The Grapevine

What Is Glaucoma? How Early Eye Disease Awareness Prevents Blindness

screening
January is Glaucoma Awareness Month. This disease, caused by eye pressure, may lead to blindness if not recognized and treated early. Get screened! Courtesy of the National Eye Institute

Early awareness and treatment helps cure many diseases. For other incurable conditions, knowing the risks, going for screening tests, and beginning treatment sooner rather than later can stall symptoms and prevent the worst from happening. In this second category you will find glaucoma, a common eye disease that, if untreated, causes blindness.

Glaucoma damages the optic nerve, the bundle of nerve fibers connecting the eye to the brain. While there are many forms of the disease, open-angle glaucoma is the most common, according to the National Eye Institute (NEI). Here, nerve damage results from rising fluid pressure inside the eye, which is caused whenever circulating eye fluid drains too slowly.

Yet some people can tolerate higher levels of eye pressure better than others. In fact, 50 to 80 percent of people with open-angle glaucoma have higher-than-average eye pressure, while the remaining patients may have normal or even low pressure. At the same time, many people with high pressure never develop glaucoma. Researchers say whether or not you eventually develop glaucoma depends on the ability of your optic nerve to withstand pressure.

Importantly, glaucoma slowly destroys peripheral vision (side vision) first, and for this reason, patients may have symptoms for years before they notice they are losing their eyesight. Along with the deterioration of your peripheral vision, many glaucoma patients, including U2 singer Bono, complain of being extra sensitive to light. Once detected, glaucoma treatment can begin; it frequently consists of a simple regimen of daily eye drops to lower eye pressure. In other cases, more invasive methods, such as lasers or surgery, may be needed while new and better drugs or innovative treatment strategies are developed and debuted. In other words, most patients have nothing to fear so it's worth it to get tested.

Am I at Risk?

The risk factors for glaucoma aren’t fully understood, yet some things are known. For instance, open-angle glaucoma is very rare in people under the age of 50. Scientists also know that open-angle glaucoma is about five times more common among African-Americans and Mexican-Americans compared to whites. African-Americans, according to the NEI, tend to develop symptoms earlier and the course of their disease is more rapid.

Glaucoma also runs in families. Your risk of developing open-angle glaucoma is about 10 times higher if your parent or sibling has it, while your risk is higher still if your identical twin has it. Clearly, then, genetics are involved, yet the genetics are complex. Based on the current data, researchers theorize many small genetic variations influence the development of glaucoma with no one gene contributing more than a little to overall glaucoma risk. Even more, geneticists believe glaucoma only results from the interaction of many genes when combined with environmental influences.

But the specific environmental factors are hard to pin down, and so far no study of smoking, alcohol use, caffeine use, fat intake, or exercise has yet revealed a strong relationship to glaucoma. That said, one recent study proved some head-down yoga positions create eye pressure and doctors commonly advise patients to avoid certain exercises, including pushups and lifting heavy weights, due to the risk of increasing eye pressure and damaging the optic nerve.

Though researchers fruitlessly search for unfavorable environmental factors, they have made real headway uncovering the underlying genetics of eye disease. In fact, one new analysis identifies three new genes that contribute to open-angle glaucoma, increasing the total number of genes to 15.

Five Regions of the Genome

The new study focuses on data collected by the NEI's Glaucoma Human Genetics Collaboration (NEIGHBOR), which has collected genetic samples from about 4,500 patients and about 20,000 (control) individuals without the disease. This worldwide effort finds five regions of the genome strongly associated with primary open-angle glaucoma. Within each region, specific genes contribute to the disease, yet they are divided into two groups: one group impacting eye pressure only, the other group impacting the optic nerve.

According to the researchers behind the NEIGHBOR study, their findings should lead to new strategies for screening, preventing, and treating glaucoma. In the meantime, the NEI advises those who are at high risk eat healthy foods, limit alcohol, exercise regularly, and go for screening tests — anyone on Medicare is covered for a screening test once every 12 months. This is one case where recognizing a problem early may prevent terrible consequences.

Source: Cooke Bailey JN, Loomis SJ, Kang JH et al. Genome-wide association analysis identifies TXNRD2, ATXN2 and FOXC1 as susceptibility loci for primary open-angle glaucoma. Nature Genetics. 2016.

Jasien JV, Jonas JB, de Moraes CG, Ritch R. Intraocular Pressure Rise in Subjects with and without Glaucoma during Four Common Yoga Positions. PLOS One. 2015.

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