Measuring non-spherical optical surfaces.

Area of Science:

• Ophthalmic optics
• Contact lens technology
• Optical metrology

Background:

• Emerging lens designs for presbyopia utilize novel constructions for varifocal optics.
• Many designs incorporate aspheric surfaces with defined p-values.
• Manufacturer-quoted back optic zone radii are often nominal, complicating lens verification.

Purpose of the Study:

• To evaluate the accuracy and bias of a videokeratoscope and an optical microspherometer in verifying complex concave contact lens surfaces.
• To determine which instrument is more suitable for measuring the asphericity (p-value) of these surfaces.

Main Methods:

• Fifty-four concave test surfaces with known vertex curvatures and p-values were manufactured.
• Measurements were taken using both a videokeratoscope and an optical microspherometer.

Main Results:

• The optical microspherometer provided accurate vertex radius measurements but showed poor accuracy and bias for p-value verification.
• The videokeratoscope demonstrated high accuracy for vertex radius measurements, with some bias.
• The videokeratoscope was highly accurate in describing the p-value, though bias was present.

Conclusions:

• A videokeratoscope is preferred over an optical microspherometer for accurately determining the asphericity of concave optical surfaces.
• Both instruments exhibit high accuracy in measuring the vertex radius of concave surfaces.