M. Soledad Cortina

Retroprosthetic Membrane and Risk of Sterile Keratolysis in Patients With Type I Boston Keratoprosthesis

PURPOSE To evaluate whether retro-backplate retroprosthetic membrane is correlated with risk of melt in patients with a type I Boston Keratoprosthesis (KPro). DESIGN Retrospective, observational case series. METHODS Study of 50 eyes of 47 patients with type I Boston KPro and postoperative anterior segment optical coherence tomography (AS OCT) imaging performed at the University of Illinois at Chicago. Main outcome measures were presence of retro-backplate membrane and development of melt requiring explantation. For eyes with melt, membrane thickness was measured using the AS OCT images obtained at the last visit before melt occurred. For eyes without melt, the last available AS OCT images were used for measurement. RESULTS AS OCT evidence of a retro-backplate membrane was observed in 100% of eyes that melted and in 34.1% of eyes that did not (P = .0034; risk ratio, 2.9; 95% confidence interval, 1.9 to 4.4). Retro-backplate membrane thickness in the melt group was 278 μm versus 193 μm in the nonmelt group (P = .025). CONCLUSIONS The retro-backplate portion of a retroprosthetic membrane is to be differentiated from the retro-optic portion seen at the slit lamp. The retro-backplate membrane as shown by AS OCT imaging is correlated with an increased risk of sterile keratolysis, possibly because of impedance of nutritional support from the aqueous humor. Further studies are needed to better standardize the AS OCT measurements of retro-backplate membranes as well as to identify early interventions to prevent progression of thin membranes once identified on AS OCT.

Boston type I keratoprosthesis for visual rehabilitation in a patient with gelatinous drop-like corneal dystrophy.

Purpose: To report the use of a Boston type I keratoprosthesis as a primary penetrating procedure to treat gelatinous drop-like corneal dystrophy (GDLD), with presentation of pathologic findings and discussion of other surgical options. Case Report: A 49-year-old woman with GDLD in both eyes and history of recurrent corneal opacification following multiple superficial keratectomies is presented. Best corrected visual acuity (BCVA) was counting fingers in both eyes. A Boston type I keratoprosthesis was implanted in her left eye after optical iridectomy, extracapsular cataract extraction, and anterior vitrectomy. Results: The surgery was uneventful and one month after surgery, best corrected vision improved to 20/20 and has been maintained for a period of more than 14 months. No post-operative complications were observed. Histopathology of the corneal specimen is presented. Conclusions: GDLD is a rare disorder of amyloid deposition. Recurrence of this condition following surgery is extremely common. Boston type I keratoprosthesis is an effective procedure for restoring vision in affected patients.

Scanning Electron Microscopic Analysis of Biofilm Formation in Explanted Human Boston Type I Keratoprostheses

Purpose: To describe the morphological distribution of host tissue and microbial biofilms on the intraocular surfaces of Boston type I keratoprostheses (KPros) explanted because of corneal melt. Methods: Retrospective study of scanning electron microscopy (SEM) images from 4 explanted Boston type I KPros composed of polymethylmethacrylate and titanium. SEM images of KPro-associated ocular surfaces were reviewed for the presence of inflammatory cells, microbes, and/or biofilm formation. One sterile type I KPro was also imaged to serve as a (device only) control. Results: All 4 KPros were explanted because of culture-negative, clinically “sterile” donor corneal melt with impending KPro extrusion. In all cases, the rough, irregular surfaces of the device harbored more adherent corneal epithelium and stromacytes, inflammatory cells, and bacteria than the smooth, polished surface of the KPro optic. Two KPros showed not only evidence of prior bacterial colonization but marked biofilm formation. Conclusions: SEM images of explanted KPros explanted for “sterile” corneal melt demonstrated evidence of biofilm formation despite negative donor corneal cultures and the absence of clinical suspicion for infection. These results suggest that “sterile” corneal melt may be due to inflammatory host responses to low microbial burdens as seen in biofilms and/or released antigens after antibiotic-induced lysis. There was increased adherence of host tissue cells and microbial biofilms on the nonpolished surfaces of the KPro. Polishing the intraocular polymethylmethacrylate and titanium KPro surfaces may decrease microbial adhesion and biofilm formation in human subjects with KPros, but what impact this will have on rates of postoperative endophthalmitis is unknown.

Retroprosthetic membrane formation in Boston keratoprosthesis: A case-control-matched comparison of titanium versus PMMA backplate

Purpose: Retroprosthetic membrane (RPM) formation is the most common complication after Boston type 1 keratoprosthesis (KPro) implantation. It affects visual acuity and can predispose to corneal melt. Two KPro backplate materials are available: titanium and polymethyl methacrylate (PMMA). This study investigates the influence of the KPro backplate material on visually significant RPM formation. Methods: A retrospective case–control-matched study involving 40 patients; 20 eyes implanted with a titanium backplate KPro were case-matched with 20 eyes implanted with a PMMA backplate KPro between 2007 and 2015 with 1-year minimum follow-up. Results: The mean follow-up duration was 28.1 ± 8.9 and 53.6 ± 24.3 months in the titanium and PMMA groups, respectively. At 12 months postoperatively, 7 eyes with titanium and 6 eyes with PMMA backplates developed a visually significant RPM. By the end of the study, a total of 11 eyes with titanium and 9 eyes with PMMA KPros developed a visually significant RPM. There was no statistically significant difference between both groups. Three of 11 eyes with titanium KPros that had a visually significant RPM required surgical membranectomy, whereas all eyes with PMMA KPros were successfully treated with the yttrium-aluminum-garnet laser. Recurrence of RPMs was found in 7/11 eyes in the titanium group and 2/9 eyes in the PMMA group with no statistical significance. Conclusions: Titanium backplate KPros do not significantly reduce RPM formation compared with PMMA backplate KPros in a case–control-matched setting. A larger prospective study is warranted to evaluate comparative long-term performance and guide newer designs.

