Distortion, also known as metamorphopsia, is a symptom of many macular diseases. Anything that affects the macula can cause distortion; epiretinal membranes, macular holes, macular edema, diabetic retinopathy and macular degeneration. The macula is a place in the retina, the functional center. Thus, the term “macular” becomes an adjective when describing retinal disease located in the center of the retina.
The macula is a small area of the retina measuring about 1.5 x 1.5 mm. It is very sensitive and allows us our best color vision and the ability to see 20/20. A normal macula (fovea) is smooth and slightly concave (see OCT). Light falls on the normal macula giving us vision. This is very similar to a projector focusing images onto a movie screen. If there is a physical change to the macula or disease, central vision is usually affected.
Epiretinal membranes are, as the name implies, membranes that develop on the surface of the retina and cause the underlying retina to wrinkle, or “pucker.” This physical wrinkling of the macula causes decreased vision and distortion.
Surgically removing the membrane usually improves the distortion and can improve the vision, too.
If you were to poke a pin through a piece of ballon and then stretch out the rubber, you’d create a nice round hole. A macular hole is actually a stretch hole in the center of the macula. Images that fall within this hole are not seen as there literally is no retina in the center of the macula.
Symptoms include decreased vision, distortion and sometimes, scotomas, which are the fancy name for blindspots.
Swelling of the macula can occur from a variety of causes. The two most common causes germaine to this web site are diabetic retinopathy (more specificially, diabetic macular edema) and swelling secondary to choroidal neovascularization in cases of wet macular degeneration.
Other causes, however, include central serous retinopathy, central and branch vein occlusions, cystoid macular edema from cataract surgery (uncommon these days) and from cases of intraocular inflammation (aka uveitis).
As above, choroidal neovascularization can physically distort the retina and cause distortion. These abnormal blood vessels can develop in between the layers of the retina causing physical disruption of the retina. The analogy here is exactly like the “Princess and the Pea.”
Wet macular degeneration can also cause macular edema as we discussed above.
Dry macular degeneration can also cause symptoms of distortion. One of the layers of the retina, called the RPE, becomes diseased and degenerates. This loss of one of the principle layers of the retina can cause distortion.
What Does This Mean? Distortion, or metamorphopsia, can be a symptom of a variety of retinal or macular disorders, not just macular degeneration. The key for saving your sight is early detection and diagnosis. Usually this may require consultation with a retina specialist to discuss the various treatments.
A fluorescein angiogram and/or an OCT (Optical Coherence Tomography) may be very helpful to your doctor, but this can vary.
Other causes of metamorphopsia, not related to the retina, could include large amounts of astigmatism or a decentered lens.
While most causes are indeed retina related, it is also important to note that most have a treatment with the exception of dry macular degeneration. There is some rumbling; however, that there may be some promising treatments for dry macular degeneration in the near future.