How Eye Glasses Work
- Posted on: May 9 2011
Key-Whitman Eye Center, leader in LASIK, and cataract surgery in Dallas,
Fort Worth & North Texas also provides corrective lenses through their
optical center. When diagnosed with eye problems and being given prescription
lenses, it is helpful to know how those lenses work to correct eye problems.
The human eye works by bending and focusing images onto the retina through
the cornea and pupil. In some people, images focus either in front of
or behind the retina, causing blurred vision. To correct the problem,
the person usually must get prescription eyeglasses.
Lenses for Myopia
Myopia, or nearsightedness, occurs when the eyeball is too long or the cornea
has too much curvature, causing light to enter the eye improperly and
the image to be focused in front of the retina rather than directly on
it. Lenses to correct myopia have thick outer edges and a thin center.
The thin center is made up of a cluster of prisms which make light spread
out and move the focal point forward so that it lands directly on the
retina rather than in front of it.
Lenses for Hyperopia
Hyperopia, or farsightedness, occurs when the eye is too short so that it cannot
bend light correctly. This causes images to focus behind the retina instead
of directly on it. Lenses to correct hyperopia have thick centers and
thin outer edges, so that the prisms are on the outside edge of the lens,
as opposed to those for myopia with the prisms on the center of the lens.
This causes light to bend toward the middle of the eye, pushing the focal
point back onto the retina.
Lenses for Astigmatism
Most lenses are spherical with a curved over surface that is the same throughout
the lens. When someone is diagnosed with a distortion of the cornea, known as
astigmatism, lenses are ground to a curve along an axis with an angle that depends
on the degree of the astigmatism. Astigmatism is usually diagnosed along
with other forms of vision problems, such as hyperopia or myopia, and
can cause vision problems to be worse as images in the eye appear blurry.
Posted in: Eye Glasses