How to Measure Contact Lenses

Contact lenses are made of soft or rigid material and come in different sizes and curvatures. A contact lens prescription is based on specific measurements of your eye and is matched to certain specifications and measurements of contacts. Several types of equipment and methods are used to measure contact lenses.

Things You'll Need

• Ruler with millimeters
• Aberrometer
• Lens clock
• Lensometer

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Instructions

• 1

  Use a PD stick (optical ruler) to measure the diameter of the lens. This measurement is recorded in millimeters. Most contacts range from 8 to 14 mm across.

• 2

  Measure the curve of a lens with a lens clock. A lens clock is an optical instrument that measures the base curves of both eyeglasses and contact lenses. Base curves on contacts are designed to match the curvature of your cornea. The lower the number, the steeper the curve of your cornea.

• 3

  Use a lensometer, a standard piece of optical equipment, to measure the strength of lenses. Only certain types of lensometers have the ability to measure the prescription power of a contact lens, so make sure you are using a lensometer that measures contacts.

• 4

  Measure a toric contact lens by checking the lens orientation markings while the lens is on the eye. These special markings help you to know whether the contact is in the right place on the eye to correct for astigmatism. The markings are usually situated horizontally in the middle, outside part of the lens at what is called "3 and 9 o'clock." This means the markings would be sitting in the same place as 3 o'clock and 9 o'clock on a clock face.

• 5

  Use wavefront aberrometry. Aberrometers use light technology to measure the overall power and defects of the eye but recently have also been used to measure contact lenses. The machine works by tracking how light rays travel through the contact lens.