Boston type I keratoprosthesis: Review

Regardless of significant progress in the field of corneal transplantation to treat corneal opacification, some cases of corneal blindness still present a poor prognosis for conventional penetrating keratoplasty. In patients with repeated graft failure and/or with severe ocular surface disease, the Boston type I keratoprosthesis (type I BKPro) has become a viable option. Modifications in its design and postoperative management have improved the long-term outcomes of visual acuity, retention, and postoperative infection rates. These advances made the type I BKPro be considered a safe alternative for visual rehabilitation in many patients with corneal pathologies. However, postoperative handle of chronic comorbidities, such as glaucoma, is still critical for preserving the visual gains achieved with BKPro.     

Glaucoma after corneal replacement

Glaucoma is a well-known complication after corneal transplantation surgery. Traditional corneal transplantation surgery, specifically penetrating keratoplasty, has been slowly replaced by the advent of new corneal transplantation procedures: primarily lamellar keratoplasties. There has also been an emergence of keratoprosthesis implants for eyes that are high risk of failure with penetrating keratoplasty. Consequently, there are different rates of glaucoma, pathogenesis, and potential treatment in the form of medical, laser, or surgical therapy.     

Current concepts and techniques in corneal transplantation

The corneal endothelium is the most important single layer in corneal transplantation. In his Castroviejo Lecture, William Bourne, MD, summarizes his work on the corneal endothelium and its importance to corneal transplantation. Almost half the corneal transplants performed in the United States are done so because of malfunctioning, diseased, or absent endothelial cells. If just this layer could be transplanted, the long wait for better vision after keratoplasty (up to two years in some countries) can be eliminated, as well as the problems of epithelial and subepithelial graft rejection. The significant astigmatism after keratoplasty could also be reduced. Transplantation of the endothelium in deep lamellar keratoplasty is being done in limited fashion throughout the world and the first patients have now been done in the United States. In many countries where corneal tissue is difficult to obtain, keratoplasty is only performed on one eye, even though both eyes may need it. One article this year discusses binocular vision recovery in bilateral keratoplasty and the objective and subjective improvements after bilateral keratoplasty. Patients who are bilaterally blind from diseases such as Stevens-Johnson syndrome, and ocular pemphigoid have little hope of visual recovery from conventional corneal transplants. The use of a keratoprosthesis to bypass the totally abnormal conjunctival surface has helped many people in the past. The preoperative prognostic categories of patients who may benefit from keratoprosthesis has been carefully reviewed in a large number of keratoprosthesis patients and this information will help ophthalmologists decide who will benefit the most benefit from keratoprosthesis. This year, articles on corneal transplantation after conjunctival flaps, suture-related complications in keratoplasty, the implantation of an intraocular lens after penetrating keratoplasty, and long-term results of penetrating keratoplasty with glaucoma drainage tube implants are subjects that warrant in depth discussion and evaluation. Finally, eye bank considerations will be discussed concerning the long-term question of transmission of cancer through corneal transplantation.     

适宜中国国情的角膜移植技术的挑战和创新

角膜盲是我国仅次于白内障的致盲性疾病,角膜供体材料匮乏造成角膜盲患者绝对数量仍在逐年上升。与欧美发达国家不同,严重的感染性角膜炎、热烧伤、化学伤和各种眼内手术引起的大泡性角膜病仍然是我国角膜移植的主要适应证。我国角膜盲的防盲面临着患者病情重、依从性差、可支付能力低和角膜供体材料严重缺乏的多重挑战。近年来,我国的角膜专科医师根据特殊的国情,发展和创新了一系列深板层移植、内皮移植、人工角膜移植和组织工程角膜异种移植的新技术,从技术层面显著提高了供体角膜材料的利用率,降低了高危移植的排斥反应。然而,由于角膜供体材料极其缺乏的瓶颈依旧,能掌握当代角膜移植新技术的角膜专科医师数量稀少,目前推动角膜捐献的立法工作和深入组织工程异种角膜材料学研究、加强国际间眼库合作迫在眉睫,适宜国情的角膜移植技术的创新和推广工作仍然任重而道远。     

