Corneal inlays are less invasive, optically reversible, adjustable

Speaking during Refractive Surgery 2012 at the annual meeting of the American Academy of Ophthalmology, Dr Gatinel reviewed the various types of corneal inlays and the advantages and disadvantages of using inlays compared with other techniques to provide patients with presbyopia with an increased range of uncorrected vision.

"Corneal inlays may be an option for [patients with] presbyopia with good corrected distance and near visual acuity and a healthy, adequately thick cornea," revealed Dr Gatinel, head and assistant professor of ophthalmology, Rothschild Foundation, Paris, France. "They are precise and effective, with studies showing improved near visual acuity and reduced spectacle dependence and, compared with some other presbyopia-correcting options, they are less invasive, optically reversible and adjustable."

The first design comes in the form of a small-aperture inlay that works through a pinhole principle to increase depth of focus (Kamra, AcuFocus, IRvine, California, USA).

The small-aperture inlay is made of polyvinylidene fluoride. It is the thinnest (5 μm) of the three options and also the most widely used to date. Implanted into the nondominant eye under a LASIK-type flap or in a pocket, the small-aperture inlay increases depth of field on both sides of the plane of best focus, Dr Gatinel explained.

"Unlike monovision, there is minimal reduction in distance vision in the... nondominant eye [with the implant], stereopsis is preserved, and patients may also benefit with improved intermediate vision," he said. "The presbyopia-correcting effect of the small-aperture inlay is also stable over time."

To obtain optimal distance and near vision, the best candidates for the small-aperture inlay are patients who are slightly myopic (–0.75 D). However, the procedure can also be performed in combination with LASIK using a thick (200 μm) flap or as a two-step procedure with thin-flap LASIK followed by pocket inlay implantation for the correction of presbyopia in patients with ametropia. Patients with a history of LASIK who have developed presbyopia may also be eligible for the inlay through pocket creation performed at least 100 μm under the previous interface.

"Dry eye can be a problem initially in patients having combined LASIK with the inlay, but it tends to recover over time," Dr Gatinel noted.

The second design is a refractive inlay that creates a multifocal cornea (Flexivue, Presbia, Irvine, California, USA).

The refractive inlay is made of a hydrophilic acrylic polymer, has an overall diameter of 3.2 mm and maximum thickness of 15 μm. It comes in different powers (+1.25 to +3.50 D) so that the correction is customized to the patient's presbyopic status and it can be placed under a flap or into a pocket at a depth of 300 μm.

Lastly, the third option is a thin hydrogel polymer inlay that changes corneal contour and also creates a central multifocal cornea (Raindrop, ReVision Optics, Lake Forest, California, USA).

The hydrogel implant has the same refractive index as the cornea. It has the smallest diametre of all of the inlays (2 mm) and a maximum thickness of 32 μm. In order to change the central corneal curvature to provide the nondominant eye with near vision, it is implanted at a relatively shallow depth of about 150 μm.

Other techniques

Discussing other techniques for presbyopia correction, Dr Gatinel claimed that IOL-based procedures are more invasive than the inlay procedures and their outcomes depend on accurate IOL power calculation. In addition, multifocal IOLs are accompanied by quality-of-vision issues and the efficacy of accommodative IOLs remains to be proven, he concluded.

Corneal-based laser procedures to correct presbyopia are very empirical, while intrastromal incision suffers from imprecision and increases higher-order aberrations, thereby reducing visual quality.