Deposits in artificial corneas: risk factors and prevention

Biocompatibility and Transplantation Efficacy of the C-Clear Artificial Cornea in a Rabbit Chemical Burn Model

We investigated the bioavailability and stability of a C-Clear artificial cornea in a rabbit chemical burn model. Thirty-six rabbits were divided into a control group (n = 16) and a chemical burn group that used NaOH solution (n = 20). After lamellar dissection, the central posterior lamella was excised using a 3 mm diameter trephine, and an artificial cornea was transplanted into the lamellar pocket. After 2 weeks, the central anterior lamella was excised using a 3 mm diameter trephine to secure a clean visual axis. We examined the anterior segment of the eyes weekly for 12 weeks after transplantation. Successful subjects whose artificial corneas were maintained stably for 12 weeks were euthanized and underwent histologic examinations. Artificial corneas remained stable for up to 12 weeks in 62.5 and 50% of rabbits in the control and chemical burn groups, respectively. Two rabbits in the chemical burn group showed the formation of a retroprosthetic membrane, and one rabbit with visual axis blockage underwent membrane removal using a Nd:YAG laser. In histologic examinations, adhesion between artificial cornea and peripheral corneal stoma was observed. In conclusion, we confirmed structural stability and biocompatibility of the C-Clear artificial cornea for up to 12 weeks after implantation in control and chemical burn groups.

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.

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.

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.

Biocompatibility of poly(ethylene glycol) and poly(acrylic acid) interpenetrating network hydrogel by intrastromal implantation in rabbit cornea

We evaluated the biocompatibility of a poly(ethylene glycol) and poly(acrylic acid) (PEG/PAA) interpenetrating network hydrogel designed for artificial cornea in a rabbit model. PEG/PAA hydrogel measuring 6 mm in diameter was implanted in the corneal stroma of twelve rabbits. Stromal flaps were created with a microkeratome. Randomly, six rabbits were assigned to bear the implant for 2 months, two rabbits for 6 months, two rabbits for 9 months, one rabbit for 12 months, and one rabbit for 16 months. Rabbits were evaluated monthly. After the assigned period, eyes were enucleated, and corneas were processed for histology and immunohistochemistry. There were clear corneas in three of six rabbits that had implantation of hydrogel for 2 months. In the six rabbits with implant for 6 months or longer, the corneas remained clear in four. There was a high rate of epithelial defect and corneal thinning in these six rabbits. One planned 9-month rabbit developed extrusion of implant at 4 months. The cornea remained clear in the 16-month rabbit but histology revealed epithelial in-growth. Intrastromal implantation of PEG/PAA resulted in a high rate of long-term complications.

Lamellar corneal lenticule graft to treat keratolysis after AlphaCor keratoprosthesis implantation

PURPOSE

Clinical assessment of AlphaCor keratoprosthesis and evaluation of surgical method to treat keratolysis in case of stromal necrosis occurrence.

METHODS

This is a noncomparative, retrospective, interventional case series. The medical records of 12 eyes of 12 patients who underwent consecutive AlphaCor keratoprosthesis implantations were reviewed. Patients with severe bilateral corneal pathology unsuitable for a conventional corneal graft, a best-corrected visual acuity (BCVA) from light perception (LP) to 20/200, with no active ocular surface inflammation, controlled intraocular pressure prior to the surgery, and an unstimulated Schirmer test of &gt;2.5 mm at 5 minutes were included. Postoperative medications included topical dexamethasone, ciprofloxacin, and 2% cyclosporine A. Main outcome measures included BCVA and complications occurrence.

RESULTS

After a mean follow-up of 25 ± 12.3 months (range 2-38 months), 8 (66.7%) AlphaCor devices were retained. Postoperative BCVA ranged from LP to 20/63 (mean gain of 2.5 ± 3.1 lines). Seven cases of stromal melt (58.3%) occurred. Three were reversed to penetrating keratoplasty and 3 had a donor corneal layer fixated over the AlphaCor with satisfactory results (mean follow-up 23 ± 1.6 months). There were no instances of endophthalmitis, retinal detachment, or glaucoma exacerbation.

CONCLUSIONS

AlphaCor showed a low incidence of the classic keratoprosthesis complications but a high occurrence of recipient cornea necrosis. Corneal melts were successfully managed in 3 cases by lamellar corneal lenticule graft, thereby increasing the retention of AlphaCor and maintaining BCVA.

