Signs and symptoms: Patients with cystoid macular edema (CME) frequently have a history of cataract surgery or some other invasive ocular surgery. About 3% of patients undergoing cataract extraction will have visual reduction due to CME within the first postoperative year.1 While complicated surgery accounts for most cases of CME, this condition also occasionally occurs after straightforward surgery. If ocular surgery is not the cause, a long list of events may be to blame: retinal vein occlusion, diabetic macular leakage, idiopathic central serous chorioretinopathy, anterior or posterior uveitis, pars planitis, retinitis pigmentosa, radiation retinopathy, posterior vitreous detachment, epiretinal membrane formation, idiopathic juxtafoveal retinal telangiectasia, Nd:YAG capsulotomy or iridotomy. Some patients may have a history of use of topical epinephrine or prostaglandin analogs for glaucoma.

Visual acuity may or may not be reduced. If reduced, vision ranges from 20/25 to 20/400 depending on the severity of the edema. Patients may also experience metamorphopsia.

Ophthalmoscopically, the condition appears as macular thickening and swelling. Many cases exhibit a cystic appearance. Radiating cystic spaces may emanate from the macula. There is loss of the foveal light reflex. With red-free light, you may see a honeycombed appearance corresponding to the fluid-filled cysts. These cysts may coalesce into a macular cyst then form a hole.

Fluorescein angiography most effectively displays true appearance of CME, demonstrating leaky perifoveal capillaries in the early stage with a petalloid flower appearance in late phases.

Pathophysiology: CME is not a specific disease, but rather a clinical feature occurring in a number of conditions. Leaking perifoveal capillaries lead to the formation of CME. Fluid collects in the loosely arranged outer plexiform layer of Henle, the fibers of which are arranged horizontally. This produces a pettaloid pattern on fluorescein angiography.

Breakdown of the inner blood retinal barrier leading CME likely has many possible etiologies. Vasogenic as well as cytotoxic factors combine to cause this breakdown.

In Irvine-Gass syndrome, the cause may be light toxicity from the operating microscope contributing to free radical release with subsequent prostaglandin synthesis. Prostaglandins will increase vasodilation and vasopermeability.

Inflammation from surgical prostaglandin induction will also contribute to CME. In cases of CME occurring from anterior or posterior uveitis or pars planitis, the inflammatory process contributes to perifoveal capillary dilation and permeability with fluid exudation. The same goes for CME secondary to prostaglandin analog therapy for glaucoma.

Vitreoretinal traction to the macula contributes to CME. Cystoid macular edema may develop secondary to posterior vitreous detachment. Vitreoretinal traction that occurs during ocular surgery may contribute to the development of Irvine-Gass syndrome.

Management: Most cases of Irvine-Gass syndrome resolve spontaneously without intervention within 6­12 months. However, 20% of cases are evident angiographically for more than five years after development.2

When other conditions cause CME, treatment often entails managing the underlying problem. In cases of leakage due to diabetes or branch retinal vein occlusion, laser photocoagulation of the perifoveal capillaries is beneficial. Systemic corticosteroids and immunosuppressants can be useful in inflammatory diseases such as pars planitis and posterior and |intermediate uveitis.

Medications for CME include the oral nonsteroidal Indocin (indomethacin, Merck), and possibly the corticosteroid prednisone. Topical nonsteroidal medications such as Acular (ketorolac, Allergan) and Voltaren (diclofenac, Novartis Ophthalmics) can be quite successful in many cases, as can topical corticosteroid drops such as Pred Forte (prednisolone acetate, Allergan) and Lotemax (loteprednol, Bausch & Lomb). Common dosing ranges from qid to q2h. Often a loading dose of q2h is indicated, and then rapidly dropped to qid after several days. Therapy may last several days to weeks. Standard therapy calls for both Voltaren and Pred Forte (both qid).

The effort to move fluid from the retina through the choroid requires transport of fluid ions by the retinal pigment epithelium. Studies have shown that Diamox (acetazolamide, Lederle) use results in small but statistically significant decreases in CME, but does not improve vision.3

When vitreous traction contributes to CME, surgical vitrectomy can lessen the CME and improve vision. In select cases, YAG laser may be a preferable option to cut adherent strands of vitreous and relieve traction.

Clinical Pearls:

• CME is a well-known complication of cataract extraction even in uncomplicated cases. The more complicated the surgery, the greater the degree of CME and vision reduction.
• CME is more severe in cases where there is capsular rupture or vitreous incarceration.
• The angiographic incidence of CME after routine phacoemulsification is about one in five cases.
• A patient with CME in one eye has a 50% chance of it developing in the other eye.
• Use prostaglandin analogs with caution in patients with a history of incisional ocular surgery, especially if there is also a broken posterior capsule. Avoid using prostaglandin analogs in patients with a history of CME.
• New advances in diagnostic technology make it easier to identify CME. The Heidelberg Retinal Tomograph II and the Optical Coherence Tomographer are effective and noninvasive devices that can identify CME. 

1. Coscas G, Gaudric A. Natural course of nonaphakic cystoid macular edema. Surv Ophthalmol 1984 May;28 Suppl:471-84.
2. Gass JDM, Norton, EWD. Follow-up study of cystoid macular edema following cataract extraction. Trans Am Acad Ophtalmol Otolaryngol 1969;73:665.
3. Whitcup SM, Csaky KG, Podgor MJ, Chew EY, Perry CH, Nussenblatt RB. A randomized, masked, cross-over trial of acetazolamide for cystoid macular edema in patients with uveitis. Ophthalmology 1996.