A prosthetic eye to treat blindness Sheila Nirenberg

I study how the brain processes

information that is how it takes

information in from the outside world

and converts it into patterns of

electrical activity and then how it uses

those patterns to allow you to do things

to see to hear to reach for an object so

I’m really a basic scientist not a

clinician but in the last year and a

half I’ve started to switch over to use

what we’ve been learning about these

patterns of activity to develop

prosthetic devices and what I wanted to

do today is show you an example of this

it’s really our first foray into this

it’s the development of a prosthetic

device for treating blindness okay so

let me start in on the problem there are

ten million people in the US and many

more worldwide who are blind or facing

blindness due to diseases of the retina

diseases like macular degeneration and

there’s little that can be done for them

there are some drug treatments but

they’re only effective on a small

fraction of the population and so for

the vast majority of patients their best

hope for regaining sight is through

prosthetic devices the problem is that

current prosthetics don’t work very well

they’re still very limited in the vision

that they can provide and so you know

for example with these devices patients

can see simple things like bright lights

and high contrast edges not very much

more so nothing nothing close to normal

vision has been possible so what I’m

going to tell you about today is a

device that we’ve been working on that

that I think has the potential to make a

difference to be much more effective and

what I wanted to do is show you how it

works okay so let me back up a little

bit and show you how a normal retina

works first so you can see the problem

that we’re trying to solve here you have

a retina so you have an image a retina

and a brain so when you look at

something like this image of this baby’s

face it goes into your eye and it lands

on your retina on the front end cells

here the photoreceptors then what

happens is the retinal circuitry the

middle part goes to work on it

and what it does is it it performs

operations on and it extracts

information from it and it converts that

information into a code and the code is

in the form of these patterns of

electrical pulses that get sent up to

the brain and so the key thing is that

the image ultimately gets converted into

a code and when I say coda I do

literally mean code like this pattern of

is here actually means baby’s face and

so when the brain gets this pattern of

pulses it knows that what was out there

was a baby’s face and if it got a

different pattern it would know that

what was out there was say a dog or

another pattern would be a house anyway

you get the idea and of course in real

life it’s all dynamic meaning that it’s

changing all the time so the patterns of

pulses are changing all the time because

the world you’re looking at is is

changing all the time too so you know

it’s sort of a complicated thing you

have these patterns of pulses coming out

of your eye every millisecond telling

your brain what it is that you’re seeing

okay so what happens when a person gets

a retinal degenerative disease like

macular degeneration what happens this

is that the frontend cells die the

photoreceptors die and over time all the

cells and the circuits that are

connected to them they die - until the

only things that you have left are these

cells here the output cells the ones

that send the signals to the brain but

because of all that degeneration they

aren’t sending any signals anymore they

aren’t getting any input so the person’s

brain no longer gets any visual

information that is he or she is blind

so a solution to the problem then would

be to build a device that could mimic

the actions of that front-end circuitry

and said signals to the retinas output

cells then they can go back to doing

their normal job of sending signals to

the brain so this is what we’ve been

working on and and this is what our

prosthetic does so it consists of two

parts what we call an encoder and a

transducer and so the encoder does just

what I was saying it mimics the actions

of the front-end circuitry so it takes

images in and it converts them into the

retinas code and then the transducer

then makes the output cells send the

code on up to the brain and the result

is a retinal prosthetic that can produce

normal retinal output so a completely

blind retina even one with no front end

circuitry at all no photoreceptors can

now send out normal signal signals that

the brain can understand so no other

device has been able to do this okay so

I just want to take it you know a

sentence or two to say something about

the encoder and what it’s doing because

it’s really the key part and it’s sort

of interesting and kind of cool not sure

cool is really the right word but

know what I mean so what it’s doing is

it’s replacing the retinal circuitry

really the guts of the retinal circuitry

with a set of equations a set of

equations that we can implement on a

chip so it’s just math in other words

we’re not literally replacing the

components of the retina it’s not like

we’re making a little mini device for

each of the different cell types we’ve

