by Wendy Strouse Watt, O.D.
The vitreous is the fluid in front of the retina. It keeps the eye round. When we are children, it has the consistency of egg white. As we get older, it gets thicker, like clear gelatin. As it gets thicker, it degenerates and pulls off in strings, creating one type of floater. These vitreous floaters are normal, and they float in the remaining vitreous, moving with gravity. When they cast a shadow on the retina, we see them. As we get used to them, howver, we don’t notice them as much. The vitreous is attached to the retina in several places. As it changes in consistency, it can tug on the retina, causing traction. This traction can tug on the retina. The retina thinks it sees something and we see a flash of light. The traction can also pull on a piece of retina and cause a hole or tear anywhere in the retina, or it can cause a cyst to form in the center of the macula. It can also pull the entire vitreous away from the retina, causing a total vitreous detachment.
The center of the macula is the fovea. Foveal cysts are caused by vitreous traction. Eyes that develop foveal cysts may remain stable, develop full-thickness macular holes, or develop a posterior vitreous detachment (PVD). A foveal cyst seems to be a common finding in patients with foveal traction from a variety of mechanisms. The vitreous gel above the macula contains collagen fibers that attach posteriorly to the macula and anteriorly to the main part of the vitreous. Macular holes, epiretinal membranes, and macular pucker have similar origins.
Currently, the most widely accepted theory is that vitreal shrinkage over the fovea creates traction on the fovea, eventually causing hole formation. As traction continues, the tugging at the fovea causes a separation of the sensory retina from the underlying retinal pigment epithelial (RPE) cells. The foveal retina, without a firm attachment to the RPE, suffers a compromised nutrient supply and loses its ability to eliminate waste. Ultimately, the sensory retina atrophies, forming a break, and progresses to a full-thickness hole. Macular holes may also result from chronic macular edema (swelling), solar retinopathy (excessive exposure to UV light, like looking at an eclipse) and blunt ocular trauma (injury due to a blow).
In macular degeneration, the RPE cells also suffer compromised nutrient supply from the blood vessels, so a macular hole can be present without, before, or after diagnosis with the disease. The way macular holes form is a little different, but the outcome is the same as macular degeneration. Both conditions affect the RPE, and the result is decreased vision.
Epiretinal membrane is known by many names, including preretinal membrane, idiopathic preretinal macular gliosis, cellophane maculopathy, macular pucker, wrinkled retina, and surface wrinkling retinopathy. In the early stages, epiretinal membrane may be asymptomatic or it may cause only a mild reduction in acuity. As it progresses, it may cause metamorphopsia, lines appearing wavy or crooked, and can lead to severe visual impairment. The appearance of this disorder ranges from a fine, glistening membrane overlying the macula (cellophane maculopathy) to a thickened, whitish tissue that obscures the underlying blood vessels. As the epiretinal membrane progresses, traction creates a puckering effect and the doctor may see retinal folds radiating outward from the macula.
There are many causes of this condition. It can develop from inflammation within the eye, from circulation problems, or from injuries. After a posterior vitreous separation, where the gel filling the center of the eye shrinks, liquefies and separates from the retinal surface, wrinkled retina can often develop. It only develops in the macula, the central part of the retina.
In the majority of cases, the visual impact of these membranes is minor. It has been reported that 75% of people with this condition will maintain vision of better than 20/50. Often, the vision remains surprisingly stable. There is, however, a small percentage of individuals in whom the vision deteriorates significantly. This is either due to marked distortion of the retinal surface or because of swelling in the retina.
Vitrectomy surgery is performed to remove these severe membranes when vision is significantly impaired. The surgery for wrinkled retina is successful in the vast majority of patients, although it can take from 6 to 12 months for the vision to improve. The vision and symptoms in eyes with wrinkled retina can be improved in 80 to 90% of cases. The rod and cone layer is deeper in the retina and the wrinkling of the top surface of the retina will not effect it. The light enters on the top surface and the rod and cone layer is significantly deeper than the top surface where wrinkling occurs.
by Wendy Strouse Watt, O.D.