Progress in the development of a corneal replacement: keratoprostheses and tissue-engineered corneas

Rapid progress has been made in the past 5 years in the development of corneal replacements. Traditionally they are divided into two categories, keratoprostheses and tissue-engineered corneal equivalents, as replacement tissues are increasingly in demand worldwide. There are currently several different keratoprosthesis models in clinical use around the world. The most popular and most widely publicized is the AlphaCor model, which has enjoyed significant clinical success. However, improvements remain to be made, and the aim of most of the current research is to better understand the interactions between a synthetic material and the surrounding biology on a more fundamental level. This improved understanding will no doubt lead to improvements in current models and to the development of new models in the near future. While tissue-engineered corneal equivalents have been under investigation for considerably less time, there is growing evidence to suggest that a tissue-engineered corneal equivalent comprised of primarily natural materials will exist in the not too distant future. Research groups have reported strong in vitro and in vivo results. The strength of the collagen matrix and its ability to support cell infiltration have been the primary avenues of research. Various collagen crosslinking techniques have been used. Infiltration of three major cells of the cornea has been observed. Most importantly, the ability of these materials to support nerve ingrowth has been demonstrated. While challenges remain with both types of corneal replacements, the considerable progress in the recent past suggests that reliable implants for the treatment of a variety of corneal diseases will be available. This review will provide an overview of recent results, and will provide insight into the future of research on corneal replacements.

Corneal biomechanics and biomaterials

The ability to clearly observe one's environment in the visible spectrum provides a tremendous evolutionary advantage in most of the world's habitats. The complex optical processing system that has evolved in higher vertebrate animals gathers, focuses, detects, transduces, and interprets incoming visible light. The cornea resides at the front end of this imaging system, where it provides a clear optical aperture, substantial refractive power, and the structural stability required to protect the fragile intraocular components. Nature has resolved these simultaneous design requirements through an exceedingly clever manipulation of common extracellular-matrix structural materials (e.g., collagen and proteoglycans). In this review, we (a) examine the biophysical and optical roles of the cornea, (b) discuss increasingly popular approaches to altering its natural refractive properties with an emphasis on biomechanics, and (c) investigate the fast-rising science of corneal replacement via synthetic biomaterials. We close by considering relevant open problems that would benefit from the increased attention of bioengineers.

AlphaCor artificial cornea: clinical outcome

PURPOSE

The purpose of this study was to describe the long-term results of AlphaCor implantations, and to evaluate the main complications and risk factors.

METHODS

Retrospective analysis of preoperative and follow-up data from 15 AlphaCor implantations. Analysis of outcomes, trends, and associations was performed and compared with data from published clinical trials and a literature review.

RESULTS

The survival rate of the device at 1, 2, and 3 years was 87%, 58%, and 42%, respectively. Postoperative visual acuity ranged from hand movement to 0.8. The most significant complications were stromal melt (nine cases), optic deposition (three eyes), and retroprosthetic membrane formation (three eyes). The most common device-unrelated complication was trauma (three patients). All complications were managed without loss of the eye.

CONCLUSION

AlphaCor provides a treatment option for patients with corneal blindness in which a donor tissue graft would not succeed.

AlphaCor keratoprosthesis: postoperative development of six patients

PURPOSE

AlphaCor (Argus Biomedical Pty. Ltd., Perth, Australia) is an artificial, soft, one-piece keratoprosthesis (KPro) indicated for severe corneal conditions not treatable by a donor graft. To evaluate the efficacy and visual restoring of six patients with complete corneal opacification and deep neovascularizations treated with AlphaCor.

METHODS

A retrospective review of six patients with a history of corneal opacification treated with keratoprosthesis surgery. AlphaCor synthetic cornea was implanted into the corneal stroma. During the follow-up time, slit-lamp and ultrasound examinations, best corrected visual acuity (BCVA), and intraocular pressure measurements were performed.

RESULTS

Six eyes with corneal scarring and vascularizations in three to four quadrants of six patients to years of age underwent a keratoprosthesis procedure. The follow-up time was 13-36 months; mean 23 months. The operation procedure was not limited by severe complications. The preoperative BCVA was hand movement to light perception. The postoperative BCVA ranged between 20/200 and 80/100. Intraocular pressure was controlled in all cases. Three patients developed a melting of the anterior corneal lamella. The keratoprosthesis had to be explanted (15-34 months after implantation) and was replaced by a donor cornea.

CONCLUSIONS

Further evaluation is needed to evaluate the role of AlphaCor as a keratoprosthesis.

Complications of AlphaCor keratoprosthesis: a clinicopathologic report

PURPOSE

To describe the clinical and histopathologic features of intractable secondary glaucoma induced by AlphaCor keratoprosthesis.

