Intra-operative optical coherence tomography in corneal lamellar graft reinforcement for Boston type I keratoprosthesis corneal melt

Corneal melt is a sight-threatening complication of Boston type 1 keratoprosthesis (KPro). Severe corneal melt may result in hypotony, choroidal hemorrhage, and even spontaneous extrusion of the KPro, which may lead to a poor visual prognosis. Lamellar keratoplasty is one surgical option for the management of mild corneal melt, especially when a new KPro is not available. Herein, we present a new surgical technique application, intra-operative optical coherence tomography (iOCT) for the management of cornea graft melt after Boston type 1 KPro implantation. The visual acuity and the intra-ocular maintained stable at 6 months post-operatively, and the KPro remained in place without corneal melting, epithelial ingrowth, or infection. iOCT may prove to be a real-time, non-invasive, and accurate treatment for corneal lamellar dissection and suturing beneath the anterior plate of the KPro, which can effectively help the surgeon to make surgical decisions and reduce post-operative complications.

Keratoprosthesis: Current global scenario and a broad Indian perspective

Keratoprosthesis (Kpro) forms the last resort for bilateral end-stage corneal blindness. The Boston Type 1 and 2 Kpros, the modified osteo-odonto Kpro and the osteo-Kpro are the more frequently and commonly performed Kpros, and this review attempts to compile the current data available on these Kpros worldwide from large single-center studies and compare the indications and outcomes with Kpros in the Indian scenario. Although the indications have significantly expanded over the years and the complications have reduced with modifications in design and postoperative regimen, these are procedures that require an exclusive setup, and a commitment toward long-term follow-up and post-Kpro care. The last decade has seen a surge in the number of Kpro procedures performed worldwide as well as in India. There is a growing need in our country among ophthalmologists to be aware of the indications for Kpro to facilitate appropriate referral as well as of the procedure to enable basic evaluation during follow-ups in case the need arises, and among corneal specialists interested to pursue the field of Kpros in understanding the nuances of these surgeries and to make a judicious decision regarding patient and Kpro selection and more importantly deferral.

Anterior segment optical coherence tomography findings in type I Boston keratoprosthesis / Achados de tomografia de coerência óptica do seguimento anterior em ceratoprótese de Boston tipo I

ABSTRACT Purpose: To report the results of high-resolution anterior segment optical coherence tomography of patients implanted with a type 1 Boston keratoprosthesis (KPro). Methods: The retrospective study cohort included 11 eyes of 11 patients (average age, 58.4 years; range, 34-83 years). All subjects underwent anterior segment optical coherence tomography at a single posteoperative time point. The main outcome measures were retro-backplate and retro-optic membrane formation, thinning and gap formation of the corneal carrier graft (melting), and degree of angle closure. Results: Preoperative diagnoses included chemical burn (55%), failed corneal transplant (36%), and Stevens-Johnson syndrome (9%). The mean postoperative follow-up duration was 38.5 (range, 12-72) months. The most frequent findings of anterior segment optical coherence tomography were retroprosthetic membrane formation (63%, 7/11), thinning of the corneal carrier graft (melting; 55%, 6/11), and a narrow or closed angle (91%, 10/11). Other less common findings were epithelial growth over the optic surface and periprosthetic cyst formation. Retroprosthetic membrane formation was observed in all patients with melting (6/11). Conclusions: Detailed postoperative examination and visualization of subtle changes of keratoprosthesis implanted eyes by slit lamp biomicroscopy are often difficult. Anterior segment optical coherence tomography is a useful, noninvasive, and quantitative imaging technique that provides useful information to postoperatively monitor the anatomic stability of an implanted keratoprosthesis.

RESUMO Objetivos: Reportar os resultados das imagens de pacientes com Ceratoprótese de Boston tipo I (KPro) usando tomografia de coerência óptica de alta resolução do seguimento anterior (AS-OCT). Métodos: Nós realizamos um estudo retrospectivo de pacientes submetidos à KPro. Um total de 11 olhos de 11 pacientes foram incluídos. As imagens de AS-OCT foram realizadas em um único tempo de pós-operatório. Os principais resultados incluem formação de membrana retroprostética atrás do prato posterior e atrás do cilindro ótico, afinamento e lacunas na córnea doadora (melt) e graus de ângulo fechado. Resultados: Os diagnósticos pré-operatórios inclui queimadura química (55%), falência pós transplante de córnea (36%) e síndrome de Stevens Johnson (9%). A idade média foi de 58.4 anos (escala, 34-83 anos). A média de tempo de pós-operatório foi de 38.5 meses (escala, 12-72 meses). Os achados mais frequentes de AS-OCT foram: membrana retroprostética, 63% (7/11); afinamento da córnea doadora (melting), 55% (6/11); angulo estreito ou fechado, 91% (10/11). Outros achados menos comuns foram crescimento epitelial sobre a superfície ótica e cistos periprostéticos. Todos os pacientes com melting (6/11) apresentaram membrana retroprostética. Conclusões: O exame pós-operatório e a visualização detalhada das mudanças em olhos com KPro pela lâmpada de fenda pode ser difícil. AS-OCT é uma técnica de imagem útil, não invasiva e quantitativa que permite o monitoramento da estabilidade anatômica no seguimento de KPro implantadas.

