Corneal inlay improves near vision by increasing depth of focus

April 1, 2008

Clinical trials are under way evaluating a corneal inlay (AcuFocus ACI 7000, AcuFocus) for the treatment of presbyopia. An ophthalmologist summarizes the features of the inlay, its mechanism for improving near vision, and promising safety and efficacy results.

Key Points

New Orleans-Available results from foreign studies investigating an ultrathin, annular intracorneal lens (AcuFocus ACI 7000, AcuFocus) indicate that the lens is an effective treatment for presbyopia, said Jack T. Holladay, MD, MSEE, at Refractive Surgery subspecialty day during the annual meeting of the American Academy of Ophthalmology.

"Increasing depth of focus with this inlay gives about 2.5 to 3 D of added power, and results from patients who have been treated with this method show they achieve good near vision and retain good distance vision," said Dr. Holladay, clinical professor of ophthalmology, Baylor College of Medicine, Houston.

"So far, no explantations have been performed for reasons related to the material, although certain design elements, including inlay thickness and number of fenestrations, are still being refined to optimize the outcomes and biocompatibility," he said. "Nevertheless, the initial clinical experience is promising in suggesting this inlay may offer one of the best techniques for correcting presbyopia."

The inlay is constructed of a biocompatible, opaque polymer (PVDF), measures 10 μm thick (in its most widely investigated iteration), has an outer diameter of 3.8-mm, an inner diameter of 1.6-mm, and contains about 1800 20-μm, randomly distributed fenestrations in the material to allow passage of nutrients and fluid through the cornea. Although it appears opaque, the implant is minimally visible, and it does not interfere with ophthalmologic examinations of the cornea, chamber angle, or macula.

Explaining the principle for this technology, Dr. Holladay noted that it is intended for use in patients who are near emmetropia and have good distance vision. The pinhole effect is provided in photopic and mesopic conditions and increases depth of focus by reducing the circle of blur. When the pupil is smaller than the outer diameter of the inlay, peripheral rays are obscured from entering the eye by the polymer material while the central rays pass through the center opening.

"Night vision is not impeded because under scotopic conditions, the pupil dilates enough so that light rays enter the eye from around the inlay," Dr. Holladay said.

He demonstrated how the pinhole effect improves depth of focus by showing his "backyard experiment" in which he lined up a series of eye charts at different distances from a camera at a fixed location and then adjusted the camera focus and F stop. With the camera focused at about 12.5 feet and the F stop set at 3.3, simulating a pupil diameter of about 6-mm, only one target was clearly legible. While the focus was kept constant but the F stop was changed to simulate a 4.5-mm pupil, three targets were legible. Setting the camera F stop to 22, which is equivalent to a 1.6-mm pupil (the aperture of the inlay), the number of legible targets increased to 12.

Turkish ophthalmologist Faruk Yilmez, MD, has undertaken the first clinical study of the inlay, and he now has 39 patients with more than 1.5 years of follow-up. The patients have a mean age of 52 years and preoperative mean distance uncorrected visual acuity (UCVA) of 20/20 and mean near UCVA of 20/50. At 12 months, the patients have a mean distance UCVA of 20/20 and near uncorrected vision of J1+ (20/16), Dr. Holladay reported.

Results are similar in a multicenter European study. As reported by investigator Gunther Grabner, MD, Salzburg, Austria, 70 patients have had the inlay implanted to date, 36 patients have been seen at 9 months, and the longest follow-up is 14 months.

"There is some edema after the procedure, and it can take 3 to 6 months for that to clear and before patients reach maximum uncorrected vision. There have been a few inlays explanted because of the edema or some irregularity," Dr. Holladay said.

Initial experience with a 5-μm implant indicates the thinner inlay improves topography outcomes. In the European trial, a few implants needed to be re-centered, but those procedures were performed successfully.