EyeWorld is the official news magazine of the American Society of Cataract & Refractive Surgery.
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EW CORNEA 34 November 2014 by Ellen Stodola EyeWorld Staff Writer Using contact lens-assisted crosslinking (CACXL) This new technique is useful in patients with thin corneas A lthough not yet approved in the U.S., corneal crosslinking is used internationally and is getting a lot of attention. A new technique, contact lens-as- sisted crosslinking (CACXL), could extend the benefits of crosslinking to even more patients by allowing those with decreased corneal stromal thickness to become eligible for the procedure. CACXL presents cross- linking as an option to those who have a corneal stromal thickness of less than 400 μm after epithelial removal; this is the traditional cutoff for patients in order to avoid poten- tial endothelial toxicity from the UV radiation. Soosan Jacob, MS, FRCS, DNB, senior consultant ophthal- mologist, Dr. Agarwal's Eye Hospital, Chennai, India, discussed this new type of crosslinking and her experience with it. The process of CACXL "CACXL or contact lens-assisted crosslinking is a new technique that I described for crosslinking patients with thinner corneas who are not amenable to crosslinking by the standard technique," Dr. Jacob said. The technique helps increase the functional corneal thickness by placing a UV barrier free soft contact lens that has been soaked in ribofla- vin onto the cornea. "This is used to decrease UV irradiance to safe levels at the level of the endothelium." The idea Dr. Jacob said that these thin corneas were often a challenge in pa- tients with progressive keratoconus. "The very thin/ectatic ones would undergo a deep anterior lamellar keratoplasty (DALK) with excellent results, and the moderately advanced patients having a minimum corne- al thickness of more than 400 μm (after epithelial debridement) would undergo crosslinking," she said. However, there was still a group of patients who did not quite fit into either group because they were not advanced enough for DALK, but the corneas were not thick enough to safely undergo standard crosslinking. Hypotonic CXL is an excellent technique, Dr. Jacob said, and there are other epithelium-on techniques as well. However, she wanted to make the procedure easier and less dependent on the swelling proper- ties of the cornea, which can have large inter-individual variations. Another goal was to be able to retain the advantages that epi-off CXL provides, Dr. Jacob said. "This made me start thinking of possible alternate routes to increase the functional corneal thickness, and a soft contact lens seemed to be a good way to do this," she said. How it differs Dr. Jacob said that CACXL is similar to normal crosslinking. "After re- moving the central 9 mm of corneal epithelium, iso-osmolar riboflavin 0.1% is applied every 3 minutes for 30 minutes," she said. "At the same time, a SofLens daily disposable soft contact lens [Bausch + Lomb, Bridgewater, N.J.] made of hilafilcon without UV filter and of negligible power is immersed in isotonic riboflavin for 30 minutes." After 30 minutes, the appearance of a green flare in the anterior chamber using a slit lamp will confirm adequate corneal saturation with the riboflavin. The riboflavin-soaked contact lens is then applied on the corneal surface, and thickness is measured again, Dr. Jacob said. If it is more than 400 μm, treatment can be continued. "During UV application, riboflavin solution is generally reap- plied once in 3 minutes," she said. T he prevalence of keratoconus is estimated to be 1 in 500 to 1 in 2,000, making it the most common corneal dystrophy in the U.S. The concept behind corneal collagen crosslinking (CXL) came about during the 1990s when researchers noted that diabetic patients rarely developed keratoconus because of a glycosylation- mediated process that naturally strengthened the stromal tissue. Their goal was to induce a similar effect in non- diabetic corneas utilizing sugars activated by ultraviolet light. International trials in the 2000s showed stabilization of keratoconus after CXL performed using a standard technique of epithelium removal, application of riboflavin drops to the cornea until the stroma was fully saturated, followed by ultraviolet-A light illumination, whereby bonds forming across adjacent corneal stromal collagen fibers would strengthen the cornea. While the procedure is awaiting FDA approval in the U.S., there are many patients being treated in various U.S. clinical trials, and our international colleagues have a great deal to share from their experiences. This month's "Cornea editor's corner of the world" focuses on a new CXL technique that could be used to treat thin corneas that would otherwise be excluded from standard CXL techniques. Soosan Jacob, MS, FRCS, DNB, discusses the details of contact lens-assisted CXL and patient selection. Clara C. Chan, MD, FRCSC, FACS, cornea editor Cornea editor's corner of the world "Any buckling of the contact lens is handled by reapplying sufficient riboflavin solution under and above the contact lens when required, allowing it to spread uniformly and encouraging the patient not to move his eyes or squeeze his lids." Ribofla- vin that is applied over the contact lens will fill any persistent troughs on the surface of the lens and will provide a uniform layer over the lens. The pre-contact lens riboflavin film corresponds to the pre-corneal film described by Wollensak et al in standard crosslinking. "At the end of surgery, the eye is washed and a fresh bandage contact lens is applied until corneal epithelial healing," Dr. Jacob said. The postoperative regimen is similar to standard crosslinking. If mini- mum pachymetry of 400 μm is not attained after application of the soft contact lens, an additional small amount of swelling may be required, which can be easily attained by combining the principles of CACXL and hypo-osmolar CXL. A few drops of distilled water is generally sufficient to quickly and rapidly take the pachymetry above 400 μm without the need for any other special solutions. "It is preferable to use formula- tions containing riboflavin in HPMC [VibeX Rapid, Avedro, Waltham, Mass.] to avoid the intraoperative dehydration that occurs with dextran-based solutions," Dr. Jacob said. "I also prefer doing accelerated CACXL with moderate intensity UV barrier free soft contact lens soaked in riboflavin Source: Soosan Jacob, MS, FRCS, DNB continued on page 37