Boston keratoprosthesis - Clinical outcomes with wider geographic use and expanding indications - A systematic review

Dealing With Pericylindrical Melts in Keratoprosthesis: Tenon Patch Graft to the Rescue

PURPOSE

The aim of this study was to describe the outcomes of autologous Tenon patch graft in the management of Auro keratoprosthesis-related pericylindrical corneal melt.

METHODS

We report 3 cases of sterile pericylindrical corneal melt in patients with Auro keratoprosthesis implantation after a mean duration of 5 years (1.5-8 years). Case 1 was a patient with severe graft-versus-host disease. Cases 2 and 3 were cases of chemical injury.All these cases of sterile pericylindrical corneal melt (4-6 mm) underwent autologous Tenon patch graft. The technique included freshening of the edges around the melt, followed by measuring the size of the defect. A Tenon graft harvested from the patient's own eye was used to seal the defect and act as a scaffold. The Tenon patch graft was spread over the melt and held in place by the application of fibrin glue and/or interrupted 10-0 nylon sutures. A bandage contact lens was then placed on the eye.

RESULTS

Tenon patch graft was well taken in all patients. The mean duration of epithelial healing was 1 month. Globe integrity was well maintained with no postoperative complications at a mean follow-up duration of 12 months (6-18 months).

CONCLUSIONS

Corneal melt is one of the most dreaded complications of KPro because its occurrence could threaten visual prognosis and globe integrity. Autologous Tenon patch is a simple yet innovative and effective option to steer such eyes away from potentially dreadful complications.

Incidence, risk factors, and treatment of retroprosthetic membranes following Boston keratoprosthesis eyes and the impact of glaucoma surgery

PURPOSE

To assess incidence, risk factors, and treatment of retroprosthetic membrane (RPM) formation in eyes following Boston keratoprosthesis (Kpro) implantation and their correlation with glaucoma drainage device placement (GDD).

METHODS

A retrospective review was performed on eyes that underwent Kpro type I or II implantation between 2005 and 2020 at a tertiary academic center. Multiple variables were collected including preoperative characteristics, presence of RPM, management of RPM, and outcomes including corrected visual acuity (VA). A Fischer's exact test was used to evaluate the significance of risk factors of RPM formation and an odds ratio was calculated for each possible risk factor. A Mann-Whitney U test was used to evaluate comparisons between outcomes and qualitative analyses.

RESULTS

Of the 87 eyes identified, 37 (43%) developed an RPM within an average of 1.5 years (range, 31 days-7.5 years) following Kpro implantation. Mean follow-up duration was 4.3 years. Eyes that developed RPM had significantly worse preoperative VA compared to those that did not (logMAR 2.55 vs. 2.28, p = 0.022). The mean number of prior penetrating keratoplasty procedures trended higher in eyes that developed RPM (2.46 vs. 2.18, p = 0.44) but was not significant. GDD placement after Kpro implantation was associated with an increased risk of RPM formation (RR = 1.69 p = 0.026). Of the 37 eyes that developed an RPM following Kpro, 17 (47%) were treated with Nd:YAG laser, and four of those 17 (21%) also underwent pars plana vitrectomy (PPV). Seven of 37 eyes (19%) underwent PPV without Nd:YAG. Comparisons between RPM occurrence and final VA were not significant.

CONCLUSIONS

The incidence of RPM formation following Kpro implantation was 43%. Eyes that developed RPM had significantly worse preoperative VA. GDD placement after Kpro implantation increased the risk of developing RPM. Final VA and occurrence of RPM were not significantly different between the Nd:YAG and PPV treatment groups.

Use of PROSE for long-term ocular surface support in patients with a permanent keratoprosthesis

Purpose

To describe the long-term outcome of the use of a specialized scleral lens known as a prosthetic replacement of the ocular surface ecosystem (PROSE) device to support the ocular surface in patients with a Boston Keratoprosthesis (KPro) Type I. All patients in this series were unable to pursue continuous wear of a bandage soft contact lens (BSCL) - a critical aspect of post KPro implantation management intended to protect the corneal carrier tissue from desiccation and stromal melting.

