Diagnosis of astigmatism is by comprehensive eye exam test, which measures how the eye focus light and determines the corrective lens needed.
Astigmatism diagnosing tests
Astigmatism examination may include:
Testing for astigmatism may use several procedures in order to measure how the eyes focus light and to determine the power of any optical lenses needed to correct the reduced vision.
Astigmatism Visual acuity test
As part of the testing, people will ask to read letters on a distance chart. This test measures visual acuity, which is writing as a fraction such as 20/40. The top number is the standard distance at which testing is performing, twenty feet. The bottom number is the smallest letter-size that can read. A person with 20/40 visual acuity would have to get within 20 feet, for a letter that should see at forty feet in order to see it clearly. Normal distance visual acuity is 20/20.
Astigmatism diagnosis by Keratometry
A keratometer is the primary instrument used to measure the curvature of the cornea. By focusing a circle of light on the cornea and measuring its reflection, it is possible to determine the exact curvature of the cornea's surface. This measurement is particularly critical in determining the proper fit for contact lenses. A more sophisticated procedure called corneal topography may perform in some cases to provide even more detail of the shape of the cornea.
Astigmatism Refraction test
Using an instrument called a phoropter, the optometrist places a series of lenses in front of the eyes and measures how they focus light. This is performing using a hand held lighted instrument called a retinoscope that automatically evaluates the focusing power of the eye. The power is then refining by patient's responses to determine the lenses that allow the clearest vision.
Using the information obtained from these tests, the optometrist can determine if one have astigmatism. These findings, combined with those of other tests performed, will allow the optometrist to determine the power of any lens correction needed to provide clear, comfortable vision, and discuss options for treatment.