How to Measure Base Curve for Contact Lens

Written by dianne christensen-herman
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How to Measure Base Curve for Contact Lens
An eye must be measured to determine size for contact lenses. (Jupiterimages/Goodshoot/Getty Images)

Rigid contact lenses were first manufactured, then soft lenses were invented by Czech chemist Otto Wichterle, who also invented the first gel used in production. Contact lenses are available in different curvatures and sizes. A contact lens prescription consists of certain eye measurements that are coordinated with certain contact measurements and specifications. There are various methods and types of equipment used to measure contact lens base curve.

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Things you need

  • Ruler with millimetres
  • Aberrometer
  • Lens clock
  • Lensometer

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  1. 1

    Measure the diameter of the lens with a PD stick or optical ruler, which is recorded in millimetres. Contact lenses generally range from 8 to 14mm in diameter.

  2. 2

    Determine the curve of a lens with a device called a lens clock. The device is an optical instrument that measures the base curves of contact lenses and eyeglasses. The base curves on contact lenses are made to mimic the cornea's curvature. If the number is low, this means you have a large curve on your cornea.

  3. 3

    Calculate the lens strength with a lensometer, an optical device. The lensometer must be one that measures contacts, because not all of them measure the prescription power of contact lenses. Make sure the lensometer you have can do this.

  4. 4

    Figure out the measurements of a toric lens by finding the lens orientation specifications while the lens is positioned on the eye. There are marking on the contact so you know that the contact is positioned correctly for an astigmatism. These markings are usually positioned horizontally in the centre, or outside section of the lens at the 3 and 9 o'clock positions.

  5. 5

    Find measurements with an aberrometer. This is an optical device that uses light technology to measure the power and eye defects, but is also used to measure contact lenses. An aberrometer operates by tracking how light travels through contact lenses.

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