Age-related macular degeneration (AMD) is a degenerative disease of the retina. The macula—the central most part of the retina that is responsible for fine visual details—is the primary site of involvement.

Previous classification of AMD identified two manifestations: “wet” and “dry.” Newer terminology favors the use of “early” and “late” stages.

Early AMD is characterized by the presence of small drusen—yellow, focal deposits within the retina that can be visualized during dilated ophthalmologic examination. Small deposits are often found in people aged 50 years and over. Therefore, the presence of such lesions is neither essential for diagnosis nor pathognomonic. In conjunction with increased or decreased pigmentation of the epithelial layer of the retina, however, drusen are a sign of early AMD. Development of early AMD may be asymptomatic or may cause blurred vision or impaired vision in low light.[1]

As AMD progresses to late stage, central vision gradually worsens until patients are no longer able to perform tasks requiring fine visual acuity. AMD is the most common cause of legal blindness (defined as 20/200 or worse in both eyes) in the geriatric population in the United States.[2] Peripheral vision is often spared and may allow limited performance of certain daily activities.

The late stage of AMD is further subdivided into two categories based on the changes observed within the subretinal space: neovascular and non-neovascular. Neovascular AMD was previously known as “wet” AMD, due to an abnormal growth of vessels. While neovascular AMD is less common than non-neovascular AMD (10%-15% of all cases), it carries a worse prognosis and can account for extensive visual loss. Because neovascularization can progress quickly, any acute alteration in vision should prompt immediate consultation with an ophthalmologist.

Non-neovascular AMD can transform to neovascular AMD, and vice versa. Both processes may either be diagnosed in the same eye, or each eye may show unique changes. It is not clear whether neovascular and non-neovascular AMD are different manifestations of the same disease or two different entities.[3]

AMD is thought to be caused in part by exposure to ultraviolet radiation, mainly from sunlight. Just as skin can be damaged by excessive sun exposure, the pigmented layer of the retina that protects photoreceptors can also become damaged with excessive ultraviolet rays[4]. Blue light has also been found to induce similar damage.[5]

Risk Factors

Race and Ethnicity. Non-Hispanic whites in the U.S. have a 2.5% prevalence. In contrast, U.S. Black and Hispanic populations each have a prevalence of about 0.9%.[6]

Age. AMD rarely occurs in persons under age 55. The prevalence is 0.8% in those aged 70 and older, increasing to 16% in those over 90.[7]

Smoking. Individuals who smoke have a relative risk of 2.0 and greater compared with those who have never smoked. Risk may remain elevated for 15 or more years after smoking cessation.[8]

Family history. Genetic factors are linked to increased AMD risk, particularly when combined with smoking.

Alcohol. Heavy use has been linked to early disease.[9]

Sunlight. AMD is believed to be more prevalent near the equator.[5]

Other risk factors under investigation include hypertension, cardiovascular comorbidities (e.g., diabetes), and red meat consumption.[10],[11],[12],[13]

Diagnosis

The minimum age for diagnosis of AMD is 50 years. The classification of disease severity is based not on visual acuity, but on the characteristic findings on dilated retinal examination. These include alterations in the retinal pigmented epithelium, periretinal hemorrhages, retinal atrophy, and/or retinal scarring.[14] As noted above, drusen are not pathognomonic.[15]

• Ocular coherence tomography (OCT) is the gold standard in diagnosing and managing patients with neovascular AMD.
• Slit-lamp photography of the macula is sometimes performed to document progression.
• Fluorescein angiography detects the presence and location of any subretinal neovascularization, but the introduction of OCT has replaced it as a tool.
• The Amsler grid can be used to identify defects in central vision and to monitor changes in patients with established AMD.[16]

Late stages of both neovascular and non-neovascular AMD can resemble other ophthalmologic diseases, which must always be ruled out first.[3]

Treatment

Nutritional Considerations

Dietary factors appear to play an important role in AMD. In epidemiologic studies, the following factors are associated with reduced risk of onset or progression of the disease:

Maintenance of ideal weight. Studies have found a higher risk for AMD in patients with metabolic syndrome.[28] Measures of adiposity, including body mass index and waist/hip ratio, can assist in determining undiagnosed metabolic syndrome in those without any other indicators.[17],[29],[30]

