KERATOPROSTHESIS Dr. Krati Gupta Dr. Saurabh Deshmukh www.eyelearn.in KERATOPROSTHESIS Keratoprosthesis a) Types b) indication 8+2 J2018 Write a note on “ Kerato-prosthesis”? (10) D2011 Definition Keratoprosthesis is a surgical procedure where a severely damaged or diseased cornea is replaced with an artificial cornea to restore useful vision or to make the eye comfortable in painful keratopathy. It is usually the last option for the surgeon and the patient who has visual potential in an eye with severely compromised cornea. Concept • The basic concept of using an artificial cornea to replace a damaged and opaque cornea is as obvious as placing a window on a house to be able to see out. • Keratoprosthesis restores sight to an eye with damaged cornea by means of a special tube that acts as a "periscope" from the eye to the outside world. • The keratoprosthesis extends both inside the eye and outside into the environment. • The tube passes out of the eye either through the eyelids or between the fused lids. • The tube is ordered to a specific optical power to help restore the patient's sight, but the patient may have to wear refractive correction for clear vision. • It provides patients with just a type of tunnel vision. • The extent of the visual field increases with increasing diameter and decreases with increasing length of the optical cylinder. Year Author Procedure 1789 Pellier de Quengsy Glass lens in silver ring for leukomatous cornea 1853 Nussbaum Published the first human trial using quartz crystal implant 1860 Heusser Inserted a glass plate in the cornea of a 19 year old patient 1898 Dimmer, Salzer Celluloid plates and egg membranes were used to stabilize glass lenses in the cornea 1930 Verhoeff Use of Quartz button 1935 Filatov Implanted penetrating glass device into leucomatous cornea and covered it with a double conjunctival flap 1950 Stone & Herbert, Cardona PMMA prosthesis designs in rabbits 1963 Strampelli B Osteo - odonto – keratoprosthesis 1979 Pintucci Pintucci keratoprosthesis 1998 Chirila AlphaCor Prosthesis Cardona and coworkers Cardona device Singh & worst Worst ‘champagne cork’ 1960 Claes H. Dohlman Boston Keratoprosthesis Type 1 FDA-1992 • All these all Keratoprosthesis failed within weeks or months. • The interest in keratoprostheses declined following the development of successful penetrating keratoplasty (PKP) in the first decade of the 20th century • The realization that transplanting a human cornea would not be successful in all cases of corneal blindness • During the Second World War, the incidental discovery of corneal tissue tolerance to plexi-glass fragments from airplane canopies suggested a new direction for future research Dr. Krati Gupta | Dr. Saurabh Deshmukh As an alternative to PK in certain cases • Corneal opacification is a leading cause of blindness worldwide effecting 10 million people. Disease or trauma can cause loss of corneal transparency and loss of vision. • When this process becomes irreversible, it is treated surgically by Penetrating Keratoplasty (PK). • Major Limitations of PK i. Depends on availability of healthy human corneas ii. Requires a technically sophisticated Eye Banking System iii. Grafted corneal button may itself not remain transparent iv. It is subject to immunologic rejection v. Rarely but donor corneal tissue can transmit devastating disease (Hepatitis, Jacob- Creutzfeldt disease) Indications Candidates for keratoprosthesis implantation can be classified into three main prognostic groups. In increasing order of success, these groups are: 1. Autoimmune-related corneal opacity and ulceration, 2. Chemical injury, and 3. Corneal allograft failure (non-autoimmune). General indications for use of individual keratoprosthesis devices Device type Corneal allograft failure Chemical injury Severe autoimmune disorder OOKP − + + AlphaCor + − − Boston KPro + + + Indications Kpro Indications OOKP chemical injury Cicatricial conjunctivitis with corneal blindness in severe mucous membrane pemphigoid AlphaCor Corneal allograft rejection, Contraindicated in herpes simplex keratitis, autoimmune disorders, and can become opaque with specific combinations of topical medications. Boston Opacity when accompanied by extensive corneal neovascularization making allograft success Kpro unlikely. Opacity with limbal stem cell deficiency syndromes including but not limited to aniridia, Kpro indications- • A temporary device is used intra-operatively to aid in visualization and is removed following surgery. The examples include Eckardts keratoprosthesis, Landers Foulk and Landers wide field lenses • Permanent keratoprosthesis are used to treat patients with severe corneal disease where corneal transplantation is inappropriate or has repeatedly failed Dr. Krati Gupta | Dr. Saurabh