Table 2

Transforming the astigmatism from 0–180 (Axint cylinder notation) to 0/180–90 (“by the rule” notation, ie, mirror equivalents). This allows the ATR and oblique astigmatism values to be grouped together. This may be computed with an if, then, else statement—eg, if θ > 90, then ′θ = 180 − θ, else ′θ = θ