Introduction
Astigmatism is a refractive error resulting from unequal bending of the incident rays of light by the dioptric system in different meridian of the eye. It’s also the distortion of vision due to irregular curvature of the refractive surfaces of the eye especially the corner and the crystalline lens. This therefore results in multiple points of foci on the retina. While some may fall in front of the retina, the others may fall behind it.
A person with this type of error is called an astigmat. This error is not restricted to a particular age unlike the presbyopia both young and old could be affected.
Definition of astigmatism
Astigmatism is a refractive error, meaning it is not an eye disease or eye health problem. It is a problem with how the eye focuses light. In astigmatism light fails to come to a point focus on the retina to produce clear vision. Instead multiple focus point occurs, either in front of the retina or behind (or both).
Astigmatism is a condition in which the eye does not focus light evenly on to the retina, the light-sensitive tissue at the back of the eye. This can cause image to appear blurry and stretched out.
Astigmatism is a condition where the cornea is not shaped perfectly spherical.
Astigmatism is a refraction error that occurs in some individuals. It major symptom is blurred vision. The front surface of the eye (cornea) of a person with astigmatism is not properly curved. The curve is irregular that is one half is flatter than the other the other area appears steeper. It is con-genital (present at birth) but can develop after an eye operation or injury to the eye.
Types of astigmatism
There are three (3) types of astigmatism namely:
- Single Astigmatism: This type of astigmatism is further divided into two which are:
- Simple Myopic Astigmatism:
This is the process whereby light rays from an object entering the eye goes to focus at different foci on the retina. One on the retina and the other in front of the retina.
- Simple Hyperopic Astigmatism: –
This is a situation whereby rays of light from an object entering the eyes goes to focus at different point in the eye one on the retina the other at the back of the retina.
- Compound Astigmatism: This type of astigmatism is also divided into two namely:
- Compound Myopic Astigmatism: –
This is a type of astigmatism where by light entering the eye goes to focus at different point in the eye. One in front of the retina the other far in front of the retina behind the lens.
- Compound Hyperopic Astigmatism: –
This is a situation where the light rays entering the eyes goes to focus at different focal point one behind the retina the other far behind the retina.
- Mixed Astigmatism: This is the last type of astigmatism whereby light rays focus at different distance on the retina one in front the other behind the retina.
Causes of astigmatism
Astigmatism usually is caused by an irregularly shaped cornea. Instead of the cornea having a symmetrically round shape (like a baseball) . It is shaped more like a football, with one meridian being significantly more curved than the meridian perpendicular to it.
N.B: The Steepest and flattest meridian of an eye with astigmatism are called principal meridian.
- Astigmatism is also caused by the shape of the lens in the eye. This type of astigmatism is called lenticular astigmatism.
- Irregular astigmatism can result from an eye injury that has caused scar on the cornea from certain eye surgery or from Keratoconus (a disease that causes a gradual thinning of the cornea).
- Astigmatism could be caused as a result of alteration or error in the curvature of the refractive surface mainly the cornea. This is called curvature astigmatism.
Symptoms of astigmatism
- Astigmatism usually causes vision to be blurred or distorted
- Headache (this occurs after reading) or other prolonged visual task).
- Excessive squinting is a very common symptom.
Photophobia- Negative sensitivity to light.
Diagnosis of astigmatism
Astigmatism is detected during a routine eye examination with the same instrument used for detecting nearsightedness and farsightedness. This eye examination is carried out by an optometrist.
Correction of astigmatism
Astigmatism can be corrected with eyeglasses, contact lenses or refractive surgery. Astigmatism requires a cylindrical lens.
Treatment of astigmatism
Astigmatism can be treated with prescription eyeglasses, contact lens or a refractive surgery called Lasik surgery. The eye doctor (Optometrist) will prescribe a spherocylindrical lens or Lasik surgery where the eye doctor will use a laser to reshape the cornea so it can focus light rays to one focal point on the retina.
Conclusion
It is usually advisable for an astigmats to wear their lenses regularly to adequately relieve them of the extra efforts made at compensating for the distortion in vision. Thus “the more lenses are worn the more relief the affected individual would have. But in a more severe case lenses may not provide adequate relief. Thus there may be need for surgical intervention in form of cornea remodeling or possible transplant. (Keratoplastic Surgery).
