Screening for diabetic retinopathy and the prevention and treatment of diabetic foot ulcers are covered in the first two of a series of systematic reviews undertaken to inform national clinical practice guidelines for type-2 (non-insulin-dependent) diabetes, currently being produced by the school for health and related research at Sheffield University.
Although the guidelines are concerned only with type-2 diabetes, almost all the studies in these evidence reviews included patients with type- 1 (insulin-dependent) diabetes as well, so the findings may be generally applicable to both, and these complications require similar management. The August Effective Health Care bulletin summarises the reviews.
Screening for diabetic retinopathy
Diabetic retinopathy is the leading cause of blindness in people of working age in industrialised countries. The condition develops over a period of years, usually without visual symptoms or visual impairment. During this time, it can only be detected by eye examination. If left untreated, it leads to bleeding, scarring, and progressive loss of vision.
Retinopathy is treated by laser photo-coagulation. Large trials have shown this can prevent blindness if treatment is given sufficiently early. It has been estimated that systematic screening for diabetic retinopathy could prevent about 260 new cases of blindness a year among people aged under 70 in England and Wales.
Nevertheless, there is wide variability in screening services in England and Wales, both in coverage and methods used. A survey found that more than 40 per cent of screening programmes included fewer than half of the people known to have diabetes in the area, and 18 hospitals, covering a population of 2.5 million, had no systematic screening programmes at all.
Even where there is screening, the review revealed that many methods may be inadequate, missing large numbers of people with sight-threatening retinopathy. Few of the studies identified met the British Diabetic Association's criteria for effectiveness (greater than 80 per cent sensitivity, greater than 95 per cent specificity, technical failure rate of less than5 per cent).
There are two main types of screening method, ophthalmoscopy and retinal photography, which may be further sub-divided (see table, below). Either method is currently used with or without mydriasis (dilation of the pupils with eye drops).
In most studies, direct ophthalmoscopy was used. The sensitivity of this method is poor (cases are missed) because it does not allow the user to see a large part of the retina. Despite evidence of highly variable accuracy, ophthalmoscopy in hospital clinics has been the most widely used screening method.
Direct ophthalmoscopy is now considered obsolete by ophthalmologists. Its place has been taken by slit-lamp biomicroscopy. Two recent reports show that trained and accredited high-street optometrists using ophthalmoscopy can achieve levels of effectiveness that meet BDA criteria.
Retinal photography provides a lasting record of patients' retinas. It can be carried out in a range of settings, from clinics to mobile converted vans. It offers an effective screening method when mydriasis is used and the photographs are assessed by trained readers.
Most published studies report Polaroid or 35mm photography. This requires a relatively strong flash, which can be uncomfortable for patients. Recent reports of digital cameras suggest these may be better, although they require higher initial capital outlay.
Frequency of screening
Population studies suggest that people without retinopathy are very unlikely to develop sight-threatening disease within four years, but those who have some retinopathy are at risk. A variety of screening intervals has been assessed in modelling studies, with one and two-year intervals compared in Iceland.
The results of these studies are generally consistent with the European consensus: that all patients with diabetes not under treatment for retinopathy should have annual screening.
Cost and cost-effectiveness
Whichever method of screening is used, it is likely to be highly cost- effective if it meets BDA criteria for effectiveness. The cost of screening may be less than the cost of avoidable blindness - which could include not only the direct costs of looking after blind people, but litigation costs if they were to pursue a health authority for negligence in failing to offer adequate screening.
Actual costs can be as low as£10-£13 per patient screened by mobile retinal photography, and just over£1,000 a patient requiring laser treatment. Polaroid cameras cost about£14,000, while digital cameras currently cost£28,000. Other costs include establishing effective call, recall and quality assurance systems.
Screening by accredited optometrists in London costs£12.62 per case (including training and quality audit costs), and£581 per case identified. These figures do not include a£20 fee paid to the optometrist.
Management of foot ulcers
At some time in their life, 15 per cent of people with diabetes develop foot ulcers associated with peripheral neuropathy (nerve damage) and/or ischaemia (lack of blood supply). In a local population study, 7.4 per cent of 1,077 patients with diabetes had foot ulcers or had experienced them. Generally, 70 per cent have recurrence within five years. Diabetic foot ulcers are highly susceptible to infection, and 5-15 per cent of patients will require lower extremity amputation.
Prevention and reduction of recurrence
Patients at high risk can be identified by checking sensitivity to touch. A randomised controlled trial involving 2,001 people demonstrated that amputation rates among high-risk patients were reduced by weekly clinics providing chiropody, hygiene, hosiery, protective shoes and education.
Education and podiatry (specialist foot care), usually provided by nurses or podiatrists, can improve knowledge and may improve the condition of the feet. It includes instruction on blood glucose control, inspecting the feet, foot hygiene, footwear and dealing with infections, calluses and injuries. An intervention that appeared particularly effective was a one-off class where high-risk patients were shown slides of infected feet and amputations, and given a simple check-list of instructions. Therapeutic shoes can also reduce the relapse rate in people at high risk.
Treatments for foot ulcers
The review found no conclusive evidence for the effectiveness of any particular type of intervention. Some treatments - many of which are not currently licensed in the UK - may be beneficial, but further research is required. The most promising interventions are listed in the table above.
The review found no evidence that any particular type of wound dressing was more effective than any other, but suggested that adhesive dressings intended to improve debridement (removal of dead or infected tissue) should be avoided.
Arabella Melville is a consultant to the NHS centre for reviews and dissemination, York University.
Effective Health Care is an independent report based on systematic reviews of research evidence, produced by the NHS centre for reviews and dissemination, York University. The bulletin aims to provide NHS decision makers with information on the effectiveness of interventions and the delivery and organisation of healthcare.
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Effective Health Care is available on the web at www.york.ac.uk/inst/crd/ehcb.htm