08-31-2009, 04:21 PM
One other very important feature of the aging eye is the extent to which the pupil can dilate (widen to let in a wider cross-section of light). As we age, our ability to dilate the pupil is reduced so extensively that we see poorly in low light conditions. Hands up all of you reading over the age of 47 who need more light to read and who probably also need bifocals....yup, a lot of hands.
There is more. In addition to letting in a wider cross-section of light as it expands, the wider aperture that results also allows us to discern details better...tiny ones like two periods on the printed page placed next to one another and held about 4 feet away from the eye. This is what makes optics, such as binoculars and telescopes, so effective. In addition to letting more light into the eye (by focusing all light that gets into those big fron lenses or reflected off the mirrors), the wider aperture helps to split two similar objects and make them distinctly separate. This is important in the study of two stars close to each other, but appearing as one to the naked eye. Similarly for the aged eye, when light is generally not great, and we can't adapt by expanding the iris as we could at age 20, we don't see the details that the 20 year-old can see standing beside us.
This information should help to explain why many of us move up a scale or two by the time we are 60.
-Crandell
There is more. In addition to letting in a wider cross-section of light as it expands, the wider aperture that results also allows us to discern details better...tiny ones like two periods on the printed page placed next to one another and held about 4 feet away from the eye. This is what makes optics, such as binoculars and telescopes, so effective. In addition to letting more light into the eye (by focusing all light that gets into those big fron lenses or reflected off the mirrors), the wider aperture helps to split two similar objects and make them distinctly separate. This is important in the study of two stars close to each other, but appearing as one to the naked eye. Similarly for the aged eye, when light is generally not great, and we can't adapt by expanding the iris as we could at age 20, we don't see the details that the 20 year-old can see standing beside us.
This information should help to explain why many of us move up a scale or two by the time we are 60.
-Crandell