Prediction of the implant position is the proverbial "Achilles heel" of any standard IOL calculation formula. Hoffer Q, SRK/T and Holladay 1 calculate the ELP based on axial length measurement and K reading, and assume that a long eye leads to deeper anterior chamber, as well as steep K, and vice versa. Many studies on eye anatomy have shown that short eyes often have fairly standard anterior chamber depths; this explains why these formulae tend to misestimate IOL power in non-average eyes. Barrett and Olsen use more directly related parameters to calculate the implant position. The most important parameters in this respect are anterior chamber depth (ACD) and lens thickness (LT). Modern IOLs are implanted in the capsular bag of the crystalline lens and therefore ACD and LT are directly related to the implant position post-operatively.