What do blind people "see"?

Optometrist Keziah Latham from ARU took on this question...

Keziah Latham - I think that is a very good question and the short answer is, it depends on the blind person, but probably more than you might imagine.

Of the people in the UK who are registered blind, about 95 percent of them can see something - some level of light and dark. About 75 percent people who are registered blind can read newspaper headlines. So most people have got some level of residual vision and, in fact, we no longer talk about people being registered blind, but we call it severely sight impaired these days because that's a lot more representative of what people actually see. But then what somebody actually sees kind of depends predominantly on the reason for their visual loss and it can be quite different depending on different eye conditions. So if you take something like macular degeneration, which is the most common cause of visual loss in the UK, that damages vision in the centre. So in the middle of your vision the area called the "macula" in the retina, which does the vision which is the bit that you're looking at when you look directly at something.

Chris Smith - So when I'm looking you in the eye, that's my macula doing that?

Kezaih Latham - That is the macula.

Chris Smith - So, if I had macular degeneration right now, I would look at you but what I would see is the rest of the room at lower acuity, because it's the rest of the room, but the bit where I would expect to see the most detail would be either blurry or - at worst case scenario - I just see a black patch?

Keziah Latham - Yeah.

Chris Smith - No face.

Keziah Latham - You tend not to see a black patch of sorts. That tends to be something that gets put in pictures of "this is what macular degeneration looks like". It tends not to be actually; when you actually ask people they'll say that things are kind of missing or blurred. The brain's brilliant at "filling in". So if you have got this damaged area in the centre, mostly what will happen is that that bit in the middle will be kind of filled in to sort of match the surrounding bit that is still working. And so with macular degeneration, people have still got peripheral vision - it's very, very, rare that somebody would lose their vision altogether - but that central part of vision that you would use for recognising faces, for reading that kind of thing - that would be the bit that was most impaired.

But then on the counter side to that, you've got other conditions like retinitis pigmentosa, which is an inherited retinal disorder. So that affects the receptors at the back of the eye as well, but that predominantly affects peripheral vision. So that means that somebody tends to with that kind of condition tends to lose their peripheral vision but retain their central vision. So that's a little bit like looking through a tunnel. So you can see straight ahead, but everything off to the sides has disappeared. So that makes things like mobility and getting around finding out where you are and how to get to somewhere very difficult, but it still leaves somebody with enough central vision to maybe be able to read or use their phone. So there have been some instances recently where people have got into trouble, if you like, in that they're out and about with their white cane or their guide dog and somebody spots them using a phone and goes "you're cheating! You're not blind!" - but that's complete nonsense. You try living with only your central vision and no peripheral vision and you will find that although - yes - you can use your phone, you are still very visually impaired by that.