EYE DOCTOR Century City||
How it works
Astigmatism occurs when the cornea is shaped irregularly
- like a football or a spoon as compared to a ball or sphere. The visual effect
is similar to what you may have seen in a "funny mirror" at
an amusement park - the image is stretched, usually horizontally or
vertically, although oblique (angular) distortions also occur.
How it works
Your eye is a dual lens system, one external and one internal.
The external lens of the eye is the cornea. Normally, the cornea
is shaped like a somewhat flattened ball, with its meridian along the
The internal lens, called the crystalline lens, is convex on
both sides (front and back), like this: (). This lens is also somewhat
flattened, but its meridian is vertical.
In a perfect system, the cornea and lens each contain the same
amount of curvature, but are opposite in orientation, thereby
effectively canceling each other. Because of this, the rays of light
can flow in even, parallel lines.
Sometimes, one of these two lenses may have a radius of curvature
that is too steep in one meridian, and therefore too flat in the corresponding
perpendicular meridian. Generally, this astigmatic optical error is
caused when the cornea has excessive flattening (or steepening) in
one meridian, rather than the internal lens. Then, the rays of light are distorted.
There are various types of astigmatism including regular, mixed
and irregular astigmatism, also referred to as higher and lower aberrations,
depending upon the degree of steepness and flatness involved and in
what combinations. As the relative amount of error increases, so does
the perceived blur and eye strain.
Small degrees of astigmatism do not significantly impact the
visual system, as there is a built-in compensatory mechanism.
Astigmatism can occur alone as the sole optical error, and can
be corrected by LASIK, or a lens (eyeglasses or contact lens) that
is the astigmatically warped opposite to that of the eye.
Prescriptions having three parts indicate the presence of astigmatism
and look something like this:
-3.00 +1.25 x 180
The first part indicates the main spherical correction (either
myopia or hyperopia), while parts two and three show the extent
and location of your astigmatism.
An astigmatic lens is called a toric or cylinder lens. Toric
is the physical construction of the lens, while astigmatic is
the optical effect. Sometimes these terms are used interchangeably.
Astigmatism often occurs combined with myopia or hyperopia. The
resulting lens is called a compound lens, incorporating the spherical
power to neutralize the near or farsighted optics, and cylindrical
or toric to neutralize the astigmatic error.
Laser correction for astigmatism
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guiding LASIK. See Wavefront LASIK for more information! |