See Diabetes – Macular Edema Assessment
Diabetes – Introduction to Retinopathy, Diabetes – Introduction to Retinopathy Management, Diabetes – Nonproliferative Retinopathy, Diabetes – Proliferative Retinopathy, Macular Edema.
Intravenous fluorescein angiography demonstrates microaneurysms and other areas of leakage. If sufficient loss of macular capillaries is present, the damage is likely to be irreversible and laser treatment may not be beneficial.
Other imaging investigations include ocular coherence tomography (OCT) and scanning laser ophthalmoscopy (SLO). OCT helps to determine whether reduced central visual acuity is due to retinal thickening or vitreous traction. The SLO allows quantification of macular edema.
A multi-centre, prospective clinical study (the Early Treatment Diabetic Retinopathy Study, ETDRS) has shown that laser treatment reduces the risk of visual loss from cystoid macular edema (CME) by approximately 50 percent. This was true even when visual acuity is normal prior to treatment. CME was defined as when one or more of the following signs were present (clinically significant macular edema, CSME).
- Retinal thickening within 500µm (1/3 of a disc diameter) of the centre of the fovea.
- Hard exudates within 500µm of the centre of the fovea, if associated with adjacent retinal thickening.
- Retinal thickening of 1 disc area or larger, part of which is within 1 disc diameter of the centre of the fovea.
Focal or direct treatment involves laser treatment to leaking microaneurysms and microvascular lesions, while grid treatment is applied to areas of diffuse retinal thickening (the burns are 100 to 200µm wide, and 1 burn width apart). In order to spare macular vision, laser is applied at least 500µm from the centre of the fovea.
CME usually resolves over the following few months, although there is usually a transient increase in edema for 1 to 2 weeks postoperatively. While the aim of laser treatment is to minimise future visual loss, in the EDTRS approximately 15 percent of patients experienced visual improvement. If CSME persists, and if visual acuity is less than 6/12 (20/40), treatment of lesions closer to the centre of the fovea may be considered.
Surgery and medications
Alternative treatments include pars plana vitrectomy (in the setting of posterior hyaloid traction) and intravitreal corticosteroid injections (e.g., triamcinolone; possible complications include glaucoma and cataract). These treatments are subjects of active research.
Advice & Review
Patients with CME should be reviewed at 3 to 6 month intervals. The patient is advised to report new visual symptoms immediately, and may be provided with an Amsler grid for home monitoring. Low vision aids are helpful to many patients.
Moderate non-proliferative diabetic retinopathy with exudates, dot and blot hemorrhages and moderate macula edema.
Grid pattern of focal macular photocoagulation.