Corneal Inlays and Corneal Onlays

By Marilyn Haddrill, with updates by Gary Heiting, OD; reviewed by Vance Thompson, MD

Corneal inlays and onlays are made of biocompatible materials inserted into the eye 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.

Corneal inlays or onlays also alter the way light rays enter the eye, much like contact lenses. 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 and PRK because no corneal tissue is removed. And these devices may have fewer risks than implantable lenses because the surgery takes place within the cornea, not inside the eye.

ACI 7000 Corneal Inlay

While the technology is not yet FDA-approved, 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.).

The ACI 7000 is a corneal inlay used for presbyopia correction. (Image provided by AcuFocus of Irvine, Calif.)

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 ACI 7000 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), creates greater 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 more than 18 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 (about 1/10th the width of a piece of paper), and is made of an opaque biocompatible polymer called Kynar, a thermoplastic material that softens in heat and hardens in cooler conditions.

PresbyLens Corneal Inlay

Researchers from Mexico presented early promising results from surgical implantation of the PresbyLens corneal inlay (ReVision Optics, Lake Forest, Calif.) during a 2009 American Society of Cataract and Refractive Surgery (ASCRS) conference.

These tiny (2-mm diameter) inlays are placed under a thin flap or within a pocket to steepen the cornea's shape. The inlays appear to improve near and intermediate vision, as demonstrated by a study involving 38 people who received the PresbyLens implants in their non-dominant eyes:

• All people enrolled in the study ranged in age from 45-56.
• Six months after receiving the implant, most people could perform near vision tasks such as reading a newspaper without the need for eyeglasses.
• Most subjects also did not require eyeglasses for intermediate tasks such as reading a computer screen.
• All study participants had 20/25 or better distance vision in both eyes.
• Only one adverse event was reported, when an inlay needed to be repositioned.

The PresbyLens corneal inlay is placed within the cornea under a LASIK-style flap. When in position, the PresbyLens inlay changes the curvature of the cornea so the front of the eye acts much like a multifocal contact lens. The inlay increases magnification power in the center of the cornea for near vision and allows the paracentral zones of the cornea to be used for intermediate and distance vision.

Flexivue System

The Presbia Flexivue System (Presbia Coöperatief U.A., Amsterdam) uses a laser, which creates a tiny "pocket" just below the eye's surface. Eye surgeons use a specially developed instrument to then insert the micro-lens for correction of presbyopia. The pocket seals itself to hold the lens in place.

The lens is made of hydrophilic polymer, a highly wettable synthetic substance often used in intraocular lenses that permanently replace the eye's natural lens in cataract surgery. However, the Presbia lens is permanent but can be easily removed and replaced if a stronger prescription is needed.

The tiny Presbia lens is 3 mm in diameter and only 20 microns thick at the edges — about a quarter of the width of a human hair.

This lens is being researched outside the U.S.

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.)

Corneal Onlays

W. Bruce Jackson, MD, University of Ottawa professor and chairman of ophthalmology, has helped pioneer another minimally 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.

Other researchers are investigating techniques such as using biocompatible adhesives to attach an onlay temporarily to the outside of the cornea long enough to allow epithelial cells to grow over and secure the implant.

Reversibility is a major advantage of corneal inlays and onlays, which can be removed at any time.

[Page updated October 2009]