Eyeworld

EW CORNEA 44 October 2011 Early results are similar to epi-off techniques and may be beneficial for older patients as well F or more than a decade, corneal crosslinking has been discussed, described, and used worldwide as a means of treating kerato- conus. In Europe, patients as young as 9 years are undergoing the proce- dure, but it remains under investiga- tion in the United States. The procedure has been shown in vari- ous studies to stop the progression of keratoconus, improve or reduce corneal steepness, and improve best corrected visual acuity. Once thought to be limited to younger pa- tients in whom keratoconus is still developing and progressing, some studies have shown older adults can benefit as well. Corneal crosslinking with ri- boflavin and ultraviolet (UV) light is being performed at roughly 400 cen- ters worldwide, including several in the United States under the CXL- USA Study Group. Preliminary re- sults from one of the study centers were presented earlier this year, with more results expected sometime in the third or fourth quarter, said Roy S. Rubinfeld, M.D., Washington Eye Physicians & Surgeons, Chevy Chase, Md. In the CXL-USA Study, which began in October 2009, sub- jects initially underwent the origi- nal, epithelial-off technique. Jodi Luchs, M.D., F.A.C.S., co- director, Department of Refractive Surgery, North Shore/Long Island Jewish Health System, N.Y., and one of the study investigators, explained that the epi-off technique involves anesthetic drops, epithelial removal, riboflavin drops for 30 minutes (after which the physician checks the cornea for riboflavin saturation), exposure to UV light for 30 minutes, placement of a bandage contact lens, and post-op treatment "similar to PRK," he said. In the most com- mon crosslinking procedures, the UV irradiance is about 3 milliwatts per square centimeter, and the un- corrected visual acuity is between 360 and 370 nanometers, depending on which device is being used. The CXL-USA Study Group is using a medical UV light source used off- label under an Investigational Review Board approval, said Dr. Rubinfeld, who helped design the study. In epi-off, the epithelium is de- brided "so the riboflavin can pene- trate fully through the cornea," he said. "The epithelium was originally thought to be the primary barrier to penetration of the riboflavin into the corneal stroma." Patients undergoing the epi-off procedures are "uncomfortable for the first few days as the epithelial defect is healing," Dr. Luchs said. "I think the pain with epi-off is even a little more intense than the pain from a simple PRK procedure." Other variables may dissuade some potential candidates from the proce- dure as well, he said. In most pub- lished studies, corneal curvature can increase after the epi-off procedures, and vision can worsen for months post-op before improving, he added. "The CXL-USA group postulated that an epi-on procedure might allow faster visual recovery, a much more comfortable procedure, reduce the risk of infection, and reduce the risk of late onset corneal haze," he said. Late haze after crosslinking may occur because "as the cornea starts to heal, the keratocytes start to repopulate and can become acti- vated, resulting in the deposition of non-native collagen," Dr. Luchs said, who added he has never seen late onset haze in any of his crosslinking patients, although haze following epi-off crosslinking has been de- scribed in many peer-reviewed arti- cles. Epi-on crosslinking (or transep- ithelial crosslinking) was originally described by Brian Boxler Wachler, M.D., Beverly Hills, Calif., in 2004, and then by Roberto Pinelli, M.D., in Italy, Drs. Luchs and Rubinfeld said. The main concern with an epi- on procedure is whether or not the surgeon can get enough riboflavin to penetrate the cornea, Dr. Luchs said. "If you can't get enough ri- boflavin, then number one, is it still a safe procedure, since one role of the riboflavin is to absorb some of the UV light? The other issue is if you don't have enough riboflavin, can you have an effective crosslink- ing procedure?" The UV energy en- tering the eye might potentially damage other intraocular structures, he said. One downside to the epi-on procedure is the longer procedure time—anywhere from 30 to 50 min- utes longer primarily to achieve good corneal riboflavin loading, Dr. Luchs said. Epi-on also cannot be combined with other simultaneous procedures involving epithelial de- bridement, such as topo-guided PRK, he said. by Michelle Dalton EyeWorld Contributing Editor Epithelial-on crosslinking shows promise Figure 1. Difference map showing the improvement in corneal shape 6 months after epi-on crosslinking Source: William Trattler, M.D. A slit lamp example of a cornea loaded with riboflavin undergoing the epi-on procedure Source: Roy Rubinfeld, M.D. An example of a patient undergoing an epi-off procedure Source: Roy Rubinfeld, M.D. Riboflavin penetrating throughout the entire corneal stroma (as demonstrated by the flare in the anterior chamber) during an epi-on procedure Source: Jodi Luchs, M.D. 40-45 Cornea_EW October 2011-dl2_Layout 1 9/29/11 3:43 PM Page 44

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