Association Between Head CT Scans and Cataracts Disputed

From the WebMD Archives

Jan. 27, 2000 (Lake Worth, Fla.) -- Contrary to previous findings, new research shows that having computed tomography (CT) scans -- a type of X-ray that is used to evaluate the head for possible diseases -- does not increase a person's risk of developing cataracts.

The risk of developing cataracts, a clouding of the natural lens of the eye that causes decreased vision, increases with age. They can also be caused or accelerated by other things, such as blunt trauma to the eye, use of certain drugs, and diseases such as diabetes. Because they can also be brought on by radiation injury, there had been some concern that having CT scans could increase their incidence.

In earlier research, the Beaver Dam Eye Study had shown a small association between a person's having a history of CT scans and developing cataracts. A new study, published in a recent issue of the American Journal of Public Health, however, shows no such association.

In this work, known as the Blue Mountains Study, investigators from the University of Sydney, Australia, surveyed 3,546 people, 18% (651) of whom reported having received a CT scan in the past. Compared with the patients in the Beaver Dam study, the Australians found that people of the same age groups in their study developed cataracts at the same rate. And, although CT scan rates were also similar in a side-by-side comparison of the studies, the Blue Mountains team did not find the association between CT scan history and cataract presence that the Beaver Dam study had shown.

There did originally seem to be a higher association between repeated CT scans and the prevalence of a certain type of common cataract. But when the researchers looked more closely at the finding and took certain factors into consideration that might have skewed this analysis (such as known cataract risk factors like the patient's age), they did not find the association valid. After having adjusted for the factors of education, hypertension, diabetes, smoking, alcohol use, steroid use, and sun-related skin damage, which have all been shown in previous studies to be related to the rate of cataract formation, there was no significant associated risk between having CT scans and developing cataracts.

Steve S. Spector, a West Palm Beach, Fla., ophthalmologist, reviewed the study for WebMD. "Basically, a cataract is a lens opacity that is related to many factors, and the amount of radiation that you're exposed to with a CT scan or X-ray is minimal," he says.

While the Australian study did not find convincing evidence of associated risk, nor could they duplicate the modest risk reported in the Beaver Dam study, they still advise proceeding with caution. "Despite our findings, strict protocols should be maintained to limit indiscriminant CT scan use and to reduce radiation dose," they write in their conclusion.

"It's an interesting study that basically corroborates what is intuitively obvious: that [radiation from] CT scans ... is very insignificant in formation of a cataract," Spector says.