Desenlaces en pacientes operados con queratoprótesis boston tipo 1 en un centro oftalmológico especializado en la ciudad de Medellín / Outcomes in patients with boston type 1 keratoprosthesis in a specialized center in Medellín

Objetivo: reportar las características y descenlaces de pacientes con queratoprótesis Boston tipo 1. Diseño: estudio observacional descriptivo de corte transversal. Método: se incluyeron los pacientes operados con queratoprótesis Boston tipo 1 residentes en Colombia, mayores de 17 años, sin queratoprótesis previas y que tuviera más de 6 meses de seguimiento, para un total de 39 ojos de 39 pacientes. La cirugía se indicó en los casos con o sin queratoplastia previa que tuvieran agudeza visual (AV) igual o inferior a cuenta dedos y déficit de limbo bilateral o vascularización corneal profunda en más de 3 cuadrantes. Se recolectó y analizó la información de la historia clínica en forma retrospectiva y prospectiva. Las variables principales fueron: agudeza visual, retención del dispositivo y complicaciones. Se realizó un análisis univariado presentando los resultados en frecuencias absolutas y porcentajes para las variables categóricas y para las variables cuantitativas como promedio y desviación estándar (DE) si tienen distribución normal o como mediana y rango intercuartil si no tienen distribución normal. Resultados: La mediana de seguimiento fue de 53.5 meses (rango 6 meses a 10 años). La mayoría de pacientes (66.7%) habían tenido previamente queratoplastia penetrante. El diagnóstico de base fue en 53.8% condiciones no inflamatorias yen 46.2% condiciones inflamatorias. La AV preoperatoria en todos los ojos estaba entre percepción de luz y cuenta dedos; posterior a la cirugía el 97.4% tuvieron mejoría de la AV. Para el fi nal del seguimiento la AV permaneció mejor que la preoperatoria en 53.8%, fue igual a esta en 17.94% y peor que esta en 28.2%. Hubo necrosis periprostética en 28.2%, y 38.5% tuvieron recambio del dispositivo. Al final del seguimiento 89.7% de los pacientes tenían una queratoprótesis in-situ. Conclusión: la queratoprótesis Boston tipo 1 es una opción viable para mejorar la AV en pacientes con trasplantes de córnea fallidos o en quienes se prevé alta tasa de fallo o rechazo de este. En la gran mayoría de los pacientes se logra mejoría inicial significativa de la AV, la cual se mantiene al final del seguimiento en más de la mitad de ellos. Refinamientos progresivos en la técnica quirúrgica y el manejo postoperatorio disminuirán las complicaciones que llevan a la perdida visual progresiva

Purpose: to report characteristics and outcomes in patients with Boston type 1 keratoprosthesis. Design: observational descriptive cross-sectional study. Method: Patients with Boston type 1 queratoprosthesis who were living in Colombia, 17 years or older, without previous keratoprosthesis and with more than 6 months follow up were included, for a fi nal of 39 eyes from 39 patients. Surgery was indicated for those with or without previous keratoplasty who had visual acuity (VA) of counting fi ngers or worse and bilateral limbal stem cell deficiency or deep corneal vascularization in more than 3 quadrants. Information was collected retrospectively and prospectively from medical registries and was analyzed. Main variables were: visual acuity, device retention and complications. An univariate analysis was conducted and results are presented in absolute frequencies and percentages for categoric variables and for quantitative variables in average and standard deviation (SD) if they have normal distribution and in median and interquartile range if they do not have normal distribution. Results: Median follow up was 53.5 months (range 6 months to 10 years). Most patients (66.7%) had previous penetrating keratoplasty. Baseline diagnoses were in 53.8% non-infl ammatory conditions and in 46.2% inflammatory conditions. Preoperative VA ranged between light perception and counting fingers in all eyes; aft er surgery 97.4% had improvement in VA. By the end of follow up VA remained better than preoperative in 53.8%, was the same as preoperative in 17.94% and worse than preoperative in 28.2%. There was periprosthetic necrosis in 28.2%, and 38.5% had keratoprothesis exchange. At the end of follow up 89.7% of patients had a keratoprosthesis in-situ. Conclusion: Boston type 1 keratoprosthesis is a viable option to improve VA in patients with previously failed corneal transplants or in cases that anticipate bad prognosis for keratoplasty. In most patients there was a signifi cant initial improvement in vision, and more than half of them retained better than initial VA on their last follow up. Further refinements in surgical technique and postoperative care would decrease complications that lead to progressive visual loss.

