Astigmatism is a type of refractive error in which the eye does not focus light evenly on the retina. This results in a distorted or blurred vision at all distances.Other symptoms can include eyestrain, headaches, and trouble driving at night.
If it occurs early in life it can result in amblyopia. The cause of astigmatism is unclear. It is believed to be partly related to genetic factors. The underlying mechanism involves an irregular curvature of the cornea or abnormalities in the lens of the eye.
Diagnosis is by an eye exam. Three options exist for the treatment: glasses, contact lenses, and surgery. Glasses are the simplest. Contact lenses can provide a wider field of vision. In Europe and Asia, astigmatism affects between 30 and 60% of adults. People of all ages can be affected. Astigmatism was first reported by Thomas Young in
Although astigmatism may be asymptomatic, higher degrees of astigmatism may cause symptoms such as blurry vision, double vision, squinting, eye strain, fatigue, or headaches.
Some research has pointed to the link between astigmatism and higher prevalence of migraine headaches
Throughout the eye Astigmatism, whether it is regular or irregular, is caused by some combination of external (corneal surface) and internal (posterior corneal surface, human lens, fluids, retina, and eye-brain interface) optical properties. In some people, the external optics may have a greater influence, and in other people, the internal optics may predominate. Importantly, the axes and magnitudes of external and internal astigmatism do not necessarily coincide, but it is the combination of the two that by definition determines the overall optics of the eye.
The overall optics of the eye are typically expressed by a person's refraction the contribution of the external (anterior corneal) astigmatism
The Five Different
Types of Astigmatism With all types of astigmatism light rays come together to form not one but two focal points. The mere fact that there are two focal points formed, instead of just one (in the normal seeing eye) creates vision problems.
First Type The first type of astigmatism is called Simple Myopic Astigmatism, where light comes to two focal points: one before the retina, and one on the retina.
Second Type The second type is called Simple Hyperopic Astigmatism, where light comes to two focal points: one on the retina and another focus point that would be a virtual point behind the retina.
Third Type The third type is called Compound Myopic Astigmatism where light comes to two focal points, both of which are before the retina but at two different locations before the retina.
Fourth Type As you might have imagined, the fourth type is called Compound Hyperopic Astigmatism where light comes to focal points both of which would be in a virtual location behind the retina but at different virtual locations behind the retina.
Fifth Type Finally, the fifth type is called Mixed Astigmatism where light rays come to two focal points, one of which is before the retina and the other of which is behind the retina
Types of astigmatism. The locations of the focal lines with respect to the retina define the type of astigmatism. The main difference between the types of astigmatism depicted in the illustration is the spherical equivalent refractive error. All of the astigmatisms depicted are with-the-rule astigmatisms—that is, they are corrected by using a plus cylinder with a vertical axis. If they were against-the-rule astigmatisms, the positions of the vertical and horizontal focal lines would be reversed.
