Eyeworld

31 EW CORNEA April 2015 by Matt Young EyeWorld Contributing Writer For example, "implantation in a cheek or lower lid to allow bio-in- tegration of connective tissue into the apron or tooth," would occur first, he said. Then placement of the cylinder into a patient's own cornea and coverage of the apron (or tooth) with buccal mucosa would occur. "What's the ideal skirt? It has to be soft, chemically inert, you don't want corneal melt, you don't want to start the rejection process with collagenase, it has to integrate and it has to be able to be autoclaved," he said. "The oral mucosa [that] is employed to cover the colonized skirt is the best because it is more vascularized and has a faster cellular turnover than skin, conjunctiva, and other tissues." It also serves as a barrier to micro-organisms. Non-integrated types typically are 1-stage procedures. AlphaCor (developed by Argus Biomedical, Australia) is an integrat- ed keratoprosthesis that involves lamellar dissection. "The retention rate is only about 62% because we get leaks, etc.," he said. Meanwhile, the osteo-odonto- keratoprosthesis [OOKP] procedure is very difficult, he said. "You use the patient's tooth and the dentine for the integration," he said. "It has to be buried for about 3 months. The retention rate is better than the AlphaCor at 85%, although you do get complications. The upside is that it is good for thin corneas; the downside is that it is very complex." The Boston KPro is the most popular type, he said. This non-in- tegrated approach could be used for both adults and infants, and there is a version for dry eyes. One version even can be used after herpes zoster and aniridia. In children, the Boston KPro has worked after repeated PK rejections, and it is excellent in children with no prior surgery. EW Editors' note: Drs. Maskati and Schultz have no financial interests related to their comments. Contact information Maskati: qureshmaskati@hotmail.com Schultz: geraldschultzmd@aol.com corneal conditions. We have about 10 million people in the world blind from corneal scars alone." Many of those blind are in countries with few or no eye banks for cadaver corneas, he said. In- tegrated keratoprostheses are the alternatives, he said. There are several types of kerato- prosthesis that can be classified by location, he said. The epi-corneal type sits on top of the cornea. With the intrastromal type, you make a lamellar dissection. The collar stud is a full penetration keratoprosthesis, as is the nut and bolt type. The collar stud type is "probably the most popular now, where you use a host cornea," Dr. Schultz said. "You could use the patient's cornea —take it off and sew it back. But typically we use a cornea ordinarily rejected by an eye bank that is not good for visual purposes. But it is a good platform for this type of implant." Keratoprosthesis can be fur- ther classified into integrated and non-integrated varieties. "Integrated allows bio-integra- tion of connective tissue and vessels into the supporting haptic (skirt) to reduce risk of melts and extrusions," Dr. Schultz said. Fabric typically includes Dacron or nylon bound to an optical cylin- der and alloplastic, such as a tooth, bone, or cartilage. It requires remov- al of the lens and iris, and usually is a 2-stage procedure. Alternatively, he said, some patients are properly indicated for the Pintucci KPro/MOOKP. "Bilaterally blind patients with at least accurate perception of light in one eye," are good candidates. "A B-scan showing an attached retina, no deep cupping of glaucoma [is important as well]." There are a number of contrain- dications for all keratoprostheses. "Unless the patient is able to follow up, it's a waste," he said. "The amount of effort that goes into doing a keratoprosthesis would be worthwhile only if patients can follow up with you or with some- one you trust, who will give you an accurate report. It's not difficult with digital photography. Otherwise, you will lose the patient to infections or inflammation." If patients are unable to under- stand the importance of compliance to their treatment regimen, that would be a reason to avoid kerato- prosthesis implantation. Understanding the variations Gerald R. Schultz, MD, FACS, associate clinic professor, Loma Linda University Medical Center, Loma Linda, Calif., agreed that keratoprosthesis could be a first choice therapy in select cases. "At one time it was thought to be the last resort for patients with corneal opacification after they had numerous penetrating keratoplas- ties," Dr. Schultz said. "But now, it can be the first choice for some Boston KPro still favored globally, after keratoplasty N ever do a keratoprosthe- sis—that is, unless you have reason to doubt standard keratoplasty. "Keratoplasty is always ideal, except in children in select cases," said Quresh B. Maskati, MS, DOMS, FCPS, FICS, Mumbai, India. "Whenever you feel you can do a keratoplasty and get away with it [do that]." When to use a keratoprosthesis now That said, there are a number of situations in which keratoprosthe- sis would be a first-line treatment option. "Any opaque cornea with vas- cularization and stem cell deficiency where you can't do a real graft" would be an indication for the Bos- ton KPro (also called the Dohlman- Doane, developed at Massachusetts Eye and Ear Infirmary, Boston), Dr. Maskati said. Any vascularized, failed graft would be another indica- tion, he said. An eye with good visual po- tential—no glaucoma, a normal posterior segment, and the anterior segment not severely disfigured— would also be appropriate for the Boston KPro, he said. Good tear secretion and good lid blink and apposition are indications the device could be used. "If you have these criteria, there's a 90% or greater chance that the person will achieve excellent vision with the Boston KPro," said Dr. Maskati, who noted this has become a keratoprosthesis of choice internationally. "It's in the most unlikely coun- tries like Cambodia and Vietnam, also in India for the last 5 to 6 years," Dr. Maskati said. "So should every opaque cornea be offered a KPro? No. Corneal transplant gives excellent results in the majority of cases. In infectious keratitis, only a natural cornea will save the eye. You can't use an artificial cornea there." Eyes with poor tear secretion, keratinized corneas, those with pre- vious corneal melts, and eyes with poor lid blinks and mal-opposed lids are poor candidates for the Boston KPro. The right keratoprosthesis now Pintucci keratoprosthesis Source: Quresh B. Maskati, MS

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