Corneal implants for the correction of refractive error (interventional procedures consultation)
NATIONAL INSTITUTE FOR HEALTH AND CLINICAL EXCELLENCE
Interventional Procedure Consultation Document
Corneal implants for the correction of refractive error
Short-sightedness is the inability to see clearly at a distance. Eyesight can usually be corrected by wearing spectacles or contact lenses. The insertion of clear plastic implants into the cornea is an interventional procedure aiming to restore eyesight in short-sightedness.
The National Institute for Health and Clinical Excellence is examining corneal implants for the correction of refractive error 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 the correction of refractive error.
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.
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
Note that this document is not the Institute's guidance on this procedure. The recommendations are provisional and may change after consultation.
|1.1||Current evidence on the efficacy of corneal implants for the correction of refractive error shows limited and unpredictable benefit. In addition, there are concerns about the safety of the procedure for patients with refractive error which can be corrected by other means, such as spectacles, contact lenses, or laser refractive surgery. Therefore, corneal implants should not be used for the treatment of refractive error in the absence of other ocular pathology such as keratoconus.|
Myopic refractive error occurs when light from a distant object is brought into focus in front of the retina rather than on it. This is usually because the eye is too long, but it may be due to the cornea being too steeply curved. Near objects are seen clearly but more distant ones are blurred. This procedure may not be appropriate for patients with a high degree of astigmatism.
Focusing (refractive) errors are usually corrected by wearing spectacles or contact lenses, both of which correct visual acuity and are acceptable solutions to the majority of patients. In addition, surgical treatments can be used to treat myopia, including photorefractive keratectomy (PRK) and laser in situ keratomileusis (LASIK).
|2.2||Outline of the procedure|
|2.2.1||Corneal implants are flexible, crescent-shaped rings of polymethyl methacrylate that are placed in the periphery of the cornea. They affect refraction in the eye by physically changing the shape of the cornea, flattening the front of the eye.|
|2.2.2||The procedure is undertaken under local or general anaesthesia. An incision is made in the cornea and channels are created in it by rotating a lamellar dissector or by using a femtosecond laser. One corneal implant segment is introduced to each channel. Various implants with a range of implant thicknesses are available for different degrees of correction.|
In a matched case analysis, uncorrected visual acuity (UCVA) 3 months after the procedure was reported to be 20/20 or better in 75% (58/77) of eyes receiving corneal implants, and 67% (84/126) of eyes undergoing LASIK. Statistical significance was not reported.
In two case series, UCVA of 20/20 or better 1 year after the procedure was reported in 74% of eyes (absolute numbers not provided) and 43% (35/79) of eyes. In the latter study, 20/20 vision or better rose to 64% (27/42) at 5 years. Statistical significance was not reported.
|2.3.3||One case series of 159 eyes receiving corneal implants found that the change in manifest refraction spherical equivalent (a measure of visual acuity) was 0.32 (? 0.79) dioptres (D) between 1 and 3 months' follow-up, but only 0.01 (? 0.58) between 6 and 12 months' follow-up. Statistical significance was not reported.|
|2.3.4||The proportion of eyes in which correction of vision was within 1.0 D of the intended correction ranged from 68% (28/42) to 100% (16/16) in two case series. In the same case series, the proportion corrected to within 0.5 D ranged from 41% (17/42) to 81% (13/16). Statistical significance was not reported.|
|2.3.5||In one study, patient satisfaction was rated 'excellent' by 47%, 'good' by 41%, 'fair' by 9%, and 'poor' by 2% of 104 patients surveyed at 1-year follow-up. For more details, refer to the sources of evidence (see Appendix).|
|2.3.6||The Specialist Advisers considered the expected benefits of the procedure to be a correction of low myopia with a rapid recovery time and minimal ocular morbidity. One Specialist Adviser noted that, although there is work demonstrating the safety and efficacy of this procedure for myopia of up to -3.0 D, it has not been widely used due to the simultaneous development of laser correction technology. One Adviser considered that a potential consideration is loss of effect over time.|
The rates of corneal perforation in the included studies were 0% (0/21), <1% (3/452),="" and="" 2%="" (3/163).="" one="" case="" series="" reported="" a="" single="" case="" of="" infectious="" keratitis="" among="" 452="" patients="">1%>
|2.4.2||Visual complications following the procedure were reported in two studies and included poor night vision in 5% of patients, glare in 1% (absolute numbers not provided) and 2% (2/104) of patients, halos in 1% (absolute numbers not provided) and 2% (2/104) of patients, and photophobia in <1% (absolute="" numbers="" not="" provided)="" and="" 1%="" (1/104)="" of="" patients,="">1%>|
|2.4.3||One patient experienced partial extrusion of an implant following thinning of the corneal stroma at 5 years' follow-up. The implants were successfully removed and best spectacle-corrected visual acuity (BSCVA) recovered to 20/25 at 4 weeks.|
|2.4.4||In a non-randomised trial, loss of two or more lines of BSCVA was reported in 9% (7/76) of eyes treated with corneal implants compared with 1% (1/126) of LASIK-treated eyes at 3-month follow-up. In one case series, this degree of visual loss was reported in 5% (4/79) of eyes at 1-year follow-up and 7% (3/42) at 5 years. In a second case series, two lines were lost in 4% (5/138) of eyes, and more than two lines were lost in 2% (3/138) of eyes at 12 months. However, none of these patients requested removal of implants. No statistical significance was reported. For more details, refer to the sources of evidence (see Appendix).|
|2.4.5||The Specialist Advisers noted that reported adverse events include photophobia, glare, foreign body sensation, extrusion, corneal perforation and infection, all of which may lead to implant removal. Additional theoretical adverse events cited by Specialist Advisers include ring erosion, inflammation, corneal melt and damage to the retina or optic nerve through increased intraocular pressure.|
Chairman, Interventional Procedures Advisory Committee
|Appendix:||Sources of evidence|
The following document, which summarises the evidence, was considered by the Interventional Procedures Advisory Committee when making its provisional recommendations.
This page was last updated: 30 March 2010