How to Read Toric Lens Sizes

Your optometrist may prescribe toric contact lenses to correct astigmatism, a condition that occurs when the surface of the eye curves more in one direction than in other directions. Astigmatism generally results in blurry vision at all distances. Toric lenses correct for astigmatism by rotating the cylinder axis of the lens. The "axis" number on a contact lens prescription or box denotes the degree of rotation in the lens. Toric prescriptions also include a number labeled "CYL" or "cylinder" which describes the power of the astigmatism correction. However, the lens size is measured the same way for toric lenses as it is for regular contact lenses.

Instructions

• 1

  Look at your contact lens box or prescription and find where it is marked "BC" and "DIA." These two numbers together describe the size of your contact lenses.

• 2

  Read the number next to "DIA" to determine the diameter of your contact lens in millimeters. Your optometrist prescribes this number based on the size of your eye.

• 3

  Read the number next to "BC" to find the base curve for your lenses. This number indicates the amount of curvature on the inside of the lens. Your optometrist measures the curvature of the surface of your eye to prescribe this number.