just like abstracted what the what the

retinas doing with a set of equations

and so in a way the equations are

serving as sort of a codebook an image

comes in goes through the set of

equations and outcomes streams of

electrical pulses just like a normal

retina would produce okay so now let me

put my money where my mouth is and show

you that we can actually produce normal

output and what the what the

implications of this are okay so here

are three sets of firing patterns the

top ones from a normal animal the middle

ones from a blind animal that’s been

treated with this encoder transducer

device and the bottom ones from a blind

animal treated with a standard

prosthetic so the bottom one is the

state-of-the-art device that’s out there

right now which is basically made up of

light detectors but no encoder so what

we did was we presented movies of you

know everyday things people babies park

benches you know regular things

happening and we record the responses

from the retinas of these three groups

of animals just to orient you each box

is showing the firing patterns of

several cells and just as in the

previous slides each row is a different

cell and I just made the pulses a little

bit smaller and thinner so I could show

you like a long stretch of data okay so

as you can see the firing patterns from

the blind animal treated with the

encoder transducer really do very

closely match the normal firing patterns

and it’s not perfect but but it’s pretty

good and the blind animal treated with

the standard prosthetic the responses

really don’t and so with the standard

method the cells do fire

they just don’t fire in the normal

firing patterns because they don’t have

the right code how important is this

like what’s the what’s the potential

impact and a patient’s ability to see so

I’m just going to show you one one

bottom line experiment that answers is

and of course I got a lot of other data

so if you’re interested I’m happy to

show to show more okay so the experiment

is called a reconstruction experiment so

what we did is we took a moment in time

from these recordings and asked what was

the retinas seeing at that moment can we

reconstruct what the retina was seeing

from the responses from the firing

patterns so when we did this for

responses from from the standard method

and from from our encoder and transducer

so let me show you and I’m going to

start with a standard method first okay

so you can see that it’s pretty limited

and because the firing patterns aren’t

in the right code they’re very limited

in what they can tell you about what’s

out there so you can see that there’s

something there but it’s not so clear

what that something is

and this just sort of circles back to

what I was saying in the beginning that

with a standard method patients can see

high contrast edges they can see light

but it doesn’t easily go further than

that okay so what was the image it was a

baby’s face okay so what about with our

approach adding the code and you can see

that it’s much better not only can you

tell that it’s the baby’s face but you

can tell that it’s this baby’s face

which is a really challenging task okay

so on the left is the encoder alone and

on the right is from an actual blind

retina to the encoder and the transducer

but the key one really is the encoder

alone because we can team up the encoder

with a different transducer this was

just actually the first one that we

tried I want to just wanted to say

something about the standard method when

this first came out it was just a really

exciting thing you know the idea that

you could even make a blind retina

respond at all but there was this this

this limiting factor the issue of the

code and how to make the cells respond

that produce normal responses and so

this was our contribution okay so now I

just want to wrap up and as I was

mentioning earlier of course I have a

lot of other data if you’re interested

but I just wanted to give this sort of

basic idea that this idea that of being

able to communicate with the brain in

its language and the potential power of

being able to do that so it’s different

from the motor prosthetics where you’re

communicating from the brain to to a

device here we have to communicate from

the outside world into the brain and be

understood and be understood by the

brain okay and then the last thing I

wanted to sort of say really is that is

to emphasize that the idea generalizes

so the same strategy that we use to find

the code for the retina we can also use

to find the code for other areas for

like for example the auditory system in

the motor system so for treating

deafness and for and for motor disorders

so just the same way that we were able

to jump over the you know the damaged

circuitry and the retina to get to the

retinas output cells we can jump over

the damaged circuitry in the in the

cochlea to get the auditory nerve or

jump over damaged areas and the cortex

in the motor cortex to bridge the gap

produced by a stroke okay so I just want

to end with a simple message that

understanding the code is really really

important and if we can understand the

code you know the language of the brain

things become possible that didn’t seem

obviously possible before thank you