Legeais BioKpro III keratoprosthesis implantation: long term results in seven patients

Replace or Regenerate? Diverse Approaches to Biomaterials for Treating Corneal Lesions

The inner structures of the eye are protected by the cornea, which is a transparent membrane exposed to the external environment and subjected to the risk of lesions and diseases, sometimes resulting in impaired vision and blindness. Several eye pathologies can be treated with a keratoplasty, a surgical procedure aimed at replacing the cornea with tissues from human donors. Even though the success rate is high (up to 90% for the first graft in low-risk patients at 5-year follow-up), this approach is limited by the insufficient number of donors and several clinically relevant drawbacks. Alternatively, keratoprosthesis can be applied in an attempt to restore minimal functions of the cornea: For this reason, it is used only for high-risk patients. Recently, many biomaterials of both natural and synthetic origin have been developed as corneal substitutes to restore and replace diseased or injured corneas in low-risk patients. After illustrating the traditional clinical approaches, the present paper aims to review the most innovative solutions that have been recently proposed to regenerate the cornea, avoiding the use of donor tissues. Finally, innovative approaches to biological tissue 3D printing and xenotransplantation will be mentioned.

Ocular involvement in autoimmune bullous diseases

Autoimmune bullous diseases represent a heterogenous group of disorders caused by autoantibodies against adhesion molecules; the location of the target protein determines the level of cleft formation. The spectrum of ocular lesions in autoimmune bullous diseases can range from mild symptoms to severe involvement with sight impairment and even, in some cases, blindness. In pemphigus vulgaris, the prevalence of ocular involvement has been reported to be between 7% and 26%. The most common clinical sign of ocular pemphigus vulgaris is bilateral conjunctivitis with hyperemia. Ocular involvement also occurs in 41% to 70% of patients with paraneoplastic pemphigus. The main ocular manifestations are bilateral cicatrizing conjunctivitis with symblepharon formation, and shortening of the fornices. In mucous membrane pemphigoid, ocular involvement is seen in 61% to 70% of patients; the most frequent ocular finding is cicatricial conjunctivitis. Patients with autoimmune bullous diseases having common ocular involvement should be assessed by an ophthalmologist to avoid serious complications. Diagnostic procedures and treatment require multidisciplinary care based on the close cooperation between dermatologists and ophthalmologists.

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.

Short-Term Clinical Outcomes of a Novel Corneal Prosthetic Device in a Rabbit Model

PURPOSE

To evaluate the clinical performance and biocompatibility of a novel synthetic corneal device.

METHODS

Synthetic, single-piece, foldable, suturable, optic-and-skirt design prototype devices were fabricated using expanded polytetrafluoroethylene. A combination of intralamellar and full-thickness penetrating techniques was used for implantation. A topical antibiotic-steroid regimen was used postoperatively. Rabbits were examined weekly using penlight and at monthly intervals under an operating microscope with integrated optical coherence tomography. Optical quality, retention, and complication rates at 3 and 6 months were assessed.

RESULTS

Nineteen rabbits underwent surgery. There were no device-related intraoperative complications. Creation of lamellar pocket was problematic in 2 younger rabbits with inadequate chamber depth. Two rabbits had early postoperative infectious keratitis attributed to bandage contact lens wear, which was ceased. Rabbits were treated using fourth-generation fluoroquinolone drops and did well over a period of 6 months without device extrusion or further complications. Four other rabbits had late postoperative infectious keratitis because of exposed suture(s), which progressed to endophthalmitis. One rabbit had sterile keratolysis and retraction of the anterior corneal lamella. There was no retinal detachment, glaucoma, anterior or posterior synechiae, or cataract formation in any of the rabbits. All devices remained in situ with clear optics without spoliation. Light microscopic examination of the globes demonstrated intact epithelium overlying the skirt and new collagen integration into the porous structure of the skirt without significant inflammation.

CONCLUSION

Our results demonstrated favorable short-term anatomical clinical outcomes of this novel synthetic corneal prosthesis. Further studies are warranted to characterize the biointegration of this device.

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.

Ocular involvement in epidermolysis bullosa acquisita with long-term follow-up

Background/aims

To describe the ocular manifestations associated with epidermolysis bullosa acquisita (EBA).

Methods

This retrospective study was conducted at a tertiary bullous disease clinic. Consecutive patients were enrolled with biopsy proven diagnosis of EBA, with ocular involvement and a follow-up of at least 36 months. A multidisciplinary team of dermatologists, ENT specialists and ophthalmologists evaluated all patients. Immunological workup included direct (including immune-electron microscopy) and indirect immunofluorescence. Ophthalmological examination included best-corrected visual acuity (BCVA) and slit-lamp examination with grading of conjunctival fibrosis using the Tauber classification.

