The lens factor (LF) used to calculate the implant position is similar to the A-constant, surgeon factor, or C-constant of other formulae. However the Universal II formula recognised that this component of the estimated lens position (ELP) is also influenced by anatomic factors such as AL, K, ACD, lens thickness (LT), and white-to-white. In a recent retrospective study on pooled data of more than 5’900 eyes, it was shown that the Barrett Universal II formula performed significantly better than the standard formulae Haigis, Hoffer Q, Holladay 1 and SRK/T in average, short (AL ≤ 22.5mm) and long (AL ≥ 25.5mm) eyes. On the pooled data, Unversal II achieved 81% of the eyes within 0.5 D of the intended refractive result.