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Corneal inlays a potential alternative for presbyopic treatment
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Corneal refractive surgeries and IOL implantation have revolutionized the treatment of refractive errors in the past 2 decades. The last hurdle for refractive surgeons is presbyopia, which is unavoidable in every individual after the age of 40 years.
Numerous methods for the treatment of presbyopia have been tried over the years, and a few of them are now in active use. Unfortunately, none of them are perfect or close to perfect. Monovision, by LASIK or IOL, is one of the most common surgical ways to tackle presbyopia. It requires the use of both eyes simultaneously but with a different focus in each, one at distance and the other at near. This surgically induced anisometropia, although effective, not uncommonly causes neuroadaptation problems, especially in the elderly. A multifocal IOL offers multiple focuses at different distances in a single eye, but the image quality is frequently compromised, not to mention the possible presence of glare and halos. IOL exchange is sometimes required. An accommodating IOL has the theoretical advantages of mimicking the human lens in changing focuses, but the amount of accommodation created is usually limited. The durability of this movement remains to be evaluated, and its effect is less prominent in highly myopic eyes.
Corneal inlays have recently shown some good progress in treating presbyopia. The idea of implanting a lens into the cornea dates back to 1949, when José Barraquer attempted to implant a lens made of flint glass intrastromally. Since then, a number of different materials and designs were tried but failed, either due to excessive tissue reaction or disrupted nutrition supply to the cornea, causing thinning, melting or scarring. This technology has re-emerged in the last decade because of the discovery of the optimal depth for implantation combined with the precise technology (femtosecond laser) in creating a corneal flap or pocket at this optimal depth. This has significantly reduced the chance of complications and made the procedure more reversible.
There are three types of corneal inlay available at this time. The Kamra (AcuFocus) employs the pinhole effect with a central 1.6-mm aperture surrounded by an outer non-transparent ring. The pinhole effect increases the depth of field and hence improves near vision. The Flexivue Microlens (Presbia) is a 3.2-mm diameter lens with a central neutral power zone for distance and a peripheral positive power zone for near. The Vue+ (Revision Optics), or PresbyLens in the U.S., is a 2-mm hydrogel inlay with a convex shape. It increases the curvature of the central cornea and hence adds plus power to it. All of the inlays can be combined with laser refractive surgery, such as LASIK, to correct ametropia simultaneously.
While corneal inlays have many advantages and are a potentially reversible procedure, each one has its own limitations and potential complications. The most frequent drawback of corneal inlays is the reduction of distance vision in the implanted eye. Therefore, it is usually the nondominant eye that is recommended for the implant. Also, dry eyes and corneal haze may be potential problems.
Overall, the latest development in corneal inlays offers a new option to people who are presbyopic. Current evidence and experience suggest that the optimal age for implantation is between 45 years and 65 years. The procedure may be combined with laser refractive surgeries, if the patient is ametropic, or cataract surgery, if cataract is significant. Although potentially reversible, the inlay is recommended for the nondominant eye only because it may compromise distance vision. While the results of the latest versions of corneal inlays appear encouraging, more studies are warranted to show the safety and efficacy of these new devices before they can become the procedure of choice for treating presbyopia.
References:
Bouzoukis DI, Kymionis GD, Limnopoulou AN, Kounis GA, Pallikaris IG. Femtosecond laser-assisted corneal pocket creation using a mask for inlay implantation. J Refract Surg. 2011;27(11):818-820.
Seyeddain O, Riha W, Hohensinn M, Nix G, Dexl AK, Grabner G. Refractive surgical correction of presbyopia with the AcuFocus small aperture corneal inlay: two-year follow-up. J Refract Surg. 2010;26(10):707-715.
Tomita M, Kanamori T, Waring GO 4th, et al. Simultaneous corneal inlay implantation and laser in situ keratomileusis for presbyopia in patients with hyperopia, myopia, or emmetropia: six-month results. J Cataract Refract Surg. 2012;38(3):495-506.
For more information:
Dennis S.C. Lam, MD, FRCOphth, can be reached at Hong Kong Eye Hospital, The Chinese University of Hong Kong, 3/F, 14K Argyle Street, Kowloon, Hong Kong, SAR, China; +852-2762-3157; fax: +852-2715-9490; email: dennislam8@cuhk.edu.hk.
Disclosure: Lam and Fan have no relevant financial disclosures.