Here's how the two eye conditions compare.

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When you think of conditions that can affect the eyes, two main ones probably come to mind: glaucoma and cataracts. They can both lead to vision loss—one is permanent, while the other, thankfully, is reversible with surgery. And there's really no proven way to prevent either. Your chances of developing them come down to the luck of the draw, and a few more specific risk factors.

While glaucoma and cataracts have a few things in common—like typically being diagnosed in older individuals—they can also be very different in terms of diagnosis and treatment options. Here's what you need to know about how the two eye conditions compare.

What is glaucoma?

According to the National Eye Institute (NEI) glaucoma is a group of eye diseases that causes damage to the optic nerve. The optic nerve is a nerve in the back of each eye that functions as a line of communication between the eye and the brain. Optic nerve damage causes irreversible vision loss, and ultimately, if it becomes very damaged, can lead to blindness.

Most people with glaucoma have high eye pressure. Here's the deal: The eyes contain fluid, called aqueous humor. It keeps the eye plump and brings nutrients to the lens and cornea, both of which have no direct blood supply. The eyes constantly make new fluid and drain the old fluid. In a normal eye, fluid production and drainage are perfectly balanced, and the eye pressure stays within normal range. When something prevents the eye from draining effectively, or when someone causes the eye to produce new fluid too quickly. Over time, this imbalance can lead to high eye pressure. High eye pressure wears on the optic nerve, damaging it slowly over time, Christopher Starr, MD, ophthalmologist at Weill Cornell Medicine and NewYork-Presbyterian tells Health.

In rarer cases, glaucoma can happen when something narrows or obstructs the angle between the iris and the lens. The iris is the colored part of the eye that contracts and expands to accommodate changes in light; the lens is behind the iris and is responsible for focusing light onto the back of the eye (retina) where it then gets sent to the brain via the optic nerve. When the opening between the iris and lens gets closed off, fluid cannot drain properly, and the pressure in the eye rises.

What are cataracts?

A cataract is a clouding of the lens of the eye, according to the National Institute of Health. They're extremely common later in life. In fact, more than half of all Americans either have a cataract or have had cataract surgery by the time they reach 80. But they can form earlier than that.

Cataracts form when the proteins in the lens of your eye start to break down and clump together, according to the National Eye Institute. This creates a cloudy spot that over time, expands and clouds more of the lens. This cloudiness can greatly impact vision quality.

Are glaucoma and cataracts connected at all?

For the most part, glaucoma and cataracts are totally different eye conditions. The biggest similarity is that the risk of each condition goes up dramatically with age. Very advanced cataracts may also increase the risk of angle-closure glaucoma, says Dr. Starr.

Similarly, cataract surgery can potentially help lower eye pressure, says Daniel Laroche, MD, director of glaucoma services and president of Advanced Eyecare of New York and assistant professor of ophthalmology at the Mount Sinai School of Medicine—and that may reduce the risk of glaucoma down the road. "The lens can get larger naturally with aging, and when we take it out, it stops rubbing and opens up the drainage," Dr. Laroche tells Health. Of course, this isn't always the case, but there can be a connection here. Dr. Laroche says that in his experience, doing earlier cataract surgery can help prevent some people from going on to develop glaucoma.

Some eye surgeons are also starting to plan cataract and glaucoma surgeries at the same time in order to minimize the number of surgeries a person has to go through. "Cataract surgery is the most commonly performed ambulatory [outpatient] surgery in the US. A lot of patients needing cataracts surgery also have glaucoma, so if we're going to go in and do surgery, it's often recommended to do minimally invasive glaucoma surgery (MIGS) as an add-on," says Dr. Starr. MIGS is a category of newer glaucoma surgeries that have minimal complications compared to other glaucoma surgeries. During these procedures, very tiny incisions are made to insert microscopic stents that increase drainage in the eye. 

"We open up the drain [while we're in there], and in 80 percent of cases, patients don't have to use eye drops after that," Dr. Laroche says. Of course, the type of glaucoma you have, and its severity, will factor into whether this approach is right for you. But it's promising.

What are the similarities and differences between glaucoma and cataracts?

Symptoms

The most common forms of glaucoma are asymptomatic until the optic nerve has suffered significant damage. When this happens, the first noticeable symptom will usually be a loss of peripheral (side) vision or feeling like you're looking through a tunnel. Other forms of glaucoma—including angle-closure and some secondary glaucomas—can cause redness of the eye, blurred vision, halos around light, and severe eye and head pain.

With cataracts, it's also normal to have no symptoms when cataracts are in the beginning stages. Once a cataract is more developed it can cause cloudy or blurry vision; colors appear faded; glare from headlights, lamps, or sun; halo around lights; poor night vision; and double vision.

Risk factors

Glaucoma is much more common with age. It also tends to have a genetic component—if you have a first-degree relative with glaucoma, there's a greater chance you'll develop it, says Dr. Starr. Eye injury or surgery, high blood pressure, thin corneas, and steroid use can also increase your risk. People of African descent and Hispanics also have an elevated risk compared to people of European descent, according to the Glaucoma Research Foundation.

The risk of developing cataracts also increases dramatically with age. Other risk factors include a family history of cataracts, drinking and smoking, an eye injury or surgery, spending a lot of time in the sun, certain health problems (like diabetes), and certain medications—most commonly, steroids.

Diagnosis

High eye pressure is detected during a routine eye exam using a test called tonometry. Your doctor will give you eye drops to numb the eye, and then will gently tap a device against the cornea to measure the pressure. They'll also use drops to dilate (widen) your pupils so that they can take a look inside the eye and see if the optic nerve looks normal. If either of those things seem off, they can do a series of other in-office tests to check other parts of the eye and determine if glaucoma is likely.

With cataracts, your doctor will take a look at the lenses in each eye as part of a routine eye exam or if you're having problems seeing and go to the doctor. Using the same test that checks for optic nerve health, your doctor will give you drops to dilate your pupils and take a good look inside your eye to see if the lens looks normal or if they notice any buildup and clouding.

Progression

Glaucoma progresses very slowly at first, and then usually rapidly once vision loss sets in. We don't currently have any methods of repairing the optic nerve, so once it's damaged, it can't be repaired. Any loss of eyesight from glaucoma is permanent.

Cataracts progress very slowly. Although cataracts can cause vision loss, it's reversible. The vast majority of people who get cataract surgery notice an improvement in their vision.

Treatment

Early treatment is necessary to prevent vision loss and preserve eyesight. First-line treatment is usually eye drops, which work in various ways to lower eye pressure. If eye drops are not sufficient, there are a handful of minimally invasive surgeries that can be helpful, including laser surgery and a MIGS. More invasive surgeries may be needed in cases of advanced glaucoma.

Treatment isn't super urgent. If a cataract is not bothering you too much, it's totally fine to wait to treat it until it's convenient for you. If cataracts start to interfere with your life, you can get cataract surgery. During the surgery, the clouded lens is removed and replaced with an artificial lens. According to the National Eye Institute, cataract surgery is very safe and successful. Your doctor may choose to do cataract and glaucoma surgery at the same time if you're a good candidate for it.

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