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The macula or macula lutea is the central part of the retina, which is the light-processing layer of the back of the eye. Upon examination, the macula is a yellowish gray area with a bright yellow reflex in the very center, representing the most sensitive area for vision, the fovea. Responsible for acute visual discrimination, the macula contains the highest percentage of cone cells, which are the photoreceptors that process bright light and color perception. Damage to the macula results in loss of central vision or distortion of the visual image. Macular degeneration, a progressive, degenerative disease of the macula, is the most common cause of serious vision loss in persons older than 50 years of age.
Yellow pigmentation in the macula lutea represents light reflected from the screening pigments of the macula — zeaxanthin and lutein. The macular pigments work like filters, screening out damaging blue and ultraviolet light. Light rays with shorter wavelengths, like blue and ultraviolet light, cause damage to the lens and retina by producing toxic molecules called free radicals. Acting in concert with the lens, the macular pigments block or deflect the harmful wavelengths to protect the fovea.
Two unique anatomic features of the macula lutea explain the occurrence of a cherry red spot with certain eye conditions. Unlike the rest of the retina, the macular blood supply derives from the choroidal circulation, deep to the retina. The rest of the retina receives blood through the central retinal artery. If a central retinal artery occlusion occurs, the entire retina is deprived of blood except for the macula. Against the surrounding pale, non-perfused retina, the macula appears bright red.
Cherry red spots may also accompany certain congenital lipid storage diseases, like Tay-Sachs disease. These storage disorders lead to the accumulation of fatty material in the retinal cell layers. The macula lutea is relatively devoid of cells and is, therefore, spared from the fatty accumulation. A normal macula adjacent to the lipid-laden peripheral retina appears cherry red.
Macular degeneration decreases central vision but does not cause total blindness. Risk factors for the disease include advanced age, positive family history of macular degeneration, and cigarette smoking. Almost 90 percent of patients with macular degeneration have the slowly progressive dry form of macular degeneration. The other ten percent of macular degeneration patients have the wet form, which can progress rapidly and cause significant vision loss due to leaky blood vessels. Nutritional supplements, including zinc, lutein, and the antioxidant vitamins, help to reinforce the macular structures and stave off the debilitating forms of macular degeneration.
Macular edema is fluid retention or swelling within the macula lutea. This condition can occur after trauma or surgery due to inflammation. It can also result from leaky blood vessels. Diabetic retinopathy, a condition affecting the retinal blood vessels, is a common cause of macular edema. Swelling in the macula can distort or reduce the vision.