Superposition of sphero-cylindrical lenses using contour graphs.
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.
Hemenger
R P
RP
Southern California College of Optometry, Fullerton 92831, USA.
D005139:Eyeglasses; D006801:Humans; D008433:Mathematics; D055656:Prescriptions; D012030:Refractive Errors / Q000503:physiopathology / Q000628:therapy*; D014792:Visual Acuity