Management of the Patient with Age-Related Macular Degeneration

Tina Scheufele Cleary

Claudia U. Richter

Age-related macular degeneration (AMD) is a major cause of vision loss in the elderly, affecting an estimated 46.2% of persons older than the age of 75 years. Advanced AMD—defined as having one eye with either geographic atrophy (advanced dry) or neovascular (wet) AMD—affects as many as 16% of people older than the age of 80 years in the United States. With the anticipated sharp increase in the number of elderly individuals in the United States over the next 20 years, the prevalence of AMD is expected to rise dramatically from 1.75 million with advanced disease in the year 2000 to nearly 3 million by the year 2020.

Proper geriatric eye care includes early recognition of macular degeneration and prompt ophthalmologic referral so that the risk of visual impairment can be minimized. With new treatments available for neovascular (wet) AMD, 94% to 95% of patients undergoing regular treatments maintained visual acuity after 2 years, and many regained some of the vision they lost if they were treated in a timely manner.

PATHOPHYSIOLOGY AND CLINICAL PRESENTATION (1, 2, 3, 4, 5, 6, 7 and 8)

The retinal pigment epithelium is critical to the maintenance of healthy retinal photoreceptors; any compromise to it can lead to a loss of vision. In macular degeneration, the retinal pigment epithelium begins to degenerate; deposits of debris called drusen accumulate between the epithelial cell and the underlying basement membrane (Bruch membrane). The precise mechanisms are poorly understood, but inflammatory mediators and genetic factors are believed to play roles.

Drusen deposits are categorized by their ophthalmoscopic appearance. Hard or nodular drusen are pinhead-sized, yellowwhite lesions visible ophthalmoscopically in the macular region. Soft or granular drusen are larger and have less distinct edges. The presence of diffuse, or confluent, drusen and extensive retinal pigment epithelial changes (hyper- or hypopigmentation) places a patient at high risk for advanced AMD.

Risk factors include increasing age, race (more common in whites), cardiovascular disease, atherosclerotic risk factors, sun exposure, and dietary factors (e.g., lack of antioxidants, zinc). Cigarette smoking is the most important modifiable independent risk factor, with a dose-response relationship, particularly in women. Community-based cohort study reveals an association between regular aspirin use of greater than 10 years and risk of advanced AMD with neovascularization (hazard ratio, 1.63 and incidence, 1.76%); no increase in risk was seen for geographic atrophy-type AMD.

Mutations in the complement factor H gene are associated with an increased risk of AMD; many more genetic variants have been identified that either increase the risk or are protective. Genetic tests have begun to be marketed for predicting risk of progression to advanced (dry or wet) AMD or neovascular (wet) AMD, though the utility of such tests remains to be established.

Detachment of the retinal pigment epithelium results from the degenerative process that both weakens and thickens the Bruch membrane. Detachment leads to visual loss as the overlying photoreceptor cells atrophy. In addition, new blood vessels may form (neovascularization) in response to the degenerative changes in the Bruch membrane. These fragile, abnormal new vessels leak and/or bleed underneath the retina, resulting in vision loss. If the condition is left untreated, fibrovascular scarring may ensue. Fortunately, only about 10% of people with AMD develop neovascularization, or wet AMD.

Clinical Presentation and Course

Because the degenerative process is concentrated in the macula, central visual acuity is most affected. Patients may complain of a loss of visual acuity that is not corrected by eyeglasses. In patients without neovascularization, the loss of visual acuity tends to be gradual. Macular examination of such persons may reveal drusen, retinal pigment epithelial changes, and/or geographic atrophy.

“Wet” Versus “Dry” Macular Degeneration

The distinction is based on the presence or absence of neovascularization. Ten percent of AMD patients with neovascularization develop wet or exudative AMD. After one eye develops wet AMD, the risk to the other eye increases to 40% over the next 5 years. Close to 90% of persons with severe central vision loss have wet AMD. When neovascularization develops, vision loss may be acute. Distorted vision (metamorphopsia) may herald the onset of fluid leaking into and underneath the retina. In addition to revealing drusen, macular examination may show subretinal fluid and/or hemorrhage. Long-standing cases often develop fibrotic macular scarring.

The 90% of AMD patients without neovascularization are labeled as having dry or nonexudative disease, which usually has a more benign clinical course and prognosis. Nonetheless, even patients with dry AMD may lose significant vision over time due to retinal atrophy; however, the rate of vision loss is usually slow and progressive, rather than sudden.

DIAGNOSIS (4)

Suggestive historical features include gradual or sudden loss of central visual acuity or distorted vision (metamorphopsia) in an elderly person. The latter suggests the development of choroidal neovascularization, or wet AMD. Metamorphopsia can be detected at home by using an Amsler grid, a 10 × 10-cm card with a crisscrossed grid of vertical and horizontal white lines every 5 mm and a central dot. The patient is asked to focus on the dot and note whether any of the lines appear wavy or distorted or whether any of the boxes formed by the intersecting lines are missing. Each eye is tested separately with any prescribed corrective lenses worn and the grid held at a comfortable reading distance.

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