Fyodorov–Zuev keratoprosthesis implantation: long-term results in patients with multiple failed corneal grafts

Advances in Microgravity Directed Tissue Engineering

Tissue engineering aims to generate functional biological substitutes to repair, sustain, improve, or replace tissue function affected by disease. With the rapid development of space science, the application of simulated microgravity has become an active topic in the field of tissue engineering. There is a growing body of evidence demonstrating that microgravity offers excellent advantages for tissue engineering by modulating cellular morphology, metabolism, secretion, proliferation, and stem cell differentiation. To date, there have been many achievements in constructing bioartificial spheroids, organoids, or tissue analogs with or without scaffolds in vitro under simulated microgravity conditions. Herein, the current status, recent advances, challenges, and prospects of microgravity related to tissue engineering are reviewed. Current simulated-microgravity devices and cutting-edge advances of microgravity for biomaterials-dependent or biomaterials-independent tissue engineering to offer a reference for guiding further exploration of simulated microgravity strategies to produce engineered tissues are summarized and discussed.

A Review of the Diagnosis and Treatment of Limbal Stem Cell Deficiency

Limbal stem cell deficiency (LSCD) can cause significant corneal vascularization and scarring and often results in serious visual morbidity. An early and accurate diagnosis can help prevent the same with a timely and appropriate intervention. This review aims to provide an understanding of the different diagnostic tools and presents an algorithmic approach to the management based on a comprehensive clinical examination. Although the diagnosis of LSCD usually relies on the clinical findings, they can be subjective and non-specific. In such cases, using an investigative modality offers an objective method of confirming the diagnosis. Several diagnostic tools have been described in literature, each having its own advantages and limitations. Impression cytology and in vivo confocal microscopy (IVCM) aid in the diagnosis of LSCD by detecting the presence of goblet cells. With immunohistochemistry, impression cytology can help in confirming the corneal or conjunctival source of epithelium. Both IVCM and anterior segment optical coherence tomography can help supplement the diagnosis of LSCD by characterizing the corneal and limbal epithelial changes. Once the diagnosis is established, one of various surgical techniques can be adopted for the treatment of LSCD. These surgeries aim to provide a new source of corneal epithelial stem cells and help in restoring the stability of the ocular surface. The choice of procedure depends on several factors including the involvement of the ocular adnexa, presence of systemic co-morbidities, status of the fellow eye and the comfort level of the surgeon. In LSCD with wet ocular surfaces, autologous and allogeneic limbal stem cell transplantation is preferred in unilateral and bilateral cases, respectively. Another approach in bilateral LSCD with wet ocular surfaces is the use of an autologous stem cell source of a different epithelial lineage, like oral or nasal mucosa. In eyes with bilateral LSCD with significant adnexal issues, a keratoprosthesis is the only viable option. This review provides an overview on the diagnosis and treatment of LSCD, which will help the clinician choose the best option amongst all the therapeutic modalities currently available and gives a clinical perspective on customizing the treatment for each individual case.

Artificial Cornea: Past, Current, and Future Directions

Corneal diseases are a leading cause of blindness with an estimated 10 million patients diagnosed with bilateral corneal blindness worldwide. Corneal transplantation is highly successful in low-risk patients with corneal blindness but often fails those with high-risk indications such as recurrent or chronic inflammatory disorders, history of glaucoma and herpetic infections, and those with neovascularisation of the host bed. Moreover, the need for donor corneas greatly exceeds the supply, especially in disadvantaged countries. Therefore, artificial and bio-mimetic corneas have been investigated for patients with indications that result in keratoplasty failure. Two long-lasting keratoprostheses with different indications, the Boston type-1 keratoprostheses and osteo-odonto-keratoprostheses have been adapted to minimise complications that have arisen over time. However, both utilise either autologous tissue or an allograft cornea to increase biointegration. To step away from the need for donor material, synthetic keratoprostheses with soft skirts have been introduced to increase biointegration between the device and native tissue. The AlphaCor™, a synthetic polymer (PHEMA) hydrogel, addressed certain complications of the previous versions of keratoprostheses but resulted in stromal melting and optic deposition. Efforts are being made towards creating synthetic keratoprostheses that emulate native corneas by the inclusion of biomolecules that support enhanced biointegration of the implant while reducing stromal melting and optic deposition. The field continues to shift towards more advanced bioengineering approaches to form replacement corneas. Certain biomolecules such as collagen are being investigated to create corneal substitutes, which can be used as the basis for bio-inks in 3D corneal bioprinting. Alternatively, decellularised corneas from mammalian sources have shown potential in replicating both the corneal composition and fibril architecture. This review will discuss the limitations of keratoplasty, milestones in the history of artificial corneal development, advancements in current artificial corneas, and future possibilities in this field.

