Corneal implants for the correction of refractive error

# Guidance
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.# The procedure

# Indications
Myopic refractive error occurs when light from a distant object is brought into focus in front of the retina rather than on it. Near objects are seen clearly but more distant ones are blurred. This is usually because the eye is too long, but it may be due to the cornea being too steeply curved (this is called keratoconus; NICE has produced separate guidance on the use of this procedure in keratoconus).
Focusing (refractive) errors are usually corrected by wearing spectacles or contact lenses, both of which correct visual acuity and are acceptable solutions for the majority of patients. In addition, surgical treatments can be used to treat myopia, including laser refractive surgery.

# Outline of the procedure
Corneal implants are flexible, crescent-shaped rings of polymethyl methacrylate that are inserted 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.
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.

# Efficacy
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 laser refractive surgery. 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 (452 patients studied, but 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.
In a non-randomised trial, loss of two or more lines of best spectacle-corrected visual acuity (BSCVA) was reported in 9% (7/76) of eyes treated with corneal implants compared with 1% (1/126) of laser refractive surgery-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.
The proportion of eyes in which correction of vision was within 1.0 D (dioptres) 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.
In one study, patient satisfaction was rated 'excellent' by 47%, 'good' by 41%, 'fair' by 9%, and 'poor' by 2% of 104 patients surveyed a 1-year follow-up. For more details, refer to the 'Sources of evidence' section.
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 refractive surgery. One Adviser considered that a potential consideration is loss of effect over time.

# Safety
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 treated.
Reported visual complications following the procedure included poor night vision in 5%, glare in 1%, halos in 1% of patients, and photophobia in <1% of patients (absolute numbers not reported) in a case series of 452 patients. In another case series of 104 patients, reported complications included glare in 2% (2/104), halos in 2% of patients (2/104) and photophobia in 1% (1/104) of patients.
One case report described a patient with partial extrusion of an implant following thinning of the corneal stroma at 5 years' follow-up. The implants were successfully removed and BSCVA recovered to 20/25 at 4 weeks. For more details, refer to the 'Sources of evidence' section.
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.# Further information
The Institute has published interventional procedures guidance on photorefractive (laser) surgery for the correction of refractive errors.
Andrew DillonChief ExecutiveJuly 2007

# Sources of evidence
The evidence considered by the Interventional Procedures Advisory Committee is described in the following document.
'Interventional procedure overview of corneal implants for the correction of refractive error', November 2006.

# Information for patients
NICE has produced information describing its guidance on this procedure for patients and their carers ('Understanding NICE guidance'). It explains the nature of the procedure and the decision made, and has been written with patient consent in mind.# About this guidance
NICE interventional procedure guidance makes recommendations on the safety and efficacy of the procedure. It does not cover whether or not the NHS should fund a procedure. Funding decisions are taken by local NHS bodies after considering the clinical effectiveness of the procedure and whether it represents value for money for the NHS. It is for healthcare professionals and people using the NHS in England, Wales, Scotland and Northern Ireland, and is endorsed by Healthcare Improvement Scotland for implementation by NHSScotland.
This guidance was developed using the NICE interventional procedure guidance process.
We have produced a summary of this guidance for patients and carers. Information about the evidence it is based on is also available.
Changes since publication
January 2012: minor maintenance.
Your responsibility
This guidance represents the views of NICE and was arrived at after careful consideration of the available evidence. Healthcare professionals are expected to take it fully into account when exercising their clinical judgement. This guidance does not, however, override the individual responsibility of healthcare professionals to make appropriate decisions in the circumstances of the individual patient, in consultation with the patient and/or guardian or carer.
Implementation of this guidance is the responsibility of local commissioners and/or providers. Commissioners and providers are reminded that it is their responsibility to implement the guidance, in their local context, in light of their duties to avoid unlawful discrimination and to have regard to promoting equality of opportunity. Nothing in this guidance should be interpreted in a way which would be inconsistent with compliance with those duties.
Copyright
 National Institute for Health and Clinical Excellence 2007. All rights reserved. NICE copyright material can be downloaded for private research and study, and may be reproduced for educational and not-for-profit purposes. No reproduction by or for commercial organisations, or for commercial purposes, is allowed without the written permission of NICE.
Contact NICE
National Institute for Health and Clinical ExcellenceLevel 1A, City Tower, Piccadilly Plaza, Manchester M1 4BT
www.nice.org.uk
    nice@nice.org.uk