Myopia itself is a common disorder resulting from excessive lengthening of the eye which causes short-sightedness. The level of myopia is 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 usually at a younger age.
What causes myopic macular degeneration?
Myopia itself is a common disorder resulting from excessive lengthening of the eye, which usually develops gradually in children and teenagers. In a myopic, or short-sighted, eye the eyeball is not spherical but instead is too long, tending towards the shape of a rugby ball. This means light rays entering the eye are unable to focus on the light-sensitive part of the eye, called the retina. Wearing glasses or contact lenses with diverging lenses can restore sharp vision in myopia by getting light to focus properly on the retina.
In high myopia, the excessive elongation of the eyeball can lead to degeneration of the retina and in particular to the macula, which has the highest concentration of light sensitive cells that interpret colour images, causing myopic maculopathy. 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 called myopic choroidal neovascularisation (mCNV). This causes more dramatic and sudden sight loss. By the age of 85 years-old, as many as 2 in 5 individuals with high myopia will develop impaired vision due to myopic maculopathy.
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.
For those who are already short-sighted, little can be done to reduce the risk of maculopathy, although ensuring high blood pressure is controlled is warranted, as high blood pressure is believed to be associated with risk of myopic maculopathy.
The treatment options are similar to those for age-related macular disease (AMD) and depend on the precise cause. For the majority of patients there is no treatment available. However, yearly monitoring by an optometrist or ophthalmologist is advisable for those with high myopia because of the risk of mCNV. Any sudden changes in vision or an increase in 'floaters' should also prompt an urgent check-up visit to the optometrist.
Treating mCNV with anti-VEGF to stop the leakage of the abnormal blood vessels can help preserve vision. On average, patients need fewer injections to stabilise the leak, compared to those 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
As with AMD, myopic maculopathy may be associated with formation of a macular hole.This might require surgery called a vitrectomy.
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.
Much of the research going on in myopia is looking into what causes high myopia, and preventing children and teens becoming myopic or high myopic in the first place. The slowly progressive nature of myopia means there is a long window during childhood when treatment can be given to slow the rate of progression. Atropine eye drops are the most effective treatment currently known. However, these drops can have side effects and are still undergoing clinical trials in the UK.
The aim of all these therapies is to reduce the level of myopia reached by adulthood, in the hope that this will cut the risk of maculopathy.