Observations

Four eyes of four patients with a Boston KPro Type I were included. All four had failed BSCL wear and were instead treated with PROSE device wear. All four patients had underlying diagnoses associated with a diseased ocular surface (Stevens-Johnson Syndrome [one patient], prior failed penetrating keratoplasty associated with herpes zoster-related neurotrophic keratopathy [one patient], and prior failed penetrating keratoplasty associated with severe dry eye disease [two patients]). Causes of failure of BSCL wear included poor retention, discomfort, and poor vision. PROSE device wear was initiated on average seven and a half (range four to 14) months post-KPro implantation. The wear schedule varied and ranged from waking-hour wear only to 24-h wear. The average duration of device wear was 59.3 (range 28-103) months. Two patients exhibited persistent corneal epithelial defect formation with waking-hour wear, which resolved within 10 days with 24-h device wear. All patients exhibited improvement in vision with PROSE compared to baseline, averaging six and a half (range six to eight) lines of improvement in Snellen acuity, and all patients reported increased comfort. There was no incidence of microbial keratitis, KPro device instability, or other complication throughout the duration of device wear.

Conclusions and Importance

This report offers a novel alternate approach to long-term support of the ocular surface in patients with a Boston KPro who fail standard continuous BSCL wear.

Review of clinical trials addressing the Boston Keratoprosthesis

OBJECTIVE

The Boston Keratoprosthesis (KPro) has gained recognition as an alternative for patients with severe corneal disease and a poor probability of success with traditional penetrating keratoplasty. This review summarizes the knowledge clinical trials have brought to KPro and discusses ongoing trials.

DESIGN

Systematic review.

METHODS

A literature review across PubMed, Ovid MEDLINE, Cochrane CENTRAL, and ClinicalTrials.gov was performed to identify relevant published clinical trials reporting on the KPro from all years up until September 2021. All published trials were included.

RESULTS

There are 6 published and 6 ongoing clinical trials studying the Boston KPro. The number of patients included per trial ranged from 8 to 37. The average age of patients included per trial ranged from 39 to 62 years. Patients were followed for an average of 36.3 ± 41.8 months. Fifty percent (3 of 6) of KPro clinical trials were randomized. Indication for KPro was reported in 67% of trials (4 of 6), with primary KPro accounting for 22% of unique eyes (13 of 58) and KPro after corneal graft failure accounting for 41% of unique eyes (24 of 58), when reported. Using version 2 of the Cochrane risk-of-bias tool for randomized trials (RoB 2) to assess quality and risk of bias, 50% of trials (3 of 6) had a low risk of bias, 33% (2 of 6) had some bias concerns, and 17% (1 of 6) had a high risk of bias.

CONCLUSIONS

There are few clinical trials published and underway on the Boston KPro, and none directly compare KPro outcomes with repeat corneal transplantation. There is a need for long-term clinical trials on the KPro to provide quality evidence for clinical decision making.

Toward electron-beam sterilization of a pre-assembled Boston keratoprosthesis

PURPOSE

To evaluate the effects of electron-beam (E-beam) irradiation on the human cornea and the potential for E-beam sterilization of Boston keratoprosthesis (BK) devices when pre-assembled with a donor cornea prior to sterilization.

METHODS

Human donor corneas and corneas pre-assembled in BK devices were immersed in recombinant human serum albumin (rHSA) media and E-beam irradiated at 25 kGy. Mechanical (tensile strength and modulus, and compression modulus), chemical, optical, structural, and degradation properties of the corneal tissue after irradiation and after 6 months of preservation were evaluated.

RESULTS

The mechanical evaluation showed that E-beam irradiation enhanced the tensile and compression moduli of human donor corneas, with no impact on their tensile strength. By chemical and mechanical analysis, E-beam irradiation caused a minor degree of crosslinking between collagen fibrils. No ultrastructural changes due to E-beam irradiation were observed. E-beam irradiation slightly increased the stability of the cornea against collagenase-induced degradation and had no impact on glucose diffusion. The optical evaluation showed transparency of the cornea was maintained. E-beam irradiated corneal tissues and BK-cornea pre-assembled devices were stable for 6 months after room-temperature preservation.

CONCLUSIONS

E-beam irradiation generated no detrimental effects on the corneal tissues or BK-cornea pre-assembled devices and improved native properties of the corneal tissue, enabling prolonged preservation at room temperature. The pre-assembly of BK in a donor cornea, followed by E-beam irradiation, offers the potential for an off-the-shelf, ready to implant keratoprosthesis device.

Sputter Deposition of Titanium on Poly(Methyl Methacrylate) Enhances Corneal Biocompatibility

Purpose

To evaluate titanium (Ti) sputtering of the poly(methyl methacrylate) (PMMA) stem of the Boston Keratoprosthesis (BK) as a method to enhance interfacial adhesion between the PMMA and the recipient corneal tissue.

