[Long-term visual outcomes of Boston type I keratoprosthesis in Canada]

BACKGROUND/PURPOSE

To evaluate long-term visual outcomes of Boston type I keratoprosthesis (KPro) surgery and identify risk factors for visual failure.

METHODS

Single surgeon retrospective cohort study including 85 eyes of 74 patients who underwent KPro implantation to treat severe ocular surface disease, including limbal stem cell deficiency, postinfectious keratitis, aniridia and chemical burns. Procedures were performed at the Centre hospitalier de l'Université de Montréal from October 2008 to May 2012. All patients with at least 5 years of follow-up were included in the analysis, including eyes with repeated KPro. Main outcome measures were visual acuity (VA), visual failure, defined as a sustained VA worse than the preoperative VA, postoperative complications, and device retention.

RESULTS

Mean follow-up was 7.2±1.3 years (±SD). Mean VA was 2.1±0.7 (logarithm of minimal angle resolution) preoperatively and 1.9±1.2 at last follow-up. In total, 2.4% of patients had VA better than 20/200 preoperatively vs. 36.5% at last follow-up. Maintenance of improved postoperative VA was seen in 61.8% of eyes at 7 years. Preoperative factors associated with visual failure were known history of glaucoma (HR=2.7 [1.2 to 5.9], P=0.02) and Stevens-Johnson syndrome (HR=7.3 [2.5 to 21.4], P<0.01). Cumulative 8-year complication rates were 38.8% retroprosthetic membrane formation, 25.9% hypotony, 23.5% new onset glaucoma, 17.6% retinal detachment, 8.2% device extrusion and 5.9% endophthalmitis. The majority (91.8%) of eyes retained the device 8 years after implantation.

CONCLUSION

Nearly two-thirds of patients exhibited improved VA 7 years after KPro implantation. Preoperative risk factors for visual failure were known glaucoma and Stevens-Johnson syndrome.

Integration and remodelling of a collagen anterior lamellar keratoplasty graft in an animal model - A preliminary report

There is an international shortage of donor corneas for transplantation to treat the 1.5-2.0 million new cases of blindness secondary to corneal disease. Research has therefore been directed towards the development of artificial corneas using alternative materials such as collagen. The biocompatibility of an acellular collagen-based scaffold for anterior lamellar keratoplasty was investigated in vivo in a rabbit model. This scaffold has previously shown promise as a corneal substitute in vitro. Slit-lamp and Optical Coherence Tomography examinations were carried out at 2 weeks, 1, 2, 3, and 6 months post-operatively. Graft-host integration was investigated using immunohistochemistry of the cornea at 6 months. Results showed that the graft was biocompatible, supported corneal re-epithelialisation, and showed no signs of rejection. Migration of stromal cells into areas of the graft was observed, however this was accompanied by extensive graft digestion. Whilst the scaffold was biocompatible, further modifications to the material or supplementation with matrix metalloproteinase inhibitors are required to bring us closer to a stable and fully integrated corneal substitute.

A Foldable Nonpenetrating Keratoprosthesis: Medium to Long-Term Clinical Results in Patients with Corneal Blindness due to Noninflammatory Anterior Cornea Disease

PURPOSE:

To report the medium to long-term safety and performance outcomes of the KeraKlear nonpenetrating artificial cornea (KeraKlear) as the primary procedure in patients with corneal blindness due to noninflammatory anterior cornea disease.

METHODS:

Fifteen patients with corneal blindness (preoperative visual acuity [VA] of ≥20/200) due to a non-inflammatory anterior corneal condition were included in this prospective, single-center study. Preoperative diagnoses included corneal scars, keratoconus, and corneal dystrophies. Diseased corneas were implanted with the KeraKlear (KeraMed Inc., Irvine, California, USA) by a single surgeon (JMV) using a femtosecond laser to create all incisions. Participants were followed up with for as long as 64 months. Uncorrected Snellen VA and postoperative complications were recorded.

RESULTS:

The average age at the time of surgery was 49.6 years old and 67% of patients were female. The patients experienced an average improvement in uncorrected Snellen VA of 7.6 lines (−1.17 logMAR). Average uncorrected vision at the last visit was 20/100 (0.73 logMAR), and median uncorrected vision at the last visit was 20/70 (0.54 logMAR). One patient experienced extrusion of the KeraKlear due to infection. There were no cases of glaucoma, retroprosthetic membrane, or endophthalmitis, the three most common complications of penetrating keratoprostheses (KPro).

