All About Cataracts

Results of a new study show that implantation of a light-filtering intraocular lens (IOL) during cataract surgery increases the amount of important nutrients in the eye and may reduce the risk of age-related macular degeneration.

The special IOL blocks high energy visible light (also called HEV light or blue light) that has been associated with damage to the retina. This damage occurs in the most sensitive part of the retina called the macula, which is responsible for central vision and color vision.

Prolonged exposure to blue light depletes macular pigments that protect important visual cells in the retina called photoreceptors. The blue light-filtering IOL helps preserve or increase these pigments, thereby reducing the risk of macular degeneration, according to the researchers.

Macular pigments include lutein and zeaxanthin.

In the study, 42 patients scheduled for cataract surgery were randomly assigned to have either the blue light-filtering acrylic IOL or a standard acrylic IOL implanted during their procedure.

Macular pigment optical density and blood serum levels of lutein and zeaxanthin were measured prior to surgery and at one week and three, six and 12 months after surgery.

The researchers found that there was an increase in protective macular pigments over time (as measured by optical density) in eyes with the light-filtering IOL implant, but no such increase in eyes with the standard IOL.

They concluded that this suggests the light-filtering IOL may reduce the risk of macular degeneration after cataract surgery, but they cautioned that further and long-term study is needed to determine if this is true.

Macular pigments are obtained entirely from the diet and are transported to the retina through the blood. Because of growing evidence that macular pigments play a role in reducing the risk or progression of macular degeneration, many commercially-available eye vitamins contain lutein and zeaxanthin.

A full report of the study appears in the October issue of Investigative Ophthalmology & Visual Science, the journal of The Association for Research in Vision and Ophthalmology (ARVO).

Certain age-related cataracts may be due to problems with a specific gene, according to researchers at Case Western Reserve University School of Medicine (Cleveland, Ohio).

A gene called EPHA2 appears to be involved in maintaining the health and normal structure of proteins in the lens of the human eye. When this gene is absent or damaged, lens proteins begin to clump together and form lens opacities, or cataracts, say investigators Bing-Cheng Wang, PhD, and Sudha K. Iyengar, PhD.

Drs. Wang and Iyengar are collaborating in research with several other investigators in laboratories across the U.S. and in Australia and the U.K.

So far, the researchers have identified several mutations of the human EPHA2 gene that appear to be associated with age-related cataracts, and they continue to look for more.

By better understanding the processes by which the EphA2 gene helps maintain clarity of the human lens, they researchers may be able to find ways to prevent cataracts and possibly reverse them, perhaps reducing the need for cataract surgery.

The researchers also say other studies suggest common genes and pathways may be involved in both age-related cataracts and neurodegenerative diseases (e.g. Alzheimer’s disease) that affect the elderly.

Their report, “EPHA2 is associated with age-related cortical cataract in mice and humans,” appears in the July 2009 issue of PLoS Genetics.

Carnosine, a dietary supplement available without a prescription, may be able to prevent or treat cataracts, according to a study published in the July 14 issue of the American Chemical Society journal Biochemistry.

If true, taking daily supplements of carnosine may reduce the risk of developing cataracts, decreasing the need for cataract surgery.

Carnosine is a small molecule composed of two amino acids. It is found in relatively high concentrations in several body tissues, including muscles, nerves and the brain. The exact role of carnosine in the body is not fully understood but it appears to have an antioxidant effect.

The researchers exposed tissue cultures of lenses taken from healthy rat eyes to either guanidine — a substance known to form cataracts — or a combination of guanidine and carnosine. The lens tissue exposed to guanidine became completely cloudy, while the lens tissue exposed to guanidine and carnosine developed 50 to 60 percent less cloudiness. Carnosine also restored clarity to clouded lens tissue.

Cataracts occur when the primary structural protein in the eye’s lens, alpha-crystallin, forms abnormal clumps. These clumps make the lens cloudy and impair vision. Carnosine appears to play a role in blocking the formation of these clumps and/or reversing them.

Though further research is needed, the findings of the study prompted the researchers to suggest that carnosine could potentially prevent and treat cataracts in humans.

Source: Protective effects of l- and d-carnosine on a-crystallin amyloid fbril formation: Implications for cataract disease. Biochemistry. Published online July 14, 2009.

Cataracts are a common cause of vision loss in older adults.

In 2004, the Eye Diseases Prevalence Research Group (EDPRG), estimated that 20.5 million Americans (17.2 percent) over age 40 had a cataract in either eye, and 6.1 million (5.1 percent) already had a cataract removed. And according to the National Eye Institute (NEI), by age 80, more than half of all Americans either have a cataract or have had cataract surgery.

But, besides advancing age, are there other risk factors associated with the development of cataracts?

A large study of 3,721 adults in Australia found the following additional risk factors for cataracts:

•  Women are more likely than men to develop cortical cataracts. (This was also true in the American study by EDPRG, which found that women are almost 40 percent more likely than men to develop cataracts.)
• Working as a laborer (compared to having a white-collar occupation) and myopia also are risk factors associated with cortical cataracts.
• Cigarette smoking and a history or arthritis are associated with the development of nuclear cataracts.
• Diabetes and taking calcium channel blockers (medications commonly used to treat high blood pressure) for more than five years are risk factors associated with posterior subcapsular cataracts.

It is likely that in the United States, there will be an increase in diabetes-related cataracts in the future. According to the Centers for Disease Control and Prevention, 34 percent of Americans over age 20 are obese, and obesity is a primary risk factor for Type 2 diabetes. Currently, 24 million Americans (8 percent) have known diabetes, and an estimated 57 million (19 percent) have “pre-diabetes,” meaning they have blood glucose levels that are higher than normal but not yet high enough to be diagnosed as diabetes.

Some researchers believe that by the year 2050, the number of diabetes-related cataracts will increase by over 200 percent. Also, the number of Americans with diabetic retinopathy (another vision-threatening complication of diabetes) is expected to increase from 1.2 million to 3.4 million over the same period. 

The take-home message: If you want to lower your risk for cataracts, two steps you can take are to avoid or quit smoking and, if you are overweight or have pre-diabetes, to consult with your doctor and begin a diet and exercise program to lower your risk of diabetes.

Sources:

1. Prevalence of cataract and pseudophakia/aphakia among adults in the United States. Archives of Ophthalmology. April 2004.
2. Development of cataract and associated risk factors: The Visual Impairment Project. Archives of Ophthalmology. January 2006.
3. Diabetes and obesity: A challenge for every ophthalmologist. Archives of Ophthalmology. March 2009.