Intacs Corneal Inserts or
Implants: A Proven Treatment
for Keratoconus

By Rob Murphy; reviewed by Brian S. Boxer Wachler, MD,
and Charles Slonim, MD

Intacs corneal inserts or implants are a minimally invasive surgical option primarily now used for correcting bulging (keratoconus) caused by thinning of the eye's front surface.

Originally FDA-approved in 1999 for mild myopia (-1.0 to -3.0 diopters), Intacs (Addition Technology, Des Plaines, Ill.) are two tiny, clear crescent-shaped pieces of a plastic polymer that are inserted into the cornea.

The FDA in July 2004 granted Intacs a Humanitarian Device Exemption to allow corrections of keratoconus largely because of Intacs' safety record and because only a few treatment options, such as corneal transplants, are available for keratoconus.

The approval allows Intacs to be marketed for reduction or elimination of myopia and astigmatism in keratoconus patients where functional vision is no longer obtained with contact lenses or eyeglasses.

In early January 2006, the FDA also formally acknowledged that the Intacs implants are therapeutic devices that can be described in company literature as corneal implants, rather than prescription inserts.

The corneal implants are designed for long-term vision correction. If you are among the 4 percent of people who are not satisfied with results or you have troubling visual symptoms, you can ask a surgeon to remove the Intacs.

Intacs can be replaced with different-size implants or removed for good. You have the option of replacing them with new rings at a later date if your prescription changes with age.

If Intacs are removed permanently, vision tends to return to the way it was before surgery within three months. Those receiving replacement Intacs have obtained good visual results as well, and no serious problems with repeating the procedure have been reported.

How Do Intacs Work?

For treating nearsightedness, Intacs correct vision by flattening the cornea to refocus light rays and improve vision. For keratoconus, Intacs work by flattening the steep part of the cornea or cone to reduce vision distortions.

Intacs are made of the same biocompatible material found in cataract lens implants (intraocular lenses), so there is not much risk of adverse effects from the material.

In a very few cases, however, eye irritation (blepharitis) or abnormal blood vessel growth (neovascularization) may occur. Also, Intacs may produce no corrective effect in fewer than 5 percent of individuals with keratoconus.

The procedure takes about 15 minutes and is done on an outpatient basis: you walk in and walk out later, but will need someone to drive you home after surgery. Before surgery, your doctor places anesthetizing drops in your eye and may give you a mild oral sedative.

During the procedure, your surgeon creates a tunnel between layers of the corneal stroma, outside of the central optical zone. The surgeon then chooses the appropriate ring thickness. A thicker ring in Intacs means more flattening of the cornea, which increases the level of vision correction achieved. After one or two crescent-shaped Intacs are inserted into the tunnel, the procedure is over.

After Intacs Surgery

You'll probably rest for a while, then go home (have someone else drive you). Most people have sharper vision the first day after surgery, but you may need a couple of days of relaxation to promote healing. You won't feel the ring segments, because they are beneath the cornea's nerve endings. Other people can't see them unless they look very closely into your eyes.

Intacs for myopia or keratoconus work by flattening corneal curvature. Photo provided by the manufacturer.

Results of these implants will depend on the degree of keratoconus in each individual. People with milder cases of keratoconus may not need any lenses for additional vision correction. People with moderate keratoconus may require glasses or soft contact lenses for improved vision. For more advanced cases, rigid gas permeable contact lenses may be needed to improve vision or to delay or prevent the need for a corneal transplant.

Intacs can be very effective at changing the cornea and flattening the cone caused by keratoconus. But if you have advanced keratoconus, Intacs cannot halt the progression caused by weakening of surface eye tissue (collagen) responsible for corneal strength.

Research is continuing into an investigational procedure called corneal cross-linking, which fortifies eye tissue to keep it from degrading.

Results of Clinical Trials for Intacs for Keratoconus

In 58 keratoconus eyes implanted with Intacs, almost half (25) achieved 20/40 uncorrected vision or better in a study reported in the October 2005 issue of Archives of Ophthalmology. Studies also have shown that Intacs may be able to reduce vision distortions in people with keratoconus who also have developed irregular astigmatism associated with an uneven eye surface.

The ring segments flatten your cornea similarly to the way you can flatten the top of a tent by pushing on the sides. (Graphics courtesy of the manufacturer.)

In another study, single segment Intacs improved both uncorrected vision and lens corrected vision for LASIK eye surgery patients who developed keratoconus or progressive corneal thinning (ectasia) as a complication. Single segment Intacs also were more effective than double segment Intacs in the same study reported in the March 2006 issue of American Journal of Ophthalmology.

Among 28 people in the post-LASIK study, 37 eyes were treated with either single segment or double segment Intacs. Each group was matched for factors such as age. The single segment group averaged about nine lines of uncorrected vision improvement on a standard eye chart, compared with 2.5 lines in the double segment group.

Results of Clinical Trials for Intacs for Nearsightedness

Prior to original FDA approval in 1999, Intacs underwent clinical trials in roughly 450 eyes at multiple U.S. clinics for low nearsightedness (not keratoconus). Twelve months after surgery, 97 percent of the eyes had 20/40 vision or better, and 74 percent had 20/20 or better. Thirty-nine people chose to have the implants removed, either due to side effects such as glare, halos and night-vision problems (19 eyes) or because their vision was under- or overcorrected (15 eyes). There were no serious complications.

A study of the reversibility of Intacs for nearsightedness, published in the January/February 2001 issue of Journal of Refractive Surgery, found that 20 of the 21 eyes returned to within 1 diopter of their preoperative refraction, with stable vision three months after removal. In each case, removal was safe and easy to perform.

A 1999 study published in the same journal looked at four eyes receiving replacement implants of different thicknesses. Two had been undercorrected with their initial corneal rings and two overcorrected. After the replacement, all achieved uncorrected vision of 20/16 to 20/20, with no complications.

Are You a Candidate for Intacs?

Many young adults experience changes in their glasses and contact lens prescriptions, even up to their early 30s. These are normal physiological changes, but people in this age group would not be good candidates for the procedure until their eyes have "settled down" into one prescription.

You may be eligible for corneal ring implantation if you:

• Are an adult over 21.
• Have keratoconus.
• Have stable vision.
• Have mild myopia with 1 diopter or less of astigmatism, although Intacs no longer are being marketed heavily for this type of vision correction.

After examining your eyes, your doctor can tell you more about Intacs. As for cost, it varies from surgeon to surgeon, but is generally slightly more than for laser vision correction. [Read the latest prices for LASIK and other procedures.]

[Page updated July 2009]