The National Institute for Clinical Excellence is examining insertion of hydrogel keratoprosthesis and will publish guidance on its safety and efficacy to the NHS in England, Wales and Scotland. The Institute's Interventional Procedures Advisory Committee has considered the available evidence and the views of Specialist Advisors, who are consultants with knowledge of the procedure. The Advisory Committee has made provisional recommendations about insertion of hydrogel keratoprosthesis.

This document summarises the procedure and sets out the provisional recommendations made by the Advisory Committee. It has been prepared for public consultation. The Advisory Committee particularly welcomes:

• comments on the preliminary recommendation
• the identification of factual inaccuracies
• additional relevant evidence.

Note that this document is not the Institute's formal guidance on this procedure. The recommendations are provisional and may change after consultation.

The process that the Institute will follow after the consultation period ends is as follows.

• The Advisory Committee will meet again to consider the original evidence and its provisional recommendations in the light of the comments received during consultation.
• The Advisory Committee will then prepare draft guidance, which will be the basis for the Institute's guidance on the use of the procedure in the NHS in England, Wales and Scotland.

For further details, see the Interim Guide to the Interventional Procedures Programme, which is available from the Institute's website (www.nice.org.uk/ip).

Closing date for comments: 23 March 2004

Target date for publication of guidance: June 2004

Note that this document is not the Institute's guidance on this procedure. The recommendations are provisional and may change after consultation.

Current evidence on the safety and efficacy of insertion of hydrogel keratoprosthesis does not appear adequate for this procedure to be used without special arrangements for consent and for audit or research.

Clinicians wishing to undertake insertion of hydrogel keratoprosthesis should take the following action.

• Inform the clinical governance leads in their Trusts.
• Ensure that patients understand the uncertainty about the procedure's safety and efficacy and provide them with clear written information. Use of the Institute's Information for the Public is recommended.
• Audit and review clinical outcomes of all patients having insertion of hydrogel keratoprosthesis. Publication of safety and efficacy outcomes will be useful in reducing the current uncertainty.

The manufacturer of the synthetic hydrogel cornea implant used in this procedure maintains a registry. The Institute may review the procedure upon publication of further evidence.

The cornea is the transparent part of the coating of the eyeball, which covers the iris and pupil and admits light to the interior of the eye. Injury or disease can make the cornea opaque, hindering the passage of light and resulting in loss of vision. Diseases that can cause the cornea to deteriorate include keratoconus, bullous keratopathy and herpetic eye disease.

A corneal transplant is the standard treatment when the cornea becomes damaged by injury or disease. This procedure involves the removal of a disc comprising the majority of the cornea using a trephine and replacing it with a corresponding disc from the cornea of a donor eye. In penetrating keratoplasty, the disc removed is the entire thickness of the cornea and so is the replacement disc. Some patients can not undergo the standard procedure using donor tissue for several reasons, such as disease severity, severe involvement of the conjunctivae objection to the use of donor tissue, failed past donor tissue transplants, or when measures required to prevent graft rejection are medically contraindicated. For these patients, penetrating keratoplasty using an artificial cornea or keratoprosthesis is an option.

The implantation of a synthetic hydrogel cornea is a two-stage surgical procedure. The first stage involves making a 270 degree partial thickness incision at the junction of the cornea and sclera, to allow an intralamellar pocket to be created within the cornea. The superficial flap is then reflected to allow a portion of the central part of the posterior lamella to be removed using a trephine, and the synthetic hydrogel cornea to be inserted into the intralamellar pocket. The superficial flap is repositioned and the incision closed. In most cases, the operation is completed by forming a flap of tissue from the conjunctiva (the outer layer of the 'white' of the eye), which is used to cover the surface of the front of the eye. This may cause changes in the cosmetic appearance of the eye.

The second stage of the procedure is performed 12 weeks later, and involves removing the conjunctival cover and the superficial flap of the cornea exposing the synthetic hydrogel cornea to light. The eye may still not appear completely 'normal' after this stage of the operation.

Evidence on the efficacy of this procedure was based on small, uncontrolled studies with short-term follow-up. Initial results indicated that visual acuity improved (although still poor) or remained the same in most patients. In a report of 41 patients with a mean preoperative visual acuity of hand movements, mean best corrected visual acuity for 21 patients at 12 months follow-up was 20/300. The authors of this report also stated that among the 41 patients undergoing implant of a synthetic cornea, 26 implants remained in situ (63%) with a mean follow-up of 16 months. Patient selection criteria have changed, however, since the first trial on this procedure, and it is unclear what impact this will have on efficacy outcomes. For more details, refer to the Sources of evidence (see Appendix).

The Specialist Advisors considered that this procedure should be restricted to those individuals who can not be treated with established procedures and who have no useful vision in the other eye. One Advisor stated that while postoperative vision is not very good for most patients it is better than their preoperative vision.

Safety

Stromal melting is a frequent complication for all keratoprostheses and is common following this procedure. In a review of 41 non-herpetic patients, 41.5% (17 patients) developed a stromal melt. In this particular review the number of patients requiring device removal as a result of this complication was unclear, however in a series by the same authors it was reported that 12.5% (5/40) implants were removed because of melting. Other complications included cellular depositions on the device itself (22%), development of retroprosthetic membranes (7.3%), and retinal detachment (4.9%). The literature seemed to suggest that certain patients were at increased risk of complications, namely patients with herpetic eye disease and smokers. For more details, refer to the Sources of evidence (see Appendix).

The Specialist Advisors considered that the long-term complication rate of this procedure is still unknown. Although endophthalmitis is thought to be the most significant potential complication of any artificial cornea, the Advisors noted that this had not yet been reported following this procedure.

Data were based on small numbers of patients.

The following document, which summarises the evidence, was considered by the Interventional Procedures Advisory Committee when making its provisional recommendations.

• Interventional procedure overview of insertion of hydrogel synthetic keratoprosthesis, October 2003

Available from: www.nice.org.uk/ip225overview