Eyeworld

EW REFRACTIVE 136 March 2018 Presentation spotlight by Stefanie Petrou Binder, MD, EyeWorld Contributing Writer According to A. John Kanel- lopoulos, MD, medical director, LaserVision.gr Institute, Athens, Greece, and clinical professor of ophthalmology, New York Univer- sity Medical School, New York, who performed the experimental surgery, combining xenograft ICRS with CXL achieved significant flattening in this ex vivo model. "We assessed the outcomes with the WaveLight Topolyzer [Alcon, Fort Worth, Tex- as], and noted significant differences in the ex vivo cornea pre- to postop. We saw significant flattening, thus proving the feasibility and efficacy of this ex vivo xenograft implanta- tion," he said. "We have worked extensively in the past with using Intacs [Addition Technology, Lombard, Illinois] in keratoconus patients following the innovative work of the late Joseph Colin, MD. Though our interim re- sults were effective in flattening the cone and dramatically improving visual function, they were limited by interim and late complications relat- ed to corneal stroma melts, segment migration and extrusion, and even severe infections. 1,2 Most of those ICRS were eventually removed. We attributed these severe limitations to the actual material of the ICRS and its biocompatibility in the human cornea, especially in keratoconus pa- tients, and have even proposed that a better material may combine the A novel ex vivo technique makes an interesting case for porcine implants I ntracorneal ring segments (ICRS) were originally proposed for refractive surgical proce- dures as an alternative means to reducing myopia and astigma- tism in patients ill-suited for inter- ventions involving corneal ablation. ICRS are now commonly used to flatten misshapen areas of the cor- nea as well, which has proven to be a beneficial treatment for patients with keratoconus and post-LASIK keratoectasia. These small crescent shaped implants spare the central cornea and enhance the cornea's physiologic, prolate shape. When used for keratoconus, the treatment is generally coupled with corneal crosslinking (CXL), which addresses the core problem of keratoconus by strengthening the inherently weak- ened corneal stroma. Intracorneal ring segments are made out of PMMA, which is a substance that is generally known to be well tolerated in the eye, but is it the best material for intracorneal im- plants? An investigation presented at the XXXV Congress of the ESCRS tested this idea by using gamma irradiated porcine intracorneal ring segments instead of PMMA in an ex vivo setting. Replacing PMMA with porcine intracorneal ring segments Figure 2. Treatment incision planning Figure 1. Placido topography showing significant flattening up to +7.23 D proven benefits with less complica- tions," Dr. Kanellopoulos said. Novel technique Dr. Kanellopoulos used a Barron trephine to generate ring segments from a gamma irradiated porcine cornea, and employing a gamma irradiated acellular porcine cornea on an artificial chamber, he simu- lated ICRS insertion. The WaveLight FS200 femtosecond laser (Alcon) was implemented to create the circular channel into which the ICRS would be placed. Using the precision of the femto laser allowed for the creation of a defined insertion channel, which contributed to avoiding digressions to false pathways within the cornea during ring segment insertion. Using a marker, the inser- tion point was marked manually on the cornea, and the Intacs channel maker was implemented to find the pathway into the femto laser-created channels, making sure the road was open for implantation. The parameters of the corneal channel as created by the WaveLight FS200 were: outer diameter 8 mm, inner diameter 5.5 mm, and depth 500 µm. The platform length was 1.5 mm, platform width was 1.5 mm, and a 0-degree incision posi- tion. The thinnest pachymetry was 750 µm. After dissecting the rings of xenograft tissue to create two intra- corneal ring segments for a total of 310 degrees, Dr. Kanellopoulos was able to implant both rings easily in a similar fashion to Intacs, with the help of a forceps. By inserting the segments parallel to the corneal channel, he could easily lead the xe- nograft segments along the channel. He was able to visualize the porcine ICRS with the operating room slit lamp and noted that they were placed well. "The gamma irradiat- ed porcine cornea was trephinated and cut to create two ring segments made of corneal stroma, not PMMA. We were interested in determining the feasibility of this novel proce- dure," he said. Intracorneal ring segments tar- get flattening of the cornea, howev- er, they do not treat the underlying structural problem in keratoconus eyes, which is weakened collagen. Combining ICRS with corneal cross- linking/riboflavin maximizes the effect on the cornea. A retrospective, non-randomized case series in 12 eyes of nine patients showed that the addition of C3-R to inferior seg- ment Intacs placement resulted in better outcomes than ICRS insertion alone. The authors of the study pro- posed that C3-R not only caused an additive effect but also an enhance- ment of the corneal segments. 3 Following implantation in Dr. Kanellopoulos' study, the ICRS channels were filled with VibeX Xtra 0.25% riboflavin solution (Avedro, Waltham, Massachusetts), which is

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