Different types of cataracts produced identifiable and repeatable results using wavefront diagnostic equipment

Aug 2 2004

A study published today in the August edition of the Journal of Cataract & Refractive Surgery reports that wavefront technology, a new way of measuring how vision is distorted by irregularities in the eye, offers a widely accepted means for corroborating cataract patients' vision complaints, which may lead to earlier treatment with attendant enhanced patient safety and less loss of quality of life.

The study, Higher-Order Aberrations of Lenticular Opacities, by N. Sachdev, S. Ormonde, T. Sherwin, and C. McGhee, found that different types of cataracts produced identifiable and repeatable results using wavefront diagnostic equipment. These results could explain the significant visual symptoms in patients with early cataracts that the most commonly used vision test does not demonstrate. The study was performed at the Departments of Ophthalmology at the University of Auckland and the Auckland Public Hospital in New Zealand.

The significance of this study is that it shows wavefront testing can be used to accurately measure the visual errors that show up as glare and other problems that cataract patients experience. This will give insurance companies a reliable and widely accepted means of testing for the effects of cataracts on patients' vision and for making reliable determinations of the medical need for a cataract operation. Its impact on patient welfare is that it can reduce the number of patients who are unable to receive early treatment because alternative testing means are inadequate or not widely accepted.

Cataracts are the leading cause of preventable blindness worldwide, and cataract surgery is among the most common surgical procedures in people over 65 years of age in the United States. Last year, 2,775,000 procedures were performed in the U.S. (one procedure = one eye). A cataract is the clouding of the normally clear, natural crystalline lens of the eye. As cataracts increase in size and density, they reduce the amount of light passing through the lens, which results in blindness if not treated. In the U.S., Medicare, the federal government's health insurance program for the elderly, paid for 1.733 million procedures in 2002, according to the most recent data. Modern cataract treatment surgically removes the damaged lens and replaces it with an artificial one.

Because cataracts tend to grow gradually, one of the most important treatment issues is determining when they degrade vision to the point that the patient is at an increased risk of falls or accidents, or that their quality of life has been significantly undermined. (An August 2002, study reported in the Journal of the American Medical Association found that cataract patients who had surgery to treat the condition had 50 percent fewer car accidents than those patients who did not.)

Medicare and most insurance programs will pay the cost of cataract removal once a patient's vision has deteriorated to 20/50 or less when reading the standard (Snellen) eye chart, which was developed about 100 years ago. By contrast, states typically require at least 20/40 vision for driving without glasses.

Cataract patients often complain of glare, double vision, a shift in colors, and other problems. "There have been innumerable articles and textbook chapters noting that the Snellen test does not document the visual deficits experienced by cataract patients," said Samuel Masket, MD, chair of the Eye Surgery Education Council. While some insurance companies will cover the cost of cataract surgery based on additional testing, there is no widely accepted test that can corroborate patient's vision complaints.

"Patients are often in the position of having to curtail night driving because cataracts have made it dangerous or they have to cut back participation in other activities that enrich their lives, but they can't seek treatment because insurance testing criteria exclude them from coverage until their vision degrades to a point that is measurable by an outdated test," Masket said.

Wavefront technology involves the use of a laser that beams light into the eye. As the light is reflected through the eye, it is distorted by abnormalities in the eye's components. The distorted light is analyzed by a computer program, which can display the aberrations as mathematical values or as a map of the eye. Wavefront technology is being used to make custom treatment maps of the eye and guide lasers during LASIK to correct nearsightedness, farsightedness, and astigmatism.