Evaluation of stability and biocompatibility of PHEMA-PMMA keratoprosthesis by penetrating keratoplasty in rabbits / 한국실험동물학회지

Artificial corneas have been developed as an alternative to natural donor tissue to replace damaged or diseased corneas. This study was conducted to evaluate the stability and biocompatibility of PHEMA-PMMA [poly (2-hydroxyl methacrylate)-poly (methyl methacrylate)] keratoprostheses in rabbits following penetrating keratoplasty. Sixteen male New Zealand White rabbits aged 16 weeks were divided into three groups. Group I and group II contained six rabbits each, while the control group had four rabbits. Experimental surgery was conducted under general anesthesia. The cornea was penetrated using an 8 mm diameter biopsy punch. In group I (core 5 mm & skirt 3 mm) and group II (core 6 mm & skirt 2 mm), the keratoprosthesis was placed into the recipient full thickness bed and sutured into position with double-layer continuous. In the control group, corneal transplantation using normal allogenic corneal tissue was performed with the same suture method. After four and eight weeks, keratoprosthesis devices were evaluated by histopathological analysis of gross lesions. Post-operative complications were observed, such as extrusion and infection in experimental groups. Most corneas were maintained in the defect site by double-layer continuous suture materials for 4 weeks and kept good light transmission. However, most artificial cornea were extruded before 8 weeks. Overall, combined PHEMA and PMMA appears to have sufficient advantages for production of artificial corneas because of its optical transparency, flexibility and other mechanical features. However, the stability and biocompatibility were not sufficient to enable application in humans and animals at the present time using penetrating keratoplasty. Further studies are essential to improve the stability and biocompatibility with or without other types of keratoplasty.

Osteo-Odonto-Keratoprosthesis (OOKP) for patients with corneal blindness: A review.

Anatomically, the cornea is the outermost layer of the eye and is primarily responsible for light refraction which allows for central and peripheral vision. Corneal diseases are among the major causes of global blindness, secondary to cataracts. This paper intends to review Osteo-odonto Keratoprosthesis (OOKP), which is a two stage procedure whereby dental and buccal tissue is auto-transplanted into eye to serve as a synthetic cornea. Our purpose is to inform readers about the relevant anatomy, two-stage producer, surgical inter-professionalism, indications, contraindications, complications, long-term functional and anatomical results and patient outcomes of OOKP. The present manuscript was constructed by extensive review of literature of various review articles and case reports and the data was collected from 32 review articles and case reports.

Clinical research progress of Boston type l keratoprosthesis / 国际眼科杂志(Guoji Yanke Zazhi)

?Boston Type l keratoprosthesis is currently widely used. ln this article, the indication, number of cases, best-corrected visual acuity ( BCVA ) , retention, and complications in all the international published case reports will be sum up; then the main post-operative complications and their respective treatments one by one, which include retrospective membrane, glaucoma, infection will be introduced.

Histopathological observation of new soft one-piece keratoprosthesis skirt implanted into alkali burned rabbit corneas / 中国组织工程研究

