Corneal Inlays and Corneal Onlays

Corneal inlays and onlays are made of biocompatible materials that closely resemble the clear surface of the eye itself. And if current and future clinical trials prove successful, these devices may soon represent a new form of vision correction surgery.

In LASIK and PRK, vision correction is achieved when laser energy reshapes the cornea to alter the way light rays enter the eye. But with corneal inlays or onlays inserted just beneath the eye's surface, laser energy some day could be used to sculpt this artificial material instead of the eye itself.

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Even without laser reshaping, corneal inlays or onlays alone also may work much like contact lenses to provide vision correction. Unlike contact lenses, however, these devices never require regular removal or ongoing care. And they differ from surgically implanted lenses because they are not placed behind the cornea. Also, a corneal inlay or onlay is designed to seamlessly "merge" with the eye's surface.

Through use of inlays and onlays for vision correction, eye surgeons may avoid complications sometimes associated with procedures such as LASIK, PRK, and implantable lenses because the eye's natural surface tissue is left virtually undisturbed.

While the technology is not yet approved by the U.S. Food and Drug Administration, clinical trials began in early 2006 for one device created by AcuFocus (Irvine, Calif.), which has formed a business alliance with Bausch & Lomb (Rochester, N.Y.). [Read more.]

This corneal inlay, known as the ACI 7000, is designed to correct near vision focusing problems caused by aging, a condition known as presbyopia. With this inlay, a thin flap is created on the eye's surface where the device is applied. The flap then is replaced over the inlay to hold it in place.

The procedure takes less than 15 minutes and can be performed in the eye surgeon's office. Sutures are not required, and only topical anesthesia in the form of eye drops is used. According to Bausch & Lomb, the inlay is designed to block certain light rays reflecting from near objects that ordinarily would not be focused correctly by the presbyopic eye.

"Its optical principle is the pinhole phenomenon, which when used in photography (in terms of a small aperture), allows depth-of-focus and thus allows clear vision at all distances — near, intermediate, and distance," said Vance Thompson, MD, who is participating in clinical trials for the ACI 7000.

Thompson, a member of AllAboutVision.com's editorial board, said it's important to remember that the device is still in investigational phases, but that early results are very promising.
 

"Having worked in the field of presbyopia correction for over 17 years, I find it is such a pleasure to use a device like the AcuFocus Corneal Inlay," Thompson said. "It provides our patients who have needed reading glasses with good near vision, while still maintaining good distance vision."

Thompson said the ACI 7000 is very thin, only 10 microns wide, and is made of an opaque biocompatible polymer called Kynar, a thermoplastic material that softens in heat and hardens in cooler conditions.

The corneal onlay is made up of artificially produced tissue similar to the eye's surface or cornea and can be used to reshape the eye. (Illustration provided by Dr. W. Bruce Jackson.)

W. Bruce Jackson, MD, University of Ottawa professor and chairman of ophthalmology, has helped pioneer another non-invasive vision correction technology known as the corneal onlay. These devices are made of mostly liquid, genetically engineered collagen-like material.

Corneal onlays do not require a thin flap, as occurs with inlays, but instead are placed in an artificially created pocket under the outer layer of the cornea (epithelium). This pocket then holds the onlay in place until the disturbed epithelial cells grow back to cover the device.

Jackson told AllAboutVision.com that laser energy ultimately might be applied to the onlay to sculpt it for vision correction, just as the eye's natural surface is now reshaped in LASIK and PRK.

The corneal onlay technology described by Jackson is still in experimental stages.