When a normal sighted person
looks at something distant, the natural lens of the eye relaxes
to its normal shape. When that same person looks at something close,
the muscles around the lens stretch or squeeze the lens to change
its focus. This change of the lens shape for close vision is called
accommodation.
Someone who is myopic has
a lens with a normal shape that focuses on things close. To see
something close, accommodation is not necessary; the lens is already
set to focus on things close. As we mature, the natural
lens in our eye expands, firms, and loses its ability to accommodate.
This normal condition is known as
presbyopia and becomes problematic for most people between 40 and 60
years of age.
Presbyopia may not be noticed in a myopic person because
the need for accommodation is diminished by the myopia. Presbyopia
can be masked by myopia. The lens may be unable to accommodate,
but since the lens is already focused for close vision and the corrective
lenses take care of the myopia, the lack of accommodation is not
so well noticed.
When a person has
refractive surgery to remove all of the myopia, suddenly the
lens is expected to accommodate. Since accommodation has not been
as much of an issue before refractive surgery, the muscles may be
weak. The stiffness of the lens was not an issue before, but now
this stiffness reduces the amount of accommodation possible to change
from distant to close vision. This is what is often called "Sudden
Presbyopia".
There are a number of ways
to deal with the focusing changes and challenges caused by presbyopia.
People with a small amount of residual nearsightedness can simply
remove their glasses to read. Some may need to use reading glasses
for close work such as reading, using a computer, or sewing.
Bifocals and
trifocals can also be used to provide both near and far vision
correction without having to constantly put on and take off a pair
of glasses or switch between two pairs of glasses.
Monovision can help by providing one eye focused for near vision
and one eye focused for distance vision. The brain will combine
the two images to create one focused image of near and far.
If you are ready
to choose a doctor to be evaluated for Lasik or any refractive
surgery procedure, we highly recommend you consider a doctor who
has been evaluated and certified by the USAEyes nonprofit organization.
Locate a USAEyes Evaluated & Certified Laser Eye Surgeon.
