Royal College of Ophthalmologists Guidelines 

Screening for Diabetic Retinopathy

It is widely accepted that screening for diabetic retinopathy represents both good clinical practice and cost-effective healthcare. The natural history of the disease is known, and early detection and treatment of retinopathy has been shown to be effective in preventing visual impairment.^5-6 With appropriate medical and ophthalmological intervention, including good glycaemic and blood pressure control, it has been estimated that blindness may be prevented in at least one ye in 60-70% of cases with maculopathy and 90% of cases of proliferative retinopathy. The disability caused by blindness and partial sight, as well as the social costs in terms of loss of earning capacity and the required social support are considerable.⁷ Lack of screening may also result in costly compensation claims. The recent debate has focused on what is the most suitable screening test to use.

STANDARDS FOR DIABETIC RETINOPATHY SCREENING

The performance of a screening system may be judged by its sensitivity (the ability to detect true positives) and its specificity (the ability to detect true negatives) as well as on it s practical and financial implications. The British Diabetic Association (Diabetes UK) has established standards for any diabetic retinopathy screening programme of at least 80% sensitivity and 95% specificity. An effective screening service needs to have a systematic call and recall of eligible patients, trained professionals, recorded outcomes with targets and standards, and quality assurance. Promotion of uptake of the screening programme, and efficient and appropriate follow-up of those with retinopathy are also important features.

Screening is important not only for the detection of sight-threatening retinopathy, but also for the detection of any retinopathy so that particular effort can be made to improve blood pressure and glycaemic control.

Currently there is great variation in the provision of diabetic retinopathy screening services throughout the UK. In some areas there is well organised systematic screening whilst in others there are ad hoc schemes with variation in screening methods and population coverage, and no recording of service outcomes.⁸

EFFECTIVENESS OF DIFFERENT SCREENING METHODS

There have been a number of studies assessing the effectiveness of different screening modalities. Comparison between the studies can be difficult as a number of different reference standards have been used, there are variations in the definitions of retinopathy used for grading, and some studies involved only a small number of patients and observers.

Direct ophthalmoscopy

Studies from the UK have shown sensitivity levels for the detection of sight-threatening diabetic retinopathy of 41-67% for general practitioners, 48-82% for optometrists, 65% for an ophthalmologist, and 27-67% for diabetologists and hospital physicians using direct ophthalmoscopy.^9-13

Indirect ophthalmoscopy

There are few studies specifically assessing the use of dilated slit-lamp indirect ophthalmoscopy, but it does appear that the required standards may be achieved by trained individuals. Sensitivities for the detection of referable retinopathy by optometrists have been found to be 77-100%, with specificities of 94-100%.¹⁴

The use of ophthalmoscopy has the disadvantage that there is no hard record, which makes quality assurance more difficult. Audit of test positives or of adverse events is not sufficient for quality assurance purposes, and patients would need to be recalled to assess test negatives, for which attendance rates may be very low. The personnel performing the examination require considerable training and accreditation.

Photographic methods

Photographic methods currently in use involve 35mm film, digital images, or polaroid instant film prints with subsequent grading by trained individuals. The use of mydriasis results in improved sensitivity for the detection of sight-threatening retinopathy and fewer ungradeable images. ^9,10,12 Sensitivities for the detection of sight-threatening diabetic retinopathy of 87-100% have been found for a variety of trained personnel reading mydriatic 45° retinal photographs, with specificities of 83-96%.^9-11 The results were similar between different personnel performing the grading, including trained non-medical graders. it appears that there is good agreement in the grading of retinopathy between 35mm colour film and digital images despite the lower resolution of the latter,15 but further evaluation of this is needed. Sensitivities for the detection of sight-threatening retinopathy are lower with instant polaroid photographs. Digital images have the advantage that they are easier to acquire, store and transfer than 35mm film, and that images can be reviewed with the patient at the time of screening. patients also find the lower intensity flash more comfortable.

THE NATIONAL SCREENING COMMITTEE REVIEW OF DIABETIC RETINOPATHY SCREENING

The National Screening Committee has recently considered the issues surrounding screening for diabetic retinopathy and after wide consultation has provided recommendations on screening and the practicalities of a national programme. Details of these can be seen on the website: http://www.diabetic-retinopathy-screening.nhs.uk/ The National Institute for Clinical Excellent (NICE) is also reviewing the evidence and will be producing guidelines concerning screening and early management for diabetic retinopathy later this year.

Principal recommendations of the National Screening Committee are:

• Annual screening for all diabetic patients aged over 123 years, or post-puberty. 
• Digital imaging is the preferred modality. 
• Quality assurance should be included in any programme. 
• Direct ophthalmoscopy should not be used as a primary method for systematic screening as it does not meet the required quality criteria. 
• Indirect slit-lamp ophthalmoscopy may meet the sensitivity and specificity requirements but requires considerable skills and training, and it is hard to perform adequate quality assurance. 
• The screening programme should be accessible to all patients with diabetes. The exact details of a programme for a particular area will be determined by local factors. 
• The proposed national programme would be rolled out over a period of 3-4 years, as both funding and trained staff become available. 

The quality assurance measures proposed in such a programme will represent a significant workload for some ophthalmologists, and their implementation will be the subject of further discussions.

COST ESTIMATIONS FOR THE PROPOSED NATIONAL SCREENING PROGRAMME

The National Screening Committee has calculated the estimated costs for the proposed national screening programme for diabetic retinopathy and has put forward a bid to the Comprehensive Spending Review under the auspices of the National Service Framework for diabetes. Such a programme would require pump-priming funds of about £67 million pounds in England, phased over several years, with 70% of the funding for a particular health authority in the first year to allow for start-up costs. Such a programme can be calculated to cost about £1,370 per case treated in the first year, £12,000 per prevention of severe visual loss, and about £2,000 per sight year gained.¹⁷ By the fourth year, it is hoped that the programme could be funded by anticipated revenue savings from a reduction in the number of cases requiring treatment for advanced disease.

CONCLUSION

Systematic screening for diabetic retinopathy should make an important contribution to the preservation of vision for people with diabetes and a national screening programme has now been proposed. Its full implementation will depend on the Diabetes National Service Framework which is expected to be published soon. At present health authorities are being advised to take account of the recommendations of the National Screening Committee in making decisions on investment in equipment and staff training.

Clare Bailey, consultant ophthalmologist, Bristol Eye Hospital.

References

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