Final answer:
The primary cause of legal blindness in adults over 65 in North America is age-related macular degeneration (AMD). AMD leads to the death of cells in the macula, causing a central black spot in vision which grows over time. Cataracts are another significant cause but are more easily treated when adequate medical care is available.
Step-by-step explanation:
The leading cause of legal blindness among North American adults over the age of 65 is age-related macular degeneration (AMD). AMD is characterized by the death of retinal pigment epithelium cells, which are essential for the health of the macula—an area essential for high visual acuity located at the center of the retina. As the disease progresses, individuals affected by AMD may notice a black spot in the center of their vision which can grow over time, eventually leading to significant vision loss and blindness.
While cataracts are also a major cause of blindness, affecting around 60% of individuals aged 65 to 74, they are more easily treatable with successful replacement of the eye's lens with a plastic one. Therefore, cataracts are less often the cause of irreversible blindness in regions where adequate medical care is available.
Preventive measures for cataracts include protecting the eyes from UV-B rays with plastic sunglasses, which are more effective than glass ones. Vitamins A and C are also noted to potentially protect against the formation of cataracts.