INTRASTROMAL CORNEAL RING TECHNOLOGY

The use of synthetic intracorneal implants for the correction of refra ctive disorders was initially conceptualized by Barraquer in 1949 [1]. In 1966, he summarized the relatively discouraging results of what he termed alloplastic keratophakia [2]. Since that time, new techniques as well as new methods and materials have been designed to adapt the i mplantation of various intrastromal devices for the correction of myop ia, astigmatism, hyperopia, and presbyopia. Among the most promising o f these intrastromal devices are the ICR(R) (Intrastromal Corneal Ring : KeraVision, Inc., Fremont, CA) and the ICRS(TM) (ICR Segments, KeraV ision, Inc.). ICR technology shows great promise as an alternative sur gical approach for the reduction of myopia (Fig 1A,B). The theoretical and practical clinical advantages of this new technique include a num ber of features, outlined below. 1. Surgical preservation of the centr al cornea. The large diameter and peripheral insertion of the ICR is e ffective in correcting myopia without surgically disturbing the centra l optical zone. This has advantages in eliminating the adverse effects of postsurgical corneal haze and surface irregularities. 2. Independe nt of corneal wound healing. Most surgical refractive procedures requi re an incision, reduction, or addition of corneal tissue to achieve a change in refractive effect. These tissue altering procedures wound th e native cornea, resulting in a healing response that may affect the p redictability and stability of the outcome. The ICR is a synthetic, bi ocompatible intracorneal inlay that mechanically flattens the cornea. It involves an approximately 1.8 to 2 mm incision and lamellar channel into which the ICR device is placed; it does not rely on the host's w ound healing mechanisms. 3. Maintenance of corneal asphericity. ICR te chnology acts in part by shortening the are length of tile central cor nea. Central flattening is achieved while maintaining a prolate aspher ic shape. ?This more physiological means of reshaping the corneal curv ature has the theoretical advantage of reducing spherical aberration a nd its untoward effects, such as changes in contrast sensitivity, glar e, and halos. 4. Reversibility of the refractive effect, Since the imp lantation of a synthetic material is unaffected by corneal wound heali ng, the synthetic implant can be easily explanted, potentially allowin g for reversibility of the refractive effect. 5. Adjustability of outc ome. Since an ICR implant can be easily removed, it is possible that a slightly thicker or thinner device could be substituted to allow for titration of the refractive effect. This potential for adjustability w ithout permanent removal or increased incising of corneal tissue would provide surgeons and patients with a flexible refractive surgery alte rnative.