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Early types of keratoprosthesis surgery

A keratoprothesis is an 'artificial cornea', but until recently designs of keratoprosthesis bore little similarity to the physical form of the natural cornea. All the early designs used polymethylmethacrylate (PMMA) as the material for the optical part of the device, and this was mounted in a plate-shaped supporting ring which stabilised the optic in the visual axis ('nut and bolt' design). Because of poor biocompatibility, the early keratoprostheses had a high incidence of failure - particularly from infection and extrusion. In an attempt to overcome these problems, the osteo-odonto-keratoprosthesis used a tooth derived from the prospective recipient as a platform to mount the optical cylinder, whilst the surrounding periosteum of the tooth acted as an bio-compatible anchor to stabilise the device on the surface of the eye. Modern day practitioners using this device, such as Professor Falcinelli in Rome, have managed to achieve an excellent success rate, but this operation remains a complex, costly procedure and requires a preliminary operation to harvest the tooth and part of the adjacent jaw bone. The optical device is mounted into the tooth, and then the prepared prosthesis is buried in the eyelid for a couple of months to stabilise the device and ensure that it is free from infection. A second operation is then conducted to implant the mounted prosthesis in the eye, the whole implant being covered by a mucous membrane graft, again derived from the patient's mouth.

Figure 1: Boston Type I Keratoprosthesis

Boston keratoprosthesis devices require regular monitoring to assess for the presence of and corneal melt. Anterior segment optical coherence tomography (OCT) is a useful study to assess for the presence of corneal thinning or melt. We regularly use OCT to monitor the status of the cornea around the device.

Eckardt Keratoprosthesis, phakic 7 mm | Products | Vitreq

AlphaCor keratoprosthesis - EyeRounds

There is significant long-term risk of complications for those with a keratoprosthesis. Because the KPro is a foreign body, there is risk of infection or extrusion of the device. Post-operative glaucoma is common and intraocular pressure is difficult to evaluate as the hard optic makes traditional tonometry impossible. For this reason, glaucoma tube shunts are typically placed at the time of the corneal transplant at the University of Iowa. The is currently the preferred way to measure intraocular pressure in these patients in our institution. Patients can form retroprosthetic membranes requiring treatment with a Nd:YAG laser or surgical membranectomy ().

There is significant long-term risk of complications for those with a keratoprosthesis. Because the KPro is a foreign body, there is risk of infection or extrusion of the device. Post-operative glaucoma is common and intraocular pressure is difficult to evaluate as the hard optic makes traditional tonometry impossible. For this reason, glaucoma tube shunts are typically placed at the time of the corneal transplant at the University of Iowa. The is currently the preferred way to measure intraocular pressure in these patients in our institution. Patients can form retroprosthetic membranes requiring treatment with a Nd:YAG laser or surgical membranectomy ().

Long-Term Outcomes of Boston Keratoprosthesis Type …

Boston Keratoprosthesis (KPro) for congenital aniridia

Over the past few years impressive advances in keratoprosthesis design have been made by Professor Legeais in Paris. His keratoprosthesis uses a synthetic polymer optic similar to a contact lens, which has a flexible woven PTFE polymer 'skirt' (haptic) intimately bonded to its edge. The microporous skirt allows invasion of the patient's tissue into the material and achieves an improved level of biocompatibility between the synthetic 'cornea' and the eye. Since the optical part of the Legeais keratoprosthesis is thin and shaped like the natural cornea, this prosthesis design offers a much wider field of vision than was possible with the older style 'nut and bolt' prosthesis.

Such 'nut and bolt' keratoprostheses have a long optical cylinder (the 'bolt') which protrudes both into the eye and externally. Optically it performs poorly, giving only a restricted field of vision to the patient.

The Legeais Keratoprosthesis

Full text Keratoprostheses for corneal blindness: a review of contemporary devic OPTH
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Corneal melt around Boston type I keratoprosthesis

The other major indications for keratoprosthesis surgery are eyes where there is extensive damage to the ocular surface membranes (conjunctiva), as a result of chemical injury or disease such as cicatricial pemphigoid, trachoma etc. In these situations a conventional graft is likely to fail due to the instability of the corneal epithelium in the absence of a healthy tear film and normal eyelid function.

Candida infection of a Boston Type I Keratoprosthesis (KPro)

The Boston Type I Keratoprosthesis is a prosthetic corneal replacement used to restore vision in individuals with severe corneal disease and contraindications to traditional keratoplasty techniques. Like other artificial implants in the body, the KPro may be a nidus for infection. Fungal infections may occur around the device stem and appear milky-white, as seen in these photographs. Also shown is a photograph prior to the infection for comparison (figure 1).

Mohamed Abou Shousha, M.D. - Bascom Palmer Eye …

Many corneal diseases can be effectively treated by corneal transplantation, so the use of keratoprostheses is largely restricted to patients whose eye condition is such that corneal transplantation offers little hope of success. These include patients who have had multiple previous penetrating grafts with graft failure from rejection, leading to an eye highly sensitised to donor antigens with an extreme risk of rejection of further grafts.

Physician profile for Mohamed Abou Shousha, M.D.

Keratoprosthesis implantation is a procedure that involves full-thickness removal of the cornea and replacement by an artificial cornea. The Boston Type I Keratoprosthesis is currently the most commonly used keratoprosthesis device in the US. It consists of a clear plastic polymethylmethacrylate (PMMA) optic and back plate sandwiched around a corneal graft and secured with a titanium locking ring (Figure 15). After the device is assembled, a partial-thickness trephination is performed on the host cornea. Full-thickness resection of the patient's cornea is then completed using curved corneal scissors. The keratoprosthesis is then secured to host tissue using interrupted or running sutures. Generally, patients who have a history of multiple failed PKs are candidates for a keratoprosthesis transplant. Other indications include severe keratitis or ocular surface disease resulting from limbal stem cell failure, such as (Figure 16), , (Figure 17) and chemical injury (, ). The Boston Type II Keratoprosthesis is a similar device with a longer optic designed to extend through an opening made in the upper eyelid (Figure 19). It is indicated for the most severe cicatrizing ocular surface diseases.

Corneal Remodeling - Medical Clinical Policy Bulletins | Aetna

Keratoprosthesis implantation is a procedure that involves full-thickness removal of the cornea and replacement by an artificial cornea. The Boston Type I Keratoprosthesis is currently the most commonly used keratoprosthesis device in the US. It consists of a clear plastic polymethylmethacrylate (PMMA) optic and back plate sandwiched around a corneal graft and secured with a titanium locking ring (Figure 15). After the device is assembled, a partial-thickness trephination is performed on the host cornea. Full-thickness resection of the patient's cornea is then completed using curved corneal scissors. The keratoprosthesis is then secured to host tissue using interrupted or running sutures. Generally, patients who have a history of multiple failed PKs are candidates for a keratoprosthesis transplant. Other indications include severe keratitis or ocular surface disease resulting from limbal stem cell failure, such as (Figure 16), , (Figure 17) and chemical injury (, ). The Boston Type II Keratoprosthesis is a similar device with a longer optic designed to extend through an opening made in the upper eyelid (Figure 19). It is indicated for the most severe cicatrizing ocular surface diseases.

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