What is astigmatism?
Astigmatism is one of a group of eye conditions known as refractive errors. Refractive errors cause a disturbance in the way that light rays are focused within the eye.
What causes astigmatism?
Astigmatism usually occurs when the front surface of the eye, the cornea, has an irregular curvature. Normally the cornea should be smooth and equally curved in all directions. In astigmatism, the front surface of the cornea is shaped more like a football than a basketball. This abnormality may result in vision that is much like looking into a distorted, wavy mirror. The distortion results because of an inability to focus light rays to a single point.
Astigmatism is not a disease nor does it mean that you have ‘bad eyes’. It simply means that you have a variation in the shape of your cornea. Not all corneas are perfectly curved, just as sets of teeth are seldom perfectly aligned. There are many variations that might occur in the corneal surface. The degree of variation determines whether or not you need corrective eyewear.
The exact reason for differences in corneal shape remains unknown, but the tendency to develop astigmatism is inherited (runs in the family). For that reason, some people are simply more prone to develop astigmatism than others are. Patients with astigmatism wear cylindrical lenses to focus light on the retina.
How Does Astigmatism Affect your Vision?
To fully understand why astigmatism causes a disturbance in sight, it is helpful to understand the process of sight. The clear cornea is situated at the very front surface of the eye and enables light to enter the eyeball. At that point of entry the cornea accomplishes about four-fifths of the focus needed for clear vision, bending light rays towards one another into a point. The lens further refines the refractive work begun by the cornea and directs that point of light towards a precise location on the retina called the fovea. If light is not focused into that fine point, the image that reaches the retina cannot be clearly transmitted to the brain.
When astigmatism is present, the surface of the cornea instead of being spherical is distorted. Therefore, light rays entering the eye are not focused into the fine point needed for clear vision. Rather, some light rays may focus into a point, while other light rays meet either before they get to the retina or actually behind the retina. Usually, astigmatism causes blurred vision at all distances.
Who develops astigmatism?
Astigmatism is a very common problem. Some experts agree that most people have some degree of astigmatism, often present at birth. The degree of astigmatism may remain the same throughout life.
What are the symptoms of astigmatism?
The symptoms of astigmatism include a distortion or blurring of images at all distances – nearby as well as distant. Even though vision may be fairly sharp, when slight degrees of astigmatism are present, the condition may cause headache, fatigue, squinting, and eye discomfort or irritation. Of interest to parents and those who work with children, astigmatism may contribute to poor schoolwork but is often not detected during routine eye screening in schools.
How is astigmatism diagnosed?
Astigmatism is diagnosed through the process of a comprehensive eye health examination.
Your Optometrist will recommend corrective eyewear to help the eye focus in a more effective manner. This can be in the form of spectacles and sometimes contact lenses.
Astigmatism often occurs with the refractive conditions such as nearsightedness or farsightedness. The corrective lenses needed are called cylinders and have greater light bending power in one axis than in others. Your Optometrist will perform precise tests during your comprehensive eye health examination to determine precisely the ideal lens prescription.