METHODS

An elderly woman with pseudoexfoliation glaucoma and pseudophakic bullous keratopathy in the right eye had graft failures after penetrating keratoplasty. Her best-corrected visual acuity at presentation was counting fingers in the right eye and 20/30 in the left eye. Examination showed severe corneal neovascularization. Chirila keratoprosthesis type II was implanted in 2 stages. Ten months later, the patient developed dense retrocorneal membrane, 360 degrees occlusion of angles, intractable glaucoma, no light perception, and nasal stromal melting associated with partial extrusion of the keratoprosthesis.

RESULTS

Histopathology revealed invasion of the porous material of the keratoprosthesis by reactive fibroblasts and multinucleated foreign-body giant cells. In the area of dehiscence, we noted thinning and lysis of the collagen fibers, infiltration of lymphocytes, and plasma cells with a sheet of fibroinflammatory tissue extending into the anterior chamber.

CONCLUSIONS

Corneal stromal melting and retrocorneal prosthetic membrane formation after AlphaCor keratoprosthesis implantation led to intractable glaucoma and extrusion of the implant.

Clinicopathologic Correlation of Explanted AlphaCor Artificial Cornea After Exposure of Implant

PURPOSE

To describe the clinical presentation and histopathologic findings in a case of explantation of an AlphaCor artificial cornea implant caused by exposure of the skirt.

METHODS

We describe the case report of a 46-year-old man who suffered trauma to the right eye, resulting in 4 failed penetrating keratoplasties (PKPs). Subsequently, an AlphaCor implantation was performed with some visual improvement. Slightly more than 2 years after the implant, skirt exposure occurred, possibly secondary to infectious keratitis in an area of a ruptured bulla, and explantation was performed. Corneal stability was established with repeat corneal transplantation.

RESULTS

Histopathologic evaluation of the surgical specimen revealed chronic nongranulomatous inflammation and fibrosis in the peripheral skirt, indicating that biointegration was maintained. However, peripheral corneal stromal melting led to skirt exposure. Focal calcification, as well as retroprosthetic membrane formation, was also identified.

CONCLUSIONS

The AlphaCor implant is a viable method of treatment for multiple failed PKPs, but it may be associated with unique complications, including corneal stromal melting, focal calcification, and retroprosthetic membrane formation. Infectious keratitis may be a risk factor for corneal stromal melting and needs to be managed aggressively. Explantation of the implant is essential if the skirt is exposed.

Precipitation of calcium salts on a hydrophilic acrylic intraocular lens after a vitreous hemorrhage: case report and histopathologic correlation

We describe the formation of calcium phosphate deposits on the external anterior surface of a single-piece foldable 26% hydrophilic acrylic intraocular lens (IOL) after vitreal bleeding. The IOL was explanted 20 months after uneventful phacotrabeculectomy because opacification was causing significant visual disturbance. Light microscopy and Raman spectroscopy of the explanted IOL showed that the opacification consisted of calcium phosphate on the IOL surface.

AlphaCor: Clinical outcomes

PURPOSE

To study the outcomes of AlphaCor implantation.

METHODS

: The AlphaCor artificial cornea is indicated for corneal blindness not treatable by donor grafting. Prospective preoperative and follow-up data were collected. Data were evaluated using SPSS for statistical analysis of outcomes, trends, and associations.

RESULTS

This report includes data returned through February 28, 2006, for all 322 devices implanted, with mean follow-up in situ of 15.5 months and a maximum of 7.4 years. The probability of AlphaCor retention at 6 months and 1 and 2 years for protocol cases was 92%, 80%, and 62%, respectively, and off-label cases were at higher risk (P = 0.010), as were cases not prescribed medroxyprogesterone (MPG; P = 0.001). Currently, the most common complications were stromal melting, fibrous reclosure of the posterior lamellar opening, and white intraoptic deposits, with incidences in 2005 of 11.4%, 5.1%, and 2.6%, respectively. MPG seems to protect against melts, and eyes with a history of herpetic keratitis were not at increased risk. A history of glaucoma or the presence of tubes did not affect device retention. Complications culminated in loss of an eye in 1.3%. Mean preoperative visual acuity (VA) was hand movements. The VA achieved postoperatively (light perception to 20/20) was affected by previous pathology and postoperative course, with a mean improvement of 2 lines.

CONCLUSION

AlphaCor provides a treatment option where a donor tissue graft would not succeed in severe corneal conditions, while being reversible to a donor graft in the event of complications for anatomic integrity. Surgical technique and adjunctive therapies are evolving with experience. Continued data collection is important for a fuller understanding of AlphaCor's role.

