All About Cataracts

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.

Cataract surgery does not cause a progression of early age-related macular degeneration (AMD) to a more sight-threatening stage of the disease, according to a new study.

Researchers in Australia performed cataract surgery on 27 eyes of 27 patients with early macular degeneration to see if removal of their cataracts would improve the patients’ vision and quality of life without increasing their risk of AMD progression and vision loss from choroidal neovascularization (CNV).

CNV is the growth of fragile new blood vessels in the choroid layer of the eye underlying the retina. In macular degeneration, these blood vessels can leak into the retina, causing “wet” macular degeneration and severe vision loss.

Prior to the phacoemulsification cataract surgery performed in the study, all patients underwent a test called fundus fluorescein angiography (FFA) to make sure no eyes had pre-existing CNV.

Data gathered 6 months after surgery revealed a 2.8-line mean improvement in visual acuity (measured with a standard eye chart) and a 2.1-fold average gain in quality of life scores (measured by a patient survey) after cataract removal. One eye (3.7 percent) developed CNV within 6 months of surgery.

The researchers concluded that there was no significant increase in short-term risk of progression from dry AMD to CNV following uncomplicated phacoemulsification cataract surgery, and that there are distinct benefits of cataract surgery in people with early macular degeneration.

Source: Cataract surgery in high-risk age-related macular degeneration: A randomized controlled trial. Clinical & Experimental Ophthalmology. Published online June 22, 2009.

Bilateral cataract surgery intentionally designed for monovision produces good visual acuity and high patient satisfaction, according to a study published in the Journal of Cataract and Refractive Surgery. 

Researchers in Australia evaluated the outcomes of cataract surgery performed on both eyes of 26 patients. In all cases, a monovision correction was performed with intraocular lenses (IOLs). The target refractive endpoint of the second eye corrected for near vision was mild to moderate myopia ranging from -1.00 D to -1.50 D. 

Visual acuity, contrast sensitivity, stereopsis, and patient satisfaction were measured prior to surgery and 3 to 4 months post-operatively. Patients were also asked how frequently they needed eyeglasses after surgery.

Monovision is a method of vision correction where one eye is fully corrected for distance vision and the other eye is made (or is left) nearsighted so a person with presbyopia can see acceptably well up close without reading glasses. Monovision can be performed with contact lenses or refractive surgery, including refractive cataract surgery.)

Results of the study included:

1. 96 percent of the patients achieved uncorrected binocular distance visual acuity of at least 20/30.
2. 92 percent achieved approximately 20/30 or better uncorrected near visual acuity. 
3. Good depth perception and contrast sensitivity were maintained after surgery. 

Patients were generally satisfied with their vision after surgery. Approximately 25 percent of patients did not need glasses for any reason; one patient was totally dependent on spectacles. No patient required an IOL exchange or other additional refractive surgery.

The authors of the study concluded monovision cataract surgery achieves good visual function and patient satisfaction without the risk of troublesome visual symptoms sometimes associated with multifocal IOLs used in cataract surgery to correct presbyopia.

Source: Patient satisfaction and visual function after pseudophakic monovision. Journal of Cataract and Refractive Surgery. June 2009.