WASHINGTON - Patients taking a widely prescribed prostate drug should alert their eye doctors before undergoing cataract surgery to avoid complications, several medical groups said Tuesday.

Advance warning can allow surgeons to modify their technique during the common operation and avoid complications seen in patients who take Flomax and similar drugs to treat enlargement of the prostate, the groups said.

The drugs, called alpha-blockers, appear to impair a muscle in the iris, the colored portion of the eye. The iris must be stimulated during surgery to replace the clouded lens of the eye to allow the opening in its center, the pupil, to dilate. The drugs seem to cause the iris to flap or billow.

Any unexpected movement during surgery can cause injuries to the iris and other complications, said Dr. David F. Chang, a clinical professor of ophthalmology at the University of California at San Francisco and a spokesman for the American Academy of Ophthalmology.

Surgeons can use tiny hooks to keep the pupil open or administer stronger dilating medicines directly inside the eye to accommodate the problem, called intraoperative floppy iris syndrome, Chang said.

Preliminary results from a recent study suggest there are no more complications following modified surgery on patients taking Flomax compared to operations on patients who don't take Flomax or similar drugs. The drugs typically are taken by men, although they are prescribed to some women for urinary retention.