performed:
Standardized screen tasks
Table tasks of activities of daily living
Letter recognition
Reports of daily life experiences
Control:
All tests (except reports of daily life experiences) were
administered with implant power source turned ‘ON’ or ‘OFF’
in a randomized order
Other eye was always occluded during tests
Tasks were performed over the course of 3 to 9 months
22. Test One:
Standardized screen tasks
Light and motion tests
Measures light perception in full
field illumination, light source
localization, and motion
detection with a moving random
dot pattern
Basic grating acuity (BaGA) test
Measures spatial frequency
resolution in cycles per degree
(cpd)
Patient had to identify direction
of white stripes in a pattern on a
black background
Visual acuity test
Measures visual acuity using
Landolt C-rings
23. Test Two:
Table tasks of activities of daily living (ADL)
Part One:
4 of 6 geometrical objects (square,
circle, triangle, rectangle, ring or
crescent) were placed on a table
Part Two:
4 of 6 tableware objects
(small/medium-sized plates, cup, fork,
spoon, and knife) were placed around
a large plate on a table
Subjects were asked to:
Report number of objects
(identification)
Locate them (localization)
Name them (discrimination)
Performance scores ranged from 0 to 4
Scores in ON and OFF power supply
states were compared
24. Test Three:
Letter recognition
Correct reading of
alphabet letters was
recorded
Patients were not given
any information
regarding letter choice
All letters were visible
within visual field of
implant
25. Test Four:
Patient-reported experiences in daily life
Subjects were permitted to use implant outdoors,
at home, or at work
During first trial days, a mobility trainer
accompanied subjects during their visual
experiences in daily life
Documentation of specific spontaneous
perception was performed by videotaping
experiences or by recording patients' oral reports
26. Results
In all nine subjects, light-induced voltage changes
generated by implant showed reliable signal
generation
In several patients, observation period was cut short
due to technical instability of implant:
Subject (S8) developed post-operative subretinal bleeding
in area of implant and IOP increased significantly. Issue was
resolved with topical and general medication
During implant surgery for Subject (S1), the tip of the
implant touched the optic nerve head, which resulted in
failure of light perception via the implant
27. Results for Standardized Screen Tasks
Subjects (S2–S9) had light perception
Subjects (S2 and S4-S9) were able to localize light
Subjects (S4 and S6-S9) detected motion of dot patterns
Grating acuity was successfully measured in Subjects (S4-S9)
Visual acuity was assessed in Subjects (S5 and S8)
28. Results for Table Tasks of ADL
For all of the following
tasks, significant
differences between
power ON and OFF
scores were found:
Detection of objects and
localization were more
easily accomplished
than shape recognition
29. Results of Letter Recognition
Subjects (S2, S6 and S8) were able to read
several letters (e.g. T, V, L, I, O) spontaneously
Subject (S4) needed some training to correctly
discriminate among three letters in a three-
alternative-forced-choice test
Patients saw letters as complete entities
30. Results of Patient-reported
Experiences in Daily Life
Subjects (S2, S4-S6, and S8) reported visual perceptions in daily life
In near-vision range, the most relevant reports included:
Recognition of facial characteristics
Differentiation between contours of people and clothing patterns
Localization or discrimination of objects
In far-vision range, the most relevant reports included:
Finding the horizon and objects along the horizon
A river was described as a bright, reflecting stripe
Cars and glass windows were localized based on surface
reflections
Recognition of stopped and moving cars at night due to their
headlights
Recognition of letters on restaurant and store signs
31. Conclusions of Study
Study showed alpha-IMS implant, positioned in
subretinal space, can restore useful visual function
in daily life for 2/3 of the blind patients
Device may be an option for blind patients with no
alternative therapy treatments
Long-term stability and safety, as well as
development of visual recognition abilities using
learning tasks, will be addressed in future patients
over a longer observation period
32. Conclusions and Future Outlook
Visual prostheses are an innovative approach to restoring vision
Field of Visual Prosthesis has grown to include a variety of designs
The most advanced are retinal prostheses
There are two in advanced stages of development:
Argus II by Second Sight is close to commercial availability
Alpha-IMS by Retina Implant AG is entering more test trials and may
produce an alternative concept with a subretinal implantation
These devices have demonstrated improvements in motion
detection, object recognition, and letter recognition
Prostheses that target optic nerve and visual cortex are also in
development
Plans for more sophisticated designs and increasing number of
electrodes (to improve resolution and detail quality) are also in
current development
Editor's Notes
Optic Nerve:
--consists of axons of ganglion cells joined together
Retina:
--Photoreceptors: convert light into electrical signals, which process signals within the retina and forward them via ganglion cell axons to visual cortex of the brain for processing.
Two types of photoreceptor cells:
--Rods: responsible for peripheral vision and night vision
--Cones: responsible for central visual acuity and color vision
--Other cells located in front of rods and cones are bipolar cells, ganglion cells, horizontal cells, amacrine cells
Fovea:
--Region in center of retina
--Contains only cones
Macula:
--Made up of millions of light-sensing cells that provide sharp, detailed central vision
--Most sensitive part of retina located at back of eye
Two types:
--Dry: occurs when light-sensitive cells in macula slowly break down, gradually blurring central vision; most common
--Wet: severe stage of dry degeneration that occurs when new blood vessels under macula leak blood and fluid rapidly damaging macula
Detected by:
--Visual acuity test: measures how well you can see by reading a Snellen chart
--Dilated eye exam: eyes are dilated with drops and then a Binocular Indirect Ophthalmoscope is used to visualize the inside of the eye
Detected by:
--Dilated eye examDr. will notice clumps of pigment in peripheral retinal called bone-spicules
--Electroretinography (ERG) testStudies eye’s response to light stimuli; gives information about function of rods and cones in retina
Hereditary disease:
--X-linked: passed from mother to son
--Autosomal recessive: genes required from both parents
--Autosomal dominant: gene required from one parent
Is often a sex-linked disease, so RP affects males more than females
Phosphene: spot of light
1931:
--Confirmed visual cortex does not lose complete function despite years of deprivation.