Methods

PMMA specimens were plasma treated with Ar/O₂ and coated with Ti using a DC magnetron sputtering instrument. The topography and hydrophilicity of the surfaces were characterized using atomic force microscopy and a water contact angle instrument, respectively. Scratch hardness and adhesion of the Ti film were measured using a mechanical tester. Biocompatibility assessments were performed using cultured human corneal fibroblasts and whole blood ex vivo. The optical quality of the Ti sputtered BK was evaluated using a custom-made optical bench.

Results

By contact angle studies, the Ti coating improved PMMA hydrophilicity to match that of medical-grade Ti (Ti-6Al-4V-ELI). Ti sputtering of contact surfaces resulted in a plate-like morphology with increased surface roughness, without impacting the transparency of the BK optical component. Scratch testing indicated that the mechanical behavior of the Ti coating was similar to that of casted Ti, and the coating was stable in pull-off adhesion testing. Sputtered Ti film was highly biocompatible based on tests of cell viability, adhesion, proliferation, differentiation, collagen deposition, and keratocan expression, the properties of which exceeded those of uncoated PMMA and did not induce increased complement activation.

Conclusions

Titanium coating of the BK stem generated a mechanically and biologically favorable interface, which may help to enhance corneal stromal adhesion and biocompatibility.

Translational Relevance

Improving the biocompatibility of the BK PMMA stem may improve long-term outcomes of implantation.

Intrinsic Optical Properties of Boston Keratoprosthesis

Purpose

To benchmark the optical performance of Boston Keratoprosthesis (B-KPro).

Methods

Back focal lengths (BFL) of B-KPros for various eye axial lengths were measured using an optical bench, International Organization for Standardization–certified for intraocular lens characterization, and compared against manufacturer's specification. The modulation transfer function (MTF) and the resolution efficiencies were measured. The theoretical geometry-dependent higher-order aberrations (HOA) were calculated. The devices were characterized with optical profilometry for estimating the surface scattering. Aberration correction and subsequent image quality improvement were simulated in CODE-V. Natural scene-imaging was performed in a mock ocular environment. Retrospective analysis of 15 B-KPro recipient eyes were presented to evaluate the possibility of achieving 20/20 best-corrected visual acuity (BCVA).

Results

BFL measurements were in excellent agreement with the manufacturer-reported values (r = 0.999). The MTF specification exceeded what is required for achieving 20/20 visual acuity. Astigmatism and field curvature, correctable in simulations, were the primary aberrations limiting imaging performance. Profilometry of the anterior surface revealed nanoscale roughness (root-mean-square amplitude, 30–50 nm), contributing negligibly to optical scattering. Images of natural scenes obtained with a simulated B-KPro eye demonstrated good central vision, with 10/10 visual acuity (equivalent to 20/20). Full restoration of 20/20 BCVA was obtainable for over 9 years in some patients.

Conclusions

Theoretical and experimental considerations demonstrate that B-KPro has the optical capacity to restore 20/20 BCVA in patients. Further image quality improvement can be anticipated through correction of HOAs.

Translational Relevance

We establish an objective benchmark to characterize the optics of the B-KPro and other keratoprosthesis and propose design changes to allow improved vision in B-KPro patients.

Outcomes and complications of Boston keratoprosthesis type I implantation in unilateral versus bilateral corneal blindness

OBJECTIVE

To compare the outcomes of Boston keratoprosthesis (KPro) type I implantation between patients who are legally blind versus sighted in the contralateral eye.

DESIGN

Single centre retrospective comparative case series.

PARTICIPANTS

Patients who underwent Boston KPro type I implantation between 2008 and 2017.

METHODS

Single-center retrospective comparative case series. Patients were divided into 2 groups based on the preoperative best-corrected visual acuity (BCVA) in the contralateral eye: group I (>20/200) and group II (20/200).

MAIN OUTCOME MEASURES

Postoperative BCVA, device retention, and complications.

RESULTS

Group I (56 eyes) and group II (53 eyes) had similar demographics, median preoperative BCVA (hand movements) in the operated eye, and median duration of postoperative follow-up (76.92 vs 85.6 months, respectively). Final postoperative BCVA of the operated eye was statistically better in group I compared with group II (20/400 and hand movements, respectively, p = 0.03). There was no statistical significance in device retention mean survival time. The most common complication in both groups was retroprosthetic membrane. Cystoid macular edema occurred more frequently in group I (p = 0.004), whereas retinal detachment was more common in group II (p = 0.052).