Stem cell-based therapeutic strategies for corneal epithelium regeneration

Any significant loss of vision or blindness caused by corneal damages is referred to as corneal blindness. Corneal blindness is the fourth most common cause of blindness worldwide, representing more than 5% of the total blind population. Currently, corneal transplantation is used to treat many corneal diseases. In some cases, implantation of artificial cornea (keratoprosthesis) is suggested after a patient has had a donor corneal transplant failure. The shortage of donors and the side effects of keratoprosthesis are limiting these approaches. Recently, researchers have been actively pursuing new approaches for corneal regeneration because of these limitations. Nowadays, tissue engineering of different corneal layers (epithelium, stroma, endothelium, or full thickness tissue) is a promising approach that has attracted a great deal of interest from researchers and focuses on regenerative strategies using different cell sources and biomaterials. Various sources of corneal and non-corneal stem cells have shown significant advantages for corneal epithelium regeneration applications. Pluripotent stem cells (embryonic stem cells and iPS cells), epithelial stem cells (derived from oral mucus, amniotic membrane, epidermis and hair follicle), mesenchymal stem cells (bone marrow, adipose-derived, amniotic membrane, placenta, umbilical cord), and neural crest origin stem cells (dental pulp stem cells) are the most promising sources in this regard. These cells could also be used in combination with natural or synthetic scaffolds to improve the efficacy of the therapeutic approach. As the ocular surface is exposed to external damage, the number of studies on regeneration of the corneal epithelium is rising. In this paper, we reviewed the stem cell-based strategies for corneal epithelium regeneration.

Biomimetic bone-like composites as osteo-odonto-keratoprosthesis skirt substitutes

Osteo-odonto-keratoprostheses, incorporating dental laminate material as an anchoring skirt around a central poly(methyl methacrylate) (PMMA) optic, have been used to replace the cornea for many years. However, there are many intricacies associated with the use of autologous dental laminate material, surgical complexity and skirt erosion. Tissue engineering approaches to bone replacement may offer suitable alternatives in osteo-odonto-keratoprosthesis (OOKP) surgery. In this study, a hydrogel polymer composite was investigated as a synthetic substitute for the OOKP skirt. A novel high strength interpenetrating network (IPN) hydrogel composite with nano-crystalline hydroxyapatite (nHAp) coated poly (lactic-co-glycolic acid) PLGA microspheres was created to mimic the alveo-dental lamina by employing agarose and poly(ethylene glycol) diacrylate (PEGDA) polymers. The incorporation of nHAp coated PLGA microspheres into the hybrid IPN network provide a micro-environment similar to that of skeletal tissues and improve cellular response. Agarose was used as a first network to encapsulate keratocytes/3T3 fibroblasts and PEGDA (6000 Da) was used as a second network with varying concentrations (20 and 40 wt %) to produce a strong and biocompatible scaffold. An increased concentration of either agarose or PEG-DA and incorporation of nHAp coated PLGA microspheres led to an increase in the elastic modulus. The IPN hydrogel combinations supported the adhesion and proliferation of both fibroblast and ocular human keratocyte cell types during in in-vitro testing. The cells endured the encapsulation process into the IPN and remained viable at 1 week post-encapsulation in the presence of nHAp coated microspheres. The material did not induce significant production of inflammatory cytokine IL-6 in comparison to a positive control (p < 0.05) indicating non-inflammatory potential. The nHAp encapsulated composite IPN hydrogels are mechanically strong, cell supportive, non-inflammatory materials supporting their development as OOKP skirt substitutes using a new approach to dental laminate biomimicry in the OOKP skirt material.

Corneal epithelium tissue engineering: recent advances in regeneration and replacement of corneal surface

Currently, many corneal diseases are treated by corneal transplantation, artificial corneal implantation or, in severe cases, keratoprosthesis. Owing to the shortage of cornea donors and the risks involved with artificial corneal implants, such as infection transmission, researchers continually seek new approaches for corneal regeneration. Corneal tissue engineering is a promising approach that has attracted much attention from researchers and is focused on regenerative strategies using various biomaterials in combination with different cell types. These constructs should have the ability to mimic the native tissue microenvironment and present suitable optical, mechanical and biological properties. In this article, we review studies that have focused on the current clinical techniques for corneal replacement. We also describe tissue-engineering and cell-based approaches for corneal regeneration.