Cultured human ocular surface epithelium on therapeutic contact lenses

BACKGROUND

This study was initiated after observation of some intriguing epithelial growth properties of contact lenses used as a bandage for patients after pterygium surgery.

AIM

To determine the efficacy of culturing human ocular surface epithelial cells on therapeutic contact lenses in autologous serum with a view of using this system to transfer epithelial cells to patients with persistent corneal or limbal defects.

METHODS

Excess graft tissue resected from patients undergoing pterygium surgery (n = 3) consisting of limbal epithelium was placed on siloxane-hydrogel contact lenses (lotrafilcon A and balafilcon A). Limbal explants were cultured in media with 10% autologous serum. Morphology, proliferative capacity and cytokeratin profile were determined by phase contrast, light and electron microscopy, and immunohistochemical analysis.

RESULTS

Lotrafilcon A contact lenses sustained proliferation and migration from limbal tissue. Cells became confluent after 10-14 days and consisted of 2-3 layers with a corneal phenotype (CK3(+)/CK12(+)/CK19(-)) and a propensity to proliferate (p63(+)). Electron microscopy showed microvilli on the apical surface with adhesive projections, indicating that these cells were stable and likely to survive for a long term. Growth was not observed from limbal explants cultured on balafilcon A contact lenses.

CONCLUSION

A method for culturing human ocular surface epithelium on contact lenses that may facilitate expansion and transfer of autologous limbal epithelial cells while avoiding the risks associated with transplanting allogeneic tissue has been developed. This technique may be potentially useful for the treatment of patients with limbal stem cell deficiency.

Screening for drug-induced spoliation of the hydrogel optic of the AlphaCor™ artificial cornea

Clinical experience and in vitro investigations demonstrated that AlphaCor, a hydrogel keratoprosthesis, can undergo both surface spoliation and internal depositions/colourations after exposure to certain medications, alone or in combination. While the most commonly used medications have not been associated with spoliation in vivo, many medications are reportedly used due to the complex co-pathologies in many recipients, and regional variations in available medications. We screened a number of drugs used or proposed by surgeons for use in AlphaCor patients to evaluate their potential to cause visually significant optic spoliation (surface or intragel, or colour changes). Poly(2-hydroxyethyl methacrylate) discs with an identical composition to AlphaCor's optic were incubated with each medication and then with simulated aqueous humour (SAH) at 37 degrees C for 7 days. They were then examined under magnification and by histology (selected samples). Clinical feedback for the test medications was reviewed and compared with the in vitro results. A minority of the drugs caused surface spoliation (TobraDex, Prednefrin Forte, Azopt) or colour staining (including Zymar, Vigamox, Quixin) when tested alone, but SAH appeared to promote hydrogel cloudiness and surface deposits. The in vitro spoliation occurred more frequently than in vivo reports of spoliation in recipients of the same medications. This study is consistent with earlier findings in demonstrating involvement of topical medications in hydrogel spoliation, although a much lower incidence of spoliation is reported for AlphaCor in human recipients than indicated by the laboratory findings. The interactions of biological fluids and drugs require further study.

Histology of AlphaCor skirts: evaluation of biointegration

PURPOSE

To report histologic findings in 14 AlphaCor artificial corneas implanted during clinical trials and subsequently explanted from human subjects following complications, so as to evaluate biointegration within the device skirt.

METHODS

Explants were fixed and sectioned in paraffin. Histologic findings related to the device skirt were compared with earlier histologic results from animal studies and correlated with clinical histories.

RESULTS

Two devices had been removed due to complications related to the optic alone, 11 following stromal melting overlying the biointegratable sponge skirt and 1 due to a retroprosthetic membrane. All devices demonstrated normal skirt porosity. Biointegration was similar to that found in animal studies but qualitatively appeared reduced in the affected areas in patients with overlying stromal melting prior to explantation. Patients with a longer history of melting prior to explantation demonstrated presence of inflammatory cells around the device.

CONCLUSIONS

Histologic findings of the AlphaCor skirt in humans are consistent with earlier animal studies. This study confirms that biointegration by host fibroblastic cells, with collagen deposition occurs after AlphaCor implantation in humans. In cases in which stromal melting had occurred, biointegration is seen to be reduced. On correlating preoperative clinical factors with biointegration observed histologically, preoperative vascularization appears not to be required for AlphaCor biointegration.

