Cystoid Macular Edema (CME) usually occurs due to ocular inflammation. The inflammation within the eye produces chemicals which cause the retinal vessels to leak. This results in fluid accumulation in the central retina, and the formation of small retinal cysts. CME due to inflammation can occur in uveitis (see section on Ocular Inflammation) or following eye surgery. CME can also be caused by mechanical irritation of the retina as occurs in an epiretinal membrane.

Importantly, CME occurs in some people following cataract surgery, even if the surgery itself is perfect. CME following cataract surgery is usually not severe, and the majority of cases respond to treatment and resolve within 6 months.

Symptoms
CME usually causes a decline in central vision. Visual acuity may range from 20/20 to 20/400. Distortion of images and decreased color vision may also be present. Peripheral vision is unaffected.

Diagnosis
In addition to a dilated eye exam, a test called Fluorescein Angiography may be required. During this test a dye is injected into a vein in the arm. Special photographs are taken of the retina as the dye passes through the eye. Leakage and accumulation of dye into cystic spaces becomes apparent to the physician. Optical Coherence Tomography (OCT) which provides a scan, or slice of the retina is very useful in illustrating the cysts within the retina, and the increase in retinal thickness.