Special corneal devices for vision correction

Tuesday, January 19th, 2010 at 2:18 pm Post in Vision Surgery

As a potentially new form of refractive surgery, corneal inlays and onlays are special. Like LASIK and PRK, corneal inlays and onlays alter the way light rays enter the eye. However, they are different from contact lenses, which require regular removal and lens care. Corneal inlays and onlays are permanently inserted into the eye and seamlessly merge with the eye’s surface.

Corneal inlays and onlays are also unlike surgically implanted lenses, which are placed behind the cornea. These devices take place within the cornea and cause lower risks. Like CK, corneal inlays and onlays do not remove any corneal tissue, so that conventional complications aroused by LASIK and PRK can also be eliminated. There are several types of corneal inlays and onlays.

ACI 7000 corneal inlay can correct presbyopia, which involves a prior flap. With the help of anesthesia eye drops, the doctor will then replace the flap with the corneal inlay and stabilize it. ACI 7000 corneal inlay is based on the pinhole phenomenon, which creates greater depth focus. The device also blocks certain light rays reflecting from near objects so that it can provide better near vision. Made of an opaque biocompatible polymer, ACI 7000 inlay is as thin as 10 microns. The material softens in heat and hardens in cool.

Another type of corneal inlays called PresbyLens inlay has also been reported with promising effects. This type of inlay is placed within the cornea under a flap and thus changes the curvature of corneal surface. Acting like a multifocal contact lens, PresbyLens inlay appears to improve both near and intermediate vision. It also provides magnification effects in the center of the cornea. As the name reflects, PresbyLens inlay has been proved to help people perform near vision tasks such as reading newspapers. Participants of a clinical trial can also get 20/25 or better distance vision.

Corneal onlays made of liquid, genetically engineered collagen-like material are also used to correct refractive vision problems. These special devices are placed in an artificial pocket under the outer layer of the cornea, rather than using a flap required by inlays. After the procedure, epithelial cells will gradually grow back to cover the onlay. Researchers also want to use biocompatible adhesives to maintain the onlay before the re-growth of epithelial cells. Corneal onlays are still under clinical trials and they are reversible.