Corneal inlay uses pinhole effect

April 1, 2010

An intracorneal inlay for the treatment of presbyopia uses the pinhole effect to increase depth of focus by selecting for the central light ray and minimizing refraction.

This intracorneal inlay currently is in FDA clinical trials for the treatment of near-plano and plano presbyopia. Initial studies outside the United States combining the inlay with other refractive procedures to treat ametropia and presbyopia have been promising. A major advantage of this technology is that the inlay is removable.

Although the inlay is implanted unilaterally, it does not create a monovisual state. The eye with the implant remains emmetropic so both eyes work together at distance, and the lack of image magnification prevents aniseikonia. Examination and imaging of ocular structures are not affected by the inlay, and visual field testing of subjects with the inlay implanted show thresholds remaining within preoperative values.

Implanting the inlay

The inlay is implanted into a femtosecond laser-enabled pocket at a depth of 210 µm, centered on the line of sight of the patient's non-dominant eye. This target depth is deep enough to prevent topographic changes and shallow enough to minimize light scatter and maximize visual recovery.

The pocket provides a number of distinct advantages. First, the majority of peripheral corneal nerves are preserved, which allows for maintained corneal sensitivity.

The transient dryness that can be observed after lamellar corneal refractive surgery is minimized with pockets. Pocket procedures also preserve the peripheral biomechanical properties of the cornea, which, like the anterior stroma, provide a majority of the biomechanical stability. Lastly, striae are not a concern because a lamellar flap is not created.

A combined LASIK and KAMRA procedure is gaining popularity outside the United States for the simultaneous treatment of ametropia and presbyopia. In this "SIM-LASIK" procedure, the inlay is placed under a 200-µm LASIK flap after an excimer ablation. This procedure allows surgeons to set the postoperative refractive target, thereby optimizing a patient's refractive status and outcomes.

Regulatory status and results

Enrollment in the current FDA Investigational Device Exemption clinical study was completed recently, and clinical trials are underway to fulfill requirements for FDA approval. To date, safety and efficacy results have been excellent.

Conclusion

The intracorneal inlay represents a new paradigm in the treatment of presbyopia. By utilizing the pinhole concept, this seemingly simple yet high-tech device selects for non-bent rays of light, which provides one of the broadest depths of focus of any of the known treatments for presbyopia. Future applications may include implantation in patients with pseudophakia and post-laser vision correction emmetropia

George O. Waring IV, MD is a clinical assistant professor, Emory University School of Medicine, Atlanta, and is the world surgical monitor for AcuFocus.