What is an epiretinal membrane?
An epiretinal membrane is similar to a piece of cellophane sitting on the surface of the retina. Sometimes, epiretinal membranes do not cause any symptoms at all. In some cases, however, they contract and pull on the retina, distorting the it. This contraction results in gradually worsening distortion and blurring of the vision. Epiretinal membranes affect only the central vision; the peripheral vision remains intact. The photograph to the right shows an epiretinal membrane. Notice the whitish area just to the left of center; this is the thickest portion of the membrane, and it is distorting the surrounding retina. You can see that the retinal blood vessels are being drawn toward the membrane:
The image to the left shows a black-and-white photograph (left) and optical coherence tomography (right) of an epiretinal membrane. Notice, on the left, how the blood vessels are distorted due to the epiretinal membrane. The image on the right shows the central macula in cross-section. The epiretinal membrane is the white line at the top of the image. The macual is thicker than normal, due to the effects of the epiretinal membrane; we call this macular edema.
What causes an epiretinal membrane?
Usually, epiretinal membranes develop after the vitreous separates from the retina. The vitreous is a clear gel that fills the back part of the eye. At birth, the vitreous is quite solid, like firm gelatin, and is in contact with the retina. You can think of the eye at birth like a hard-boiled egg; the vitreous is like the egg white and the retina is like the shell. As years pass, the vitreous becomes more liquid and begins to separate from the retina. Eventually, in most eyes, the vitreous separates completely from the retina and “floats” in front of the retina (this is a common cause of “floaters”). The separation of the vitreous creates a space between the vitreous and the retina, allowing various cells to settle on the retinal surface and form a cellophane-like sheet.
Sometimes, the separation of the vitreous from the retina causes a retinal tear. As a result, cells from beneath the retina can now enter the vitreous, settle onto the retinal surface and form an epiretinal membrane. Since retinal tears are a possible cause of an epiretinal membrane, your retina specialist will often examine the peripheral retina for tears when he/she detects an epiretinal membrane. Sometimes, a retinal tear leads to a retinal detachment. Epiretinal membranes sometimes develop after surgical repair of a retinal detachment.
The vitreous does not have to separate from the retina for an epiretinal membrane to develop. Sometimes the vitreous, itself, contracts along the surface of the retina, much as an epiretinal membrane does. In fact, it looks just like a typical epiretinal membrane on examination. This contraction of the vitreous can distort the retina and cause visual loss.
An epiretinal membrane can be caused by a variety of other retinal disorders. For example, a blockage in a retinal vein or inflammation in the eye can lead to an epiretinal membrane.
How is an epiretinal membrane treated?
Epiretinal membranes are removed with vitrectomy surgery. Literally, “vitrectomy” means “removal of the vitreous.” This is the initial step in the procedure. Next, specialized instruments are used to gently peel the membrane from the retinal surface. Logically, this step of the procedure is known as membrane peeling. As you recall from above, the vitreous sometimes remains attached to the retina but gives the appearance of an epiretinal membrane. In these cases, the vitreous, itself, is peeled from the retinal surface, in addition to any epiretinal membrane.