角膜移植的研究进展

角膜移植是用透明、健康的供体角膜组织替换混浊病变的角膜组织,使患者复明或控制角膜病变,达到增进视力或治疗某些角膜疾病的眼科治疗方法.传统角膜移植分为穿透性角膜移植和板层角膜移植.近10a,深板层角膜移植和内皮细胞移植手术逐渐崛起.而目前,人工角膜移植手术的发展为不适合传统穿透性角膜移植手术的患者提供一种新的选择.本文综述了目前角膜移植领域手术技术的适应证、术后并发症等.     

A tectonic keratoprosthesis using expanded polytetrafluoroethylene as a supporting skirt in humans.

A tectonic keratoplasty was performed with a keratoprosthesis using expanded polytetrafluoroethylene as a supporting skirt, on the left eye of a 23-year-old woman who needed an emergency corneal transplantation due to corneal perforation. The keratoprosthesis implanted, consisted of a supporting skirt which was made of expanded polytetrafluoroethylene (PTFE), and an optic portion which was made of polymethylmethacrylate (PMMA). The optic portion and the supporting skirt were attached by cyanoacrylate tissue adhesive (Histoacryl). Two months post-operatively, the keratoprosthesis was extruded, leaving an opacified, vascularized cornea. A penetrating keratoplasty was performed 1 month later. The excised cornea was composed of granulation tissue. To our knowledge, this is the first case of tectonic keratoprosthesis using expanded PTFE as a supporting skirt in humans.     

人工角膜支架及其生物相容性的研究进展

除了传统的穿透性角膜移植术和角膜内皮植入术外,人工角膜植入术是一种严重性角膜疾病终末期光学增视性选择性治疗方法.人工角膜最常见的结构是柱镜-裙带型,即由中央透明光学柱镜和周围裙边支架两部分组成.支架材料良好的生物相容性是人工角膜植入成功的关键.随着高分子材料科学的发展,支架材料的种类愈加丰富,对生物相容性的要求也愈加提高.目前常见的人工角膜主要以无机、有机或/和生物材料作为支架,不同材料在实际应用中的相容性和优劣性有所差异,了解这些特性有助于提高人工角膜植入的成功率.     

The osteo-odonto-keratoprosthesis (OOKP)

The osteo-odonto-keratoprosthesis (OOKP), although described over 40 years ago, remains the keratoprosthesis of choice for end-stage corneal blindness not amenable to penetrating keratoplasty. It is particularly resilient to a hostile environment such as the dry keratinized eye resulting from severe Stevens-Johnson syndrome, ocular cicatricial pemphigoid, trachoma, and chemical injury. Its rigid optical cylinder gives excellent image resolution and quality. The desirable properties of the theoretical ideal keratoprosthesis is described. The indications, contraindications, and patient assessment (eye, tooth, buccal mucosa, psychology) for OOKP surgery are described. The surgical and anaesthetic techniques are described. Follow-up is life-long in order to detect and treat complications, which include oral, oculoplastic, glaucoma, vitreo-retinal complications and extrusion of the device. Resorption of the osteo-odonto-lamina is responsible for extrusion, and this is more pronounced in tooth allografts. Regular imaging with spiral-CT or electron beam tomography can help detect bone and dentine loss. The optical cylinder design is discussed. Preliminary work towards the development of a synthetic OOKP analogue is described. Finally, we describe how to set up an OOKP national referral center.     

