Lesson 7: ART Critique a cohort study

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Incidence of sight-threatening retinopathy in patients with type 2 diabetes in the Liverpool Diabetic Eye Study: a cohort study (Lancet 2003).

Introduction and aim: Until this study was conducted, screening for retinopathy was annual although this was not an evidence-based practice. Due to the high cost of screening, the Liverpool.

Diabetic Eye Study was set up in 1991 to assess screening for diabetic retinopathy in primary care. As well as the best screening interval, this study investigated the incidence and progression rates of retinopathy type 2 diabetics who were enrolled in the programme.

Methods: Patients with type-2 diabetes registered with enrolled general practices but not attending an ophthalmologist, with retinopathy data at baseline and a minimum of one other visit, were recruited. Sight threatening diabetic retinopathy was defined as moderate pre-proliferative
retinopathy or worse, or clinically significant maculopathy in either or both eyes. Type-2 diabetes was defined as age 30 or over at diagnosis, or less than 30 but not insulin-dependent.

Results and conclusions: The annual incidence of any and sight-threatening DR in patients without retinopathy at baseline was 5183 and 267 per 105, respectively, in year 1 and 6041 and 1928 per 105, respectively, in year 5. For a 95% probability of remaining disease-free of sight-threatening DR, mean screening intervals by baseline status were: no retinopathy 5.4 yrs, background 1.0 yrs, and mild pre-proliferative 0.3 yrs.

The authors concluded that the screening interval could be reduced to every three years for type-2 diabetics with no retinopathy, but other patients with some degree of retinopathy should continue to be screened annually.

Discussion points

  1. Why would the number of patients at risk decrease each year?
  2. Do you think that the results from this study are generalisable to all diabetics?
  3. Do you think the authors’ conclusions are justified?