Diabetic Macular Edema

Published on 10/05/2015 by admin

Filed under Opthalmology

Last modified 22/04/2025

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13.2

Diabetic Macular Edema

Introduction:

Diabetic retinopathy is estimated to affect one-third of people with diabetes. The prevalence and severity are affected by the duration of diabetes, glycemic control, and the presence of concurrent hypertension. DME can affect up to 7% of patients with diabetes and is the most common cause of moderate visual loss in diabetic patients.

The classic clinical descriptions of DME includes focal, diffuse and cystoid (CME), based on the clinical and angiographic appearance (Fig. 13.2.1). Focal macular edema is characterized by focal leaking microaneurysms giving a well-circumscribed area of thickening often associated with hard exudates. Diffuse macular edema is characterized by more widespread vascular abnormalities giving larger areas of thickening, a paucity of hard exudates and cystic changes in the retina. CME associated with DME appears similar to CME from other causes. It is not unusual for affected eyes to manifest two or all three of these sub-types.

Figure 13.2.1 Fundus photograph of a diabetic patient shows numerous microaneurysms, hard exudates and scattered cotton wool spots. Early frame fluorescein highlights the microaneurysms and late phase shows diffuse leakage at the macula

OCT Features (Figs 13.2.2 and 13.2.3):

In clinical practice as well as in studies, OCT is being used on a routine basis in the diagnosis of DME. Moreover, it is the single most important ancillary test in the management of DME. It is helpful for confirming the clinical diagnosis, choosing the initial therapy and monitoring the edema on follow up or after treatment. Quantitative changes in the OCT in DME are important in following the progression as well as the response to therapy. The mean central subfield thickness in the macular map is most often used. More than the absolute number, however, following the evolution of the thickness as well as the ‘spread’ of the area of thickness is important in the evaluation and follow-up of DME.

Figure 13.2.2 OCT scanning through the retina shows thickening with outer retinal cystic changes (arrows). The area and extent of thickening can be followed by the false color rendering of the thickness map over the C-scan (inset). The retinal thickness map also provides quantitative information about thickening and is useful in gauging effect of treatment. Also note the hyper-reflective clusters in the outer retina, the trace subretinal fluid or SRF (arrow) and that the external limiting membrane is relatively well-preserved in this patient (arrow) while the IS–OS/ellipsoid layer shows some disruption centrally (arrow).

Figure 13.2.3 OCT scan of the same patient after focal laser therapy. The edema and cysts are reduced, as is the retinal thickness on the thickness map. Also, the normal architecture of the IS–OS ellipsoid layer seems relatively well restored.

The OCT appearance of DME can be categorized into four major types:

▶ Thickening of the fovea with homogenous optical reflectivity throughout the whole layer of the retina.

▶ Thickening of the fovea with markedly decreased optical reflectivity in mostly the outer retinal layers (cystoid changes).

▶ Thickening of the fovea with subfoveal fluid accumulation and distinct outer border of detached retina.

▶ Thickening of the fovea with epiretinal membrane formation with or without apparent vitreofoveal traction.

The qualitative assessment of OCT scans in DME are proving increasingly important in predicting outcome as well as determining which patients will respond best to individualized treatment. Moreover, OCT may also show foveal microstructural changes such as disruption of the IS–OS/ellipsoid layer and of the external limiting membrane, which may be correlated to visual acuity in DME. Presence of hyper-reflective foci may also be associated with severity of the edema in DME and may reduce significantly with successful treatment of edema.