Deshmukh Temporary Permanent • Severe ocular trauma for • Multiple failed penetrating Keratoplasty/ Amniotic membrane anterior and posterior 1. Graft failure in non-inflammatory conditions- corneal edema, dystrophies segment reconstruction, 2. Graft failure in eyes post-inflammation- Herpes simplex Keratitis, Zoster, • Cataract extraction, Infectious ulcer, Uveitis • Modified triple 3. Chemical injury procedure, 4. Ocular cicatricial pemphigoid (stage 3 & 4) • Vitreoretinal surgery in 5. Stevens – Johnson syndrome cases of corneal opacity • Trachoma (stage C0 according to WHO) or ocular trauma • Vascularized corneas with complete stem cell loss and dryness or stem cell • Combined penetrating grafting keratoplasty and • Bullous keratopathy- cases with stromal scarring, lamellar or full-thickness vitreoretinal surgery. procedures may be required, while Kpros may be considered after serial graft failures. • Paediatric corneal opacities PK is primary procedure Prognostic categories with the Boston keratoprosthesis (2009) Prognostic category Examples Long-term outlook Autoimmune diseases Stevens-Johnson syndrome Guarded Mucous membrane pemphigoid Uveitis, lupus, rheumatoid arthritis, others Chemical/thermal injury Acid, alkali, other chemical Fair Heat Corneal allograft rejection Aniridia Other Good Post-traumatic Post-infectious Corneal degenerations Corneal dystrophies • In general, a KPro is offered to patients with bilaterally poor vision to the degree of hand moments or light perception. • Only one eye should be offered a KPro, and the second eye should be kept as a spare and must be treated fully for glaucoma and other pathology as appropriate in order to preserve the visual potential. • Patients having both eyes suitable for KPro must be carefully counselled to choose the eye for KPro implantation. Dr. Krati Gupta | Dr. Saurabh Deshmukh Types Designs and Materials - Consists of Optical cylinder and supporting flange. Non Biointegrated Non Biointegrated Biointegrated Supporting Flange (Optical cylinder materials) (Supporting flange) (Autologous tissue) Polymethyl methacrylate (PMMA) – most commonly used material Methacrylate Tooth and bone Glass Teflon (osteo-odonto-keratoprosthesis) Ceramic Dacron mesh Cartilage Quartz, Polycarbon (chondro-keratoprosthesis) Silicon Nail (onycho-keratoprosthesis) Keratoprosthesis designs have primarily been variations of 3 main types. First Type Second Type Third Type PMMA stem with skirt embedded Transparent membrane with PMMA ‘collar button’ with within the cornea porous edges inserted into the cornea between the plates cornea • It is most commonly used. • Consists of transparent plate • Less common type has a • The optical core is stabilized by a with a porous periphery, collar button shaped device permanently attached supporting allowing tissue ingrowth consisting of two plates plate or skirt implanted in a into the pores. joined by a stem, which pocket created in the collagen • Such designs have been constitutes the optical lamellae of the corneal stroma. made of portion. • Consists of central optical polytetrafluoroethylene, • This is inserted into the cylinder, supporting flange, polyurethane, or modified patient’s cornea or a donor PMMA stem. gels. cornea so that the plates • Skirt placed intralamellarly in the • By using suitable pore size, sandwich the corneal tissue stroma (made of perforated grids these devices have been well between them. of PMMA, nylon, Dacron, colonized with tissue • The optical stem is short, proplast/ covered by transplanted elements which might help allowing a generous field autologous tissue/ lid skin) to anchor the device and and wide plates stabilize prevent future extrusion. the stem so that it cannot easily deviate from the axis to the macula. PMMA- Advantages and disadvantages Advantages Disadvantages 1. Excellent transmission 1. Rigid and Hydrophobic of light 2. At points of attachment to the stroma, lack of elasticity creates stress that 2. Completely contributes to stromal necrosis and melting Transparent 3. Biologically Inert Dr. Krati Gupta | Dr. Saurabh Deshmukh 4. Can be shaped to 3. The elastic mismatch between the rigid plastic and the adjacent flexible produce High Quality tissue prevents formation of a tight interface, creating gaps that allow images epithelial down growth and leakage of aqueous humour. 5. Retains its shape and 4. Nutrients are unable to diffuse through PMMA, so an optical center of clarity with age this plastic may not be able to support epithelium on its anterior surface. 5. Cells and fibrous material do attach to the posterior surface, requiring surgical removal to restore vision. Based on material PMMA Choyce, Boston keratoprosthesis Polycarbonate Champagne cork keratoprosthesis Polyurethane Seoul keratoprosthesis