Corneal inlays show promise for presbyopia

COS 2012, July 4 - Corneal inlays are at the core of a relatively new technology that has been in development for over 50 years, but has only shown promise for helping patients with presbyopia in the past decade. Developments have surged ahead, to the point where some have been approved in Europe and others are now in clinical trials.

Dr. Bruce Jackson, professor of ophthalmology at the University of Ottawa, provided an overview of where inlays now stand. "We have newer materials, smaller size, fenestrations, how to really address the hydration and nutrition issue much better, and we also have new tools for implanting these inlays... The real appeal is the fact that these are removable and reversible," he said.

Inlay technologies use three approaches. One is changing the corneal curvature by using an inlay with the same refractive index as the cornea. An inlay in development, which does this, is the PresbyLens (or Vue+) by ReVision Optics, Inc.

Inlays that change corneal power by using a refractive lens within the cornea include Flexivue Microlens by Presbia and the InVue lens (Icolens) originally by Biovision and now produced by Neoptics AG. There are also exciting developments with small aperature optics designed to increase depth of field in the KAMRA by AcuFocus Inc.

The PresbyLens is made of a microporous hydrogel 2 mm in diameter that can be implanted under a 150 µm LASIK flap. It improves near and intermediate vision in the non-dominant eye. Two clinical trials conducted in Mexico look promising, he said. In the United States, phase 1 and 2 trials were completed, and a phase 3 trial of 300 patients is beginning.

The Flexivue Microlens is a 3-mm diameter hydrophilic polymer bifocal lens, and has a central 1.6-mm plano zone surrounded by an annulus of increasing refractive power. It is put into an intracorneal pocket by a femtosecond laser. This lens is less effective for distance vision when compared with classic monovision. It, too, is currently being tested in early human trials.

The Icolens is a 3-mm, 20-µm thick hydrophilic acrylic disc with a central plano power zone of 1.8 mm, with an annulus of up to three D in the periphery. A 0.15-mm diameter hole in the centre facilitates the passage of nutrients and oxygen. Early results from trials in Europe have found that patients with these two implants had a mean gain of 3.4 lines of uncorrected near visual acuity, 72% lost one or more lines of uncorrected distance visual acuity, and there was no change in binocular distance visual acuity.

The KAMRA inlay has been most widely used, with an estimated 11,000 having been implanted worldwide. It has a 3.8-mm diameter with a 1.6-mm central aperture, and is made of a polyvinylidene fluoride with nanoparticles of carbon. It can be implanted in a pocket during or after LASIK is performed under the flap.

Decentration has been one of the most serious stated complications with inlays, Jackson stated. There have been reports of a few patients with a decrease of one to two lines of UDVA, and a mild transient hyperopic shift. There have also been some near vision problems with low-light glare and halo and flap-related problems. "There seems to be no compromise in contrast sensitivity or stereopsis, and no biocompatability issues at this point," he said.

In general, inlays for presbyopia will "offer improved near and intermediate vision with only a slight loss of uncorrected distance visual acuity," Jackson noted, adding that it's important to select patients carefully. There are compromises with using corneal inlays, as only one eye is treated. On the other hand, the procedure is minimally invasive.