Myopic means short-sighted, both short- and long-sightedness are measured in dioptres (D). People who are mildly short-sighted are likely to have a measurement of -0.5D to -3D, whereas those with high myopia, will have a measurement of -6D or more. Those who are severely myopic, have measurements of more than -10D, are most at risk of developing myopic maculopathy.
Myopic macular degeneration is also known as Myopic maculopathy and causes similar symptoms to age-related macular degeneration (AMD), but at a younger age.
What causes myopic macular degeneration?
In a myopic, or short-sighted, eye the eyeball is not spherical but instead is too long, tending towards the shape of an egg. This means light rays entering the eye are unable to focus on the light-sensitive part of the eye, called the retina. In high myopia, the excessive elongation of the eyeball leads to degeneration of the retina and in particular to the macula, which has the highest concentration of light sensitive cells that interpret colour images.
In people with myopic maculopathy the walls of the eyeball become extremely stretched and thin. Eventually the layers at the back of the eye can become so thin that cells in the retina begin to die. This leads to a slow decline in central vision.
In around 5 to 10 per cent of people with high myopia, faults called “lacquer cracks” develop in the layers under the retina. This leads to bleeding around the macula, and the formation of abnormal new blood vessels. These cause more dramatic and sudden sight loss.
What are the symptoms?
Symptoms include distorted images and blurred or missing spots in your vision. You may also find bright light uncomfortable, have difficulty adapting to changes in light levels, or perceive colours differently.
People with high myopia are at higher risk of other eye conditions including cataracts and glaucoma, so should have regular eye examinations. If you notice sudden changes in your vision, such as flashing lights, distorted vision or floaters, you should see an eye specialist urgently.
There is no treatment for the slow-developing form of the disease, as it is not yet possible to affect the way the eyeball grows. If new blood vessels develop, injections of anti-VEGF drugs can slow their growth and preserve more of your sight for longer. On average, patients need three injections to stablise the leak, which is far less than the amount usually required for people with wet AMD. Even if the leak is stabilised, it can return in the same eye, or appear in your other eye, so it is vital to monitor your vision for any changes.
Before anti-VEGF drugs were developed, lasers were sometimes used to seal new blood vessels and stop them spreading, but this treatment can damage the surrounding retina and is rarely used today for myopic maculopathy.
New treatments continue to be developed for other macular conditions, and it is likely that some of them will be suitable for treating myopic maculopathy too.