Artificial corneas versus donor corneas for repeat corneal transplants

BACKGROUND

Individuals who have failed one or more full thickness penetrating keratoplasties may be offered repeat corneal surgery using an artificial or donor cornea. An artificial or prosthetic cornea is known as a keratoprosthesis. Both donor and artificial corneal transplantations involve removal of the diseased and opaque recipient cornea (or the previously failed cornea) and replacement with another donor or prosthetic cornea.

OBJECTIVES

To assess the effectiveness of artificial versus donor corneas in individuals who have had one or more failed donor corneal transplantations.

SEARCH METHODS

We searched the Cochrane Central Register of Controlled Trials (CENTRAL) (which contains the Cochrane Eyes and Vision Trials Register) (2019, Issue 11); Ovid MEDLINE; Ovid Embase; LILACS (Latin American and Caribbean Health Sciences Literature database); ClinicalTrials.gov; and the World Health Organization (WHO) International Clinical Trials Registry Platform (ICTRP). We did not use any date or language restrictions in the electronic search for trials. We last searched the electronic databases on 4 November 2019.

SELECTION CRITERIA

Two review authors independently assessed reports from the electronic searches to identify randomized controlled trials or controlled clinical trials. Any discrepancies were resolved by discussion or consultation.

DATA COLLECTION AND ANALYSIS

We used standard methodological procedures expected by Cochrane. For discussion purposes, we summarized findings from relevant comparative case series. We performed no data synthesis.

MAIN RESULTS

We did not identify any randomized controlled trials or controlled clinical trials comparing artificial corneas with donor corneas for repeat corneal transplantations.

AUTHORS' CONCLUSIONS

The optimal management for those individuals who have failed a conventional corneal transplantation is unknown. Currently, in some centers, artificial corneal devices are routinely recommended after just one graft failure, while in other centers, they are not recommended until after multiple graft failures, or not at all. To date, there have been no controlled trials comparing the visual outcomes and complications of artificial corneal devices (particularly the Boston type 1 keratoprosthesis, which is the most commonly implanted artificial corneal device) with repeat donor corneal transplantation, in order to guide surgeons and their patients. Such a trial is needed and would offer significant benefit to an ever-increasing pool of people with visual disability due to corneal opacification, most of whom are still in productive stages of their lives.

Surface modification of corneal prosthesis with nano-hydroxyapatite to enhance in vivo biointegration

The majority of clinical corneal prostheses (KPros) adopt a core-skirt configuration. This configuration is favored owing to the optic core (generally a cylindrical, acrylic-based material, such as PMMA), that not only provides a clear window for the patients' vision, but also confers resistance to biodegradability. The surrounding skirt (typically a biological material, such as corneal tissue) allows for host tissue integration. However, due to poor biointegration between the dissimilar core and skirt materials, it results in a weak adhesion at the interface, giving rise to clinical complications, such as bacterial infections in the tissue-PMMA interface and device extrusion. Here, we physically immobilized nano-hydroxyapatite (nHAp) on a PMMA cylinder via a dip-coating technique, to create a bioactive surface that improved biointegration in vivo. We established that the nHAp coating was safe and stable in the rabbit cornea over five weeks. More importantly, we found that apoptotic, wound healing and inflammatory responses to nHAp-coated PMMA were substantially milder than to non-coated PMMA. More mature collagen, similar to the non-operated cornea, was maintained in the corneal stroma adjacent to the nHAp-coated implant edge. However, around the non-coated cylinder, an abundant new and loose connective tissue formed, similar to bone tissue response to bioinert scaffolds. As a result of superior biointegration, tissue adhesion with nHAp-coated PMMA cylinders was also significantly enhanced compared to non-coated cylinders. This study set a precedent for the future application of the nHAp coating on clinical KPros. STATEMENT OF SIGNIFICANCE: Currently, all clinical corneal prostheses utilize as-manufactured, non-surface modified PMMA optic cylinder. The bioinert cylinder, however, has poor biointegration and adhesion with the surrounding biological tissue, which can give rise to postoperative complications, such as microbial invasion in the tissue-PMMA loose interface and PMMA optic cylinder extrusion. In the current study, we showed that surface modification of the PMMA cylinder with bioactive nano-hydroxyapatite (nHAp) significantly enhanced its biointegration with corneal stromal tissue in vivo. The superior biointegration of the nHAp-coated PMMA was signified by a more attenuated corneal wound healing, inflammatory and fibrotic response, and better tissue apposition, as well as a significantly improved corneal stromal tissue adhesion when compared to the non-coated PMMA.

