Dialysis treatment clears the blood, but does it cloud the vision?

Magnifying glasses may soon join the dialysis machine as essential equipment in dialysis centres around the country.  A new study, published in the December issue of American Journal of Kidney Diseases, the official journal of the National Kidney Foundation, suggests that elderly dialysis patients suffer high rates of visual impairment.

According to the National Kidney Foundation, the elderly represent well over half of the U.S. dialysis population—a number that recently reached 355,000.

Researchers at the University of Toronto studied 159 haemodialysis patients, all of whom were over the age of 65.  The patients were asked to participate in a series of tests to assess their vision, including a visual acuity test, a contrast sensitivity test and a depth perception test.  The visual acuity test measured the patients’ overall vision functioning, while the contrast sensitivity and depth perception tests focused on the patients’ ability to distinguish between objects of different shades of colour and the ability to determine relative distances between and within objects.

A surprising 39% of study participants were found to have significant visual impairment, compared to 28% of healthy people over 70 who experience irreparable visual damage.  Specifically, 96% had visual acuity levels less than age-expected values, 37% had poor contrast sensitivity and 31% failed the depth perception test.

Co-investigator Vanita Jassal, MD, expected that dialysis patients would have a high rate of visual impairment due to the large percentage of this population that suffers from diabetes and hypertension, two conditions that are strongly associated with visual loss. However, Jassal did not anticipate the exceedingly high number with severe depth perception issues.

Jassal does not believe that dialysis itself causes retinal damage but says the study’s findings underscore the high burden of vascular and other diseases born by dialysis patients.

“As clinicians, we don’t necessarily appreciate what loss of vision means to our patients,” says Jassal. “If we’re explaining monthly lab results by pointing to a chart and they can’t see what we’re referring to, they are missing out on key information that they need in order to stay on top of their own health care.”

Impaired vision is strongly associated with accidental falls which are in turn related to death, hospitalisation and long term institutional care, costing the U.S. an average of $5 billion.

“The degree to which the study participants suffer from vision damage, particularly depth perception problems, can have a major impact on their lives. Depth perception is necessary for basic activities, such as climbing stairs and avoiding obstacles when walking. Especially important for dialysis patients, loss of depth perception affects their ability to follow critical medication regimens,” continued Jassal.

(Source: American Journal of Kidney Diseases: National Kidney Foundation USA: January 2009)