The Chirila Keratoprosthesis: phase I human clinical trial

OBJECTIVE: To undertake a preliminary safety and performance evaluation of an artificial cornea, the Chirila Keratoprosthesis, in human patients. DESIGN: A prospective, interventional case series. PARTICIPANTS: Fourteen consecutive patients with blindness of corneal origin not treatable by repeated standard penetrating keratoplasty. METHODS: Keratoprostheses were manufactured and implanted. The patients, all with preoperative visual acuity of light perception to count fingers (CF), were followed clinically in adherence to a protocol. MAIN OUTCOME MEASURES: Safety (keratoprosthesis retention, incidence of serious complications) and performance (visual acuity, comfort, appearance). RESULTS: Ninety-three percent of keratoprostheses were retained to the date of reporting, up to 2.5 years. One keratoprosthesis (7%) was removed in a manner that restored the patient's preoperative condition. All but one patient maintained their preoperative level of visual acuity or improved on it, with most achieving their estimated full potential visual acuity, (range, count fingers - 20/20). CONCLUSIONS: This keratoprosthesis is acceptably safe and has demonstrated an ability to restore vision in cases in which alternative management would have had a poor prognosis. More extensive trials are warranted.     

Other surgical therapies for cornea burns

With limbal stem cell and amniotic membrane transplantations, penetrating keratoplasty is the most important treatment of severe corneal burns. In the acute stage, re-epithelialization failure and resultant stromal ulceration can induce corneal perforation. A lamellar or a full-thickness patch graft is indicated in order to preserve the eyeball. For small perforations, tissue adhesive can be used. In the early reparative stage, keratoplasty has its place, but corneal vascularization is a major risk factor for graft rejection. Lamellar keratoplasty is preferred because it provides tectonic support. After several graft failures, a keratoprosthesis is the last solution for these bilaterally affected patients, but evisceration cannot be always avoided.     

The Osteo-Odonto-Keratoprosthesis (OOKP)

The osteo-odonto-keratoprosthesis (OOKP), although described over 40 years ago, remains the keratoprosthesis of choice for end-stage corneal blindness not amenable to penetrating keratoplasty. It is particularly resilient to a hostile environment such as the dry keratinized eye resulting from severe Stevens-Johnson syndrome, ocular cicatricial pemphigoid, trachoma, and chemical injury. Its rigid optical cylinder gives excellent image resolution and quality. The desirable properties of the theoretical ideal keratoprosthesis is described. The indications, contraindications, and patient assessment (eye, tooth, buccal mucosa, psychology) for OOKP surgery are described. The surgical and anaesthetic techniques are described. Follow-up is life-long in order to detect and treat complications, which include oral, oculoplastic, glaucoma, vitreo-retinal complications and extrusion of the device. Resorption of the osteo-odonto-lamina is responsible for extrusion, and this is more pronounced in tooth allografts. Regular imaging with spiral-CT or electron beam tomography can help detect bone and dentine loss. The optical cylinder design is discussed. Preliminary work towards the development of a synthetic OOKP analogue is described. Finally, we describe how to set up an OOKP national referral center.     

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.     

眼前后段联合手术治疗复杂性眼病的远期疗效评价

目的 探讨临时人工角膜下行前后段联合手术治疗复杂性眼病的远期疗效。方法1994年6月至2001年6月,107例(107只眼)眼前后段复杂病变的患者于我院在临时人工角膜下行玻璃体视网膜手术,再联合穿透性角膜移植术,术后局部及全身应用糖皮质激素,并随访观察患者视力、眼压、角膜植片及眼底情况。手术治愈标准:(1)植片透明;(2)视网膜复位;(3)眼压正常或经药物控制眼压正常。结果 达到手术治愈标准者78只跟(72.9％),手术后眼球保存者92,只眼(86.0％),术后发生植片免疫排斥者34只眼(31.8％),眼球萎缩13只眼(12.2％),继发性青光眼15只眼(14.0％)。术前存在增生性玻璃体视网膜病变(PVR)患眼的视网膜手术治愈率与无PVR者比较,差异有显著意义(x2=3.90,P<0.05)。结论 临时人工角膜下眼球前后段联合手术是治疗角膜明显混浊合并玻璃体视网膜病变的有效方法。远期失败的主要原因是角膜植片内皮功能失代偿和增生性玻璃体视网膜病变。(中华眼科杂志,2004,40:514-516)     

