Source: DGNews  |  Posted 2 years ago

By Fred Gebhart

SAN FRANCISCO -- October 27, 2009 -- A new wave of interest in corneal inlays,
each made of different material, having a different mechanism of action to
correct presbyopia, and distinctive in size, were discussed at the 2009 Joint
Meeting of the American Academy of Ophthalmology and the Pan-American
Association of Ophthalmology (AAO-PAAO).

Growing concerns about quality of life issues among aging baby boomers have
helped rekindle interest in corneal inlays for the treatment of presbyopia. The
current generation of inlays offers the same advantages considered important
more than a decade ago, when inlays were being developed to treat myopia and
hyperopia. They remain removable, reversible, and repeatable, unlike more
familiar corneal subtraction procedures such as laser-assisted in situ
keratomileusis (LASIK) and photorefractive keratectomy (PRK).

Several corneal inlays are undergoing clinical trials, noted Francisco Sanchez
Leon, MD, Instituto Novo Vision, Mexico City, Mexico, in his October 23
presentation “Clinical Performance of Clinical Inlays.” Current entrants
include AcuFocus, InVue, and PresbyLens. None are approved for marketing in the
United States, and all are implanted in the nondominant eye, but they have few
other similarities.

The AcuFocus corneal inlay (AcuFocus, Irvine, California) is 2.8 mm in diameter
and 5 microns thick and has a 1.6-mm pinhole in the centre. The opaque inlay is
designed to function like a camera lens with a small aperture that increases
depth of field. In bright light, the pinhole effect enhances visual acuity, Dr.
Leon explained; whereas, in dim light, the pupil dilates well beyond the opaque
ring, allowing adequate light to enter from the sides while preserving central
visual acuity. It is implanted either in a corneal pocket or under a flap.
Micropores 5-11 microns in diameter aid corneal circulation and transport.

The device was originally made to be placed under a corneal flap created by
either a microkeratome or femtosecond laser, Dr. Leon continued, but he
recommended implantation in a pocket. A pocket can be carved into the middle
stroma, deeper than a flap placement. Placing the inlay deeper alleviates
concerns about anterior nutrition and neutrophic corneal disease. A pocket also
holds the inlay more securely because there is little room for movement or
slippage.

InVue (BioVision AG, Bruggs, Switzerland) is a water-permeable hydrogel lens 3
mm in diameter and 10 microns thick at the edge. Centre thickness depends on
the add power of the lens in an annular ring surrounding a central clear area.
The lens transforms an emmetropic cornea into a multifocal cornea. The central
area is for reading, the peripheral zone for distance, and the mid-periphery
for middle distance tasks. A multifocal cornea tends to provide significantly
improved reading ability but at the cost of a slight decrease in contrast
sensitivity, which degrades distance vision, Dr. Leon explained. Like other
multifocal optics, a multifocal cornea can induce night-vision symptoms,
particularly haloes.

The PresbyLens corneal inlay (ReVision, Lake Forest, California) is a polymer
lens 1.5 mm in diameter. The lens is similar to a soft contact lens but sits
beneath a corneal flap. Placing the lens just beneath the corneal surface
changes the corneal topography and optical profile to create a multifocal
system to enhance near vision while leaving distance vision almost unchanged.

“This is an additive effect,” explained Stephen Slade, MD, Laser Center of
Houston, Humble, Texas, in his presentation entitled “A Study of the Efficacy
of the PresbyLens Corneal Inlay.” “It just adds to the central area of the
cornea.”

Dr. Leon noted that the manufacturer is developing a pocket placement technique.

Presentation title: Refractive Surgery Section V: Introstromal Implants
for Refractive Surgery. Friday, October 23, 2009