power calculation of intra ocular lens (IOL)

SANDERS, RETZLAFF, KRAFF ( SRK)  FORMULA FOR IOL POWER CALCULATION-
IOL power(P) = A  - 2.5*AL  -0.9*Km
A=(SPECIFIC CONSTANT )
AL= (AXIAL LENGTH IN MILIMETERS)
Km=(CORNEAL POWER IN DIOPTRES-  TAKE THEIR AVERAGE OF 2 MERIDIANS , normal values 43-46.5D average 44D )

REPEAT  BIOMETRY(AL, Km)- if their is difference >=0.3 mm in AL of rt and lt eyes, >=1.5D difference in Km values of 2 meridians
APPLIED WHEN AL IS 22-24.5 mm

SRK 2 FORMULA- replace  A constant  by-
AL <20           :        A+3
AL= 20-20.99 :         A+2
AL=21-21.99  :         A+1
AL=22-24.5   :          A
AL> 24.5       :          A-0.5

MODIFIED SRK 2 FORMULA-
IF
AL <20 : A+1.5
AL 20-21: A+ 1
AL 21-22: A+0.5
AL 22-24.5: A
AL 24.5-26 : A-1
AL>26      : A-1.5