Dr Nick Sarkies, Addenbrooke's Hospital, Cambridge
Part of the show Science of Sight, Eye Diseases and Animal Vision
Chris - So sight must be the sense that we value more than anything.
Nick - Yes I think that people do value their sight enormously.
Chris - But how does your eye actually work?
Nick - Well it converts light into chemical energy and then into electrical energy and that's transmitted by a nerve into the specialised cells in the brain.
Chris - Ok but obviously the environment is full of light. How does it actually end up getting to the right place in the eye? What's going on at the front?
Nick - It has to be focussed. So the front part of the eye is concerned with focussing it onto the retina and the retina is very highly specialised to receive the light and convert it into chemical energy.
Chris - But what about the fact that, I reckon, about half of the population wear glasses. Why is that? Why have we ended up with a problem with our eyes that we need glasses?
Nick - Good question. And it's very disturbing particularly in countries such as China and the rest of Asia. Myopia, which is the inability to focus light accurately on the retina because the eye is too big, seems to be increasing. The question is why?
Chris - But what's actually happening in the eye when someone is short or long sighted?
Nick - The problem is that the retina is not at the right focal length. If someone is short sighted, then the retina is too far back and if they're long sighted, then the retina is too far forward as it were.
Chris - Ok, so now if we go to how the eye can actually go wrong, there must be lots of diseases that can make eyes worse, especially as we get older, apart from just short and long sightedness.
Nick - Yes there are lots of diseases. The three most common, and the commonest worldwide, which is curable, is cataract. That's still the commonest cause of blindness worldwide.
Chris - So what's going on in someone with a cataract?
Nick - A cataract is a lens that's become cloudy. The crystalline lens within the eye is designed to remain transparent. But as it ages, it tends to change its chemical structure so that it's no longer transparent.
Chris - It becomes foggy.
Nick - Exactly.
Chris - So do we know why that happens?
Nick - We know why it happens in some people with rare metabolic conditions. We don't really understand why it happens to everybody eventually.
Chris - Is it a familial thing?
Nick - It can run in families, although it's unusual.
Chris - So obviously it's pretty routine to put it right now.
Nick - It's become probably the most common operation that's done worldwide: removing the crystalline lens and replacing it with an artificial lens.
Chris - How do you actually do it?
Nick - With some high tech equipment in the western world, but it can be done much more simply without high tech equipment. It tends to be done more like that in other countries in the world.
Chris - So go on Nick, tell us about the nuts and bolts of what happens during a cataract operation. There are probably lots of people out there that have been told that they're in the early stages of cataract, because it's not an all or nothing thing. Some people have a bit of cataract change and it's not sufficient that they need it replacing there and then but they will do one day. So what are they going to be facing?
Nick - They're going to be facing an operation where the lens is removed and replaced with an artificial lens. In order to do that, we have to make an incision into the eye, so it's a major operation. That's why it's not carried out unless the cataract is causing individual trouble. Perhaps they can't read very well or recognise their friends over the other side of the street.
Chris - So you make a small incision
Nick - You make a small incision into the eye and with an ultrasound device, we soften the hard part of the lens. This is called the nucleus. We suck it out and then suck out the surrounding part of the lens, called the soft lens matter. Into the capsule, where the lens was, we insert an artificial lens.
Chris - Correct me if I'm wrong, but we have muscles in the eye that either stretch or compress the lens to make it fatter or thinner so that it focuses light on the retina when it's working properly. So does your implant or artificial lens that you put in have that capability or not?
Nick - Not yet. There are attempts to try and design materials and a lens that will have some flexibility within the eye, but so far they're not very successful.
Chris - So does that mean that people who have this done do end up a bit short sighted or a bit long sighted as a result and can that be corrected for?
Nick - Yes, if they prefer they can be long or short sighted. It depends on preference really. People who have been short sighted all their lives often like to remain short sighted and so we put a lens in that keeps them a little bit short sighted so that they can read unaided.