Abnormal Optic Nerves in a Healthy Young Woman

A woman in her 30s was referred for evaluation of bilateral papilledema. She had no specific chief complaint other than intermittent floaters. A review of systems as well as her medical, family, and social history were unremarkable. She was not taking any medications and did not have any allergies. Best-corrected visual acuity was measured 20/25 OD and 20/20 OS. Extraocular movements were intact and pupils were round and reactive with no afferent pupillary defect. Intraocular pressure by applanation was 18 mm Hg OU. Her anterior segment examination was within normal limits. Examination of her fundus revealed the optic nerves seen in Figure 1. The remainder of her posterior segment was unremarkable. Right eye A Left eye B

History of the Artificial Cornea

The concept of an artificial cornea for transplantation predates work with corneal tissue transplants. Guillaume Pellier de Quengsy described the first known design for a keratoprosthesis in 1789. In his original paper, he asks the question, “would it not be possible to implant an artificial cornea instead of the natural one when one is certain that the loss of vision comes from the opacity of this tunic? This will be easy to verify. Here is the operation one could attempt… Use a clear, thin piece of glass…convex outside, with the diameter of the cornea, place it inside a small circle of silver… Around the exterior circle, have a groove made proportional to the thickness of the natural cornea so that the sclera can exactly adapt to it by secreting new juices….”

Boston KPro Type I: Complications

As with any new surgical procedure, the description of the related complications and its management constitutes a very relevant section. We have had the opportunity to include the expertise of a group of excellent international expert surgeons, who used to manage such a group of difficult situations.

The Use of Boston Keratoprosthesis in Severe Ocular Surface Disease

The Boston keratoprosthesis (KPro) is an alternative to traditional corneal transplantation in eyes that have had multiple graft failures or have a poor prognosis for graft survival due to the presence of significant corneal neovascularization or limbal stem cell deficiency. Briefly, the device is a collar button design composed of an optical front plate with a stem and backplate that is secured with a titanium locking ring or clicks into place within a groove in the stem. The central optic is made of PMMA and is unaffected by conjunctivalization or failure of the donor cornea. Also, as the front plate provides a spherical anterior curvature, there is no significant astigmatism as seen in traditional keratoplasty. The carrier corneal graft is sandwiched between the front and backplates and secured to the patient’s cornea with interrupted nylon sutures. The backplate is made from either polymethyl methacrylate (PMMA) or titanium and contains holes that allow aqueous to provide nutrition to and hydration of the corneal graft. A bandage contact lens is usually used continuously to protect the ocular surface and reduce evaporative forces. The type I KPro is more commonly implanted; the type II KPro is utilized only in end-stage dry eye conditions and requires a permanent tarsorrhaphy through which an anterior nub protrudes. The KPro is available in pseudophakic and aphakic models customized for the eye’s axial length (Dohlman et al. Expert Rev Ophthalmol 1:41–48, 2006; Dohlman et al. CLAO J 28(2):72-4, 2002). The following cases highlight the challenges of using KPro in patients with severe ocular surface disease and likewise illustrate strategies that can potentially improve the outcomes and reduce the risk of complications.

Innovative Approaches to Glaucoma Management of Boston Keratoprosthesis Type 1

Purpose of ReviewGlaucoma remains a prevalent disorder and visual limiting factor after Boston keratoprosthesis type 1 implantation. In addition, there are no standard guidelines for glaucoma surveillance and monitoring after keratoprosthesis surgery. This report provides a review of the current literature and offers innovative strategies that will overcome the challenges in managing glaucoma in the setting of a Boston keratoprosthesis type 1 implant.Recent FindingsPatients with glaucoma have worse initial and late visual acuity outcomes after otherwise successful keratoprosthesis implantation. Management of glaucoma in the setting of a keratoprosthesis is challenging because of relatively rapid progression and an inability to accurately measure intraocular pressure (IOP). The topics that will be discussed in this section include alternative methods for IOP measurement, rationales and surgical techniques for a pars plana tube placement for glaucoma drainage device, effective medical and laser treatments, the risk for IOP elevations after YAG laser, and practical guides to glaucoma surveillance and monitoring.SummaryManagement of glaucoma in Boston type 1 keratoprosthesis remains a challenge. In eyes with preexisting glaucoma, glaucoma drainage device before or at the time of keratoprosthesis should be performed. Most importantly, early detection and prompt treatment of IOP elevations and glaucoma progression is required to prevent poor visual outcomes.

Imaging of Boston Keratoprosthesis Type 1

Boston keratoprosthesis is an important surgical alternative for visual rehabilitation in patients with end-stage corneal or ocular surface disease. However, due to potential postoperative complications including inflammation, infection, and scarring, frequent examination and monitoring are required. Clinical examination techniques such as slit lamp biomicroscopy and gonioscopy provide limited observation of the anterior segment and angle anatomy. Recent advances in imaging techniques including ultrasound biomicroscopy and optical coherence tomography (anterior segment, optic nerve head, macula) are valuable and noninvasive tools that provide detailed visualization of ocular anatomy and augment current clinical examination methods. Thus, evaluation and monitoring of postoperative complications such as infection, corneal melt, retroprosthetic membrane formation, glaucoma, and macular edema may be improved. Furthermore, these imaging modalities may play an important role in evaluating and improving current device design and surgical technique as further details of KPro-anterior segment dynamics become better understood.