Low fat intake. Studies have found an association between a high intake of saturated fat and cholesterol and AMD.[31],[32] Vegetable fat and total fat intake have also been implicated as culprits in the development of early AMD.[33],[34],[35] People who regularly consume processed baked goods doubled their risk of AMD, compared with those who rarely consume these products. The effect may relate to adverse effects on blood lipids or to an inflammatory response.[33]

In general, following a healthful dietary pattern—defined in a 2020 review as prudent, Mediterranean, or Healthy Eating Index—is associated with a protective effect against AMD, while Western dietary patterns are associated with an increased progression of the disease.[36] Some have suggested that routine intake of fish is associated with reduced AMD prevalence, at least in certain populations. This is presumably due to the omega-3 content, found as DHA and EPA (eicosapentaenoic acid and docosahexaenoic acid, respectively).[31],[33],[34],[37] However, the Age-Related Eye Disease Study 2 (AREDS2), a randomized, double-blind, placebo-controlled study, found no protective benefit of DHA or EPA at 5-year follow-up.[38] A 2015 systematic review supported these findings.[39] Genetics may influence the effect of fatty acids on AMD, but more research is warranted.[40],[41],[42]

High consumption of fruits and vegetables. Lutein and zeaxanthin are the principal carotenoids in the macular region of the retina. They are abundant in dark green, leafy vegetables and may play an important role in the prevention of macular degeneration.[43],[44] Several studies have found that people with high intake of fruits and vegetables had a significantly lower risk for AMD compared with those with lower intake.[45],[46],[47] The Health Professionals Follow-Up Study and Nurses’ Health Study found an inverse association between fruit intake and risk for neovascular age-related maculopathy.[48]

Antioxidant supplements. In the Age-Related Eye Disease Study, individuals with moderate or advanced AMD who received 500 mg of vitamin C, 400 IU of vitamin E, 15 mg of beta carotene, and 80 mg of zinc oxide (along with 2 mg of cupric oxide to prevent copper deficiency) had significantly reduced progression of their disease, compared with subjects receiving a placebo.[20] Caution is advised, however, for several reasons: This evidence derives from a single study. Also, some evidence suggests that beta-carotene supplementation may increase lung cancer risk among smokers. Finally, daily doses of vitamin E exceeding 400 IU may increase cardiovascular and all-cause mortality.[49]

In the lutein antioxidant supplementation trial (LAST), a 10-mg supplement of lutein taken daily, alone or with an antioxidant vitamin combination, increased macular pigment density and improved visual function when compared with a placebo.[50] Lutein supplementation also improved visual performance (visual acuity and glare sensitivity) in other controlled trials.[51] Due to a saturation of transport mechanisms for these carotenoids, some individuals do not achieve increases in macular pigment density following supplementation, despite increases in blood levels of lutein and zeaxanthin.[52] Other individuals may not benefit if they are overweight because lutein and zeaxanthin will be taken up by adipose tissue, rather than by the macula.[53] An ophthalmologist should make patient-specific recommendations because the age of the patient, disease severity, duration of treatment, and potential inhibitory effect of lutein supplementation on other carotenoids must be taken into account.

Orders

See Basic Diet Orders chapter.

Emphasize fresh fruits and vegetables, particularly leafy greens, such as collards or turnip greens, kale, and spinach. Orange peppers, corn, and squash are also good sources of lutein and zeaxanthin.

Consider the following daily supplements in consultation with an ophthalmologist: vitamin C 500 mg, vitamin E 400 IU, beta-carotene 15 mg, zinc oxide 80 mg, and cupric oxide 2 mg.

Lutein should be dosed per ophthalmologist recommendations.

Smoking cessation.

What to Tell the Family

Appropriate medical care and self-care can slow the loss of vision due to AMD. It is important to encourage smoking cessation, along with a diet that is low in fat and cholesterol and high in fruits and vegetables. That means including at least 1 serving daily of a dark leafy green vegetable, such as spinach, kale, collards, or turnip greens, along with 3 servings of fresh fruit per day. This diet is also beneficial to family members, who may have a higher risk of AMD. Supplemental lutein and certain vitamins and minerals (C, E, beta-carotene, and zinc/copper oxide) may be beneficial, but their use should be supervised by an ophthalmologist. Low-vision aids (such as specialized lighting and magnifiers) are available through eye clinics.

References