What is Involved in an Astigmatism Test?

There are several different types of astigmatism tests that can be performed to diagnose this condition. The most basic astigmatism test requires the patient to examine a series of geometric, evenly spaced lines on an eye chart. In most cases, a test is performed using a tool called a keratometer, which measures how light is reflected off the cornea. A third astigmatism test, called corneal topography, creates a three-dimensional map of the surface of the cornea.

Astigmatism is usually caused by the cornea of the eye being curved inappropriately, often leading to blurred or fuzzy vision. In some cases, a distortion in the eye's lens may be the cause. Astigmatisms can vary quite a bit in intensity. Individuals who experience severe astigmatisms may have blurred, distorted vision, and often complain of headaches and eye pain, while others with minor astigmatism may not even require correction to overcome the condition. Most astigmatism tests look at the curvature of the cornea to diagnose the condition.

A basic astigmatism test will require the patient to look at a picture or sign that is composed of several thin lines that are spaced relatively close together, and typically have a geometric shape. The picture will be adjusted in order to be directly at eye level and about 14 inches (35.6 centimeters) away from the face of the person being tested in order to ensure optimal results. Once the patient is positioned properly, the optometrist will cover one eye, and instruct the person to look at the chart. Those who have a difficult time distinguishing between the various lines on the chart may be diagnosed with astigmatism. The physician will repeat the test with the opposite eye covered as well.

One of the most frequently used types of astigmatism test is a keratometry, which uses a keratometer to see how light reflects off the cornea. Although there are different types of karatometers, one of the most common uses a circle of light to see how it reflects off the surface of the cornea. The patient is seated in front of the device, with his or her chin resting on a fixed form and glasses or contacts removed. The light is projected onto the eye, and measurements are taken.

Corneal topography is a more sophisticated astigmatism test. In this test, the patient sits facing a pattern — usually a series of rings — that is illuminated. This pattern is focused on the cornea and reflected back into the machine. A digital image is captured by the machine, and a computer creates a topological map of the cornea.

When having an astigmatism test, the patient should always bring along any contacts or glasses that are currently in use, as the doctor may want to see how effective the eyeware is at treating the condition. Those who experience severe symptoms without glasses or contacts but not once they are on typically will not require any changes. In contrast, those who have symptoms with the glasses or contacts both on and off will usually need a new prescription in order to accurately treat the condition.

Most doctors will want to schedule a series of ongoing appointments for those who are diagnosed with an astigmatism. Appointments as common as every six months are not uncommon. The doctor will want to monitor any changes in the shape of the eye and make sure that any contacts or glasses are still working effectively.