Understanding Base Curve & Diameter: Essential Contact Lens Measurements

Base curve and diameter are terms used by optometrists and other eye-care professionals to measure your eyes and fit you with the proper contact lenses. Base curve is a measure of the curve of the contact lens, and diameter is a measure of the diameter of the contact lens. Both of these measurements are derived from the sizing of your corneas. Optometrists used to use keratometry to measure your corneas, but today a more accurate analysis is used called corneal topographical analysis.

Things You'll Need

• Corneal topographer

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Instructions

• 1

  Turn on the corneal topographer, and wait until the bowl lights up and the pattern of concentric rings appears inside.

• 2

  Sit in front of the instrument, and place your forehead against the bar and your chin in the holder. Adjust the bar and/or holder by twisting the levers above or below the device.

• 3

  Hold your head still for a few seconds while the corneal topographer is working. The machine focuses the concentric ring pattern on the back of your corneas and reflects the image back to a placido disk within the machine.

• 4

  Remove your head, and print out the report generated by the corneal topographer. A topographical map of your corneas will be printed along with your base curve and diameter measurements.