CONCLUSIONS

Most patients who underwent Boston KPro type I implantation experienced an improvement in their vision, with final BCVA being superior in the unilateral blind group. Despite similar complication rates and device retention, there are additional socioeconomic factors that need to be considered in sighted individuals. Because the prognosis is tied to the underlying etiology, it is important to recognize that some diagnoses may influence a better outcome.

Systematic Review and Meta-Analysis of the Medium- and Long-Term Outcomes of the Boston Type 1 Keratoprosthesis

PURPOSE

The Boston type 1 keratoprosthesis (KPro), used in patients with high risk of corneal graft failure, is increasingly being used. However, the medium- to long-term outcomes are currently unclear. We analyzed the medium- (2-5 years) and long-term (>5 years) efficacy and safety of the Boston type 1 KPro in terms of visual outcomes, device retention, and postoperative complications.

METHODS

We last searched electronic databases (Ovid MEDLINE, Ovid MEDLINE In-Process and Other Non-Indexed Citations, Ovid MEDLINE Daily, Ovid MEDLINE Epub Ahead of Print, EMBASE, and CENTRAL) on March 31, 2018. Visual outcomes and device retention at 2 and 5 years, alongside postoperative complications, were primary outcome measures.

RESULTS

We identified 407 articles. Thirty studies were included in this systematic review and meta-analysis. The combined proportion of eyes with ≥6/60 vision was 62% at 2 years and 51% at 5 years. The combined retention rate was 88% at 2 years and 74% at 5 years. Retroprosthetic membrane (36.6%) and glaucoma (39.3%) were found to be the most common long-term complications. Very few studies showed visual outcomes or retention rates at 5 years, with results sparse and collectively not meaningful because of small patient numbers and ambiguous reporting of follow-up times.

CONCLUSIONS

The 2-year results indicate that there is a place for the Boston type 1 KPro in the management of corneal blindness. However, there is scarce evidence regarding its medium- and long-term efficacy and safety. The high rate of reported complications necessitates strict patient selection and stringent follow-up.

[Boston keratoprosthesis: 73 eyes from Germany : An overview of experiences from two centers]

BACKGROUND

The Boston Keratoprosthesis (B-KPro) is a therapeutic option for corneal replacement for visual rehabilitation in eyes with poor a prognosis for penetrating keratoplasty (high-risk eyes). Since 2009, this approach has been used in the MVZ Prof. Neuhann, Munich, and since 2013 also at the Department of Ophthalmology, University of Cologne. An overview of results from the first 73 eyes in these departments is presented.

METHODS

All recipient eyes of both centers which received a B-KPro type I (BI-KPro) between November 2009 and March 2017 were included. Indications, preoperative findings, intraoperative procedures, and clinical results, as well as postoperative complication and retention rates were documented and analyzed.

RESULTS

A total of 73 eyes from 68 patients (mean age 55 ± 21.1 years, range 7 months-93 years; 26 women, 42 men) were treated with a BI-KPro. In 53 eyes (72.6%) the BI-KPro was implanted due to corneal graft failure, whereas BI-KPro was used as the primary corneal replacement in 20 eyes (27.4%). In 46 eyes (63.0%) a long-term increase in visual acuity was achieved and in 21.9% visual acuity was stabilized, while a decrease in preoperative visual acuity occurred in 15.1% of cases. During an average follow-up of 24.7 ± 23.0 months (range 1-78 months), 1.7 ± 2.4 re-interventions (range 0-9) were required. Only 4 keratoprostheses (5.5%) could not be retained. In 3 eyes (4.2%), a change of the BI-KPro device was necessary.

CONCLUSION

There is a wide range of indications for BI-KPro in eyes with a poor prognosis for conventional keratoplasty. The surgical technique is safe but with a notable postoperative complication rate, which does not seem to decrease in the medium or long term. The retention rate is excellent for eyes without stem cell deficiency. Nevertheless, the BI-KPro is the only therapeutic option for high-risk eyes and leads to a gain in visual acuity in most cases.

Boston keratoprosthesis type 1: outcomes of the first 38 cases performed at Moorfields Eye Hospital

PURPOSE

To evaluate outcomes of Boston keratoprosthesis type 1 (K-Pro) surgery in a cohort of high-risk patients at Moorfields Eye Hospital. Our patients were referred to us at the end-point of their ocular disease.

METHODS

A retrospective review of all K-Pro surgery performed between March 2011 and July 2015 with a minimum follow-up of 12 months.

