When vision goes wrong: age-related macular degeneration
A part of the back of the eye called the retina is a crucial part of the visual system, it's here that light is converted to the electrical signals which are sent up to the brain. Issues with the retina can have severe consequences, and one such condition involves degeneration of the macula part of the retina, which can lead to the loss of central vision. Now scientists have implanted retinal tissue from stem cells into a small number of patients with age-related macular degeneration, and who’s sight has been restored. Pete Coffey from UCL’s Institute of Ophthalmology and Moorfields Eye Hospital spoke to Katie Haylor. First off Katie asked Pete to explain what the retina actually is...
Pete - We call it the neural retina, which is at the back of the eye which is a multilayered, thin piece of tissue, which, essentially, contains the light-sensitive cells plus the connecting cells which then take that information to the brain.
Katie - What are these light-sensitive cells?
Pete - The rods and cones. The rods deal with what’s called scotopic vision which is night vision, low level vision, and the cones deal with bright, colour vision. As Kez said, there’s an area in the retina which accounts for 10% of the whole of the back of the eye, which the macular region. It’s about 6mm in diameter and that contains the high contrast, the colour vision, the cone receptors which allow us to read, drive, recognise faces.
Katie - Once light hits the retina it gets converted into electrical signals which shoot on up the optic nerve. How does that conversion process happen?
Pete - There’s a number of events which occur. The light sensitive component, the cones, actually have packets of chemicals at the tips of those cells, which we call outer segments which contain the chemicals, the aldehydes which use chemical processes to convert light into electrical activity. That activation is then linked to the cell which then takes it into the brain via one more cell, which is called the bipolar and then its connection to the ganglion cell which takes that information and presents it to the rest of the brain.
Katie - We mentioned age-related macular degeneration; it’s one example of what can go wrong with the retina, so what exactly is it and who gets it.
Pete - People over the age of 65, and it’s the layer of cells which give nutrients to the seeing part of the eye, the neural retina, that die. There’s about 30% of people over the age of 65/70 will have some form of age-related macular degeneration. There are two forms: dry and wet. The distinction is the wet form is due to blood that appears at the back of the eye as well, which is rapid. That is the only treatable form of the disease, but that only counts for 10% of the clinical population - 90% is untreatable. There’s checks on whether you smoke; smoking can increase the rate of the disease. There’s some nutrients which can be given but, basically, the only form which is treatable is the wet form.
Katie - Tell us about your work on treating AMD, because this involves stem cells, doesn’t it?
Pete - It does. In age-related macular degeneration those cells which support the seeing part, the neural retina, die. There’s a number of reasons why that occurs but, effectively, because those cells die the seeing part of the eye no longer has the nutrients, etc. and therefore, over time, it itself dies. What we’ve engineered is making those eye cells, those support cells which are called retinal pigment epithelium, and we put them back in exactly the same format as they are at the back of the eye. So they’re in a single layer, on a carpet of cells, which we’ve surgically then implanted into the back of the eyes of those patients, and they’ve been there now for nearly 2½ years.
Katie - That does not sound like an easy process, so what was involved in creating these cells from these stem cells?
Pete - Actually, it is an easy process. I get very embarrassed about that particular position, because most people who are trying to make a specific cell from a stem cell have gone through a very difficult process, so people who are trying to make cells for Parkinson’s disease, or heart cells, or liver cells. Literally, all we have to do is take one component out of the fluid in which we keep cells and that’s just one component. It’s called basic fibroblast growth factor and then the cells spontaneously make the eye cells that we want.
Katie - Oh brilliant!
Pete - So actually it’s quite easy. Anyone could do it so to speak. Although it did take us a bit of time to realise that!
Katie - How many people did you put these cells into?
Pete - We’ve only put them in two patients but there’s been a lot of preclinical work to make sure that if we put those cells back, we are going to see a difference. They’re reading again, which wasn’t possible. They couldn’t even see the book before we did the operation.
Katie - Lastly, what could this mean for AMD sufferers in the future? Do you think this could be cost-effective enough to use in thousands of people in the future?
Pete - Yeah. There’s 700,000 patients who suffer from AMD. Not all of those would be treatable with this particular therapeutic, but a good 10% of them could be. I mean, that’s till a big number, you know, that’s 70,000 patients. We believe that we can produce enough of these patches to treat that type of a clinical population and the cost would be a huge saving to the NHS, and not maintaining people but actually giving them some sight back. This is probably one of the first studies which has actually shown that regeneration, in terms of stem cell regenerative medicine, is feasible and does have some efficacy.