Keratoconus is a disease of the cornea which affects the shape of the eyeball and causes refractive errors, some of which cannot be corrected by spectacles or contact lenses. The insertion of clear plastic implants into the cornea is an interventional procedure aiming to restore eyesight in patients with this condition.

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

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 recommendations
  
• 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• The Advisory Committee will then prepare draft guidance which will be the basis for the Institute's guidance on the use of the procedure in the NHS in England, Wales, Scotland and Northern Ireland.

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

Closing date for comments: 24 April 2007
Target date for publication of guidance: July 2007

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

Keratoconus is a progressive disease in which the normally round corneal surface becomes thinner and begins to bulge into a cone like shape. This changes the normal physical properties of the cornea and affects refraction. Keratoconus is often associated with astigmatism. Patients should have clear central corneas in order for them to be suitable candidates for the insertion of corneal implants.

In mild keratoconus, spectacles or soft contact lenses may help. In more severe disease, other treatments may include collagen cross-linking riboflavin eye drops. Invasive procedures include penetrating keratoplasty to modify the shape of the cornea. Ultimately a corneal transplant may be required in some patients.

One case series (n = 34 eyes) reported that best spectacle corrected visual acuity (BSCVA) improved significantly from baseline to 6 months after insertion of corneal ring segments; 62% of eyes gained two to eight lines, 32% had no change and 6% lost two or more lines (p < 0.001).="" an="" uncorrected="" visual="" acuity="" (ucva)="" score="" of="" 20/40="" or="" more="" was="" recorded="" in="" 24%="" (8/34)="" of="" eyes="" at="" 12-month="" follow-up,="" compared="" with="" 4%="" (2/53)="" of="" eyes="" at="" baseline="" (p=""><>

A second case series reported that UCVA had improved by 2 lines or more in 72% (53/74) of eyes, and BSCVA had improved by 2 lines or more in 45% (33/74) of eyes at 9-month follow-up (p values not reported). A third case series of 31 eyes reported that BSCVA had improved by 2 lines or more in 87% (27/31) of eyes and UCVA had improved by the same amount in 81% (25/31) of eyes at 12-month follow-up (p - values not reported).

One case series of 57 eyes reported that there were no intraoperative complications or clinically significant postoperative complications. In another case series, creation of a superficial channel perforated the Bowman's layer in 1% (1/74) of eyes, although the implant was successfully rechannelled and fitted.

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

• ' Interventional procedure overview of corneal implants for keratoconus', January 2007