RESULTS

39 eyes of 38 patients were included. Mean follow-up was 28.4 months (range: 12-56). The main indication for surgery was bullous keratopathy from multiple failed grafts (56%). 26 cases (72.2%) had known posterior segment disease pre-operatively. Mean BCVA for the entire cohort (n = 39) initially improved from HM vision to 1/60 before returning to CF vision by 6 months and was maintained for the duration of follow-up. By final follow-up (n = 39), 46% had improved vision (1 line improvement in 10%; 2 lines or more in 36%) and 31% maintained pre-operative visual acuity. Anterior segment pathology was not an independent variable in visual outcome. However, absence of posterior segment disease was significant and performed best, improving from HM to 6/15 and maintaining that vision in the longer term. There were 13 (33%) cases of progressive glaucomatous optic neuropathy, 10 (26%) retinal detachments, 8 (21%) retroprosthetic membranes, 3 (8%) infective keratitis and 2 (5%) vitritis of which 1 progressed to endophthalmitis. In all, 3 (8%) had NPL vision and 4 (10%) required removal of the K-Pro.

CONCLUSIONS

Implantation of the Boston K-Pro can lead to improved vision, with the main limiting factor being posterior segment pathology.

[Boston-keratoprosthesis : Preliminary experiences in 13 high-risk eyes from the Department of Ophthalmology of the University of Cologne]

BACKGROUND

Corneal transplantation in high-risk eyes remains a challenge. The Boston keratoprosthesis (B-KPro) is a final option for patients with end-stage corneal disease and a poor prognosis with conventional penetrating keratoplasty. In this article the results of the first 13 eyes that received a B-KPro type I at the Department of Ophthalmology, University of Cologne, Germany are reported and the usefulness of postoperative slit-lamp optical coherence tomography (SL-OCT) for control purposes is evaluated.

MATERIAL AND METHODS

All recipients of a B-KPro type I between September 2013 and May 2015 were included in the study. The feasibility of the operation, clinical outcomes, complications and revision surgery were investigated. The visualization of wound healing by SL-OCT was analyzed.

RESULTS

The age of the patients ranged from 26 to 92 years (mean 57.3 ± 20.9 years). In all 13 eyes from 12 patients (6 males and 6 females) dense corneal opacification with vascularization and sometimes also conjunctivalization was present. Preoperative visual acuity was reduced and ranged from mere light perception up to a maximum of 1/35 eye chart. All 13 eyes could be supplied with a B-KPro type I without any intraoperative complications, in 6 eyes no significant postoperative complications occurred, whereas in 7 eyes various additional surgical interventions were required and 1 B-KPro could not be preserved. Postoperative visual acuity ranged from light perception to 20/32 and was significantly improved in 85 % of the treated eyes. The use of SL-OCT reproducibly allowed the postoperative assessment of stromal thinning.

CONCLUSION

The B-KPro provides the possibility of visual rehabilitation in high-risk eyes that could never be achieved without artificial cornea replacement. Despite higher complication rates this technique represents a significant progress in the surgical treatment of complex corneal pathologies. Regular and intensive postoperative controls are necessary to achieve good long-term results.

Corneal blindness and current major treatment concern-graft scarcity

According to World Health Organization, the global prevalence of blindness in 2010 was 39 million people, among which 4% were due to corneal opacities. Often, the sole resort for visual restoration of patients with damaged corneas is corneal transplantation. However, despite rapid developments of surgical techniques, instrumentations and immunosuppressive agents, corneal blindness remains a prevalent global health issue. This is largely due to the scarcity of good quality corneal grafts. In this review, the causes of corneal blindness, its major treatment options, and the major contributory factors of corneal graft scarcity with potential solutions are discussed.

The Ocular Surface and How It Can Influence the Outcomes of Keratoprosthesis

Severe ocular diseases may result in partial or complete limbal cell deficiency. Besides conservative options, treatment options include conjunctival replacement procedures and limbal autografting. Limbal allografts are an option in patients with bilateral limbal cell deficiency. In many of these cases, a keratoprosthesis (KPro) is the last option to restore functional vision in patients with severe corneal blindness with no other options.

Progress in Corneal Stromal Repair: From Tissue Grafts and Biomaterials to Modular Supramolecular Tissue-Like Assemblies

Corneal injuries and degenerative conditions have major socioeconomic consequences, given that in most cases, they result in blindness. In the quest of the ideal therapy, tissue grafts, biomaterials, and modular engineering approaches are under intense investigation. Herein, advancements and shortfalls are reviewed and future perspectives for these therapeutic strategies discussed.