Current concepts and techniques in keratoprosthesis

PURPOSE OF REVIEW

Diseases affecting the cornea are a major cause of blindness worldwide, second only to cataract in overall importance, with an estimated 10 to 15 million affected people. Although keratoplasty is by far the most successful transplantation surgery, the outcomes in high-risk adult patients, including those with ocular surface diseases and multiple graft rejections, and in pediatric patients with congenital corneal opacities are disappointing.

RECENT DEVELOPMENTS

Regrettably, no significant clinical developments have been achieved in the field of corneal transplantation since the introduction of steroids for graft rejection. Furthermore, obtaining donor corneal tissues and eye banking, particularly in the developing countries where corneal blindness is most prevalent, are problematic. Although the postoperative complications may be severe and limit the use of currently available devices, keratoprosthesis--artificial corneal implantation--has a role in the management of corneal blindness in carefully selected patients with complex ocular diseases who are at high risk for graft failure.

SUMMARY

This article reviews the recent ophthalmic literature published on the current concepts and techniques of keratoprosthesis surgery.

Preliminary results after implantation of four AlphaCor artificial corneas

PURPOSE

The purpose was to evaluate the validity of implantation of the artificial cornea (AlphaCor) in human corneas considered too high risk for penetrating keratoplasty with donor tissue.

METHODS

Four keratoprostheses, made from poly(2-hydroxyethyl methacrylate) (PHEMA) with a porous skirt and a transparent optical part, were implanted into the cornea of four patients. Keratocytes invading the skirt provide a watertight fixation with the scarred corneal tissue. Deep to the clear optical part, the posterior corneal lamella was excised to a diameter of 3.5 mm before the device was implanted, and the anterior lamella was trephined similarly 3 months after AlphaCor implantation.

RESULTS

The eyes selected to receive an artificial cornea had significant neovascularisation, and 0-3 previous failed grafts. Follow-up for 6 months revealed best visual acuity between 20/400 and 20/50. Factors limiting the visual acuity outcome were optic atrophy and age-related macular disease. One patient underwent an extracapsular cataract extraction after the device was implanted, as a senile cataract was then noted. One complication occurred, a central corneal stromal melt, which was managed by covering with a 9-mm donor lamella.

CONCLUSION

The flexible device AlphaCor may provide a substitute for donor corneal tissue in desperate cases. Advantages include the simple implantation technique, which avoids trauma to the surrounding structures. Visual acuity results may be limited by pre-existing pathology, but it appears that a patient's visual potential can be achieved. Further follow-up to exclude long-term complications is required.

Two cases of AlphaCor surgery performed using a small incision technique

The authors have evaluated the AlphaCor artificial cornea (previously Chirila KPro) in human patients since 1998, utilizing an intrastromal technique requiring extensive corneal lamellar dissection and recommending conjunctival flaps in all cases. Recent availability of low-profile instruments has facilitated a simpler technique, which was first evaluated in two subjects followed for over 1 year prior to recommending the technique for wider adoption. The new technique is presented and illustrated herein, and its benefits and limitations compared with the traditional AlphaCor implantation are discussed.

Effect of multipurpose solutions for contact lens care on the in vitro drug-induced spoliation of poly(2-hydroxyethyl methacrylate) in simulated aqueous humour

Drug-induced spoliation of hydrogels as contact lenses or as implants in the anterior eye is a frequent occurrence in clinical practice. This study explores the capacity of three commercial multipurpose solutions for contact lens care to reduce the spoliation of poly(2-hydroxyethyl methacrylate) (PHEMA) specimens exposed to a simulated aqueous humour formulation and to three topical drugs commonly administered after insertion of artificial corneas (Predsol, Optimol and Depo-Ralovera). ReNu MultiPlus (Bausch & Lomb), Complete Blink-N-Cleantrade mark Lens Drops (Allergan) and Complete Protein Remover Tablets dissolved in Complete ComfortPLUS (both from Allergan) were evaluated. All multipurpose solutions were able to dislodge passively the deposits formed on hydrogels in the simulated aqueous and in the presence of Predsol and Optimol, but none were effective against the deposits induced by Depo-Ralovera. A reduction of the calcium content in deposits caused by Predsol and Optimol was confirmed after treatment with the protein remover preparation, while the other multipurpose solutions caused the complete removal of the deposits. In experiments designed to evaluate the preventive action of the multipurpose solutions, no such effects were observed regardless of the drug involved. The prospect of using multipurpose solutions as eye drops following implantation of a hydrogel artificial cornea is a valid alternative for reducing device spoliation, however it appears to depend on the nature of the postoperative medication.