Results from a retrospective study suggest that prior ocular surface stem-cell transplantation (OSST) in eyes with cicatrizing disease can reduce the risk for melt-related complications following implantation of the type I Boston keratoprosthesis (Boston KPro), according to Clara C. Chan, MD.

Toronto-Results from a retrospective study suggest that prior ocular surface stem-cell transplantation (OSST) in eyes with cicatrizing disease can reduce the risk for melt-related complications following implantation of the type I Boston keratoprosthesis (Boston KPro), according to Clara C. Chan, MD.

Dr. Chan presented findings from analyses based on data from 2004 to 2010 for 126 eyes of 106 patients that underwent Boston KPro implantation at the Cincinnati Eye Institute, Cincinnati, OH. A total of 44 eyes (35%) had severe ocular surface disease with conjunctival deficiency related to severe chemical injury (26 eyes), Stevens-Johnson syndrome (SJS, 15 eyes), or ocular cicatricial pemphigoid (OCP, three eyes), and 35 (80%) of these 44 eyes had prior OSST.

During a mean follow-up of 25 months, 19 (15%) of the 44 eyes with conjunctival deficiency developed a melt, leak, or extrusion requiring surgical repair. Five (26%) of the 19 eyes had multiple melt episodes, resulting in a total of 28 melt-related complications, reported Dr. Chan, who is now lecturer, department of ophthalmology and vision sciences, University of Toronto, Ontario, and was previously a cornea fellow at Cincinnati Eye Institute.

“Use of the type I Boston KPro as a primary procedure is not ideal in patients with ocular cicatrizing disease whose extreme dryness and chronic inflammation predispose to complications with the device, including melts and extrusion. However, we believe that prior OSST replacing both limbal stem cells and conjunctival stem cells can allow for better outcomes after keratoplasty by providing a more stable ocular surface,” she explained.

“The results of our study seem consistent with that idea considering that our incidence of melts in this high-risk population is lower than in other series of [eyes with the Boston KPro], despite the fact that their cohorts included lower proportions of eyes with conjunctival deficiency.”

At the Cincinnati Eye Institute and the University of Toronto, OSST is the preferred technique for ocular surface reconstruction in young patients who have good health but poor lids and fornix, whereas older patients and those in poor health but with good lids and fornices undergo primary type I Boston KPro surgery. After OSST, patients with residual deeper corneal scarring are candidates for keratoplasty.

“In a study to be published in the journal Cornea, we report the presence of a stable ocular surface with intact corneal epithelium and control of conjunctival inflammation in 77% of eyes that underwent OSST over an average 4.5 years of follow-up. Despite the required systemic immunosuppression, these patients also had few adverse events,” said Dr. Chan.

She added, “The replacement of conjunctival stem cells in addition to limbal stem cells is important in OSST, but at times overlooked. The addition of conjunctival goblet cells that produce mucin helps to maintain a stable tear film and a healthier ocular surface.”

All eyes included in the retrospective study had a minimum follow-up of 3 months and the maximum follow-up duration was 66 months. The 28 melt-related complications included 20 melts, defined as stromal necrosis at high risk for extrusion, five leaks in which there was no stromal necrosis but a positive Seidel test, and three extrusions, defined by a severe melt leading to exposure of the device backplate.

The patients with a melt-related complication had a mean age of 49 years at the time of their Boston KPro surgery and two-thirds were female. Two-thirds had the type I Boston KPro design with the 8.5-mm, 16-hole, PMMA backplate, and they were all receiving prophylactic antimicrobial therapy and wearing a contact lens if able. About half of the eyes had glaucoma, 90% had undergone previous penetrating keratoplasty (PK), and 53% had prior OSST. Twelve (63%) of the 19 eyes had conjunctival deficiency, and this subgroup accounted for four of the five eyes that had multiple melt complications. Other diagnoses among eyes with melt-related complications were immunologic PK failure (four eyes), congenital aniridia (two eyes), and hypotony (one eye).

Analyses were also conducted to identify features associated with melt-related complications. The risk was increased fivefold in eyes with infectious keratitis while conjunctival deficiency, persistent epithelial defect, and contact lens intolerance each increased the risk by threefold. Gender was not a risk factor, and the rate of Boston KPro melts was similar among eyes with and without exposure to systemic immunosuppression.

In the eyes that had melt-related complications, mean follow-up after surgical repair was 11 months. Compared with prior to Boston KPro implantation, vision was stable or improved at last follow-up in 68% of eyes.

“Whereas 84% of the 19 eyes had 20/200 or worse vision prior to the implantation of the type I Boston KPro, vision was between 20/40 and 20/60 in 26% of eyes after melt repair surgery. Our study highlights the importance of close monitoring for complications in eyes with the Boston KPro, particularly in those with conjunctival deficiency, infectious keratitis, persistent epithelial defects, and contact lens intolerance. With timely identification of complications and prompt surgical intervention, vision can often be salvaged,” Dr. Chan said.

Reviewing other studies reporting on melts with the Boston KPro, Dr. Chan noted that Bradley et al. [Cornea 2009;28:321-327] reported a 23.3% incidence in a series of 30 eyes. However, only 13.3% of the population had diagnoses of SJS, chemical injury, or OCP, and none had prior ocular surface stem cell transplantation. Recently, Sejpal et al. [Cornea 2011; Aug 31 Epub ahead of print] reported a melt rate of 17.7% (14 of 79 eyes); 19 (24%) of the 79 eyes had conjunctival deficiency, but only five (26%) had prior OSST.

“In a multicenter study of the Boston KPro by Zerbe et al. [Ophthalmology 2006;113:1779.e1-7] including 141 eyes, 3.5% of eyes developed a melt. However, the mean follow-up time was only 8.5 months, which is not long enough to capture possible cases of melt fully. In our series, melt-related complications occurred, on average, 16 months after KPro implantation,” Dr. Chan said.

Dr. Chan has no financial interest in the subject matter she discussed.

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