Demographics of corneal transplantation in Canada in 2004

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.

Awareness and attitudes toward corneal donation among Canadians: informational and motivational videos can increase willingness toward corneal donation

OBJECTIVE

To assess the knowledge of corneal transplantation, willingness toward corneal donation, and the efficacy of a short informational and motivational video in increasing the willingness toward corneal donation among Canadian adults.

METHODS

Cross-sectional interventional study. A survey targeted Canadian adults, assessing their knowledge and attitude toward corneal donation and the efficacy of a 1-minute-long informative and motivational video on increasing willingness toward corneal donation.

RESULTS

The survey was accessed by 1361 individuals and 1013 completed the questionnaire (74% completion rate). The sample consisted of 36% males and 64% females, with an average age of 37.0 ± 15.3 years. The majority (58%) thought to lack basic knowledge about corneal donation. Similarly, objective knowledge of corneal donation was relatively low, with an average score of 7.8 ± 4.5 (out of 20). In our sample, 44% had not opted-in for organ donation, among whom willingness to donate one's own cornea increased from 59% pre-video to 79% post-video (relative increase of 34%; p < 0.001). Lack of awareness about the benefits of corneal donation was the most commonly cited reason for unwillingness to donate.

CONCLUSIONS

The results demonstrated a general lack of awareness of corneal donation among the Canadian population and highlighted the efficacy of a short informative and motivational video in increasing willingness to donate corneal tissue. With lack of awareness about the benefits of corneal donation being among the primary reasons for the unwillingness to donate, simple but efficacious interventions via informative and motivational videos can increase tissue donors and help reduce corneal tissue shortage.

Frozen versus fresh corneal graft carriers in Boston keratoprosthesis surgery: 10-year outcomes

OBJECTIVE

To compare 10-year clinical outcomes of frozen versus fresh corneal graft carriers for the Boston Keratoprosthesis type 1 (KPro).

DESIGN

Prospective, non-masked randomized controlled trial.

PARTICIPANTS

Nineteen eyes of 19 patients having undergone Boston KPro type 1 implantation using a fresh or frozen graft carrier.

METHODS

All patients that underwent Boston KPro type 1 implantation by a single experienced surgeon using an allograft carrier between October 2008 and March 2010 at the Centre Hospitalier de l'Université de Montréal were considered. Patients were excluded if they had a history of prior KPro implantation in the same eye. A subset of the patient cohort enrolled in the initial study protocol of 24 months continued follow-up to 120 months. Participants were randomized to receive either a fresh or frozen corneal graft carrier depending on tissue availability from the eye bank on the day of KPro implantation.

RESULTS

Nineteen eyes of 19 patients were included, with 11 in the fresh group and 8 in the frozen group. At 10 years, in the fresh and frozen groups respectively, device retention was 91% and 75%; mean best corrected visual acuity increased from counting fingers preoperatively to 20/300 and 20/125; and incidence of complications per patient was 2.36 and 2.37. There were no statistically significant differences between groups for any of these outcome measures (p > 0.05 for all analyses).

CONCLUSIONS

Fresh and frozen corneal graft carriers offer similar clinical outcomes for KPro implantation in terms of device retention, change in visual acuity, and rate of complications at 10 years.

Significance of Crosslinking Approaches in the Development of Next Generation Hydrogels for Corneal Tissue Engineering

Medical conditions such as trachoma, keratoconus and Fuchs endothelial dystrophy can damage the cornea, leading to visual deterioration and blindness and necessitating a cornea transplant. Due to the shortage of donor corneas, hydrogels have been investigated as potential corneal replacements. A key factor that influences the physical and biochemical properties of these hydrogels is how they are crosslinked. In this paper, an overview is provided of different crosslinking techniques and crosslinking chemical additives that have been applied to hydrogels for the purposes of corneal tissue engineering, drug delivery or corneal repair. Factors that influence the success of a crosslinker are considered that include material composition, dosage, fabrication method, immunogenicity and toxicity. Different crosslinking techniques that have been used to develop injectable hydrogels for corneal regeneration are summarized. The limitations and future prospects of crosslinking strategies for use in corneal tissue engineering are discussed. It is demonstrated that the choice of crosslinking technique has a significant influence on the biocompatibility, mechanical properties and chemical structure of hydrogels that may be suitable for corneal tissue engineering and regenerative applications.