[Morphological changes in rabbit cornea after implantation of a new keratoprosthesis supporting plate]

PURPOSE

To evaluate biocompatibility of the new keratoprosthesis supporting plates (KSP) in rabbits in vivo.

MATERIAL AND METHODS

The study included 15 chinchilla rabbits. In the first group (5 rabbit eyes) KSP made of hydrophobic acryl with square penetrating holes of 220×220 micron (model 1) were inserted into rabbits' corneas. In the second group (5 eyes), KSP made of hydrophobic acryl were used that had trapezoidal fenestrations with size (from 170×130 micron to 180×70 microns) gradually changing from periphery to the center of KSP (model 2). The control group rabbits (5 eyes) had ¹/₂ of Fyodorov-Zuev KSP made of titanium implanted. All animals were observed for up to 3 months with biomicroscopy and optical coherence tomography of the anterior segment. The animals were then euthanized and had their corneo-scleral discs excised and then examined with optical microscopy and scanning electron microscopy (SEM).

RESULTS

After 3 months, there was only one case of KSP protrusion in the first group. In the second group, thinning of the corneal layers above the central part of KSP occurred in one case. The presence of polymer KSP (of both models) in the corneal stroma was found not to cause formation of rough fibrotic tissue. At the same time, adhered cellular and fibrous elements were discovered on the surface and inside the holes of the polymer KSP, while on the surface of the titanium plate cellular elements were absent.

CONCLUSION

Supporting plates made of hydrophobic acrylic material can potentially serve as a foundation for the new keratoprosthesis design.

3D bioprinting for artificial cornea: Challenges and perspectives

Corneal disease is one of the most important causes of blindness worldwide. Currently, the dominating treatment of corneal blindness is corneal transplantation. However, the main source of cornea for transplantation is based on donations which is far from enough to meet the requirement (less than 1:70 of cases). The severe shortage of donor cornea promotes the studies of effective corneal alternatives. However, many problems remain and can't be solved in current researches, such as original geometry reconstruction and ocular optical function restoring. 3D bioprinting can be a promising approach for corneal substitution. The advantages of this technology in corneal regeneration enable personalized corneal implant and single or multi-layer corneal equivalents with controllable structure and designed refractive ability. In this review, the progress, applications and limitations of most influential works among current keratoprosthesis and tissue-engineering cornea researches are discussed. Then the applications of 3D bioprinting in manufacturing multi-layered structures and surface are mentioned. Further, the potential, advantages in current research of 3D bioprinting single or multi-layer corneal equivalents and alternatives are discussed. Finally, an insight into the technical challenges and prospective facing the future research of 3D bioprinting corneal alternatives in vivo and in vitro is provided.

Cold War Legacy in Public and Private Health Spending in Europe

Cold War Era (1946-1991) was marked by the presence of two distinctively different economic systems, namely the free-market (The Western ones) and central-planned (The Eastern ones) economies. The main goal of this study refers to the exploration of development pathways of Public and Private Health Expenditure in all of the countries of the European WHO Region. Based on the availability of fully comparable data from the National Health Accounts system, we adopted the 1995-2014 time horizon. All countries were divided into two groups: those defined in 1989 as free market economies and those defined as centrally-planned economies. We observed six major health expenditures: Total Health Expenditure (% of GDP), Total Health Expenditure (PPP unit), General government expenditure on health (PPP), Private expenditure on health (PPP), Social security funds (PPP) and Out-of-pocket expenditure (PPP). All of the numerical values used refer exclusively to per capita health spending. In a time-window from the middle of the 1990s towards recent years, total health expenditure was rising fast in both groups of countries. Expenditure on health % of GDP in both group of countries increased over time with the increase in the Free-market economies seen to be more rapid. The steeper level of total expenditure on health for the Free-market as of 1989 market economies, is due mainly to a steep increase in both the government and private expenditure on health relative to spending by centrally-planned economies as of the same date, with the out-of-pocket expenditure and the social security funds in the same market economies category following the same steepness. Variety of governments were leading Eastern European countries into their transitional health care reforms. We may confirm clear presence of obvious divergent upward trends in total governmental and private health expenditures between these two groups of countries over the past two decades. The degree of challenge to the fiscal sustainability of these health systems will have to be judged for each single nation, in line with its own local circumstances and perspectives.

