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Intro
Presbyopia affects 100% of the population by age 50. Currently,
bifocals are the only successful way to treat presbyopia.
Optics
 The
crystalline lens allows the eye to vary its optical power, permitting
individuals with normal vision to view distant objects and refocus
their eyes to see near objects sharply. This ability begins to decline
around age 40 with the onset of presbyopia (literally "old
eye") when the lens starts to lose its flexibility. Presbyopic
individuals with normal vision need reading glasses while nearsighted
and farsighted patients need bifocals for clear viewing at both
distance and near.
People who have low myopia ( 3 diopters or less) often notice that
they can read fine print comfortably without their glasses well
past the age of 40. This is because their nearsightedness allows
them to focus at near without the use of any additional optical
power from their crystalline lens.
Spectacle Correction
Bifocal lenses allow the user to view distance objects through
the top portion of their glasses, and near objects with magnifiers
added to the bottom portion of their glasses. Recently, these lenses
can be blended together to produce a "progressive add"
or "no line" bifocal.
Special Refractive Surgery Considerations
It is important that you understand that refractive surgery DOES
NOT PREVENT the age-related loss of the eye's ability to vary its
focusing power. If you are over 40 and have both your eyes fully
corrected for distance vision, you will need reading glasses for
near work. As an alternative to reading glasses for near work, you
may elect to leave one eye slightly nearsighted; an outcome called
monovision.
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