Final answer:
Decreased visual function in older adults is commonly caused by age-related macular degeneration (AMD), which leads to the death of cells in the macula and central vision loss, and presbyopia, where the eye loses its ability to focus on near objects due to reduced elasticity of the lens and weakening of the muscles around the lens.
Step-by-step explanation:
Common causes of decreased visual function in older adults include a variety of conditions. One major cause is age-related macular degeneration (AMD), which is a leading cause of blindness where cells of the macula die, leading to a loss of central vision. Another vision problem is presbyopia, an age-associated condition where the eye gradually loses its ability to focus on close objects. This is because the lens may become less elastic and the muscles controlling the lens may lose strength as one ages. People often need reading glasses after the age of 55 because their lens no longer focuses correctly.