Causes and Risk Factors for Macular Degeneration
Age-related macular degeneration may be influenced by a combination of environmental and genetic factors. Factors that may predispose a person to develop AMD include conditions and behaviors that interfere with the blood supply to the macula:
- Hypertension (high blood pressure; constricts blood vessels)
- Arteriosclerosis (thickening of arterial walls due to plaque deposits)
- Diet low in antioxidants and high in saturated fat (increases the tendency for fatty deposits to stick to vessel walls)
- Hypercholesterolemia (excess cholesterol in the blood)
- Smoking (constricts blood vessels)
Because the condition often runs in families, AMD may be hereditary.
Signs and Symptoms of Macular Degeneration
The main symptom is central vision loss, which is gradual in dry AMD and sudden in wet AMD. Other symptoms include
- blurry or fuzzy vision;
- dark, empty spots in the center of vision;
- difficulty reading or performing detail work; and
- seeing straight lines as wavy or bent (e.g., telephone poles, sentences on a page).
Diagnosis of Macular Degeneration
Vision testing, Amsler grid test, retinal exam, and fluorescein angiography are used to diagnose macular degeneration. Visual acuity is tested using the standard eye chart, which features black letters on a white background. The chart measures vision at various distances and can detect vision loss due to AMD.
The Amsler grid test assesses distorted or reduced vision and small irregularities in the central field of vision. The grid consists of evenly spaced horizontal and vertical lines printed on black or white paper, with a small dot in the center. Using one eye at a time, the patient stares at the dot, which limits the image to the macula. Distortion of the grid lines or blank areas may indicate a change that requires a thorough retinal examination.
The retinal exam is performed with a slit lamp microscope, which enables the doctor to examine different parts of the eye under magnification. After instilling drops to dilate the pupil the microscope is used to detect drusen and abnormal areas. If the exam reveals abnormalities that suggest neovascularization, such as fluid or blood beneath the retina, other testing may be required.
Fluorescein angiography determines the presence and location of neovascularization. A small amount of dye is administered intravenously and photographs of the retina are taken as the dye passes through the blood vessels.