Anterior chamber depth plays critical role in IOL calculations

Essentially all formulae for calculating IOL power for cataract surgery have the same structure: a vergence calculation and a way of determining the anterior chamber depth and the final resting position of the optic. This effective lens position, or ELP, is the principal way that the formulae differ, with the vergence calculation being essentially identical across the board. The anterior chamber depth, or ACD, relates directly to the ELP and therefore has a critical role in the accuracy of the IOL calculations.Jack T. Holladay, MD, MSEE, FACS, has taught us that eyes can have a shallow, normal or deep anterior chamber in the setting of a short, average or long axial length. These various combinations can have large differences in lens calculations. For example, a small anterior chamber in a short eye is the typical nanophthalmic eye in which we can expect the IOL power to be high. However, an equally short eye with a deep anterior chamber will produce a far larger IOL power and more uncertainty in the IOL power calculation because the ELP will be farther from the cornea and closer to the retina.