BACKGROUND:Polyhydroxyethyl methacrylate has excel ent optical properties and good hydrophilicity which has been widely applied in biological materials, such as contact lenses, intraocular lenses. In previous experiments, artificial corneas made of polyhydroxyethyl methacrylate subcutaneously implanted or implanted into normal rabbit cornea have showed good biocompatibility and tear resistance. OBJECTIVE:To evaluate the histopathological results of the porous skirt of new type one-piece keratoprosthesis made of polyhydroxyethyl methacrylate implanted to alkali burned rabbit corneas. METHODS:New blood vessels and wal eyes formed in New Zealand rabbits at 3 months after alkali burned rabbit corneas. The porous discs of polyhydroxyethyl methacrylate were inserted into the lamel ar pocket of alkali-burned corneas and the corneas were observed clinical y, histological y and ultrastructural y at 2, 8, 16 and 28 weeks after implantation,. RESULTS AND CONCLUSION: Histopathology suggested that mild inflammatory reaction and no calcification were seen in al specimens, fibroblasts and deposition of col agens were found in the pores of the dics at 2 weeks after implantation;stable connection with cornea was formed by the end of 16 weeks;the pores were almost completely fil ed with new tissue, the number of cel s decreased, and mature fibers were mainly found at 28 weeks. Scanning electron microscope showed new tissue grew into the pores which were closely connected with the corneas. Transmission electron microscope exhibited cytoplasm migrating into the material was rich in rough endoplasmic reticula, showing strong synthetic function, col agen, proteoglycans, and other extracel ular matrix deposition. These findings indicate that the porous skirt of polyhydroxyethyl methacrylate implanted into the alkali burned rabbit corneas al owed corneal cel s migration, proliferation, secretion of the deposition of extracel ular matrix and the formation of new tissue to complete the stable connection with cornea, showing a better biocompatibility.

Boston keratoprosthesis and Ahmed glaucoma valve for visual rehabilitation in congenital anterior staphyloma.

Congenital anterior staphyloma entails grave visual prognosis. The majority of reported patients have undergone enucleation. We report a promising result of staphylectomy with implantation of a keratoprosthesis and a glaucoma drainage device in a seven-month-old child with a large, congenital anterior staphyloma.

Short-term outcome of Boston Type 1 keratoprosthesis for bilateral limbal stem cell deficiency.

This study reports the short-term functional and anatomical outcome of Boston Type 1 keratoprosthesis (Boston Kpro) implantation for bilateral limbal stem cell deficiency (LCSD). Retrospective analysis was done on eight eyes of eight patients who underwent Boston Kpro implantation between July 2009 and October 2009. The best corrected visual acuity (BCVA) and slit-lamp biomicroscopy findings were assessed at 1, 3 and 6 months postoperatively. All eight eyes retained the prosthesis. BCVA of 20/40 or better was achieved in 8, 6, and 5 eyes at 1, 3, and 6 months, respectively, postoperatively. One patient each developed epithelial defect, sterile stromal melt and fungal keratitis in the late postoperative period associated with antecedent loss of the soft contact lens from the eye. Boston Kpro has good short-term visual and anatomical outcome in patients with bilateral LSCD, provided compliance with postoperative care can be ensured.

Nursing of patients undergoing vitreoretinai surgery under temporary keratoprosthesis combined with penetrating keratoplasty / 中国实用护理杂志

Objective To discuss the perioperative nursing points of vitreoretinal surgery under tempo-rary kerstoprosthesis combined with penetrating keratoplasty for treatment of complex ocular trauma and anteri-or and posterior ocular segment lesion. Methods Clinical data of 21 patients (21 eyes) undergoing vitreo-retinal surgery under artificial cornea combined with penetrating keratoplasty were analyzed, perioperative nursing problems were evaluated and corresponding nursing measures were adopted. Results Visual acuity of 16 eyes were greatly improved,other 5 eyes showed no amelioration.By effective nursing mea-sures, all nursing problems were settled. Conclusions Although the functional outcome of a combined procedure is limited,it contributes to preserve vision of patients. Good periopertive nursing is pivotal for successfal operation.

Hydroxyapatite modified titanium promotes superior adhension and proliferation of corneal fibroblast in comparison with pure titanium / 国际眼科杂志(Guoji Yanke Zazhi)

AIM: To determine whether hydroxyapatite modified titanium promotes superior adhension and proliferation of rabbit corneal fibroblast in comparison with pure titanium.METHODS: We used bioactive hydroxyapatite to modify titanium surfaces. Fourth passage fibroblasts of rabbit cornea were seeded on hydroxyapatite modified titanium surfaces, pure titanium and glass surfaces. Cell adhension, proliferation and morphology were detected at 24 hours, 48 hours, and 72hours using a acridine orange stain. Further studies of cell morphology were performed using scanning electron microscopy.RESULT: Ceil counts were significantly greater on hydroxyapatite modified titanium surfaces at each time point(P＜0.05).At 24 hours, cell spreading was greater on hydroxyapatite-coated titanium and glass than on the pure titanium. At 72 hours, compared with pure titanium and glass surfaces, the cells on hydroxyapatite modified titanium surfaces had greater spreading area and longer stress fibers.CONCLUSIONS: Hydroxyapatite modified titanium promotes superior adhension and proliferation of rabbit corneal fibroblast in comparison with pure titanium.