CONCLUSIONS:

Medium and long-term outcomes of the KeraKlear indicate that this device is a viable alternative to corneal transplantation as a primary procedure in patients with non-inflammatory causes of corneal blindness, especially when corneal tissue is not available. The KeraKlear does not penetrate into the anterior chamber, and therefore, is less susceptible to the most common complications of penetrating KPro including endophthalmitis, glaucoma, and retroprosthetic membrane. The KeraKlear also has a comparable or improved adverse event rate compared to penetrating keratoplasty.

Development, structure, and bioengineering of the human corneal stroma: A review of collagen-based implants

Bio-engineering technologies are currently used to produce biomimetic artificial corneas that should present structural, chemical, optical, and biomechanical properties close to the native tissue. These properties are mainly supported by the corneal stroma which accounts for 90% of corneal thickness and is mainly made of collagen type I. The stromal collagen fibrils are arranged in lamellae that have a plywood-like organization. The fibril diameter is between 25 and 35 nm and the interfibrillar space about 57 nm. The number of lamellae in the central stroma is estimated to be 300. In the anterior part, their size is 10-40 μm. They appear to be larger in the posterior part of the stroma with a size of 60-120 μm. Their thicknesses also vary from 0.2 to 2.5 μm. During development, the acellular corneal stroma, which features a complex pattern of organization, serves as a scaffold for mesenchymal cells that invade and further produce the cellular stroma. Several pathways including Bmp4, Wnt/β-catenin, Notch, retinoic acid, and TGF-β, in addition to EFTFs including the mastering gene Pax-6, are involved in corneal development. Besides, retinoic acid and TGF- β seem to have a crucial role in the neural crest cell migration in the stroma. Several technologies can be used to produce artificial stroma. Taking advantage of the liquid-crystal properties of acid-soluble collagen, it is possible to produce transparent stroma-like matrices with native-like collagen I fibrils and plywood-like organization, where epithelial cells can adhere and proliferate. Other approaches include the use of recombinant collagen, cross-linkers, vitrification, plastically compressed collagen or magnetically aligned collagen, providing interesting optical and mechanical properties. These technologies can be classified according to collagen type and origin, presence of telopeptides and native-like fibrils, structure, and transparency. Collagen matrices feature transparency >80% for the appropriate 500-μm thickness. Non-collagenous matrices made of biopolymers including gelatin, silk, or fish scale have been developed which feature interesting properties but are less biomimetic. These bioengineered matrices still need to be colonized by stromal cells to fully reproduce the native stroma.

Femtosecond Laser-Assisted Surgery for Implantation of Bioengineered Corneal Stroma to Promote Corneal Regeneration

The femtosecond laser has achieved widespread use in ophthalmology owing to its ability to deliver focused high energy that is rapidly dissipated and thereby does not damage surrounding tissue outside the precise focal region. Extremely accurate and smooth cuts can be made by the laser, enabling a range of applications in anterior segment surgery. Minimally invasive corneal surgical procedures can be performed using the femtosecond laser, and here we describe the application of such procedures to improve implantation of bioengineered materials into the cornea. Bioengineered corneal tissue, including the collagenous corneal stroma, promises to provide a virtually unlimited supply of biocompatible tissue for treating multiple causes of corneal blindness globally, thereby circumventing problems of donor tissue shortages and access to tissue banking infrastructure. Optimal implantation of bioengineered materials, however, is required, in order to facilitate postoperative wound healing for the maintenance of corneal transparency and avoidance of postoperative complications such as scarring, inflammation, and neovascularization. Moreover, the avoidance of a detrimental physiological physiological wound healing response is critical for facilitating the corneal stromal regeneration enabled by the bioengineered stroma. Without proper implantation, the tissue response will favor inflammation and pathologic processes instead of quiescent keratocyte migration and new collagen production. Here we describe several procedures for optimized biomaterial implantation into the corneal stroma, that facilitate rapid wound healing and regenerative restoration of corneal transparency without the use of human donor tissue. A step-by-step methodology is provided for the use of the femtosecond laser and associated techniques, to enable seamless integration of bioengineered materials into the corneal stroma.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSION

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

Boston keratoprosthesis type 1 for limbal stem cell deficiency after severe chemical corneal injury: A systematic review

PURPOSE

To systematically review the published literature on outcomes of Boston keratoprosthesis type 1 for the treatment of limbal stem cell deficiency secondary to severe chemical corneal injury.

METHODS

Literature searches were conducted in MEDLINE (Ovid), Embase, Web of Science, and the Cochrane Central Register. The main outcome measures assessed were the proportion of eyes with best-corrected visual acuity (BCVA) ≥ 20/200 and the proportion retaining their original keratoprosthesis, both at the last recorded visit.

