What is astigmatism?
With astigmatism images
blur or objects you look at are distorted. In ordinary far- and near-sight
the eye refracts all light rays with the same degree of error, in astigmatism
the error varies in different planes. Typically the cornea have the greatest
refractive power at the vertical meridian The 12 o’clock, 6 o’clock
line of the watch dial. This is known as with-the-rule astigmatism or direct
astigmatism. This is by far the most common type of astigmatism, about 88%
of all cases. The less common against-the-rule
astigmatism occurs when the refractive power of the cornea is greater along
the horizontal meridian, or the 9 o’clock – 3 o’clock line
on the watch. About 5% of all cases are against-the-rule astigmatism. Indeed,
it is possible to have astigmatism at any point of the compass and it is also
possible to have horizontal as well as oblique astigmatism. The conventional explanation
is that the fault is inherent in the eyeball – either in the cornea or
the entire eyeball is supposed to be congenitally distorted. Ophthalmologists
define astigmatism as generally caused by toroidal anterior corneal surface. A number of researchers
including Fairmaid (1959), Lopping and Weale (1965), Bannon (1971) and Millodot
and Thibauldt (1985) have reported that convergence of the eyes is accompanied
by a falling of the horizontal meridian, bringing about a slight increase
in with-the-rule astigmatism or a decrease in against-the-rule astigmatism.
Looing and Weale (1965) and Bannon (1971) have estimated that the decrease
in power of the horizontal corneal meridian accompanying convergence is from
–.245 to 0.5 diopter in non-presbyopic eyes. Hofsteller and Rife (1953)
concluded that astigmatism was mostly an environmentally determined trait.
Lyle (1965) believed that no hereditary patterns was discernable for astigmatism
under 2 diopters. In other words astigmatism
is an irregularity in the curvature of the cornea caused by tension and pressure
on the eyeball. In rare instances, astigmatism forms in the lens or the retina. Optometrists correct astigmatism
by introducing a cylinder lens element. The combination of spherical and cylindrical
elements forms a complex curved shape, somewhat like the sections of a football. Many people have the misconception
that astigmatism is an actual disease which it is not. There are people who
can spontaneously generate up to 3 diopters of astigmatism. Contrary to traditional
belief, astigmatism is very fluid and easy to correct. Relaxation is the key
to correcting astigmatism
