Once an easily-overlooked cause of visual loss, cystoid macular edema is now better understood. Its causes are legion, and its effects can be ephemeral...at first.
Cystoid macular edema (CME) is a term used to describe the formation of fluid-filled spaces within the layers of the macular retina. The macula is a high-density area of cells that is responsible for fine central visual acuity, such as that needed for reading.
Normally, macular neurons are closely aligned, with minimal intervening space. When the macula is distorted by swelling, visual changes occur; these can vary from metamorphopsia (warping and distortion of lines and shapes) to blurring or patchy loss of central visual detail and unusual perceptions of light.
Isolated occurrences of CME do not necessarily lead to permanent visual loss. However, frequent or prolonged episodes of CME can irreversibly damage retinal cells.
Causes of CME
Cataract Extraction: Most cases of cystoid macular edema follow cataract extraction or other intraocular surgery (about 1% of cataract patients will develop CME, and up to 45% of successful retinal reattachment procedures lead to CME). Presumably, the trauma of surgery leads to the production of inflammatory chemicals. These chemicals (prostaglandins and cytokines) then cause the breakdown of capillaries and the subsequent leakage of fluid. 90% of such cases eventually return to a visual acuity of 20/40 or better.
Diabetes: This disease affects the eye in several ways, including the proliferation of abnormal blood vessels—which often break and bleed—and the development of CME.
Age-related Macular Degeneration (ARMD): ARMD occurs in two forms: exudative (wet) or atrophic (dry). The exudative form, if untreated, can cause detachment of the retina overlying the macula and resultant CME.
Uveitis: The uvea is a tunic of vessels that envelops the eye. It includes the iris, which is the colored ring that surrounds the pupil. Various conditions can cause inflammation of this tunic, including autoimmune illnesses (lupus, rheumatoid arthritis, Reiter’s syndrome, etc.), infection, or surgery.
Retinal Vein Occlusion: The veins that drain blood from the retina can become blocked, causing increased “back pressure.” This pressure causes leakage of fluid into the intercellular spaces of the macula.
Traction: Occasionally, membranes attached to the retina (or the vitreous gel within the eyeball) shrink away from the retina. The resultant traction is believed to cause inflammation in the macula, leading to CME.
Medications: High-dose niacin therapy for hypercholesterolemia has been implicated in the development of a CME-like condition in middle-aged men. Topical treatment with certain iodides has led to visual loss from CME. Latanoprost (Xalatan), an eye drop used for glaucoma treatment, has been linked to CME.
Tumors: Certain tumors of the eye, like malignant melanoma or capillary hemangioma, have been associated with CME.
Radiation: Prior irradiation to the eye or surrounding orbit can evoke a condition very similar to the maculopathy and CME found in diabetics.
Others: Cytomegalovirus (frequently seen in AIDS patients or others who are immuno-compromised); orbital pseudotumor; retinitis pigmentosa; Coat’s disease; certain genetic disorders, including a dominantly-inherited “macular dystrophy.”
While a change in visual acuity may not necessarily herald the onset of cystoid macular edema, the symptoms associated with CME can be quite subtle, at first. Since CME is treatable in many instances—and since management of underlying conditions like diabetes is sometimes key to managing CME—any abrupt alteration in vision should prompt a visit to one’s ophthalmologist.
The copyright of the article What is Cystoid Macular Edema? in Patient Health Education is owned by Stephen Allen Christensen. Permission to republish What is Cystoid Macular Edema? in print or online must be granted by the author in writing.
