ASTIGMATISM

Astigmatism is a refractive error in which light rays entering the eye are not
refracted uniformly in all directions. A point focus on the retina is not attained
and blurred vision results. Corneal astigmatism occurs when the radius of
curvature of the cornea is not equal in all directions.

1. Regular Astigmatism - occurs when the corneal curvature is uniformly
different in meridians at right angles to each other.

2. Irregular Astigmatism - occurs when the rays of light in different meridians
ar focused differently and without a pattern, especially if there is an asso-
ciated pathological condition of the cornea.
For example:
- developmental abnormality
- keratoconus
- corneal scars
- trauma
- inflammation

Treatment:
(a) Regular Astigmatism - a cylindrical lens bends the rays of light in one
meridian only, by combining it with a spherical lens, rays of light from
all the meridian can be focused on the retina. A cylindrical convex
lens is used for hypertropic contact lens may form a smooth evenly
curved artificial surface of the cornea and so can correct corneal
astigmatism.

(b) Irregular Astigmatism - cannot be completely corrected with spectacles.
It may be improved by hard contact lenses which ride over the irregular
parts of the cornea.

In more severe cases, penetrating keratoplasty (corneal graft) will be
required to replace the abnormal cornea.