Results

Nine patients (five females, four males) were included. The mean age at diagnosis was 32 years (range 1–52 years). Follow-up ranged from 3 to 18 years (mean 10.7 years). Conjunctival fibrosis was present in all affected eyes and was stage III or greater in 60% of patients. Eight patients (14 eyes) had corneal involvement most frequently associated with trichiasis-associated mechanical irritation or extensive cicatrising conjunctivitis. Corneal lesions developed on three eyes of three patients without eyelid disease or severe fibrosis or any identifiable triggering factor. Eyelids were affected in six patients, with trichiasis being the most common feature (affecting three patients, four eyes). Corneal-related blindness occurred in at least one eye in 44% of the patients.

Conclusion

EBA may be associated with devastating ocular manifestations. Most patients develop severe cicatrising conjunctivitis. A subset of patients may present with isolated corneal lesions. Further studies are warranted to assess the effects of systemic treatments on the evolution of ocular manifestations.

Oral mucosa grafting in periorbital reconstruction

To provide an extensive literature review on the clinical indications of oral mucosa grafts (OMG) and minor salivary gland grafts (MSGG) in periorbital reconstruction together with safe practice graft harvesting techniques to minimize donor-site morbidity. A literature review was performed by searching the databases of PUBMED, EMBASE, and COCHRANE library using the keywords: minor salivary glands; oral mucosal graft; orbit; and eye. The bibliographies of the pertinent articles were examined for additional papers. Indications for OMG include treatment of recurrent pterygia; socket contracture in anophthalmic patients; repair of eyelid deformities; ocular surface and fornix reconstruction following tumour resection, cicatricial ocular surface disorders, or chemical burns. More novel uses include repair of glaucoma aqueous drainage device erosions or leaking trabeculectomy blebs; scleral buckle exposure; and keratoprosthesis-related corneal melts as well as lining the dacryocystorhinostomy tract to prevent closure. Simultaneous MSGG transplantation may be used in the treatment of severe dry eyes or dry anophthalmic cavities. Harvesting from the inner cheek is preferred to lower lip as it causes less post-operative discomfort and neurosensory deficits. Suturing is recommended for smaller ovoid grafts as it allows less painful closure without tension, while larger rectangular defects are best left to heal by secondary intention. OMG and MSGG transplantation is a viable alternative to replace conjunctiva and restore the ocular surface. The donor site is readily accessible and widely available in most patients, grafting is fast and cheap, and the same site may undergo repeated harvesting with few donor site complications.

Macroporous thin membranes for cell transplant in regenerative medicine

The aim of this paper is to present a method to produce macroporous thin membranes made of poly (ethyl acrylate-co-hydroxyethyl acrylate) copolymer network with varying cross-linking density for cell transplantation and prosthesis fabrication. The manufacture process is based on template techniques and anisotropic pore collapse. Pore collapse was produced by swelling the membrane in acetone and subsequently drying and changing the solvent by water to produce 100 microns thick porous membranes. These very thin membranes are porous enough to hold cells to be transplanted to the organism or to be colonized by ingrowth from neighboring tissues in the organism, and they present sufficient tearing stress to be sutured with surgical thread. The obtained pore morphology was observed by Scanning Electron Microscope, and confocal laser microscopy. Mechanical properties were characterized by stress-strain experiments in tension and tearing strength measurements. Morphology and mechanical properties were related to the different initial thickness of the scaffold and the cross-linking density of the polymer network. Seeding efficiency and proliferation of mesenchymal stem cells inside the pore structure were determined at 2 h, 1, 7, 14 and 21 days from seeding.

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.

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.

Treatment strategies in mucous membrane pemphigoid

Mucous membrane pemphigoid (MMP) is an autoimmune blistering disorder that is characterized by subepithelial bullae. Various basement membrane zone components have been identified as targets of autoantibodies in MMP. Considerable variability exists in the clinical presentation of MMP. Mucous membranes that may be involved include the oral cavity, conjunctiva, nasopharynx, larynx, esophagus, genitourinary tract, and anus. A multidisciplinary approach is essential in the management of MMP. Early recognition of this disorder and treatment may decrease disease-related complications. The choice of agents for treatment of MMP is based upon the sites of involvement, clinical severity, and disease progression. For more severe disease, or with rapid progression, systemic corticosteroids are the agents of choice for initial treatment, combined with steroid-sparing agents for long-term maintenance. Due to the rarity of this disease, large controlled studies comparing the efficacy of various agents are lacking.