Clinical study of combined penetrating keratoplasty with vitreoretinal surgery / 国际眼科杂志(Guoji Yanke Zazhi)

AIM: to assess the effectiveness of a combined procedure ( pars plana vitrectomy with temporary keratoprosthesis, vitreoretinal surgery, and penetrating keratoplasty). in the complicated cases and the risk factors for the surgical failure.METHODS: Restrospectively reviewed charts of patients who underwent penetrating keratoplasty in combination with vitreoretinal surgery between 1990 and 2005, with a follow-up of 3mo to 9a. Analysis was focused on ocular history, indications for surgery, visual acuity (VA), anatomic results, and complications.RESULTS: 18 eyes had light perception or VA of hand motions only. The best-corrected VA improved during the first 3mo, increased in 72.2% of all eyes, remained unchanged in 27.78%, and no decreased. In 3 of 18 eyes (16.67%), VA was better than finger counting and hand motions, and nine eyes(50%) showed useful vision (0.05) postoperatively. 10 eyes showed a clear corneal graft (55.56%). 2 eyes needs the second keratoplasty, Bullous corneal edema was evident in 3 eyes, band keratopathy was evident in a 3 eyes. 10 patients were observed for more than 2a;6 had a clear graft (60%). Two eyes (11.11%) had silicone oil-corneal endothelium contact and all of these grafts failed.CONCLUSION: Although the functional outcome of a combined procedure is limited by primary and secondary tissue destruction, preserving ambulatory vision is possible and thus improves the quality of life, at least in patients with single remaining eyes.

Two Cases of Boston (Dohlman-Doane) Type I Keratoprosthesis

PURPOSE: This article reports two cases of Boston (Dohlman-Doane) Type I Keratoprosthesis procedures that were performed for the first time in Korea. METHODS: Using the Boston Type I keratoprosthesis, we implanted ultimately these to two cases of corneal blinded patients. RESULTS: Two Boston (Dohlman-Doane) Type I Keratoprosthesis procedures were performed successfully. The first case had poor visual prognosis due to preexisting optic neuropathy and vitreous hemorrhage, but was showed better for cosmetic effect. The second case had maintained an uncorrected visual acuity of 0.1 at postoperative 3 months. CONCLUSIONS: We hope to perform additional procedures and long-term follow-ups to further evaluate this new surgical technique for stability and efficiency.

Outcome of Vitreoretinal Surgery and Penetrating Keratoplasty using Temporary Keratoprosthesis

PURPOSE: Using a temporary keratoprosthesis(TKP), earlier surgical treatment became amenable in eyes with coexisting vitreoretinal and corneal disease. We analysed our experience with this type of surgery. METHOD: Medical records of patients who had undergone pars plana vitrectomy(PPV) using Eckardt TKP from 1994 to 2000 were reviewed. Analysis was focused on preoperative conditions, surgical outcome and complications. RESULT: Of 34 eyes of consecutive 34 patients, 25(73.5%) showed trauma-related indications and 4 had IOFB. Retinal detachments were present in 24(70.6%) eyes, proliferative vitreoretinopathy in 8(23.5%) and vitreous hemorrhage in 10(29.4%) eyes. Penetrating keratoplasty(PKP) with donor corneas were performed in only 3 patients at the time of surgery and patient's excised corneas were sutured to 31 patients, 9 of whom underwent PKP later. After mean follow up period of 14 months, retinas remained attached in 27(79.4%) eyes and 3 eyes were phthisical. Visual acuity improved in 18(53%) eyes and worsened in 5 eyes. CONCLUSIONS: In cases with coexisting corneal and vitreoretinal pathology, PPV using TKP was effective for preserving vision and globe. Timing of grafting clear cornea might be delayed when donor cornea was not available.

Histological Changes of Rabbit Cornea Implanted with Seoul Type Keratoprosthesis

Keratoprosthesis implantation is the only alternative method to restore vision in patients who might invariably fail allograft coneal transplantation. Seoul type keratoprosthesis adapted 20 micrometer pore sized expanded polytetrafluoroethyl-ene[PTFE, Gore-Tex]as a skirt material in this study. To evaluate compatibility of this material as a skirt we performed in vitro cell culture experiment and animal experiment. For in vitro experiment, expanded PTFE membrane was cultured with rabbit keratocytes in 24-well culture plate for a week.For animal experiment Seoul type keratoprosthesis was implanted in the rabbit cornea. Two months after the operation specimens for pathologic examination were retrieved. In culture experiment no keratocyte invaded pores. In animal experiment no keratocyte but only many inflammatory cells mainly polymorphonuclear leukocytes infiltrated pores of skirt and surrounding cornea. In conclusion, 20 micrometer pore sized expanded PTFE is not good as a skirt material of keratoprosthesis.

