The space in the back part of the eye, behind the inner crystalline lens, is filled with a gelatin-like substance known as the vitreous, also called the vitreous humour. The vitreous makes up about 80% of the volume of the eye and helps it keep its normal, round shape. Part of the function of the vitreous is to hold the retina in place against the back of the eye which helps to provide clear, undistorted vision.
The vitreous contains numerous fine strands of connective tissue that hold it in position and attach it to the inside of the eye. As we age, this gelatin gradually shrinks and will usually pull away slightly from the retinal surface in a common condition called a posterior vitreous detachment (PVD). Most of the time, there are no adverse effects on vision except for an increase in vitreous floaters. Floaters get their name from their appearance in the field of view, like small particles or cobweb-like strands; floaters are not serious and rarely causes any effect on vision at all, although they may be somewhat annoying.
Sometimes, however, vitreous shrinkage can cause microscopic damage to the surface of the retina, and cause the formation of scar tissue that is attached to the retina and can pull on the retina and cause puckering or distortion. It is this sheet of scar tissue that forms the epiretinal membrane (ERM) is located just above the retina and usually doesn’t effect vision unless it forms in front of the macula, where the retinal nerve fibers are the most sensitive and provide our clear central vision. When this happens, the scar tissue may cause vision to blur or become hazy and distorted. The changes to vision shown in the illustration are usually more severe than that experienced by most people with ERM, but it does show how a pattern of lines called an Amsler Grid might appear: the lines could be wavy, slanted or even have areas that are missing.
Other names for epiretinal membrane include macular pucker, premacular fibrosis and cellophane retinopathy. Epiretinal membrane is a separate and distinct condition from age-related macular degeneration (AMD) or a macular hole, although these can have similar symptoms.
Frequently Asked Questions
What causes an epiretinal membrane? Usually ERM is related to a posterior vitreous detachment (PVD), which commonly occurs in people over the age of 50. Other disorders such as detached retina and inflammation of the eye, called uveitis, can trigger the formation of ERM, as well as diabetes. ERM can also be caused by trauma to the eye, either by surgery or accidental eye injury. The incidence of ERM in the fellow eye is increased after it develops in the first eye.
What are the symptoms of ERM? Although ERM can cause severe vision loss if the scar tissue is thick and occurs in front of the macula, most vision loss is minor and is sometimes not noticed at all. Mild difficulty with seeing detail and fine print, a gray area in the vision or mild disturbances such as straight lines that appear wavy. Occasionally there may be a blind spot.
Most people with ERMs have no symptoms, although metamorphopsia (a difference in the perceived size of an image). Some people notice double vision in the effected eye.
Can ERM be prevented? There is no evidence of any effective treatment for ERM that isn’t caused by trauma or surgery; there are no eyedrops or nutritional supplements that have been shown to be effective in preventing the development of an ERM.
How is ERM treated? An ERM usually needs to treatment, because in many cases the symptoms of distortion and blurriness are mild and not noticeable. Most people with an EM become accustomed to any mild distortion and don’t notice the vision changes.
Sometimes the scar tissue that forms the ERM separates from the retina and clears upon its own. Rarely, vision deteriorates until it affects daily routines and activities, and in these cases, surgery may be recommended. The procedure consists of removing the vitreous humour and replacing it with a saline solution. Because the vitreous is formed mostly of water, people don’t notice any vision changes between that and the saline. Removing the vitreous removes the scar tissue that has formed, so the cause of the wrinkling of the retina is gone. Called a vitrectomy, this procedure is usually performed under local anesthesia.
After the vitrectomy, the eye will be patched for a day or two to protect the eye, and antibiotic eye drops will be needed to prevent infection.
How successful is surgery for ERM? A vitrectomy is a very delicate surgical procedure; most of the time vision improves, but usually not to the same level as before the ERM developed. On average, vision is restored to about half that lost to the membrane. While some people have better results, others may experience significant vison loss. Recovery of vision may take up to two or three months.
What are the complications of vitrectomy surgery? Complications of vitrectomy are the same as for any other ocular surgery, with infection being the biggest risk, followed by retinal detachment either during or after the surgery. The incidence of cataract formation was thought to be increased after surgery, but it is unclear whether the cataracts may have occurred anyway, or were caused by the surgery after several years had passed in some cases.
There is a small risk of recurrence (about 1%) of ERM.
How can I find out if my symptoms are caused by an epiretinal membrane? See your eyecare practitioner for a vision and eye examination. Because ERM has similar symptoms with other conditions, the only way to be sure is to consult an expert.