Before cataract surgery can be performed, it is necessary to determine the dioptric power of the intraocular lens that will be used to replace the cataract. The most important pre-operative measurement is the axial length of the eye: the distance between the cornea and the retina. Using the precision of a laser and employing the technology of partial coherence interferometry,  the IOL Master is consistently accurate to within ±0.02 mm or better. The axial length value (in millimeters) is then placed in a formula to generate the correct power of the implant.

The IOL Master also performs other important measurements including: corneal curvature, depth of the anterior chamber and the refractive power of phakic IOLs ( STAAR Visian ICL ).