In vitro characterization of electrochemically compacted collagen matrices for corneal applications

Loss of vision due to corneal disease is a significant problem worldwide. Transplantation of donor corneas is a viable treatment option but limitations such as short supply and immune-related complications call for alternative options for the treatment of corneal disease. A tissue engineering-based approach using a collagen scaffold is a promising alternative to develop a bioengineered cornea that mimics the functionality of native cornea. In this study, an electrochemical compaction method was employed to synthesize highly dense and transparent collagen matrices. We hypothesized that chemical crosslinking of electrochemically compacted collagen (ECC) matrices will maintain transparency, improve stability, and enhance the mechanical properties of the matrices to the level of native cornea. Further, we hypothesized that keratocyte cell viability and proliferation will be maintained on crosslinked ECC matrices. The results indicated that uncrosslinked and 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide-N-hydroxysuccinimide (EDC-NHS) crosslinked ECC matrices were highly transparent with light transmission measurements comparable to native cornea. Stability tests showed that while the uncrosslinked ECC matrices degraded within 6 h when treated with collagenase, EDC-NHS or genipin crosslinking significantly improved the stability of ECC matrices (192 h for EDC-NHS and 256 h for genipin). Results from the mechanical tests showed that both EDC-NHS and genipin crosslinking significantly improved the strength and modulus of ECC matrices. Cell culture studies showed that keratocyte cell viability and proliferation are maintained on EDC-NHS crosslinked ECC matrices. Overall, results from this study suggest that ECC matrices have the potential to be developed as a functional biomaterial for corneal repair and regeneration.

In Vivo Functionality of a Corneal Endothelium Transplanted by Cell-Injection Therapy in a Feline Model

PURPOSE

To evaluate the functionality of a corneal endothelium reconstituted by injection of corneal endothelial cells (CEC) in the anterior chamber of a feline model.

METHODS

We operated the right eyes of 16 animals. Eight underwent central endothelial scraping and injection with 2 × 10(5) (n = 4) or 1 × 10(6) (n = 4) feline CEC supplemented with Y-27632 and labeled with 3,3'-Dioctadecyl-5,5'-Di(4-Sulfophenyl)Oxacarbocyanine (SP-DiOC18[3] or DiOC). After total endothelial scraping, two eyes were injected with 1 × 10(6) labeled CEC and Y-27632. The central (n = 3) or entire (n = 3) endothelium was scraped in six eyes followed by Y-27632 injection without CEC. Subjects were positioned eyes down for 3 hours. Outcomes included graft transparency, pachymetry, CEC morphometry, histology, electron microscopy, and function and wound healing-related protein immunostaining.

RESULTS

Postoperatively, corneas grafted with 2 × 10(5) CEC and centrally scraped controls displayed the best transparency and pachymetry. Corneas grafted with 1 × 10(6) CEC yielded intermediate results. Entirely scraped controls remained hazy and thick. Histopathology revealed a confluent endothelial monolayer expressing sodium-potassium adenosine triphosphatase (Na(+)/K(+)-ATPase) and zonula occludens-1 (ZO-1) in corneas grafted with 2 × 10(5) CEC and centrally scraped controls, a nonuniform endothelial multilayer without expression of functional proteins in centrally scraped corneas grafted with 1 × 10(6) CEC, and a nonfunctional fibrotic endothelium in entirely scraped grafts and controls. Expression of DiOC in grafts was scarce.

CONCLUSIONS

Injected CEC contributed little to the incompletely functional endothelium of grafted corneas. Y-27632 injection without CEC following scraping reconstituted the healthiest endothelium. Further studies investigating the therapeutic effect of Y-27632 alone are needed to validate these conclusions.

