While the vast majority of those who develop cataracts are senior citizens, this vision-blurring condition is not always related to age.

More than 90 percent of Americans have at least one cataract by age 65, and half of those between 75 and 85 have lost some vision because of the condition, according to the University of Michigan Kellogg Eye Center.

Causes & risk factors

Cataracts occur when the eye's lens, the clear layer that focuses light on the retina, becomes cloudy. Because of this, the lens cannot send a sharp image to the retina, the light-sensitive layer at the back of the eye that transmits nerve signals to the brain recording what is seen.

If the eye is a camera, a cataract happens when the lens gets cloudy, said Dr. Mitchell Weikert, an associate professor of ophthalmology at Baylor College of Medicine in Houston, Texas.

"No matter how good your camera is, you're going to take a darker picture, because light has to pass through the cloudy lens," Weikert told Live Science. A cloudy lens can blur the image and scatter light to create glare. "It filters light out to so you need brighter lights in order to see."

Typically, this clouding develops because the protein that helps comprise the lens begins clumping together on its surface, making it opaque and blurring vision, according to the National Eye Institute (NEI).

However, some babies are born with cataracts, and others develop them because of eye injuries or genetic disorders. Certain risk factors also increase the likelihood of developing cataracts. According to the Mayo Clinic, these include:

• Diabetes
• Smoking 
• Excessive sunlight exposure
• Excessive alcohol use
• High blood pressure
• Obesity
• Radiation exposure, such as X-rays and cancer radiation therapy
• Previous eye surgery
• Prolonged use of corticosteroid drugs

Wearing UV-absorbent sunglasses and a brimmed hat can help people protect their eyes from the sun, Weikert said. 

Symptoms

In the early stages of cataract formation, no symptoms may be present and the condition may progress very slowly. Over time, however, certain signs tend to show up. 

"Many times, patients won't know they have cataracts in the beginning," said Dr. Eric Donnenfeld, a clinical professor of ophthalmology at New York University Langone Medical Center. "It's a continual degradation in their quality of sight, in that their vision just gets worse and worse over time."

According to the American Optometric Association (AOA), symptoms include:

• Blurry, cloudy or hazy vision
• Reduced color intensity
• Increased sensitivity to light and glare, especially when driving at night
• Increased difficulty seeing at night
• Seeing "halos" around lights
• Double vision in a single eye
• Frequent prescription changes for eyeglasses or contact lenses

Diagnosis & testing

Diagnosing cataracts is a relatively simple process, according to the Mayo Clinic, and involves a comprehensive eye exam that may include several different parts:

• Visual acuity test, using an eye chart with progressively smaller letters
• Dilated eye exam, using eye drops to widen the pupils to view the retina and optic nerve with special equipment
• Tonometry, using an instrument to measure internal eye pressure
• Slit-lamp exam, using light and magnification to illuminate the cornea, iris, lens and the space between the iris and cornea

"Visiting an eye doctor for a full examination is the most effective and safe way," to diagnose a cataract, Donnenfeld said. "We recommend that everyone over the age of 50 should have an annual eye exam." 

Treatment

While the use of new eyeglasses, magnifying devices and brighter lights may stave off cataracts' effects on vision for a period of time, surgery is the only treatment. Surgery is usually considered when cataracts begin to impinge on quality of life, affecting driving, reading or the ability to perform normal activities. Since cataracts don't damage the eye, there is no harm in delaying the procedure, according to the NEI.

Cataract surgery is the most common operation among those over age 65, according to the Kellogg Eye Center, and more than 2 million are done each year on people of all ages. The surgery lasts about 30 minutes and vision typically improves within a day. Three types of surgery are available:

• Small incision cataract surgery: Also called phacoemulsification, this is the most common type. During the procedure, a tiny probe is inserted into the eye through a small incision on the side of the cornea. This probe releases ultrasound waves that soften and split the lens into pieces, which are suctioned away.
• Extracapsular surgery: A longer incision is made on the side of the cornea and the cloudy core of the lens is removed in one piece. The rest is suctioned away.
• Laser-assisted cataract surgery: Instead of using a handheld blade to make the incision, doctors can use a precise laser to make the cuts instead. The laser may also help break up the cataract, which can lessen the amount of ultrasound surgeons need to break up the cataract later, Donnenfeld said. This relatively new technique has additional out-of-pocket costs for patients, he said.

In all of the procedures, the removed lens is replaced with an artificial one made of plastic, according to the NEI. It becomes a permanent part of the eye and cannot be felt or seen.

Patients can choose from several lens implants. Most people choose a monocular single focus lens for both eyes, and rely on reading glasses for near-visual tasks. Others ask to have one eye corrected for distance and the other for near-vision, although this practice can compromise depth perception. 

Bifocal implants, another option, can help patients see at both distances. But they can also cause glare and haloes, and are not fully covered by most insurance plans. People may ask the doctor to fix their astigmatism, a condition in which the cornea or lens is shaped like a football and makes vision blurry. Surgeons can use special lenses or techniques to fix astigmatism, but it also has an out-of-pocket cost.  

A meeting with an ophthalmologist can help people decide which artificial lenses are best for them. 

"We’ll talk with the patient and ask them where they want to be optimally focused," Weikert said. 

As with all surgery, cataract removal has risks, including infection, bleeding and retinal detachment, according to the Mayo Clinic.

People who have received LASIK surgery, an operation that reshapes the cornea of the eye, may have variable outcomes, and some may need glasses following the surgery. "If you have had LASIK, no matter what, there is more variability in our calculations for what lens to put in the eye than for someone who has not had LASIK," Weikert said. 

New, wavefront technology may help LASIK patients, although some variability remains. Wavefront, or custom LASIK, involves a laser that is guided by a thorough mapping of one's cornea. Once the cataract is removed, wavefront technology machines can help doctors choose the proper powered lens for former LASIK patients, Weikert said.