What is Myopic Macular Degeneration?
Myopic macular degeneration (MMD), also called pathological myopia or degenerative myopia, is closely associated with choroidal neovascularization (CNV), which is the leading cause of visual impairment in those younger than 50 in the US.1 In highly myopic (very nearsighted) eyes, the ocular tissues are gradually stretched as the eye elongates, and in some individuals this stretching may lead to structural damage characteristic of MMD.
Facts about MMD
An individual with MMD may have a gray spot in their central vision (scotoma) or experience distortions (metamorphopsia) in vision. If he/she has CNV, the impairment may be more serious. CNV is a condition in which leaky blood vessels grow at the back of the eye, and these abnormal vessels may leak fluid or bleed, resulting in progressive loss of central vision. It is important to recognize that individuals with mild or moderate myopia are generally not at risk for MMD, as this disease most often occurs in those with high myopia.2
How common is myopic macular degeneration?
Worldwide, the prevalence of MMD ranges from 0.9% - 3.1%, and the visual impairment resulting from MMD ranges from 0.1% - 1.4%.3 Among patients with MMD, the rate of CNV ranges from 5.2% - 11.3%, and is bilateral (affects both eyes) in about 15% of patients.3 MMD can occur at any age, but typically affects patients between the ages of 30 and 40; in individuals under the age of 50, it’s often associated with CNV.4
What are the risk factors for MMD?
The origin of MMD is thought to be complex, stemming from both genetic and environmental factors. High-grade myopia often has a genetic component, and general myopia is seen more in some ethnic groups than in others. Whites have a significantly higher rate of myopia than African Americans, and Chinese and Japanese groups have a rate of myopia of more than 50-70%.5
MMD symptoms are similar to other types of macular degeneration and can include6:
- Distorted vision (lines look wavy)
- Dry MMD causes a gradual loss of central vision; wet MMD is like wet AMD and can cause rapid loss of central vision
- Blank spots in vision, especially central vision
- Trouble seeing shades of colors
- Difficulty in adjusting your eyes going from brightly lit to dim spaces, and vice-versa
The retina is a layer of nerve tissue located at the back of the eye, near the optic nerve. It converts light into signals and sends these signals to the brain, which then interprets the signals and tells us what we see. In MMD, the outer wall of the eyeball keeps growing in an elongated fashion, stretching and thinning the inner ocular tissues such as the retina and choroid. Over time, these stretched inner ocular tissues can develop cracks (lacquer crack) and gaps (atrophy), leading to degeneration and visual impairment. CNV develops when abnormal blood vessels underneath the retina grow into these cracks, and subsequently leak fluid or bleed to further decrease vision.
Diagnosis of MMD
If this condition is suspected or if you have MMD, you should have regular eye exams to check for growth of abnormal blood vessels in the eye as well as other associated changes. This can be done during any regular eye exam, although sometimes a retinal specialist may take enhanced photographs that involve the injection of dye into the arm in order to better visualize abnormal blood vessels. CNV can be a very serious complication of MMD, and the sooner it is found, the sooner it can be treated appropriately.
Treatment of MMD
While there is no treatment for dry MMD, if there is choroidal neovascularization with MMD, or “wet” MMD, it is treated like wet AMD in many cases. This typically involves eye injections with anti-VEGF agents.7 Each person is different, though, and if you are diagnosed with MMD, talk with your eye doctor about the type of MMD you have and what options you have to treat it.
What can you do?
Although MMD can be a very serious eye disease, there is treatment for it – which is why it’s important to recognize the signs of the condition and get regular eye exams, to keep on top of eye health and catch any abnormalities at the earliest possible stages. Talk with your doctor about your risk of MMD, any other symptoms that you should look for, and what treatment options might be right for you.