Boston Keratoprosthesis Type 1: A Randomized Controlled Trial of Fresh versus Frozen Corneal Donor Carriers with Long-Term Follow-up

PURPOSE

To compare the long-term clinical outcomes of fresh versus frozen corneal graft carriers for the Boston Keratoprosthesis type 1 (B-KPro).

DESIGN

Prospective, single-center, nonblinded, randomized controlled trial. All participants were followed through the initial study protocol of 24 months and were approached to enter an extension phase, with continuing follow-up visits to 60 months.

PARTICIPANTS

All patients undergoing B-KPro surgery between October 2008 and December 2009 by a single experienced surgeon at the Centre Hospitalier de l'Université de Montréal using an allograft carrier were considered. Patients were excluded if they had previously undergone B-KPro implantation.

METHODS

Participants were randomized individually to receive a B-KPro using a frozen or a fresh corneal graft carrier on the basis of tissue availability on the day of surgery, as determined by the local eye bank.

MAIN OUTCOME MEASURES

The primary outcome measure was device retention at 24 and 60 months. Secondary outcome measures included surgical feasibility, visual acuity (VA), and complications.

RESULTS

Thirty-seven eyes of 37 patients were enrolled in the initial study protocol, with 19 eyes randomized to fresh and 18 to frozen carrier grafts. Thirty-six eyes were followed through to 24 months, with 1 lost to follow-up. Of these, 26 were enrolled in the extension (11 eyes with a frozen and 15 eyes with a fresh carrier graft). There were no differences in the baseline characteristics of patients enrolled in the extension phase versus those who were not. At 60 months, median corrected distance VA) in the fresh group had improved to 20/150 from a baseline of counting fingers, whereas the frozen group improved to 20/400 from a baseline of hand motions. Device retention was 100% at 24 months and 96% at 60 months. There were no significant differences in the rate of complications between groups.

CONCLUSIONS

Fresh and frozen corneal donors offer similar clinical outcomes when used as carriers for the B-KPro, with no significant differences in device retention, visual rehabilitation, or rates of complications at 24 or 60 months.

Gamma-irradiated corneas as carriers for the Boston type 1 keratoprosthesis: advantages and outcomes in a surgical mission setting

PURPOSE

The Boston keratoprosthesis (KPro) is the most commonly used KPro worldwide. There are limited data on the outcomes when irradiated corneas are used as KPro carriers. We report a retrospective analysis of corneal transplantations performed in a regular surgical mission setting in Beirut, Lebanon, using the Boston KPro type 1 and gamma-irradiated carrier corneas, and we describe visual outcomes, complications, and retention percentage.

METHODS

We conducted a retrospective analysis of 17 consecutive eyes from 16 patients who underwent Boston KPro type 1 implantation at the Beirut Eye Specialist Hospital between December 2010 and July 2012. Patient medical records were reviewed for preoperative, intraoperative, and postoperative details.

RESULTS

Postoperatively, 9 (52.9%), 5 (29.4%), and 2 (11.7%) eyes had a corrected visual acuity of 20/400 or better, 20/100 or better, and 20/40 or better, respectively, at the most recent follow-up visit. A total of 16 eyes (94.1%) improved in corrected visual acuity over the course of follow-up. Overall, 13 eyes (76.4%) developed at least 1 complication after surgery. Retroprosthetic membrane formation was the most common complication, occurring in 10 eyes (58.8%). Neither infectious keratitis nor corneal stromal necrosis was noted during the follow-up period. The retention percentage was 94.1%.

CONCLUSIONS

The visual acuity outcomes, incidence of complications, and retention percentage of the KPro using gamma-irradiated carrier corneas are comparable with the outcomes of KPro implantation reported in the literature using fresh grafts as carriers. KPro with irradiated corneal carrier grafts seems to be an effective option to increase the supply of transplantation suitable corneas in remote areas, where fresh corneal grafts may be scarce.

Sustainability of Routine Notification and Request legislation on eye bank tissue supply and corneal transplantation wait times in Canada

OBJECTIVE

To assess whether provinces with Routine Notification and Request (RNR) legislation have sustained increases in corneal tissue supply and decreases in wait times for corneal transplantation surgery.

