A cataract is a clouding of the eye's natural lens, which lies behind the iris and the pupil. Cataracts usually develop in both eyes, but sometimes they only affect one. Most cataracts occur as a result of getting older, usually sometime after age 40.
Cataracts are the most common cause of vision loss worldwide, but they are treatable.
Causes of cataracts
As we age, the proteins that make up the eye's natural lens can clump together. These clumps are the cataracts and are what cause the cloudiness. Over time, they may grow larger and cloud more of the lens, making it harder to see.
The lens inside the eye works much like a camera lens, focusing light onto the retina for clear vision. It also adjusts the eye's focus, letting us see things both up close and far away.
Water and protein make up most of the lens of the eye. The protein is arranged in a precise way that keeps the lens clear and lets light pass through it.
No one knows for sure why the eye's lens changes as we age, forming cataracts. Researchers worldwide have identified factors that may be related to cataract development. Besides advancing age, cataract risk factors include:
Ultraviolet radiation from sunlight and other sources
Prolonged use of corticosteroid medications
Statin medicines used to reduce cholesterol
Previous eye injury or inflammation
Previous eye surgery
Hormone replacement therapy
Significant alcohol consumption
One current theory is that oxidative changes in the human lens may be the cause of cataracts. Studies have shown that fruits and vegetables high in antioxidants may help prevent some types of cataracts.
A cataract starts out small and, at first, has little effect on your vision. Visual symptoms can take months to years to become noticeable. You may notice that your vision is blurred a little, like looking through a cloudy piece of glass.
Cataracts can progress at a different rate in each eye, resulting in visual symptoms in one eye and normal vision in the other. You may also notice the following symptoms with cataracts:
Light from the sun or a lamp seems too bright or glaring.
Your eyes feel more sensitive to light.
Oncoming headlights cause more glare than before when driving at night.
Visual halos around bright lights.
Seeing at night or in low light is more difficult.
Colours may not appear as bright as they once did.
To the outside viewer, an advanced cataract can cause the pupil to appear light gray instead of black.
The type of cataract you have will affect exactly which symptoms you experience and how soon they will occur. If you think you have a cataract, see an optician for an exam to find out for sure.
Types of cataracts
Nuclear cataracts are the most common form of cataract. These form in the center of the eye’s lens, gradually worsening and affecting vision.
Cortical cataracts usually are spoke-like opacities that begin near the edge of the lens and grow toward its center. These make you experience more light glare, making night driving particularly difficult.
Congenital cataracts are lens opacities that are present at birth in one or both eyes. They may be very small, with little effect on vision, or more severe.
Trauma-induced cataracts can form anywhere on the lens and often develop into a flower-petal or “rosette” shape.
Posterior subcapsular cataracts develop at the central back surface of the lens. These types of cataracts tend to develop faster than the others. Symptoms usually affect your vision around bright light and colours.
When symptoms begin to appear, you may be able to improve your vision for a while using:
Appropriate lighting or other visual aids.
Other treatment options for cataracts that have progressed may include cataract surgery.
If cataracts start to affect your quality of life, then your optician may suggest surgery. This is generally seen as a low-risk and effective way to restore your vision.
Many people consider poor vision an inevitable fact of aging, but cataract surgery is a simple, relatively painless procedure to regain vision.
Cataract surgery is very successful in restoring vision. It is the most frequently performed surgery in the United States, with more than 2 million Americans undergoing cataract surgery each year, according to Prevent Blindness.
Opticians can use different tests to diagnose cataracts.
Slit-lamp exam: A slit lamp is a large, binocular microscope with a bright light source that’s mounted on a small table. It enables your optician to closely examine your eye under high magnification (including checking the lens for cataracts).
Retinal exam: First, an optician will dilate your eyes with eye drops, causing the pupils to slowly open. This gives them a much better view inside your eye. The optician then examines the retina and optic nerve in the back of your eye. A dilated eye exam also provides the best view of any cataract formation on the lens.
Refraction: During a refraction, your optician determines the degree of your refractive errors and the eyeglass prescription that provides your best possible visual acuity. If your glasses prescription has changed and your vision can no longer be corrected to 20/20, it’s possible you may have a cataract developing.
Cataracts don’t always require treatment after they’re diagnosed, especially if they aren’t bothering you. Initially, a simple change of your eyeglass prescription may restore acceptable vision.
Currently, there is no known way to stop cataracts from developing. However, if you can limit some of the risk factors listed above, it may slow their rate of progression. Ways to limit cataract risk factors can include:
Wearing sunglasses during the day to reduce your eyes’ exposure to the sun’s UV radiation.
Eating a healthy diet and maintaining an exercise regimen.
Managing and reducing the effects of coexisting conditions like diabetes or hypertension.
Getting frequent eye exams to ensure any developing cataracts get diagnosed early.
Gary Heiting, OD, and Judith Lee also contributed to this article.
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Page published in June 2019
Page updated in June 2021