RESULTS

We identified 9 reports in which outcomes of Boston keratoprosthesis type I implantation after severe chemical injury could be determined, encompassing a total of 106 eyes of 100 patients. There were no randomized controlled studies. The median pre-operative BCVA was hand motion. Vision improved to ≥20/200 in 99/106 (93.4%) eyes after implantation. With a mean follow-up of 24.99 ± 14 months, 68/106 (64.1%) eyes retained BCVA ≥ 20/200 at the last examination. Therefore, 68/99 (68.7%) of those who improved to > 20/200 maintained at least this acuity. The originally implanted device was retained in 88/99 (88.9%) recipients for whom retention was reported. The mean time to failure was 22.36 ± 17.2 months. Glaucomatous optic neuropathy was the most common cause for BCVA <20/200 in eyes that retained the keratoprosthesis (18/27, 66.7%)..

CONCLUSIONS

Implantation of a Boston keratoprosthesis type I in eyes with corneal blindness after severe chemical ocular injury leads to functional vision in the majority of recipients. Evidence was limited by variability in outcome reporting and an absence of controlled studies..

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

BACKGROUND

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

MATERIAL AND METHODS

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

RESULTS

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

CONCLUSION

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

Biocompatibility of a fish scale-derived artificial cornea: Cytotoxicity, cellular adhesion and phenotype, and in vivo immunogenicity

PURPOSE

To determine whether a fish scale-derived collagen matrix (FSCM) meets the basic criteria to serve as an artificial cornea, as determined with in vitro and in vivo tests.

METHODS

Primary corneal epithelial and stromal cells were obtained from human donor corneas and used to examine the (in)direct cytotoxicity effects of the scaffold. Cytotoxicity was assessed by an MTT assay, while cellular proliferation, corneal cell phenotype and adhesion markers were assessed using an EdU-assay and immunofluorescence. For in vivo-testing, FSCMs were implanted subcutaneously in rats. Ologen(®) Collagen Matrices were used as controls. A second implant was implanted as an immunological challenge. The FSCM was implanted in a corneal pocket of seven New Zealand White rabbits, and compared to sham surgery.

RESULTS

The FSCM was used as a scaffold to grow corneal epithelial and stromal cells, and displayed no cytotoxicity to these cells. Corneal epithelial cells displayed their normal phenotypical markers (CK3/12 and E-cadherin), as well as cell-matrix adhesion molecules: integrin-α6 and β4, laminin 332, and hemi-desmosomes. Corneal stromal cells similarly expressed adhesion molecules (integrin-α6 and β1). A subcutaneous implant of the FSCM in rats did not induce inflammation or sensitization; the response was comparable to the response against the Ologen(®) Collagen Matrix. Implantation of the FSCM in a corneal stromal pocket in rabbits led to a transparent cornea, healthy epithelium, and, on histology, hardly any infiltrating immune cells.

CONCLUSION

The FSCM allows excellent cell growth, is not immunogenic and is well-tolerated in the cornea, and thus meets the basic criteria to serve as a scaffold to reconstitute the cornea.

The Usage of a Conjunctival Flap to Improve Retention of Boston Type 1 Keratoprosthesis in Severe Ocular Surface Disease

PURPOSE

The Boston keratoprostheses type 1 devices (KPro) are utilized in cases unfavorable to penetrating keratoplasty. The prognosis remains guarded in cases of ocular surface disease due to risk of tissue necrosis. We describe a novel surgical approach using a conjunctival flap with a delayed opening to improve retention.

METHODS

In three patients with advanced cicatrizing conjunctivitis, a Type 1 keratoprosthesis was stabilized using a full tarsal conjunctival flap. Three months postoperatively, an opening was created in the flap overlying the optical portion of the device.

RESULTS

All patients had no device related complications over a mean follow-up period of 17.7 months (range 15-21 months) and vision remained excellent at better than 20/200 for all patients.

CONCLUSIONS

Utilization of a tarsal flap either primarily as part of a two stage modified technique or secondarily in cases of tissue necrosis and impending device extrusion might maximize retention of the type 1 KPro.

In vitro collagen fibril alignment via incorporation of nanocrystalline cellulose

This study demonstrates a method for producing ordered collagen fibrils on a similar length scale to those in the cornea, using a one-pot liquid-phase synthesis. The alignment persists throughout samples on the mm scale. The addition of nanocrystalline cellulose (NCC), a biocompatible and widely available material, to collagen prior to gelation causes the fibrils to align and achieve a narrow size distribution (36±8nm). The effects of NCC loading in the composites on microstructure, transparency and biocompatibility are studied by scanning electron microscopy, ultraviolet-visible spectroscopy and cell growth experiments. A 2% loading of NCC increases the transparency of collagen while producing an ordered microstructure. A mechanism is proposed for the ordering behavior on the basis of enhanced hydrogen bonding during collagen gel formation.