How does high myopia increase my risk of glaucoma?Eye Health
I have high myopia, and have been told that this is a risk factor for glaucoma. How does high myopia increase my risk of glaucoma, and why?
The exact reason why myopia causes glaucoma is not known. One possible hypothesis is that when you have very high myopia, your eyeball becomes stretched and the tissue supporting the nerve in the eye is weaker so you are at more risk of nerve damage from high pressures (or even pressures in the "normal" range). Reduced blood flow to the optic nerve in highly myopic eyes could be another reason. However, these are all hypotheses which have yet to be proven.
What we do know from a study conducted in Singapore, is that glaucoma affects around 3 per cent of people over the age of 40 and the risk increases with age. In addition, the risk of getting glaucoma among Chinese Singaporeans with myopia, as compared to those without myopia, are as follows:
- Mild myopia (less than 300 degrees) = 2 times more likely to get glaucoma
- Moderate myopia (300 to 600 degrees) = 5 times more likely to get glaucoma
- Severe myopia (more than 600 degrees) = 15 times more likely to get glaucoma
In addition, Chinese people with a family history of glaucoma were nearly 8 times more likely to develop it later in life.
Hence, if you have myopia or a family history of glaucoma (or both), do get screened for glaucoma. It is very important to remember that the majority of cases of glaucoma are without symptoms in the early to intermediate stages of the disease. The blurring of vision, when experience, is often a late symptom and is irreversible.
Hope this helps!
There are two main types of glaucoma; acute angle closure glaucoma (AACG) and primary open angle glaucoma (POAG). High myopia tends to be associated with POAG and is the most commonly reported type of glaucoma. Elevated intraocular pressure is a well-known major risk factor for POAG. In addition, there is growing evidence that other factors including age, gender, race, refractive error, heredity, and systemic factors may play a role in glaucoma pathogenesis. Many studies found that high myopia has been associated with POAG, however, direct and convincing evidence are still lacking.
In the second type, there are usually no symptoms. Patient may only start to take notice when they bump into objects or trip over steps which indicate visual field losses. In such cases, visual field losses tend to be rather extensive and treatment should be started soonest to prevent further field losses.
In both cases, there is irreversible damage to the optic nerve resulting in visual field loss starting for the periphery (side vision). Thus, it is important to start on medications to preserve whatever remaining treatment and patient needs to be monitored over the years.
This is a common answer to why ophthalmologists are so concerned about childhood myopia!
Many epidemiological studies throughout the world including in Singapore are conclusive in the link between glaucoma and the prevalence of myopia. However, on the individual level itself, the cause of this association is less apparent.
Several theories have been proposed for this relationship. The most popular theories include that of reduced structural support in high myopes (thinner sclera/corneas due to having a larger eyeball) predispose to degeneration of the retinal nerve fibre layer (causing glaucoma), and that myopic patients have thinner retinal nerve fibre layers to begin with (associated with having a larger eyeball in general).
Suffice to say, that minimizing the severity of myopia development in children is an important priority for us as ophthalmologists in the community, as incidence rates of cataract, glaucoma, macular degeneration, and retinal degeneration conditions are all proportionately higher with the degree of myopia.
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