Periprosthetic Tissue Loss in Patients With Idiopathic Vitreous Inflammation After the Boston Keratoprosthesis

Design and Biocompatibility of a Novel, Flexible Artificial Cornea

Purpose

We sought to introduce the materials, design, and biocompatibility of a flexible and suturable artificial corneal device.

Methods

Single-piece, fully synthetic, optic-skirt design devices were made from compact perfluoroalkoxy alkane. The skirt and the optic wall surfaces were lined with a porous tissue ingrowth material using expanded polytetrafluoroethylene. Full-thickness macroapertures around the skirt perimeter were placed to facilitate nutrition of the recipient cornea. Material properties including the skirt's modulus of elasticity and bending stiffness, optic light transmission, wetting behavior, topical drug penetrance, and degradation profile were evaluated.

Results

The final prototype suitable for human use has a transparent optic with a diameter of 4.60 mm anteriorly, 4.28 mm posteriorly, and a skirt outer diameter of 6.8 mm. The biomechanical and optical properties of the device closely align with the native human cornea with an average normalized device skirt-bending stiffness of 4.7 kPa·mm4 and light transmission in the visible spectrum ranging between 92% and 96%. No optical damage was seen in the 36 devices tested in fouling experiments. No significant difference was observed in topical drug penetrance into the anterior chamber of the device implanted eye compared with the naïve rabbit eye.

Conclusions

The flexibility and biocompatibility of our artificial cornea device may offer enhanced tissue integration and decreased inflammation, leading to improved retention compared with rigid keratoprosthesis designs.

Translational Relevance

We have developed a fully synthetic, flexible, suturable, optic-skirt design prototype artificial cornea that is ready to be tested in early human feasibility studies.

Twelve-Month Clinical and Histopathological Performance of a Novel Synthetic Cornea Device in Rabbit Model

Purpose

To report the biological stability and postoperative outcomes of a second-generation, single-piece, flexible synthetic cornea in a rabbit model.

Methods

Device materials and design were amended to enhance biointegration. Optic skirt design devices were made from compact perfluoroalkoxy alkane with porous expanded polytetrafluoroethylene ingrowth surface overlying the skirt and optic wall. Sixteen devices were implanted into intrastromal pocket in rabbit eyes. Rabbits were randomly assigned to 6- and 12-month follow-up cohorts (n = 8 in each) postoperatively. Monthly examinations and optical coherence tomography assessed cornea-device integration, iridocorneal angle, optic nerve, and retina.

Results

There were no intraoperative complications. All devices were in situ at exit, with clear optics. No retroprosthetic membrane, glaucoma, cataract formation, or retinal detachment was observed. Two rabbits in the 6-month group had mild, focal anterior lamella thinning without retraction adjacent to the optic near tight sutures. Three postoperative complications occurred in the 12-month group. One rabbit diagnosed with endophthalmitis was euthanized on day 228. Mild sterile focal retraction of anterior lamella occurred in two rabbits, which were terminated on days 225 and 315. Light microscopic examination of enucleated globes demonstrated fibroplasia with new collagen deposition into the porous scaffold without significant inflammation, encapsulation, or granuloma formation.

Conclusions

Clinical evaluations, imaging, and histopathological findings indicate favorable outcomes of this synthetic corneal device in a rabbit model. Early feasibility studies in humans are being planned.

Translational Relevance

Favorable 12-month results of the device in rabbits demonstrate vision-restoring potential in corneally blind individuals at high risk of failure with donor keratoplasty.

The Boston Keratoprosthesis-The First 50 Years: Some Reminiscences

Millions of people worldwide are bilaterally blind due to corneal diseases including infectious etiologies, trauma, and chemical injuries. While corneal transplantation can successfully restore sight in many, corneal graft survival decreases in eyes with chronic inflammation and corneal vascularization. Additionally, the availability of donor cornea material can be limited, especially in underdeveloped countries where corneal blindness may also be highly prevalent. Development of methods to create and implant an artificial cornea (keratoprosthesis)may be the only option for patients whose eye disease is not suitable for corneal transplantation or who live in regions where corneal transplantation is not possible. The Boston keratoprosthesis (B-KPro) is the most commonly implanted keratoprosthesis worldwide, having restored vision in thousands of patients. This article describes the initial design of the B-KPro and the modifications that have been made over many years. Additionally, some of the complications of surgical implantation and long-term care challenges, particularly complicating inflammation and glaucoma, are discussed. Expected final online publication date for the Annual Review of Vision Science, Volume 8 is September 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Clinical Experience in Patients with Ocular Burns Treated with Boston Type I Keratoprosthesis Implantation with or Without Prophylactic Ahmed Glaucoma Valve Implantation

Introduction

To compare outcomes in eyes with ocular burns following Boston Type I keratoprosthesis (KPro) implantation with and without prophylactic pars plana tube surgery.

Methods

A retrospective review of patients with ocular burns who underwent KPro surgery at Zhongshan Ophthalmic Center was performed. Twenty-six eyes of 26 patients without a preoperative diagnosis of glaucoma before KPro surgery met the inclusion criteria. Preoperative glaucoma was defined as a history of a durable elevated intraocular pressure (IOP) ≥ 25 mmHg at different time points, which resulted in the introduction of anti-glaucoma medication or surgical intervention. Sixteen eyes underwent KPro alone (Group 1), and 10 eyes received KPro with prophylactic pars plana tube surgery (Group 2).