Five year follow up of biocolonisable microporous fluorocarbon haptic (BIOKOP) keratoprosthesis implantation in patients with high risk of corneal graft failure

AIM: To study the anatomical and visual performance following implantation of a model of artificial cornea and to evaluate the postoperative long term complications. METHODS: 11 eyes of 11 patients with bilateral corneal blindness considered as potentially having high risk of failure of penetrating corneal keratoplasty were implanted with biocolonisable Kpro keratoprosthesis (BIOKOP I, FCI, Rantigny, France) in the period between January 1996 and May 1998. Only one eye was implanted in all patients and followed up for a period of 60 months. The visual outcome, anatomical and functional stability, complications, and the general performance of the keratoprosthesis were evaluated. RESULTS: The keratoprosthesis (BIOKOP I) only 36.3% remained in position to date. In the patients' last visit five eyes (45.4%) were blind and one (9.0%) showed a slight improvement in the best corrected visual acuity (BCVA) in comparison to preoperative tests. Six eyes (54.5%) showed improved BCVA before having postoperative complications. Four eyes underwent replacement of a BIOKOP I Kpro with a BIOKOP II as a result of extrusion. The keratoprostheses remained anatomically in situ for a mean of 25.5 months and their functional performance period was limited to a mean of 22 months. CONCLUSION: Corneal keratoprosthesis (BIOKOP I, II) does not provide a stable anatomical relation with the surrounding ocular structures. Its ability to restore vision is limited to a short postoperative period in eyes implanted with severe ocular surface disease.     

Descemet's stripping with automated endothelial keratoplasty (DSAEK)

BACKGROUND: Although penetrating keratoplasty remains the gold standard for surgically treating corneal endothelial pathologies, tremendous progress has been made in recent years to improve the technology of (posterior) lamellar keratoplasty. METHODS: Literature review from PubMed and own data. RESULTS: Posterior lamellar keratoplasty using a microkeratome (Descemet's stripping with automated endothelial keratoplasty, or DSAEK) is a reliable surgical technique for Fuchs' endothelial dystrophy and pseudophakic bullous keratopathy. Visual rehabilitation is faster with lamellar keratoplasty than penetrating keratoplasty. CONCLUSION: Posterior lamellar keratoplasty techniques such as DSAEK will become an important surgical treatment option for corneal endothelial pathologies.     

Expanding Application of the Boston Type I Keratoprosthesis Due to Advances in Design and Improved Post-operative Therapeutic Strategies

Purpose:?To evaluate how the advances in design of the Boston type I keratoprosthesis and in the treatment strategies to conquer the post operative complications have expanded the indications and application of this technology.

Methods:?A review and analysis of the keratoprosthesis literature specifically examining design modifications, treatment of post operative complications, and patient selection was performed.

Results:?Over the past two decades, many modifications to the design of the Boston type I keratoprosthesis and treatment of the patient in the post operative period have occurred. Also, the technology has been more widely accepted as a primary surgical option for patients with a poor preoperative prognosis for traditional penetrating keratoplasty. The outcomes of visual acuity, retention, and post-operative infection rates have all significantly improved since the technology has been modified and offers patients an alternative for visual rehabilitation.

Conclusions:?Thanks to advances in design and perioperative care, the boston type i keratoprosthesis can now be considered a viable option for surgical visual rehabilitation in many patients with corneal pathology, and in certain groups the primary surgical procedure of choice.     

