Artificial Cornea Transplantation

There are approximately 4.9 million people with bilateral blindness secondary to corneal disease worldwide, accounting for 12% of total global blindness. Common causes are anterior corneal pathologies such as trachoma, infectious keratitis, ocular trauma, chemical injuries, and high prevalence in developing countries. Primary corneal transplantation (lamellar or full-thickness) has high graft survival of 87% and 93% at one year and 72% to 73% at 5 years in non-complex eyes. Graft survival decreases with repeat transplantation and in complex eyes, despite advances in keratoplasty techniques and more selective tissue transplantation.

High-risk factors include recurrent and chronic inflammation of the ocular surface, glaucoma, and eyes with corneal vascularisation. Globally, the availability of donor cornea material can be limited due to donor supply and the need for eye banking facilities. An artificial cornea transplant can be considered for end-stage corneal diseases such as multiple graft failures or inflammatory ocular surface disease.

There have been many proposed artificial cornea transplant devices (keratoprosthesis; KPro). Pellier de Quengsy first described the initial concept in 1789. They generally have a central clear optic with either hard skirt plates which sandwich donor cornea tissue in between or a soft optic and skirt in a one-piece integrated design. The importance of a suitable skirt material with good tissue incorporation was made clear from earlier models made from rubber, milk protein, Dacron, crystal, glass, and celluloid, which resulted in device extrusion after implantation. The successful introduction of cadaveric corneal transplantation resulted in decreased interest in artificial corneal transplantation. However, the discovery of polymethylmethacrylate (PMMA) enabled a biocompatible device to be implanted, and earlier devices have been described by Choyce and Stone.

More recently, soft polymers have been used to simulate the natural cornea. Poly-2-hydroxyethyl methacrylate was used for the AlphaCor, which gained FDA approval in 2003. After one and two years, retention rates were 80% and 62%, and stromal melt occurred in 27% of the total cases, many requiring explantation. A similar design using polytetrafluoroethylene (PTFE; Legeais BioKPro-III) had worse outcomes, with 86% of devices failing after implantation. The focus of this review is to describe indications and management for the most commonly used artificial cornea transplants currently: Boston KPro type 1 and the Osteo-odonto-Keratoprosthesis (OOKP).

Current Keratoprostheses

Boston KPro Type I
The most widely implanted artificial cornea transplant is the Boston KPro type 1. The design consists of a front plate with a central optical stem, a backplate, and a corneal donor button sandwiched in between. The front plate and optic are made from PMMA, and the optical power is determined by the radius curvature. The backplate is available in PMMA and titanium. There is no difference reported in the frequency of retroprosthetic membrane formation (RPM) between the two materials at 12 months.

Osteo-odonto-Keratoprosthesis (OOKP)

The OOKP utilizes an autologous tooth root-alveolar bone complex as the keratoprosthesis skirt material for better tissue integration. The principle of OOKP surgery is the bypass of the diseased ocular surface by a buccal mucous membrane patch and replacement of the anterior segment structures with the OOKP. OOKP can retain for a number of decades. Long-term anatomical retention is good, with 81% retention over 5 years reported in a cohort of 36 eyes, 98% retention in 85 patients over a 20-year follow-up, and 80% in 224 eyes over 18 years.

Keratoprostheses in Development

There are numerous alternative keratoprostheses in development. <more details in the original publication)

Author(s) Source
Fu L, Hollick E
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