Cystoid macular edema (CME) is characterized by intraretinal edema contained in honeycomb-like cystoid spaces. The source of the edema is abnormal perifoveal retinal capillary permeability, which is visible on fluorescein angiography as multiple small focal leaks and late pooling of the dye in extracellular cystoid spaces. Optical coherence tomography (OCT) findings in CME include diffuse retinal thickening with cystic areas of low reflectivity (reduced reflectivity), more prominently in the inner nuclear and outer plexiform layers. The OCT findings correlate with histologic studies that indicate swelling in and between müllerian glia. On occasion, a nonreflective cavity that is consistent with subretinal fluid accumulation is present beneath the neurosensory retina (see Chapter 5, Fig 5-11B, and Chapter 6, Fig 6-13A). Because of the radial foveal arrangement of both the glia and Henle inner fibers, this pooling classically forms a “flower-petal” (petaloid) pattern (Fig 7-7). Severe cases may be associated with vitritis (vitreous cells) and optic nerve head swelling.
Etiologies of CME
Abnormal permeability of the perifoveal retinal capillaries may occur in a wide variety of conditions, including diabetic retinopathy, central retinal vein occlusion (CRVO), branch retinal vein occlusion (BRVO), any type of uveitis (particularly pars planitis), and retinitis pigmentosa. In addition, CME may occur after any ocular surgery, such as cataract extraction (in which case the CME is termed Irvine-Gass Syndrome), retinal detachment surgery, vitrectomy, glaucoma procedures, photocoagulation, and cryopexy. It can also be triggered or worsened by drugs, for example the prostaglandin analogues used to treat glaucoma or anticancer drugs such as interferon.
Subretinal disease processes (eg, choroidal neovascularization, choroidal hemangioma, or subclinical retinal detachment) must also be considered when CME is detected; see Chapter 4 of this volume.
The differential diagnosis of CME in which fluorescein angiography fails to show leakage includes conditions such as X-linked hereditary retinoschisis, Goldmann-Favre disease, and retinitis pigmentosa, in addition to the effects of treatment by nicotinic acid, MEK inhibitors, and taxanes (see also Chapter 15 in this volume).
Excerpted from BCSC 2020-2021 series: Section 10 - Glaucoma. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.