Implantation of a Keratoprosthesis of Novel Design in Rabbits

Purpose To evaluate a keratoprosthesis, implanted by penetrating keratoplasty, in rabbits.Methods We implanted our keratoprosthesis (optics and flange portions of polymethylmethacrylate and a polyurethane skirt with micropores) into 14 eyes of 14 rabbits. In four eyes, we evaluated histologically the junction between the keratoprosthesis and host cornea. Long-term keratoprosthesis survival was evaluated in ten eyes by slit-lamp biomicroscopy.Results The histological study showed good approximation of the keratoprosthesis to the host cornea in the junction area, with overlying superficial corneal stroma on the skirt, keratocyte and collagen fiber ingrowth into the micropores, and partial migration of epithelial cells onto the skirt. However, in the long-term survival study, eight out of ten eyes developed acute suture-related inflammation, considered to be from bacterial infection, requiring enucleation 30 ± 18 weeks after implantation. The remaining two eyes have survived for 70 and 76 weeks.Conclusions Our keratoprosthesis was well tolerated in the short term. However, further modifications are necessary to avoid corneal infection. Jpn J Ophthalmol 2004;48:448–453 © Japanese Ophthalmological Society 2004     

Biomechanical model of corneal transplantation

PURPOSE: Refractive consequences of corneal transplants are analyzed using corneal biomechanical models assuming homogeneous and inhomogeneous stiffness distributions across the cornea. Additionally, refractive effects of grafts combined with volume removal procedures are also evaluated to develop methods to reduce postoperative refractive management of patients. METHODS: Refinements of a two-dimensional finite element model are applied to simulate the biomechanical and refractive effects of different corneal transplant procedures: anterior lamellar keratoplasty, posterior lamellar keratoplasty, and penetrating keratoplasty. The models are based on a nonlinearly elastic, isotropic formulation. Predictions are compared with published clinical data. RESULTS: The model simulating the penetrating keratoplasty procedure predicts more change in the postoperative corneal curvature than models simulating anterior lamellar keratoplasty or posterior lamellar keratoplasty procedures. When a lenticle-shaped tissue with a central thickness of 50 microns and a diameter of 4 mm is removed from the anterior corneal surface along with the anterior lamellar keratoplasty or posterior lamellar keratoplasty, the models predict a refractive correction of -8.6 and -8.9 diopters, respectively. CONCLUSIONS: Simulations indicate that a posterior lamellar keratoplasty procedure is preferable for obtaining a better corneal curvature profile, eliminating the need for specific secondary treatments.     

A historical review of artificial cornea research in Japan

Little is known or understood about the history of artificial cornea (keratoprosthesis) in Japan, mainly because of the unavailability and linguistic inaccessibility of the relevant publications. Rather strangely also, the Japanese scholars themselves have manifested only slight interest in reviewing the topic, even in their own language. As a result, the research on artificial cornea in Japan showed in fact the same pattern of historical development as that seen in the Western world. After audacious beginnings in the 19th century, an interlude of about half a century followed, when the interest of ophthalmologists was deflected to penetrating keratoplasty as a means to fight corneal blindness. The introduction in medical use of man-made polymeric materials in the 1950s triggered a revival of research on artificial cornea in Japan, and the next two decades were rich in ideas, achievements, and a plethora of reports, all published in Japanese. In the 1980s, the developmental work on keratoprosthesis became incorporated into the field of biomaterials, and the creation of materials able to mimic the corneal tissue was established as a leading concept, resulting in original designs with some sophistication. At the same time. the English language started to be used extensively for dissemination of results. These trends have continued to date. Based on rigorous documentation, we traced the history of research on artificial cornea in Japan from its origin to our time.     

Practical Applications of Anterior Segment Optical Coherence Tomography Imaging Following Corneal Surgery

Anterior segment optical coherence tomography (AS-OCT) has recently emerged as an important modality for imaging of the cornea. Since its introduction less than a decade ago, it has been clinically used for the diagnosis and management of an expanding number of corneal conditions. In this review, we will discuss the applications of anterior segment optical coherence tomography after corneal surgery, focusing on penetrating and lamellar keratoplasty, keratoprosthesis, intracorneal ring segments, collagen cross-linking and refractive surgery. Anterior segment optical coherence tomography is useful in evaluating outcomes, detecting adverse events, determining prognosis, guiding management decisions, and surgical planning.