MAR 2014

EyeWorld is the official news magazine of the American Society of Cataract & Refractive Surgery.

Issue link: https://digital.eyeworld.org/i/276058

Contents of this Issue


Page 90 of 210

E W CORNEA 88 March 2014 The KPro will have a titanium back plate option in addition to the PMMA version A new design of the Boston keratoprosthesis (Boston KPro, Massachusetts Eye and Ear Infirmary, B oston) became widely available early this year. It features a new click-on titanium back plate, which will eliminate the need for a locking ring. Doctors at Massachu- setts Eye and Ear Infirmary, where the KPro is made, have been using a titanium back plate for some time. Kathryn Colby, MD, PhD, Massa- chusetts Eye and Ear Infirmary, Amit Todani, MD, Eye Physicians P.C., Columbus, Neb., and James Chodosh, MD, Massachusetts Eye and Ear Infirmary, spoke about their experience with this technology. Anthony Aldave, MD, professor of ophthalmology, and chief of the cornea service at the Jules Stein Eye Institute, University of California, Los Angeles, said that he currently is not using the titanium back plate but plans to use it when it becomes available for patients who are at an increased risk for retroprosthetic membrane (RPM) formation. Advantages of the titanium version Dr. Colby has been using a titanium back plate for about the last five years that is similar in design to the PMMA version. "It hasn't been available outside of Mass Eye and Ear where we make the Boston KPro," she said. The older back plates, both the PMMA and titanium versions, fea- ture a locking ring that is placed over the stem of the front plate and helps to secure the back plate after it is placed over the corneal tissue. When the new click-on titanium version becomes available generally in ophthalmology, it will not have the locking ring; instead this func- tion will already be incorporated into the back plate. "The main advantage of the tita- nium back plate is it's more tissue friendly," Dr. Colby said. Addition- ally, since it is made from titanium rather than PMMA, this makes it thinner, and it takes up less space in the anterior chamber. Dr. Colby said that it appears so far that there is less RPM formation with the tita- nium compared to the PMMA. She added that the two major differences are the new design is made of tita- nium and is thinner, but otherwise, the design is basically the same. Drs. Todani and Chodosh said there are some biomechanical differ- ences in the properties of the tita- nium and PMMA versions of the KPro. "The first difference is obvi- ously the material used for manufac- turing the back plate—titanium in place of PMMA," they said. "The front plate in both versions of the KPro is still PMMA to allow visuali- zation of the carrier corneal graft and to provide a clear 'optical zone' through the stem of the front plate." Another difference that they cited is the appearance. "While PMMA back plates confer the appearance of a plastic button-like device in the cornea, the titanium back plate imparts a metallic sheen." "Titanium has a proven track record of use as a biomaterial for bi- ological implants such as dental and orthopedic implants," Drs. Todani and Chodosh said. "This is due to its high resistance to corrosion, and its ductility, bioinertness, and strength." "There are now two versions of the Boston type I keratoprosthesis, the click-on version, in which the back plate clicks onto the optic of the front plate, and the snap-on ver- sion, in which the back plate snaps onto the optic and is secured with a locking ring," Dr. Aldave said. "The new click-on version uses an 8.5 mm diameter titanium back plate, and the older snap-on version is supplied with either a 7.0 or 8.5 mm diameter back plate, which is available in both titanium and PMMA." Dr. Aldave noted that the tita- nium back plate is thinner, and it has also been associated with a lower incidence of RPM formation in one study. 1 "However, as this study did not control for factors as- sociated with an increased incidence of RPM formation, another retro- spective study that does control for these potentially confounding vari- ables or a randomized prospective study is needed to determine if the use of a titanium back plate does decrease the risk of RPM formation," he said. Ideal patients for titanium back plate Drs. Todani and Chodosh said that the titanium back plate would be in- dicated for any patient being consid- ered for Boston KPro implantation. "However, the titanium back plate can be associated with a poorer cosmesis, which may be a concern to some recipients," they said. "In general, a standard corneal transplant is the preferred surgical modality for the vast majority of patients with visually debilitating corneal diseases," they said. "Im- plantation of a KPro (whether with PMMA or titanium back plate) should be limited to patients who by Ellen Stodola EyeWorld Staff Writer Boston KPro to use new titanium back plate design T he Boston type 1 keratoprosthesis (KPro) is a device made of polymethyl m ethacrylate (PMMA) and is the most commonly used keratoprosthetic device worldwide.PIt is a useful alternative to pen- etrating keratoplasty for patients presenting with corneal pathologies with a high risk of graft failure and for those with multiple failed grafts.PIn recent years, there have been significant improvements in the KPro design resulting in improved outcomes a fter implantation. Some advancements in the design include the addition of a titanium locking ring (to prevent intraocular disas- sembly of the prosthesis), the addition of 16 holes in the back plate (to allow improved nutrition to the donor corneal stroma), and the evolution from a threaded to a thread- less assembly design (to simplify assem- bly). The most common complication from KPro implantation is retroprosthetic mem- brane formation with rates reported up to 65%.PThus, an adjustment in the KPro design that could decrease this problem would be significant.PThe newest version of the device using a titanium back plate hopes to achieve this. P This month's "Cornea editor's corner of the world" includes discussion of the modified Boston type 1 keratoprosthesis with a titanium back plate. Anthony Aldave, MD, James Chodosh, MD, Kathryn Colby, MD, PhD, and Amit Todani, MD, answer questions about this new KPro design and address its advantages, disad- vantages, and patient selection factors. Clara C. Chan, MD, cornea editor Type I Boston KPro with a titanium back plate in place in a patient with a history of multiple failed corneal transplants Source: Kathryn Colby, MD, PhD continued on page 90 Cornea editor's corner of the world 88-107 Cornea_EW March 2014-DL2_Layout 1 3/6/14 3:46 PM Page 88

Articles in this issue

Archives of this issue

view archives of Eyeworld - MAR 2014