Corneal regeneration: A review of stromal replacements

Corneal blindness is traditionally treated by transplantation of a donor cornea, or in severe cases by implantation of an artificial cornea or keratoprosthesis. Due to severe donor shortages and the risks of complications that come with artificial corneas, tissue engineering in ophthalmology has become more focused on regenerative strategies using biocompatible materials either with or without cells. The stroma makes up the bulk of the corneal thickness and mainly consists of a tightly interwoven network of collagen type I, making it notoriously difficult to recreate in a laboratory setting. Despite the challenges that come with corneal stromal tissue engineering, there has recently been enormous progress in this field. A large number of research groups are working towards developing the ideal biomimetic, cytocompatible and transplantable stromal replacement. Here we provide an overview of the approaches directed towards tissue engineering the corneal stroma, from classical collagen gels, films and sponges to less traditional components such as silk, fish scales, gelatin and polymers. The perfect stromal replacement has yet to be identified and future research should be directed at combined approaches, in order to not only host native stromal cells but also restore functionality.

STATEMENT OF SIGNIFICANCE

In the field of tissue engineering and regenerative medicine in ophthalmology the focus has shifted towards a common goal: to restore the corneal stroma and thereby provide a new treatment option for patients who are currently blind due to corneal opacification. Currently the waiting lists for corneal transplantation include more than 10 million patients, due to severe donor shortages. Alternatives to the transplantation of a donor cornea include the use of artificial cornea, but these are by no means biomimetic and therefore do not provide good outcomes. In recent years a lot of work has gone into the development of tissue engineered scaffolds and other biomaterials suitable to replace the native stromal tissue. Looking at all the different approaches separately is a daunting task and up until now there was no review article in which every approach is discussed. This review does include all approaches, from classical tissue engineering with collagen to the use of various alternative biomaterials and even fish scales. Therefore, this review can serve as a reference work for those starting in the field and but also to stimulate collaborative efforts in the future.

Keratoprosthesis: A Review of Recent Advances in the Field

Since its discovery in the years of the French Revolution, the field of keratoprostheses has evolved significantly. However, the path towards its present state has not always been an easy one. Initially discarded for its devastating complications, the introduction of new materials and the discovery of antibiotics in the last century gave new life to the field. Since then, the use of keratoprostheses for severe ocular surface disorders and corneal opacities has increased significantly, to the point that it has become a standard procedure for corneal specialists worldwide. Although the rate of complications has significantly been reduced, these can impede the long-term success, since some of them can be visually devastating. In an attempt to overcome these complications, researchers in the field have been recently working on improving the design of the currently available devices, by introducing the use of new materials that are more biocompatible with the eye. Here we present an update on the most recent research in the field.

Keratoprostheses for corneal blindness: a review of contemporary devices

According to the World Health Organization, globally 4.9 million are blind due to corneal pathology. Corneal transplantation is successful and curative of the blindness for a majority of these cases. However, it is less successful in a number of diseases that produce corneal neovascularization, dry ocular surface and recurrent inflammation, or infections. A keratoprosthesis or KPro is the only alternative to restore vision when corneal graft is a doomed failure. Although a number of KPros have been proposed, only two devices, Boston type-1 KPro and osteo-odonto-KPro, have came to the fore. The former is totally synthetic and the latter is semi-biological in constitution. These two KPros have different surgical techniques and indications. Keratoprosthetic surgery is complex and should only be undertaken in specialized centers, where expertise, multidisciplinary teams, and resources are available. In this article, we briefly discuss some of the prominent historical KPros and contemporary devices.

Long-term safety and efficacy of high-fluence collagen crosslinking of the vehicle cornea in Boston keratoprosthesis type 1

PURPOSE

The aim of this study was to evaluate the safety and efficacy of very high-fluence collagen crosslinking (CXL) as a means of achieving increased corneal rigidity and reduced enzymatic digestion in the vehicle cornea of Boston keratoprosthesis (KPro) type 1.

