11 An Update on IOL PowerCalculation Formulas
ACCOMMODATING IOL (AIOL)
The accommodating rate function (M) defined as the accommodation amplitude increase per 1.0 mm forward movement of a plus AIOL may be expressed by the Lin’s M-formula
M = (Z/1336)P[2Dc+ZZ’P] (11)
Above formula is a general form for both phakia and aphakia and also for dual-optics AIOL. As shown in Fig. 3, for the thick-IOL single-optics case, the M value is higher
for convex-concave IOL configuration (having front and back surface power of P1 and P2) which has higher P1 for a given P1+P2, when P2<0 (concave). Depending on ocular conditions, M ranges from 0.5 to 2.5 (D/mm) for AIOL-power of 10 to 20 diopters. Greater details of single-optics and dual-single-optics AIOL may be found in other Chapters of Lin in this book.
Fig. 11.8: Accommodation rate (M) vs IOL-power in single-optics IOL at various configurations
CONCLUSION
The existing IOL-power (except Lin’s) based on 2-optics system could only apply to aphakia. For phakia or piggyback IOL, a 3-optics system based on Gaussian optics is required. The Lin’s new formulas provide more accurate calculations for both phakia and aphakia presented by:
• The S-formula (to include IOL thickness and types)
• The Seff-formula (to include the role of natural lens and primary-IOL)
• The personalized r2-formula (including corneal posterior surface power post-LASIK)
• The M-formula (for accommodating IOL efficiency)
• The Z2-formula (for conversion of IOL-power in 3-optics system of phakia or piggyback IOL).
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