BREWER, Maine — To see clearly during the day, wear your contacts at night.

That’s the advice Dr. Kimberly Allen, a corneal refractive therapy-certified optometrist with Penobscot Eye Care, is giving some of her patients.

Allen prescribes CRT lenses, or night contacts, that reshape the eye while a person is sleeping so that glasses no longer are needed during the day.

“It’s a nice way to eliminate the need for corrective eyewear during the day,” she said Saturday. “I don’t know why more patients aren’t doing it.”

CRT lenses apply pressure to the cornea, temporarily changing its curvature or shape, which in turn allows the eye to focus naturally.

The specially fitted lenses can be used by people of all ages, Allen said, and studies have shown that children who use them “can slow the progression of nearsightedness” because their eyes don’t have to work as hard.

The U.S. Food and Drug Administration is in the middle of a five-year study to confirm the earlier studies and has approved CRT lenses made by Paragon in Mesa, Ariz.

CRT lenses look just like regular contact lenses and must be worn for at least four hours a night.

“The first night is the hardest,” Allen said.

Some patients say the CRT lenses are slightly uncomfortable, at first, but “for most of the time you’re wearing the lenses your eyes are closed and you are asleep,” she said.

Orthokeratology, the temporary changing of the cornea by way of night contacts, has been around for four decades and is popular in Europe, but it is still considered exploratory, Allen said. For that reason, insurance companies typically don’t cover the costs, she said.

Unlike therapeutic contact lenses of the past, the Paragon CRT lenses are for nearsighted patients only, are oxygen-permeable and allow patients to see with them in — a feature that not all night contacts offer.

“If you wake up in the middle of the night, you’ll be able to see,” Allen said.

Some users see results in as little as one day, but for many it can take up to two weeks for eyes to adjust, she said

“The higher your prescription, the longer it takes for full treatment effects,” Allen said. “Within one to two weeks you can see perfectly without them.”

Once that occurs, patients can do without glasses entirely.

“Then you [just] have to wear them at night to maintain the treatment,” she said, and added that “those with a low prescription can sometimes skip a night.”

The night contacts are “made specifically for the individual’s eyes,” Allen said. “And if something isn’t working well, you stop wearing them and your eye returns to its regular shape.”

It takes an eye about 48 to 72 hours to revert back to its original shape if a patient stops using the specialized lenses.

Nearsighted, or myopic, patients and those with astigmatism can use the Paragon CRT lenses.

The FDA has approved the lenses for those with prescriptions up to 6.00 diopters of myopia with no more than -1.75 diopters of astigmatism; however, the lenses may not work for everyone in those ranges, Allen said.

“It really has the most success under 4 or 5 diopters,” Allen said. “I have a 1.25 astigmatism, and it really wasn’t working for me. It doesn’t work at all for farsightedness.”

A diopter is a unit of measurement of the power of a lens.

Patients like CRT lenses because they are nonsurgical, noninvasive, and the effects are fully reversible, Allen said.

“It’s less risky then laser eye surgery, and there are not any long-term side effects,” she said.

The cost to get the lenses ranges between $800 and $1,200. That includes an initial visit, the computer eye scan and fitting, two sets of CRT contacts and a year of follow-up exams, Allen said. Replacing a lens is around $180.

Night contacts have a very promising future, Allen said, adding that she expects to see a big jump in use once the FDA completes its study on use by children.

In the last year, Allen has prescribed the CRT lenses to 10 patients and “only one has dropped out, but she had some issues with not wearing contact lenses properly in the past” and had some scarring.

Allen, who is the only eye doctor in the Bangor area prescribing CRT lenses, said most of her clients haven’t even heard of the science.

“We haven’t properly marketed it up here,” she said.