Bionic Eyes Sub-Retinal Implants

Michael Hutchins

Motivation •  Retinal diseases cannot be fixed with normal

corrective procedures.

•  Vision degradation is a result of age but is not inevitable.

•  There are multiple types of blindness, retinal implants cure those involving the retina.

•  Retinal implants can greatly improve vision and quality of life.

Retinal Diseases

•  A genetic disorder

•  Starts with degradation of night vision followed by tunnel vision.

• No cure, but can be staved off with Vitamin A.

Retinitis Pigmentosa

Retinal Diseases

•  Loss of vision in the center of the retina.

• Major cause of blindness in the elderly.

•  Risks of development linked to certain genes but not the cause.

•  Can be treated with painful drug injections

Macular Degeneration

Photoreceptors Rods Cones

Slow Response

Fast Response

Scattered Light

Direct Light

One Pigment Three

Pigments

Greys Color Vision

20x More

Photorecptors

Photorecptors

•  Rods (off center cells) surround cones (on center cells).

Retinal Encoding

-1/8 -1/8 -1/8

-1/8 +1 -1/8

-1/8 -1/8 -1/8

Retinal Encoding

•  The optic nerve has 10^6 nerve fibers, the eye has roughly 10^8 photoreceptors.

•  The optic nerve transfers at 8.75 x 10^6 bits/second.

•  The poor capacity of the optic nerve is still unexplained.

Optic Nerve

Photodiode

Photodiode

Optobionics

•  Optobionics makes the Artificial Silicon Retina.

•  The device has been tested in 42 patients through clinical trials.

•  Filed a patent in 2002 for methods of using electrical stimulation to treat and prevent visual loss.

ASR Device

•  2mm diameter

•  25µm thick

•  ~5000 negative intrinsic layer-positive microphotodiode pixels

•  Pixels are electrically isolated

ASR Device

•  Placed subretinally.

•  Photodiodes run solely off incident light.

•  Electric charge produces by photodiodes alter membrane potential of nearby neurons.

ASR Device •  Pixels are 20µm square.

•  9 x 9µm iridium oxide electrode

•  Pixel current is 8-12nA at 800 foot-candles (8611 Lux) of illumination

•  1,000 lux is an overcast day

•  10,000 - 25,000 lux is

Implanting

•  Placed 20˚ off axis from the macula.

•  Retina is cut and ASR is implanted beneath it.

•  The retina is re-flattened after implanting.

Absorption ASR in Rats

Post Operative Results Humphrey Central Visual Field Tests

Post Operative Results Humphrey Central Visual Field Tests

Subjective Results •  After implanting some could recognize faces, they could not do

this for ten years.

•  One patient could only see brightness, contrast and shape, afterwards could see the shadows of people.

•  Post-operatively others could sometimes make out streetlight colors and navigate without a cane.

•  Some reported unexpected improvements in areas distant from the implant.

•  Two reported perception of sensation to infrared light.

Long Term

•  No reports of rejection, discomfort or any side-effects.

•  Materials used in the ASR are known to be biocompatible: silicon, silicon oxide, titanium and iridium oxide.

•  All ASR implants were fully functioning after 18 months (this is what was published in the clinical trial paper).

Considerations

•  The ASR requires that there is some working parts of the retina.

•  It cannot work if there is severe retinal scarring.

•  It is still being clinically tested, only 47 human trials have been done so far.

Summary •  Artificial retinas can

restore sight lost due to retinal diseases.

•  There is so far no downside to getting retinal implants

•  Retinal implants may confer vision outside our normal range.

References •  Wikipedia Articles on: Retina, Retinitis Pigmentosa, Macular Degeneration,

Photoreceptors, Optic Nerve, Photodiode

•  http://optobionics.com/

•  “How Much the Eye Tells the Brain” Current Biology, Volume 16, Issue 14, 1428-1434, 25 July 2006.

•  "The Artificial Silicon Retina Microchip for the Treatment of Vision Loss From Retinitis Pigmentosa" Arch Ophthalmol. 2004;122:460-469.

•  “Jonas JB, Schneider U, Naumann GOH (1992) Count and density of human retinal photoreceptors. Graefe's Arch Clin Exp Ophthalmol 230:505-510.”

•  "Stimulation via a Subretinally Placed Prosthetic Elicits Central Activity and Induces a Trophic Effect on Visual Response" — IOVS Feb 2007, Vol 48 no.2

•  http://www.ghuth.com/2008/05/29/relationship-of-geometry-and-wavelength-on-the-retina/

•  http://misclab.umeoce.maine.edu/boss/classes/SMS_491_2003/Week_10.htm

Questions

The Artificial Silicon Retina cannot:a. see into the infrared.b. improve vision due to retinal disease.c. last longer then a year.d. be placed sub-retinally.e. none of the above.An unknown aspect of the retina is:a. how rods and cones interact.b. how light is transfered to the neurons.c. the signal encoding in the optic nerve.d. the number of photoreceptors.e. the ratio of rods and cones.