Diabetic macular oedema
is the most common cause of visual impairment in diabetic patients, particularly type 2. Diffuse retinal oedema is caused by extensive capillary leakage, and localized oedema by focal leakage from microaneurysms and dilated capillary segments.With further accumulation of fluid the fovea assumes a cystoid appearance (cystoid macular oedema – CMO).
Signs. Retinal thickening is best detected by slit-lamp biomicroscopy with a contact lens, though high-resolution non-contact lenses are also effective.
FA shows diffuse late hyperfluorescence due to retinal capillary leakage, and may have a flower-petal pattern if CMO is present
OCT shows retinal thickening and, if present, cystoid spaces . OCT is also useful in assessing response to treatment.