Results

Group 1 and Group 2 were similar in the proportions of the ocular burn type and preoperative clock hours of peripheral anterior synechiae by ultrasound biomicroscopy (1.88 ± 1.63 vs. 2.30 ± 1.83; P = 0.54). Before KPro surgery, 62.5% of eyes in Group 1 and 50.0% of eyes in Group 2 had intraocular surgeries (P = 0.53). The follow-up time was 18 months. At the final follow-up time, the two groups had similar visual acuity (1.34 ± 0.87 logMAR, 1.03 ± 0.71 logMAR; P = 0.35) and eyes with a C/D ratio ≥ 0.8 (7/16, 2/10; P = 0.21), but more eyes in Group 1 developed glaucoma de novo than eyes in Group 2 (62.5%, 20%; P = 0.04) and had undergone secondary glaucoma surgery after KPro implantation (7/16 vs. 0/10; P = 0.02).

Conclusion

In eyes injured with ocular burns, KPro implantation with prophylactic pars plana tube surgery may be a feasible option to rehabilitate visual acuity and decrease the incidence of glaucoma de novo.

Infectious Keratitis After Boston Type 1 Keratoprosthesis Implantation

PURPOSE

To identify the incidence, risk factors, and outcomes of infectious keratitis after Boston type 1 keratoprosthesis (kpro) implantation.

METHODS

Retrospective case series of kpro procedures at the Stein Eye Institute and the Centre Hospitalier de l'Université de Montréal between May 1, 2004, and December 31, 2018. Data were collected regarding ocular history, operative details, postoperative management, microbiologic profile, treatment, and outcomes. Log-rank test and Cox proportional hazard ratio (HR) were used to evaluate for an association between risk factors and outcomes.

RESULTS

A total of 349 kpro procedures were performed in 295 eyes of 268 patients. Fifty-seven cases of presumed infectious keratitis were identified after 53 procedures (15.2%) in 50 eyes (16.9%) of 49 patients (18.3%). The incidences of culture-positive bacterial and fungal keratitis were 0.014 and 0.004 per eye-year, respectively. Persistent corneal epithelial defect formation (P < 0.001) and cicatricial disease (HR: 1.98, 95% confidence interval, 1.02-3.83) were associated with a significantly higher incidence of infectious keratitis. For the 53 cases with a known outcome, medical therapy achieved resolution of infection in 34 cases (64.2%), whereas kpro explantation was required in 19 cases (35.8%). Infectious keratitis was associated with an increased risk for kpro explantation (HR: 3.09, 95% confidence interval, 1.92-4.79).

CONCLUSIONS

Infectious keratitis develops in approximately 17% of eyes after kpro implantation, with a higher rate of culture-positive bacterial than fungal keratitis. The observed rate of microbial keratitis suggests the need for additional topical antimicrobial prophylaxis in eyes at higher risk, such as those with preexisting cicatricial disease or postoperative persistent corneal epithelial defect formation.

[Treatment of vascularized high-risk eyes with a Boston keratoprosthesis]

BACKGROUND

In severely compromised and vascularized high-risk eyes, the Boston keratoprosthesis procedure is often the last treatment option. The transparency of the optics is not impaired by endothelial immune reactions.

METHODS

This review article discusses relevant literature as well as our own data and experiences with the Boston keratoprosthesis in high-risk eyes. The relevant complications as well as the postoperative management are discussed.

RESULTS

In more than 60% of the high-risk eyes a long-term increase in visual acuity can be achieved. Keratoprosthesis retention rates show a variable span with reported mean 5‑year retention rates of 75%. The most common postoperative complications include the formation of a retroprosthetic membrane and keratolysis in up to 50% each. More than 70% of the eyes already suffer from (secondary) glaucoma preoperatively, so that glaucoma surgery is performed simultaneously in at least 20% of cases and in the postoperative course further antiglaucomatous surgery is necessary in up to 31%. Vitreoretinal complications include, in particular, sterile vitritis and infectious endophthalmitis but persistent hypotonia is also described in one third of patients.

CONCLUSION

The Boston keratoprosthesis is an alternative to conventional corneal replacement if the prognosis for allogeneic transplants is poor. Postoperative complications are common; therefore, postoperative management plays an important role. For vascularized high-risk eyes, however, it is often the only remaining option for visual rehabilitation.

Keratoprosthesis: Current global scenario and a broad Indian perspective

Keratoprosthesis (Kpro) forms the last resort for bilateral end-stage corneal blindness. The Boston Type 1 and 2 Kpros, the modified osteo-odonto Kpro and the osteo-Kpro are the more frequently and commonly performed Kpros, and this review attempts to compile the current data available on these Kpros worldwide from large single-center studies and compare the indications and outcomes with Kpros in the Indian scenario. Although the indications have significantly expanded over the years and the complications have reduced with modifications in design and postoperative regimen, these are procedures that require an exclusive setup, and a commitment toward long-term follow-up and post-Kpro care. The last decade has seen a surge in the number of Kpro procedures performed worldwide as well as in India. There is a growing need in our country among ophthalmologists to be aware of the indications for Kpro to facilitate appropriate referral as well as of the procedure to enable basic evaluation during follow-ups in case the need arises, and among corneal specialists interested to pursue the field of Kpros in understanding the nuances of these surgeries and to make a judicious decision regarding patient and Kpro selection and more importantly deferral.