 Barrett Universal II Formula
 Barrett Toric Calculator
 SRK Formulas


SRK2
SRK2 formula is similar to SRK1, but provides the following adjustments to the A constant for very long or short eyes:
 L<20.00mm: add 3 to A constant
 L between 20.00mm and 20.99mm: add 2 to the A constant
 L between 21.00mm and 21.99mm: add 1 to the A constant
 L>24.50mm: subtract 0.5 from the A constant