CLASSSIFICATION FOR STAGING OF MACULAR OEDEMA

The current classification system for the staging of macular oedema is vague and is also inconsistent among researchers. An update based on clinically relevant features of the disease determined with modern diagnostic technology is therefore overdue, said Neil M Bressler MD, Wilmer Eye Institute Johns Hopkins Hospital, Baltimore, Maryland, at the 11th EURETINA Congress.

“We want to make sure we are all speaking the same language when we are talking about scientific treatments for our patients with diabetic macular oedema,†he said.

In current practice many retinal specialists classify diabetic macular oedema as being either focal or diffuse, he said. They do so on the unsubstantiated belief that focal oedema responds best to laser, that the natural course diffuse oedema is worse and that diffuse oedema responds best to steroids. However, those theories tend to fall on the first hurdle, because there is actually no consensus as to what is meant by focal or diffuse, he pointed out.

A recent review by the Diabetic Retinopathy Clinical Research Network (DRCR.NET) of 30 studies in peer-reviewed journals gave 30 very different definitions for the terms focal and diffuse macular oedema.

The examinations used in published definitions of focal and diffuse DME have been based on four methods, namely fundus biomicroscopy, colour fundus photography, fluorescein angiography, and OCT, which have findings that are not completely interchangeable and are often not completely objective, he noted.

For example, among authors using photography-based definitions the criteria might be the area of retinal thickening, but with no definite cut-off point between focal and diffuse. Others say it is the location that is most important and that when fovea is involved it is diffuse and otherwise it is focal. Still others say it is the presence of lipid that will define the oedema as local, but even among these authors there is substantial difference about whether it is quantity, configuration, or both that is most important.

Investigators using angiography to distinguish between diabetic macular oedema subtypes base their definitions on the proportion of leakage originating from microaneurysms. That is, they describe eyes with at least 2/3 of the leakage associated with microaneurysms as focal leakage, those with 1/3 to 2/3 of the leakage associated with microaneurysms as intermediate, and those with 1/3 as diffuse. However, variable leakage patterns can occur within the same eye and the assessment is very subjective

As regards OCT, not only do investigators differ regarding how to interpret the scans and their relationship to the focal or diffuse nature of macular oedema, but also newer technology is likely to render any standardised interpretations obsolete, Dr Bressler said.

“Focal and diffuse DME are not very relevant because they have no uniform definition. There is no strong evidence to suggest that such classification has any impact on treatment responses with laser or anti-VEGF therapy. The DRCR.net’s proposed new classification of diabetic macular oedema would be based on OCT determinations of location and extent of oedema, vitreomacular interface abnormalities, and the presence of lipid. This is still a work in progress and awaits tests in clinical trials and practice,†he added.