Diabetic retinopathy screening – what interval?

Living in Alabama, I must follow the diabetes literature. We (the state) are number One in per capita type II diabetes. As I teach medical students, interns and residents, I have developed my own mneumonic for ongoing diabetes care – FLECKS. FLECKS represents a checklist that we must consider every time we have a patient encounter with a diabetic patient:

• Feet
• Lipids
• Eyes
• Control
• Kidneys
• Shots (immunizations)

Today I will focus on retinopathy, because of an important article in this week’s Lancet. I first checked out the current ADA guidelines on retinopathy screening. You can find the guidelines (free) at Diabetes Care – Clinical Practice Recommendations 2003. Going to the chapter on diabetic retinopathy, I looked for the current recommendation.

Patients with type 2 diabetes should have an initial dilated and comprehensive eye examination by an ophthalmologist or optometrist shortly after diabetes diagnosis. (B)

Subsequent examinations for both type 1 and type 2 diabetic patients should be repeated annually by an ophthalmologist or optometrist who is knowledgeable and experienced in diagnosing the presence of diabetic retinopathy and is aware of its management. Examinations will be required more frequently if retinopathy is progressing. This follow-up interval is recommended recognizing that there are limited data addressing this issue. (B)

This guideline matches our current practice and teaching. The guideline appropriately admits a lack of data on the appropriate interval for examinations. The interval question is a very important question which we rarely address in medical research. However, the issue now has an important hypothesis advanced for our consideration. Incidence of sight-threatening retinopathy in patients with type 2 diabetes in the Liverpool Diabetic Eye Study: a cohort study (free registration required to view this article). I will describe the study and then present their findings.

Methods We investigated all patients with type 2 diabetes registered with enrolled general practices (except those who were attending an ophthalmologist) who had retinopathy data available at baseline and at least one further screening event. To screen patients, we used non-stereoscopic three-field mydriatic photography and modified Wisconsin grading. Sight-threatening diabetic retinopathy was defined as moderate preproliferative retinopathy or worse, or clinically significant maculopathy in either or both eyes.

Thus, they used data on patients with at least two screening examinations to determine incidence rates. Let me define incidence precisely – the incidence is the rate of occurence. Thus, we want to know in this study the probability that a patient will develop diabetic retinopathy during any interval (per year or per 3 years).

Why is incidence important? If we want to develop an examination interval recommendation, then we need to know the probability that a patient will develop important retinopathy during any interval. If we examine the patient every day, we will never miss early retinopathy. If we examine the patient every 20 years, we will miss most early retinopathy. How do we optimize that interval?

Findings Results were obtained from 20 570 screening events. Yearly incidence of sight-threatening diabetic retinopathy in patients without retinopathy at baseline was 0·3% (95% CI 0·1-0·5) in the first year, rising to 1·8% (1·2-2·5) in the fifth year; cumulative incidence at 5 years was 3·9% (2·8-5·0). Rates of progression to sight-threatening diabetic retinopathy in year 1 by baseline status were: background 5·0% (3·5-6·5), and mild preproliferative 15% (10·2-19·8). For a 95% probability of remaining free of sight-threatening diabetic retinopathy, mean screening intervals by baseline status were: no retinopathy 5·4 years (95% CI 4·7-6·3), background 1·0 years (0·7-1·3), and mild preproliferative 0·3 years (0·2-0·5).

Those data are difficult to understand. I have read the study and this summary several times. I believe that they are saying that given a normal baseline examination, the diabetic patient has less than a five percent chance of developing retinopathy until 5.4 years. They then discuss the problem of ‘losing patients to followup’ and decide to err on the side of more frequent examinations. Thus, they conclude

Interpretation A 3-year screening interval could be safely adopted for patients with no retinopathy, but yearly or more frequent screening is needed for patients with higher grades of retinopathy.

An accompanying editorial in the same issue – Screening interval for retinopathy in type 2 diabetes interprets the data.

Should the 3-year interval for dilated eye examinations in individuals without diabetic retinopathy be adopted as a new guideline for care? Some have argued that long intervals between follow-up visits may lead to difficulties in maintaining contact with patients and may give patients the impression that visual loss is unlikely and therefore not a concern. Further, it has been suggested that it is better to have a conservative guideline of yearly examinations with deviations based on evaluation of risk (eg, glycaemic and blood-pressure control) for each individual patient rather than having a uniformly longer interval. In addition, the ability to generalise the observations from the Liverpool study to other screening situations will depend on the comparability of the diabetic population being screened to those in Younis’ study, and the sensitivity of the approaches used to detect sight-threatening retinopathy and other ocular conditions.

Before adopting new guidelines for intervals for retinal examination in individuals with type 2 diabetes, effectiveness in achieving a significant reduction in vision loss from diabetes at least similar to that achieved by routine yearly dilated-eye examinations should be demonstrated.

I support this conservative approach in 2003. The Lancet data are intriguing and may well lead to an important study of examination interval. I hope investigators act on this important hypothesis generating article. If we could just extend the interval to every other year, we would save significant health care costs. Since patients go through stages with diabetic retinopathy, I believe that extending the interval in patients with normal examinations would not jeopardize vision.

Not every important study should change medical care immediately. We must remain skeptical and test this new hypothesis. That is how we make important advances in health care, methodically and one small step at a time. This article should start us on the road to more cost effective screening.