Lecture 21 & 22 - Visual Prosthesis (MI)

Question 1

Retinitis Pigmentosa (Tunnel vision)

Answer 1

Genetic eye condition that causes cells in the light-sensitive retina, located at the back of the eye, to degenerate slowly and progressively

Question 2

Age-related Macular Degeneration

Answer 2

Macula degen where insults to vasculature lead to death of photo receptors. Leads to severe impairment of central vision *No treatment for dry AMD but treatments are available for wet AMD

Question 3

Are photoreceptor nerve cells?

Answer 3

Yes - modified ones

Question 4

Eyes are furthest point from heart, so retina is susceptible to insult from vasculature system. Hence why eye can be a marker for vasculature diseases. In AMD, around 20-30% of photoreceptors still intact - this is what we are targeting in the bionic eye as they can still be electrically stimulated

Answer 4

Eyes are furthest point from heart, so retina is susceptible to insult from vasculature system. Hence why eye can be a marker for vasculature diseases. In AMD, around 20-30% of photoreceptors still intact - this is what we are targeting in the bionic eye as they can still be electrically stimulated

Question 5

Spatiotopic

Answer 5

Correct part of image to correct part of retina

Question 6

Epiretinal -what is it? Advanatges and disadvantages?

Answer 6

Electrodes between GC and vitreous
ADVANTAGES
1) Very close contact between electrodes and retinal GC - therefore info can go straight to the brain
2) It offers higher visual acuity compared to suprachoroidal/subretinal placement because the electrodes are so close to the target tissue

DISADVANTAGES

1) Surgery is more complex than for suprachoroidal as a full vitrectomy is required
2) Difficult removal as all components are inside eye (so it is hard to update software)
3) Placement less stable over time

Question 7

Subretinal - what is it? Advanatges and disadvantages?

Answer 7

Electrodes between photoR and BP cells
Advantage
1) Implants are stable

Disadvantage

1) GC are a long way from electrodes so spatial resolution is poor
2) Surgery requires a retinal detachment (using air) and reattachment. Very complex and dangerous

Question 8

Suprachoroidal- what is it? Advanatges and disadvantages?

Answer 8

Electrodes between choroid and sclera
Advantages
1) Short surgical procedure - it is outside of the eye
2) Stable placement over time

Disadvantages
1) GC long way from electrodes so spatial resolution is poor

Question 9

Components of a bionic eye - internal and external

Answer 9

Internal

1) Electrode array - inside eye
2) Silicon carrier - this is what the electrodes are embedded in
3) Data cable
4) For epiretinal device, microchip for data processing

External

1) Microchip for data processing
2) For epiretinal, magnet on device and magnet on sclera for attachment - as it is just hanging out there in the vitreous OR can use retinal tacks (nails that pops out of the sclera and connects to the device)
3) Digital video camera

Question 10

Do people with visual prosthesis have the same vision as “normal” people?

Answer 10

No - they have phosphene vision (induced perception of light by means other than light entering the eye)

Question 11

What materials do we use for the electrodes? What 3 properties should they have?

Answer 11

Platinum and diamond -Chemically inert, electrically conductive, high capacitance *High electrical resistance is not desirable though

Question 12

Phosphenes are more simple/complex closer to the fovea

Answer 12

Complex

Question 13

What is the developing epiretinal 256 channel high-acuity implant made of?

Answer 13

Diamond - no platinum