METHODS

Eleven consecutive patients fitted with a KPro (5 with a previous repeat cornea graft failure, 4 with ocular cicatricial pemphigoid, and 2 with chemical burn) underwent donor vehicle cornea pretreatment with very high-fluence prophylactic CXL in a 2-step procedure. First, the donor cornea was crosslinked with an intrastromal riboflavin instillation through a femtosecond laser-created pocket. This was followed up with a superficial CXL treatment. On the completion of the CXL pretreatment, the cornea center was trephined with the femtosecond laser, and the KPro was fitted onto the crosslinked donor cornea. Visual acuity, corneal surface, and donor vehicle cornea stability were evaluated. Follow-up evaluations were conducted over the next 9 years with a mean of 7.5 years.

RESULTS

Mean uncorrected visual acuity improved from light perception to 20/60. One patient required a follow-up surgery, because of significant melt in the host cornea. None of the eyes developed melts and/or infection, especially on the vehicle cornea on which the KPro was fitted.

CONCLUSIONS

Pretreatment with intrastromal and superficial very high-fluence CXL in conjunction with Boston type 1 KPro seems to be a safe and effective adjunctive treatment for achieving increased vehicle donor cornea rigidity. Additionally, there is an increased resistance to enzymatic degradation. This application may serve to enhance the biomechanical stability and external disease resistance of the donor vehicle cornea in patients with advanced external disease.

Visually Evoked Potentials in a Patient with a Fyodorov-Zuev Keratoprosthesis

Purpose

To describe a visually evoked potential (VEP) examination performed on a patient with a keratoprosthesis.

Methods

We report the case of a 60-year-old patient with a Fyodorov-Zuev keratoprosthesis in the right eye complained of gradual visual deterioration in that eye. His past medical history consisted of failed corneal graft procedures due to corneal dystrophy and an Ahmed valve implantation due to secondary glaucoma. A clinical examination and an ultrasound demonstrated vitreal opacities. In order to assess the visual status, a flash VEP test was conducted.

Results

VEP recorded from the right eye consisted of a broadened and poorly formed positive P1 wave, with a subnormal amplitude, but a normal latency. Consequently, the patient underwent a pars plana vitrectomy.

Conclusion

This case demonstrates the viability of VEP exams in patients with keratoprostheses.

Artificial corneas versus donor corneas for repeat corneal transplants

BACKGROUND

Individuals who have failed one or more full thickness penetrating keratoplasties (PKs) may be offered repeat corneal surgery using an artificial or donor cornea. An artificial or prosthetic cornea is known as a keratoprosthesis. Both donor and artificial corneal transplantations involve removal of the diseased and opaque recipient cornea (or the previously failed cornea) and replacement with another donor or prosthetic cornea.

OBJECTIVES

To assess the effectiveness of artificial versus donor corneas in individuals who have had one or more failed donor corneal transplantations.

SEARCH METHODS

We searched CENTRAL (which contains the Cochrane Eyes and Vision Group Trials Register) (2013, Issue 10), Ovid MEDLINE, Ovid MEDLINE In-Process and Other Non-Indexed Citations, Ovid MEDLINE Daily, Ovid OLDMEDLINE (January 1946 to November 2013), EMBASE (January 1980 to November 2013), Latin American and Caribbean Health Sciences Literature Database (LILACS) (January 1982 to November 2013), the metaRegister of Controlled Trials (mRCT) (www.controlled-trials.com), ClinicalTrials.gov (www.clinicaltrials.gov) and the World Health Organization (WHO) International Clinical Trials Registry Platform (ICTRP) (www.who.int/ictrp/search/en). We did not use any date or language restrictions in the electronic searches for trials. We last searched the electronic databases on 27 November 2013.

SELECTION CRITERIA

Two review authors independently assessed reports from the electronic searches to identify randomized controlled trials (RCTs) or controlled clinical trials (CCTs). We resolved discrepancies by discussion or consultation with a third review author.

DATA COLLECTION AND ANALYSIS

For discussion purposes, we assessed findings from observational cohort studies and non-comparative case series. No data synthesis was performed.

MAIN RESULTS

We did not identify any RCTs or CCTs comparing artificial corneas with donor corneas for repeat corneal transplantations.

AUTHORS' CONCLUSIONS

The optimal management for those individuals who have failed a conventional corneal transplantation is not known. Currently, in some centers, artificial corneal devices routinely are recommended after just one graft failure, and in others, not until after multiple graft failures, or not at all. To date, there have been no controlled trials comparing the visual outcomes and complications of artificial corneal devices (particularly the Boston type 1 keratoprosthesis which is the most commonly implanted artificial corneal device) with repeat donor corneal transplantation, in order to guide surgeons and their patients. It is apparent that such a trial is needed and would offer significant benefit to an ever-increasing pool of people with visual disability due to corneal opacification, most of whom are still in productive stages of their lives.

