ArticlesIncidence of sight-threatening retinopathy in patients with type 2 diabetes in the Liverpool Diabetic Eye Study: a cohort study
Introduction
Laser photocoagulation is highly effective in treatment of the eye complications of diabetes mellitus.1, 2 However, diabetic retinopathy remains a major cause of preventable loss of vision in the developed world3 and screening has thus been widely advocated throughout Europe and North America.4 Screening for retinopathy is a high priority in the proposed National Service Framework in Diabetes in the UK5 and for the National Eye Institute in the USA.6 Several alternative techniques of screening have been proposed that have varying sensitivities and specificities.7, 8 Many countries have attempted to standardise programmes and to introduce systematic quality assurance.
Development and progression of diabetic retinopathy have been investigated in population-based incidence studies in the USA and Europe.9, 10, 11, 12, 13 However, few data exist for incidence of diabetic eye disease in systematic retinopathy screening programmes.
Up to now, most countries have recommended a yearly screening interval for patients with no retinopathy,14, 15 but on the basis of expert group opinion rather than direct evidence. Systematic screening programmes of the whole population are expensive; to improve the cost-effectiveness of these programmes, various strategies have been proposed, including varying screening intervals by baseline grade of retinopathy.13, 16
The Liverpool Diabetic Eye Study was established in 1991 to assess various aspects of systematic screening for diabetic retinopathy in primary care. The sensitivity and specificity,7, 17 population-based prevalence at baseline,18 and cost-effectiveness of this screening programme19 have been reported previously. We aimed to investigate the incidence and progression rates of retinopathy to key endpoints in patients with type 2 diabetes enrolled in the programme and to calculate optimum screening intervals by grade of retinopathy. Present and future screening programmes can be designed and validated with this directly measured data from an established systematic programme.
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Patients
The Liverpool Diabetic Eye Study screening programme included all patients with diabetes registered with general practices within the Liverpool Health Authority and excluded those under continuing care of an ophthalmologist. Patients with diabetes entered the screening programme either by rollout in successive years to new general practices or by acquisition of new patients from enrolled practices during successive yearly rescreening. We included all patients with type 2 diabetes enrolled in
Results
By the end of 1999, 101 (97%) of 104 general practices within the Liverpool Health Authority had enrolled in the Liverpool Diabetic Eye Study screening programme. Between June, 1991, and December, 1999, 9890 patients had been newly identified with type 2 diabetes from practice registers, of whom 7615 (77%) attended for baseline screening. 5521 (73%) patients had no retinopathy; 1348 (18%) had background retinopathy; 396 (5%) had mild, 120 (2%) moderate, and 25 (0·3%) severe preproliferative
Discussion
In our investigation of a systematic screening programme, yearly incidence of sight-threatening diabetic retinopathy in patients with type 2 diabetes increased with time. The higher the grade of retinopathy at baseline, the greater the incidence of progression to sight-threatening diabetic retinopathy.
Our results differ from those of other studies of incidence and progression of retinopathy, most of which were population based9, 22, 23, 24 and reported progression to proliferative diabetic
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