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Superposition of sphero-cylindrical lenses using contour graphs
1Southern California College of Optometry, Fullerton 92831, USA.
Background:
The superposition of thin sphero-cylindrical lenses with arbitrary angles between cylindrical axes is sometimes required in a clinical setting. For example, it may be useful in some instances to perform an overrefraction which, added to the spectacle or toric contact lens in place on the eye, yields a final correcting lens.
Methods:
Computer calculations have been used to create contour graphs allowing a graphical solution to the problem of combining sphero-cylindrical lenses. Although conceptually strightforward, the method has not been presented before.
Results:
The use of contour graphs to superpose sphero-cylindrical lenses is shown by examples to be accurate and much simpler than calculational methods.
Conclusions:
Lacking a pre-programmed computer, the method of contour graphs offers a practical method of combining sphero-cylindrical lenses.