Astigmatism Measurements Decoded

After an eye exam your doctor will hand you a prescription. But have you ever tried to read and understand it?

Ophthalmologists and optometrists sometimes use different measurements for astigmatism. Their prescriptions may appear differently depending on what type of provider you see. The optical shops who make glasses and contacts have no problem reading the prescription no matter who is providing it.

+1.0 Astigmatism, +2 Astigmatism Prescription: The Meaning Behind The Numbers 

Astigmatism is measured in diopters. A perfect eye with no astigmatism has 0 diopters. Majority of people have between 0.5 to 0.75 diopters of astigmatism. People with a measurement of 1.5 or more often need contacts or eyeglasses to have clear vision.

Of the three numbers on your contacts or glasses prescription, the last two refer to astigmatism:

• Spherical indicates whether you are nearsighted or farsighted. A plus sign indicates you are farsighted, a minus sign indicates you are nearsighted. The higher the number, the stronger your prescription.
• Cylinder measures what degree of astigmatism you have, or how flat or irregular the shape of your cornea is.
• Axis is measured in degrees, and refers to where on the cornea the astigmatism is located. Axis numbers go from 0 to 180.