Nonpseudophakic Cystoid Macular Edema

Updated: Sep 28, 2016
  • Author: Hamoon Eshraghi; Chief Editor: Hampton Roy, Sr, MD  more...
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Overview

Background

Although the most common cause of cystoid macular edema (CME) is due to Irvine-Gass syndrome of CME after cataract extraction or other intraocular surgery, numerous other conditions are associated with the clinical appearance of fluid-filled, cystoid spaces in the macular region. CME is a final common pathway of many intraocular diseases, usually involving the retinal vasculature. The appearance can differ somewhat, depending on the etiology; however, CME can appear as a nonspecific clinical finding. If the cause of CME is not obvious, detailed ophthalmoscopy and, occasionally, ancillary testing may be necessary to identify the cause.

Cystoid macular edema due to nonproliferative diabetic retinopathy is shown in the image below.

Fundus photograph of nonproliferative diabetic ret Fundus photograph of nonproliferative diabetic retinopathy with clinically significant macular edema and cystoid macular edema.
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Pathophysiology

Macular edema is excessive fluid within the layers of the retina, distinct from the accumulation of fluid under or between the retinal layers (eg, subsensory fluid, serous retinal detachment). The amount of fluid normally present in the retina is maintained according to osmotic and hydrostatic pressures between the retina and the surrounding vasculature, which are compartmentalized by the blood-retinal barrier. A breakdown in the blood-retinal barrier allows for fluid to accumulate in cystoid spaces within the retina. Pathologic evidence of cell loss and Müller cell abnormalities may contribute to the resulting CME.

Several mechanisms have been proposed to explain how CME develops. The characteristic distribution of vascular leakage and retinal edema may be explained best by the diffusion of mediators (eg, prostaglandins) released in the eye. These mediators of inflammation cause increased permeability of retinal blood vessels, resulting in extravasion. This theory is supported by evidence that cyclooxygenase inhibitors (eg, indomethacin, other nonsteroidal anti-inflammatory drugs) reduce the incidence of angiographic CME. However, this finding has only been shown conclusively in pseudophakic CME associated with surgical trauma to the anterior segment.

The major determinant of fluid movement in the retina is the Müller cell. Müller cells have bicarbonate-related transport mechanisms that control movement of potassium and sodium ions (and thus fluid), partly explaining the role for carbonic anhydrase inhibitors such as acetazolamide in the treatment of cystoid macular edema. Additional routes of ion control are achieved through the Kir2.1 and Kir4.1 channels that buffer changes in intracellular potassium.

In addition, evidence shows that the reduced outflow of fluid from the retina is responsible for the buildup of edema. In particular, reduced or absent flow to the deep vascular plexus of the retina has been described. This decreased flow can result from ischemia or inflammation and is mediated by integrins, selectins, and other adhesion molecules. Extravasated leukocytes have the ability to plug capillaries, thus blocking blood flow. [1]

Another mechanism emphasizes the role of mechanical factors, such as tractional forces on the macula from disruption of the normal vitreoretinal interface. Even according to this theory, it is believed that local forces induce a release of mediators that lead to a breakdown of the blood-retinal barrier, resulting in the clinical appearance of CME.

Photic injury has been implicated in the development of pseudophakic CME; however, there is no scientific evidence that light damage to the retina causes CME. 

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Epidemiology

Frequency

United States

Frequency of CME that is unassociated with cataract surgery varies widely, both in the United States and internationally, depending on the etiology or underlying condition leading to CME. Incidence figures vary because of difficulty in observing subtle CME clinically, surgeon bias in reporting CME, and a lack in performing fluorescein angiography (FA) or optical coherence tomography (OCT) tests that would detect CME.

Mortality/Morbidity

CME from any etiology often leads to significant central visual loss, typically in the 20/40 to 20/200 range.

Race

No racial predilection has been associated with CME.

Sex

CME is distributed equally among males and females.

Age

Age of incidence of nonpseudophakic CME varies according to etiology. Since diabetic CME is secondary to diabetic retinopathy, it occurs in persons aged 40 years and older.

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