DESIGN

Cross-sectional survey of Canadian corneal transplant (CT) surgeons and eye banks.

PARTICIPANTS

Canadian CT surgeons and representatives from the 10 Canadian eye banks.

METHODS

Voluntary and anonymous surveys were distributed between July and October 2009. Eligible CT surgeons were defined as ophthalmologists who practice in Canada; currently perform Penetrating keratoplasty (PKP), Deep anterior lamellar keratoplasty (DALK), Deep lamellar endothelial keratoplasty (DLEK), Descemet stripping endothelial keratoplasty (DSEK), or Descemet membrane endothelial keratoplasty (DMEK); and have obtained tissues from a Canadian eye bank.

RESULTS

From 2006 to 2009, for provinces with RNR legislation and where data are available, mean wait times from date of diagnosis to date of CT surgery have increased: in Ontario, from 31 ± 34 weeks to 36 ± 27 weeks; in British Columbia, from 39 ± 20 weeks to 42 ± 35 weeks; in Manitoba, from 32 ± 23 weeks to 49 ± 36 weeks. In addition, the amount of corneal tissue in RNR provinces suitable for transplant, with the exception of British Columbia, has declined between 2006 and 2008: in Ontario, 1186 tissues to 999 tissues (16% decline); in Manitoba, 92 tissues to 83 tissues (10% decline); in New Brunswick, 129 tissues to 98 tissues (24% decline).

CONCLUSION

Although initially effective, RNR legislation has not sustained an increase in corneal tissue availability nor has it shortened wait times in most provinces. Incorporation of community hospitals into the RNR catchment, improved enforcement, and continued education of hospital staff regarding the RNR process may be effective in making this legislation more sustainable in the long term.

Double use of corneal graft for Descemet stripping automated endothelial keratoplasty and coverage of glaucoma drainage device tube

PURPOSE

To describe the efficacy and safety of using a single corneal graft for 2 different ocular surgeries, Descemet stripping automated endothelial keratoplasty in one patient and coverage of a glaucoma drainage device tube in another patient.

MATERIALS AND METHODS

The records of 12 consecutive patients who underwent Ahmed glaucoma valve implantation using the anterior lamella of a donor cornea that had been previously used for Descemet stripping automated endothelial keratoplasty were reviewed.

RESULTS

Nine eyes (75%) had superotemporal Ahmed valve implantation and 3 eyes (25%) had inferotemporal implantation. No intraoperative complications were encountered in any of these cases. During postoperative follow-up there were no graft rejections, wound dehiscences, tube exposures, or any glaucoma drainage device-related complications. In 1 patient, graft thinning was noticed 12 months after surgery, but without erosion of the conjunctiva or exposure of the tube. Mean intraocular pressure (IOP) before surgery was 32.8±9.3 mm Hg. The mean postoperative IOPs were 13.2±6.8 mm Hg (P<0.001) at day 1, 10.5±2.7 (P<0.001) at week 1, 12.2±3.5 (P<0.001) at month 1, 12.9±3.0 (P<0.001) at month 3, 14.2±7.0 (P<0.001) at month 6, and 13.0±6.4 (P<0.001) at the final visit. The mean reduction in IOP was 59%. Mean follow-up time after surgery was 21.7±7.5 months.

CONCLUSIONS

The use of the anterior corneal graft cap for patching a tube is safe and effective. The double use of a corneal graft is economically worthwhile and especially useful in countries where there is shortage of donor corneal tissues.

A failed corneal graft as a support for the Boston Keratoprosthesis type 1

The implantation of the Boston Keratoprosthesis (KPro) requires a corneal button, which is usually taken from a donor. Scarcity of donor tissue has been a major limiting factor in transplant surgery. Recently, autologous recipient cornea has been reported as support for the KPro. We report the successful use of an ipsilateral failed corneal graft as the carrier tissue for a patient requiring combined pars plana vitrectomy and KPro implantation.