Retroprosthetic Membrane Formation after Implantation of Experimental Keratoprothesis in Rabbit

The studies about factors influencing the retroprostheic membrane formation, one of major complications after keratoprosthesis implantation, and about histological characteristics of the retroprosthetic membrane were performed. The methods to inhibit formation and proliferation of membrane were also tried. Formation of the membrane according to corneal trephination size and the effects of lens removal to membrane formation were studied. The influence by the design of keratoprosthesis was also studied. Corticosteroid and SIMP (synthetic inhibitor of metalloproteinase) were applied topically to see the inhibitory effects of drugs to membrane. To evaluate the postoperative intraocular inflammation. Interleukin-1beta was assessed in the aqueous humor at postoperative 3 weeks. Regardless of trephination size, all trephination sites were replaced with opaque fibrous membranes. Histologically, in small trephination group (under 6mm) the membrane was regeneration of cornea showing corneal stromal fibroblast migration and proliferation and mature collagen. In large trephination group (over 7mm), the periphery of the membrane was compatible with corneal regeneration, but central portion was filled with granulation tissue. The removal of lens didn`t influenced the formation of membrane formation. In disc type keratoprosthesis implantation group, all the implants were extruded within 1 month due to retroprosthetic membrane formation. In cylinder type keratoprosthesis implantation group, the physical barrier of cylinder stopped the retroprosthetic membrane proliferation and spared the posterior surface of optic portion. The implants were not extruded for average 10 weeks. Corticosteroid and SIMP showed the effects of decreasing mature collagen formation in the membrane. The level of Interleukin-1beta at postoperative 3 weeks showed no difference according to different drugs and the highest level was checked in cylinder type keratoprosthesis implantation group.

Seoul-type Keratoprosthesis: The Deelopment of New Keratoprosthesis using Internal Scleral Fixation Method

Most of keratoprostheses that had been developed did not show consistent successful results due to the high rates of complications including extrusion. We performed this study to develop a newly designed keratoprosthesis using internal scleral fixation and access the mechanical stability and biocompatibility of the keratoprosthesis (Seoul-type keratoprosthesis, S-Kpro). The S-Kpro has the advantage of double fixation-the Gore-Tex skirt is anchored to the cornea and the prolene haptic is anchored internally to the sclera, simultaneously. And the human amniotic membrane(AM) was covered over the cornea and prosthesis to improve the biocompatibility. The 24 rabbits were divided into four groups: group 1(S-Kpro) with scleral and corneal fixation and AM transplantation, group 2 with scleral fixation and AM transplantation but without corneal fixation, group 3 with corneal fixation and Am transplantation but without scleral fixation, group 4 with scleral and corneal fixation but without Am transplantation. The average retention period of group 1(S-Kpro) was 12.3 weeks, which was significantly longer than other groups. The implanted eyes withstanded the intraocular pressure of as high as 200 to 250mmHg. The retroprosthetic membrane was not observed in all cases but retinal detachment and proliferative vitreoretinopathy were developed, and they are thought to be related with the extrusion of the prosthesis. The fibrovascular tissue invasion was not found in the Gore-Tex pores. These results suggest that double fixation technique using internal scleral fixation and AM transplantation is helpful to improve the stability of the kratoprosthesis. The further experiment with total vitrectomy, different species of animals and Gore-Tex with the large-sized pores would be needed.

Two Cases of Soft Prosthokeratoplasty on Alkali Burn

In cases of corneal opacity due to severe chemical burn, the success rate of lamellar or penetrating keratoplasty is very poor. Therefore, various types of keratoprosthesis were developed and tried in these chemical burn patients. However, the previous hard keratoprosthesis such as Cardona's bolt and nut type has disadvantages of narrow visual field and high protrusion rate. In 1991, Dr. Caldwell developed 'Soft Keratoprosthesis' made of polyurethane improved the clinical results of hard kemtoprosthesis. We performed soft prosthokeratoplasty on two cases of chemical burn and evaluated their clinical results From our experience of this soft keratoprosthesis, it may have much more longevity than the previous hard one and also have the advantage of good visual outcome and wide peripheral visual field.