Keratoprostheses in clinical practice - a review

The search for a substitute for the natural cornea dates back more than 200 years. Although several devices have been developed and trialled, very few have had successful long-term results and continue in regular clinical use. Keratoprosthesis (KPro) surgery is complex and should be performed in centres with an experienced multidisciplinary team. Currently available KPro devices range from the totally synthetic, such as the Boston KPro, to the totally biological tissue-engineered artificial cornea. The osteo-odonto keratoprothesis combines a synthetic optic with a biological haptic. All keratoprostheses have significant limitations, although visual improvement is possible with each of the devices in clinical use today. This review discusses these devices with emphasis on their indications, surgical techniques and results, before briefly exploring emerging devices and innovative approaches for the future.

Collagen and glycopolymer based hydrogel for potential corneal application

6-Methacryloyl-alpha-D-galactopyranose (MG) was synthesized, and characterized by Fourier transform infrared (FTIR) and nuclear magnetic resonance (NMR) spectrometry, and single-crystal X-ray diffraction. A series of interpenetrating polymer network (IPN) hydrogels was fabricated by simultaneously photocuring MG crosslinked by poly(ethylene glycol) diacrylate and chemically crosslinking type I collagen with 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide and N-hydroxysuccinimide. The successful incorporation of the glycopolymer, polymer MG, into collagen hydrogel was confirmed by FTIR and solid-state (13)C NMR. The optical characteristics of the IPN hydrogels are comparable to those of human corneas. The tensile strength and modulus of the hydrogels are enhanced by incorporation of polymer MG in comparison to that of the control collagen hydrogel. Biodegradation results indicated that polymer MG enhanced the stability of the composite hydrogels against collagenase. In vitro results demonstrated that the IPN hydrogel supported the adhesion and proliferation of human corneal epithelial cells and outperformed human cornea in blocking bacteria adhesion. Taken together, the IPN hydrogel might be a promising material for use in corneal lamellar keratoplasty.

Nucleation and growth of apatite on NaOH-treated PEEK, HDPE and UHMWPE for artificial cornea materials

The skirt of an artificial cornea must integrate the implant to the host sclera, a major failure of present devices. Thus, it is highly desirable to encourage the metabolic activity of the cornea by using more bioactive, flexible skirt materials. Here we describe attempts to increase the bioactivity of polyether ether ketone (PEEK), high-density polyethylene (HDPE) and ultra-high molecular weight polyethylene (UHMWPE) films. The effectiveness of different strength NaOH pre-treatments to initiate apatite deposition on PEEK, HDPE and UHMWPE is investigated. We find that exposure of PEEK, HDPE and UHMWPE films to NaOH solutions induces the formation of potential nuclei for apatite (calcium phosphate), from which the growth of an apatite coating is stimulated when subsequently immersing the polymer films in 1.5 strength Simulated Body Fluid (SBF). As immersion time in SBF increases, further nucleation and growth produces a thicker and more compact apatite coating that can be expected to be highly bioactive. Interestingly, the apatite growth is found to also be dependent on both the concentration of NaOH solution and the structure of the polymer surface.

Topical bevacizumab and ocular surface neovascularization in patients with stevens-johnson syndrome

PURPOSE

To evaluate the efficacy and safety of topical bevacizumab on ocular surface neovascularization among patients with Stevens-Johnson syndrome.

METHODS

This was a retrospective, interventional case report. Three eyes of 2 patients were examined. Bevacizumab (25 mg/mL) eyedrops were applied 4 times daily for a period of 3 months. Main outcome measures were improvement of symptoms, visual acuity, degree of ocular surface neovascularization, corneal opacification, conjunctival injection, and occurrence of adverse events.

RESULTS

Both patients completed the 3-month observation period and reported that it significantly improved ocular comfort. At the end of the study period, visual acuity improved in all 3 eyes; all eyes were observed to have decreased ocular surface neovascularization, corneal opacification, and conjunctival injection. No serious adverse events were reported.

CONCLUSIONS

Topical bevacizumab is well tolerated and may be effective in improving comfort and inducing regression of ocular surface neovascularization, conjunctival injection, and corneal opacification in patients with ocular surface disease caused by Stevens-Johnson syndrome. Further controlled and long-term studies are needed to fully evaluate the long-term effects of this novel treatment.