SANTA CRUZ, Calif. — They provide invaluable services to their human companions, serving as eyes for the sightless, performing household tasks for the wheelchair bound and providing unconditional love for victims of trauma.

So through the month of May, thousands of service dogs will receive a service of their own, with ophthalmologists from the United States, Canada and Puerto Rico donating their time and resources to check for cataracts, glaucoma and other vision abnormalities.

Registration runs through April 30. More than 250 veterinary ophthalmologists are participating in the annual event.

Dr. Ann Gratzek, who owns the Ophthalmology for Animals in Santa Cruz, is a member of the American College of Veterinary Ophthalmologists and has participated in the yearly event since its inception in 2008. But the program is little known outside veterinary circles, and she estimated she’s provided the free, 15-minute exams to only about 100 animals in the last five years, almost all of them on dogs.

"I guess theoretically, there are such things as service ponies, but I’ve never seen one," said Gratzek, who’s practiced in Santa Cruz since 1994.

One year, she examined a seeing-eye dog suffering from cataracts, recalling he was serving as his owner’s eyes all the while.

"I don’t know that I’d trust him to lead me across the street," she said, adding the dog eventually was retired. Asked what drew her to the profession, she said it allows her to work with and usually help animals both large and small without having to deal with death.

Meredith Schneider, who’s helping to publicize the event, emphasized that anyone who wants to schedule an exam should first register on the American College of Veterinary Ophthalmologists website, www.acvoeyeexam.org. The site also contains a list of participants.

When the organization put together the first event, more than 160 American and Canadian ophthalmologists provided exams to roughly 1,500 animals, according to its website. The number of participants has grown each year since, and nearly 16,000 service animals have now received free exams, Schneider said. The majority of animals seen are handicap/disability assistance dogs, followed by therapy animals, then military/public service dogs, according to ACVO.