1956:
--First idea of an electronic prosthetic device
There are a variety of prostheses categorized by its target site along the visual pathway
Retinotopic distribution: organization of the visual pathways and visual area of the brain
--Consists of 60 independently controlled electrodes
--Argus I and II are developed by Second Sight Medical Products Inc.
--Transscleral: across the “white” of the eye
Although there is growing evidence of useful spatial resolution, there is limited field of vision:
--increase field of vision by increasing size of implant
--EPI-RET3 was developed by researchers at Fraunhofer Institute for Microelectronic Circuits in Germany
--Main difference between EPI-RET3 implant and Argus II is that Argus II has all ocular devices within the globe; there is no wire passing through the sclera
Alpha-IMA was developed by Retina Implant AG in Tubingen, Germany
Microphotodiode array: light sensitive metal-oxide semiconductor chip with 1500 pixel-generating elements on polyimide foil carrying 16 electrodes for direct electrical stimulation; (i.e. it is a replacement of photoreceptors)
Advantages:
--Surgery is well understood and routine and takes only 4 hours
--Minimal disruption because implant is housed in the anterior chamber
--Location allows for heat dissipation because anterior chamber acts like a sink
--Easy upgrades can be made because the microelectronics of the device are located on the extraocular component
--Zooming helps magnify and improve visual perception
Disadvantages:
--It bypasses the processing function of bipolar and amacrine cells
--Eye movements are important for preventing image fading on the retina by constantly refreshing images during visual perception
--More sophisticated processing is required because information captured has to be processed prior to stimulation of the ganglion cells
Advantages:
--Stimulating bipolar and amacrine cells allows for processing of a substantial amount of visual information, such as motion and contrast
Disadvantages:
--Possible chance of thermal injury due to implant’s close proximity to neurons, which limits the thermal budget of the implant
This is possible because the remaining visual pathway, from the bipolar cells onwards, remains functional
Transdermal: through the skin
Photodiodes: analyze the brightness of incoming light
--Battery pack has knobs for adjusting amplification and overall brightness and contrast of perception
Cone-rod dystrophy: hereditary disease that causes deterioration of the cone and rod photoreceptor cells; causes complete blindness
Grating acuity:
--Uses a larger field of view than visual acuity test, and therefore, is measured independently of foveal function or recognition of optotypes. Thus, this provides best general description of retinal resolution in artificial vision.
Visual acuity test:
--Can be measured by optotypes, such as letters, numbers, or Landolt C-rings
--Spatial and visual resolutions were calculated for corresponding eye distance
--Subject S5 had difficulties if grating pattern and Landolt C-rings were presented on screen, so a paper-grating pattern and paper Landolt C-rings in reverse contrast were used on a table
Performance scores for each question ranged from 0 to 4:
If score was 3, then they successfully reported, located, or discriminated against three objects
Light source localization:
--Subject (S3) had trouble, which may have been caused by retina’s inability to process electrical signals due to degenerative disease
--Frequency was set at 5 Hz for the majority; others preferred 15 Hz for more continuous perception
--Subjects (S3 and S7) had implants set at only 1–2 Hz because their images faded quickly at higher frequencies due to possible variation in neuronal refractory time (i.e. electrical stimulation processing time)
Motion detection:
Current maximum recognizable speed is 35° per second, which is comparable to a car moving at 22 km/h at a distance of 10 m
Motion detection is limited by: (i) not fully restored retinal processing mechanisms (ii) working frequency of device
Visual acuity:
--Measured as 20/546 and was reproducible
--Reading without aids: .4
--Orientation and navigation: ~0.1
--Low vision: below .3
--Blindness: <.02
Therefore, implant is technically able to transform blindness into low vision; subjects described quality of vision as blurred images with grey tones
Grating acuity:
--Healthy human eye: can resolve 30 cpd
--Subject (S2) had a narrowed area of perception owing to a retinal hole
--Subject (S3) had generally weak perception and could use implant only at 1–2 Hz
--Subject (S8) recognized at 3.3 cpd, which represents the limit of resolution possible with the implant
--3.3 cpd = a visual acuity of .1 (Treat this value with caution because it may be achievable only in special circumstances)
Table Tasks of ADL:
--Significant improvement in visual function when implant was activated
--However, degree of success differed from one subject to another
--Discrimination of objects requires a larger visual field and useable spatial resolution
Subjects (S3 and S7) practically failed in task because both experienced pronounced fading
--Geometrical shape identification (p = 0.012), discrimination (p = 0.018) and localization (p = 0.012)
--Tableware object identification, discrimination and localization (p = 0.012 each)
Daily Life Experiences:
--Five subjects reported useable visual experiences in daily life with the implant, which was the most rewarding aspect
--Subjects (S3 and S7) were unable to use implant in daily life due to fading
--Subject (S9) did not reach a relevant level of visual function in daily life, despite good results in the standardized tests
Other prostheses are in development that target the optic nerve and visual cortex:
These will be critical for cases where the retina is destroyed or optic nerve is severely damaged