Eyeworld

45 EW FEATURE January 2019 • Crosslinking reach the minimum thickness. It is instilled at 5- to 10-second intervals until the corneal thickness increases to at least 400 microns. "We allow patients to close their eyes between Photrexa drops to facilitate this thickening," he said. Dr. Rajpal added that the theory behind contact lens assisted cross- linking is that either a UV blocking lens or a contact lens that has been saturated with riboflavin can act as a barrier and reduce the effective dose of UV reaching the stroma. "While it's an interesting thought, it is not a controlled method of reducing total UV energy dose, and a reduced dose may impact treatment efficacy," he said. "This has not been studied in randomized, sham controlled clinical trials." The FDA-approved approach, in which the cornea is thickened to the desired minimum thickness of 400 microns using Photrexa, has been validated as a safe and effective way to treat these thinner corneas, he added. Dr. Randleman said that 400 microns is not an arbitrary cut-off. "It was derived through extensive in vitro testing decades ago," he said. "It is likely a bit conservative of a recommendation, but that adds a layer of safety to the procedure." Most corneas can be swollen to above 400 microns, he said, but crosslinking loses some efficacy if corneas are swollen too much at the time of treatment. Adding a contact lens is not an approved technique in the U.S. but is likely a safe approach, Dr. Randleman added. "We are current- ly evaluating the potential impact of this in the laboratory, and the tech- nique appears similar in crosslinking effect." EW Reference 1. Gokul A, et al. The natural history of corneal topographic progression of keratoconus after age 30 years in non-contact lens wearers. Br J Ophthalmol. 2017;101:839–844. Editors' note: Dr. Rajpal has financial interests with Avedro. Dr. Randleman has no financial interests related to his comments. Contact information Rajpal: rrajpal@seeclearly.com Randleman: randlema@usc.edu however, progression can occur at any age. "A recent study evaluating patients over the age of 30 demon- strated that while most eyes showed little progression, up to 37% of sub- jects showed at least 1 D of progres- sion in topographic parameters in at least one eye over the study period," he said. 1 Progression in younger patients is expected, he added, and they are followed at more frequent intervals. Crosslinking is recommended as soon as indicated. "In older pa- tients, we are more critical in our assessment of progression, but we never assume that a patient is no longer at risk for progression, and we continue to pay close attention to symptoms, signs, and risk factors throughout the patient's lifetime," he said. Keratoconus vs. post-LASIK ectasia "When both entities are in the progressive phase, I do not differen- tiate between them," Dr. Randleman said. "If postoperative ectasia has occurred many years prior with no new progression, I still discuss the potential for crosslinking but do not necessarily perform the treatment." Dr. Rajpal said that in both keratoconus and ectasia following refractive surgery, the treatment goal is to slow or stop progression. "On average, patients with keratoconus tend to show more flattening after crosslinking than patients with refractive surgery ectasia, how- ever, crosslinking treatment has been demonstrated to be safe and effective in both groups," he said. "In patients with ectasia following refractive surgery, the treatment pro- tocol is the same as for those with keratoconus. The only difference is that in the ectasia cases, we take care during the epithelial removal step to avoid dislocation of the flap." Corneal thickness and CXL Dr. Rajpal said that the FDA-ap- proved protocol requires corneal thickness of 400 microns prior to initiation of the UV light. "This thickness is measured after the Pho- trexa Viscous formulation [Avedro] has been applied and riboflavin flare has been visualized in the anterior chamber," he said. If the cornea is below this threshold, Photrexa is used to thicken the cornea to I N S T R U M E N T S | S I N G L E U S E | D R Y E Y E | B I O L O G I C S Look to Stephens For sterile tissue allografts. Stephens Instruments | 2500 Sandersville Rd | Lexington KY 40511 USA Toll Free ( USA ) 800.354.7848 | info@stephensinst.com | stephensinst.com © 2018 Stephens Instruments. All rights reserved. Distributed exclusively through Stephens Instruments Learn more at halograft.org Stephens Instruments is the exclusive distributor of Halo implant patch grafts. Packaged in our patented easy-peel packaging system for rapid introduction on to the sterile field, halo tissues require no rinsing or reconstitution. Halo sterile tissues are high-quality and backed by the superior service that Stephens is known for. Stephens – more than instruments. SCLERA CORNEA PERICARDIUM

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