Cystoid Macular Edema (CME) usually occurs due to ocular inflammation within the eye which produces chemicals that cause the retinal vessels to leak. This results in fluid accumulation in the central retina and the formation of retinal cysts. CME due to inflammation can occur in uveitis or following eye surgery. It may 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. The condition following cataract surgery is usually not severe, with the majority of cases responding to treatment and resolution within six months.
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.
In addition to a dilated eye exam, a test called Fluorescein Angiography may be required during which dye is injected into a vein in the arm. Digital images of the retina are obtained as the dye passes through the eye. Leakage and accumulation of dye into cystic spaces then become apparent to the physician. Optical Coherence Tomography (OCT) provides a scan or slice of the retina is very useful in highlighting cysts within the retina and the increase in retinal thickness.
Most cases of CME involve treating the underlying inflammation. The first line of defense is usually non-steroidal and steroid eye drops, sometimes followed by injecting steroid medication next to the eye. If these treatments are ineffective, a steroid or other medication may be injected directly into the eye. Finally, if the vitreous gel is determined to be contributing to edema, the gel can be removed by performing vitrectomy surgery. If CME is caused by an epiretinal membrane, surgical removal of the membrane is necessary to lessen swelling and to improve vision.