A brief review of Boston type-1 and osteo-odonto keratoprostheses

Globally there are ≈4.9 million bilaterally corneal blind and 23 million unilaterally corneal blind. Majority of this blindness exists in the developing countries, where resources for corneal banking and transplant surgery are less than adequate. Survival of corneal grafts gradually declines over the long term. Corneal transplantation has poor prognosis in vascularised corneal beds, ocular surface disease and viral keratitis. Keratoprosthesis (KPro) remains as a final option for end-stage ocular surface disease, multiple corneal transplant failures and high-risk corneal grafts. Boston type-1 KPro and osteo-odonto-keratoprosthesis are the two devices proven useful in recent years. Choice of a keratoprosthetic device is patient specific based on the underlying diagnosis, ocular morbidity and patient suitability. KPro surgery demands a high level of clinical and surgical expertise, lifelong commitment and extensive resources. Improvements in techniques and biomaterials may in the future provide retainable KPros that do not need regular follow-up of patients, have low complications but high retention rates and may be produced at a low cost on a mass scale to be available as 'off the shelf' devices. Because KPros have the potential to effectively address the burden of surgically treatable corneal blindness and may also eliminate the problems of corneal transplantation, more research is required to develop KPros as substitutes for corneal transplantation even in low-risk cases. In those countries where corneal blindness is a major liability, we need a two pronged approach: one to develop eye donation, eye banking and corneal transplantation and the second to establish centres for keratoprostheses, which are affordable and technically not challenging, in a population where default on follow-up visits are high. Until the latter is achieved, KPros should be viewed as a temporary means for visual restoration and be offered in national and supraregional specialised centres only.

Implantation of Iakymenko keratoprosthesis in patients with severe ocular injury

AIM

To present the results of implantation of Iakymenko keratoprosthesis in five patients with vascularized corneal leukoma caused by severe ocular injury.

METHODS

Iakymenko keratoprosthesis was implanted into 5 eyes of 5 patients: 4 patients were suffered from chemical burns and 1 patient from explosive injury. The preoperative visual acuity ranged from light perception to hand motion. The implantation surgery was composed of two-stage procedures. The follow-up period was from 9 months to 11 years. The outcome measures were visual acuity, retention, and complications of the keratoprosthesis.

RESULTS

Vision improvements were achieved in most patients. All keratoprosthesis were retained within the follow-up period. Corneal melting occurred in one patient and fibrous closure in another patient, both of which were successfully treated. Retinal detachment occurred in one patient after surgery.

CONCLUSION

Iakymenko keratoprosthesis seems to be a promising alternative for the patients with severe corneal injury, but further investigation is needed to evaluate the role of Iakymenko keratoprosthesis.

Osteo-odonto keratoprosthesis: systematic review of surgical outcomes and complication rates

Case series on osteo-odonto keratoprosthesis (OOKP) published in English from 1950-June 2010 were identified in Medline/PubMed. Indications for surgery, visual acuity, anatomical survival, complication and repeat surgery rates were compared among the different studies. Our own case series is a retrospective review of all OOKP surgeries performed in our center from February 2004-July 2011. Eight case series including our own were systematically reviewed. Sample sizes ranged from 4-181 eyes. The most common indications for surgery were severe cases of Stevens-Johnson syndrome and thermal and chemical burns that were unamenable to other forms of surgery or had had previous surgical failure. Anatomical survival rate in all the studies was 87.8% (range 67-100%) at 5 years, and three studies showed survival rates of 81.0% (range 65-98%) at 20 years. Visual acuity was more than 6/18 in 52% (range 46-72%) of the eyes with OOKP surgery. The most common intraoperative complication was vitreous hemorrhage (0-52%) and the most common long-term blinding complication was glaucoma (7-47%). Endophthalmitis rates ranged from 2-8%. The most common repeat surgical procedure was mucosal trimming due to mucosal overgrowth at the optical cylinder and mucosal grafting for extrusion of the OOKP or mucosal ulceration. Of the available biological and synthetic keratoprosthesis, OOKP appears to be an excellent option for the treatment of end-stage corneal diseases.