cataracts

What is a cataract?
A cataract is a clouding of the part of the eye called the lens.  The lens sits right behind the colored part of the eye (iris), and it helps focus light onto the light-sensitive tissue that lines the back of the eye (retina).  It is normally clear.  Over time, the proteins that make up the lens begin to clump together and cause a clouding of the lens.  Most cataracts progress slowly and eventually affect vision.  While most cases involve both eyes, a cataract can develop in only one eye.

For those of you, like myself, who need a visual, here's a good video to watch.

Are there different types of cataracts? 
There are many different types of cataracts, and a person can have more than one type.

• Age-related, or senile: cataracts that result from the normal physiological changes that occur in the lens of the eye.  Most, but not all, cataracts are age-related. 
• Nuclear sclerotic cataracts involve a yellowing of the central lens. They sometimes cause a shift in prescription, leading to a temporary improvement in near vision (often referred to as "second sight"). 
• Cortical cataracts involve spoke or wedge-like opacities that often start around the periphery of the lens.
• Posterior subcapsular cataracts involve a hazing of the back of the lens. This type of cataract may progress more rapidly and affect vision more significantly than others. Posterior subcapsular cataracts may be seen more frequently in diabetic patients, in patients using steroids, and in patients who have had vitreoretinal surgery.  
• Congenital: cataracts that are present at birth. The majority affect both eyes, and they vary in severity.  If the cataracts are significant and obstruct vision, they are removed early on to allow vision to develop properly, preventing deprivational amblyopia.    
• Traumatic: cataracts that result from blunt or penetrating trauma to the eye.  

There are still other, rarer cataracts that occur secondary to disease processes. For instance, a Christmas tree cataract is often found in those with myotonic dystrophy.

Images courtesy of the AOA

Can you prevent cataract formation?
One theory suggests that cataract formation is due to oxidative changes in the lens, and some studies (1, 2, 3) have shown that antioxidant consumption can help reduce the risk of cataracts. (For more information on how diet affects the eye, check out this previous post). While cataract prevention is still being researched and debated, we do know of risk factors for progression that we can aim to reduce/eliminate.  Evidence suggests that UV exposure increases the risk of cataract development (4, 5), so wearing UV-blocking sunglasses is a good practice.  Smoking increases the rate of cataract formation (6, 7), so that's yet another reason to kick the habit.

What are the symptoms?
Early on, cataracts have few or no symptoms.  Colors may appear faded. You may begin to notice glare, especially when driving at night. Because the lens is no longer clear, it scatters light, which prevents a sharp, clear image from focusing on the retina.  As the cataracts progress, they begin to cause blurry vision that is not correctable with glasses or contact lenses.  At that point, the option of surgery is discussed.  Cataracts can be diagnosed by your optometrist during your annual dilated eye exam.

What is the treatment?
While cataracts are the leading cause of visual impairment world-wide (47.9%, according to the WHO), they are easily treated here in the US. Cataract extraction is currently the only treatment available.  This procedure involves removing the natural lens of the eye and replacing it with an intraocular lens (IOL). There are many different types of IOLs available.  It is up to the patient and his/her team of eye care professionals to discuss the options and determine which type of IOL is best suited for the patient.  Here is a video of a local ophthalmologist performing cataract surgery (if you're squeamish, you should probably pass on watching it).

The future may hold non-surgical options for the prevention and treatment of cataracts.  In a recent study, dogs who received treatment with lanosterol injections and drops showed a noteable reduction in their cataracts.

Do they recur?
No- once a cataract is removed, it is gone.  However, you can develop a posterior capsular opacification (PCO) after cataract surgery.  That's when the lens capsule that holds the implant becomes hazy.  It is sometimes referred to as an "after-cataract" or "secondary cataract," but it is not a true cataract.  A YAG laser capsulotomy is a simple procedure that involves using a laser to remove the hazy portion of the capsule that is obstructing vision.

CliffsNotes: A cataract is a clouding of the lens of the eye.  There are several different types, but the most common are the natural results of aging.  When cataracts affect vision significantly, the option of surgical extraction is discussed. 

Additional Resources:

• AOA: Cataracts
• NEI: Cataracts
• All About Vision: Cataracts
• Kellogg Eye Center: Cataracts