Javal's rule

Javal's rule is a mathematical formula used to estimate astigmatism based on keratometry readings.[1] The estimate is useful for high cylinder measures, generally over -2.00 diopters. The estimate is found by multiplying the difference in power between the two meridians by 1.25 and factoring in the average lenticular astigmatism, which is -0.50 x 090.

References
  1. Schwartz, S. Geometric and Visual Optics. pg 219-221. McGraw-Hill. 2002.


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