[Calculating the Human Eye - The Evolution of Biometry for Cataract Surgery].

Introduction: Optical biometry is the standard diagnostic tool and essential basis for IOL calculation prior to cataract surgery today. Our article will provide a short overview of the historical development of biometry of the human eye and the formulas used for IOL calculation.

Material And Methods: Selective literature search in books and journal articles via PubMed, Google Scholar and Google as well as close cooperation with IOLCon at Saarland University, Homburg/Saar (Germany).

Results: For first measurements of the eye, ultrasound was applied invasively. Today, ultrasound is mostly restricted to cases where optical biometry cannot be performed due to opaque optical media. However, today, most of the modern biometers are working with OCT non-invasively. Along with this technical evolution, numerous formulas have been developed for calculating the optical power of each respective IOL. Intraocular lenses can be calculated with different strategies: with empirical formulas, the IOL power is derived from a series of biometric data without any anatomical or physical background. With the theoretical-optical formulas, which are most commonly used today, the IOL power is extracted from a paraxial optical model which simplifies the eye to linear Gaussian optics. With modern raytracing settings, the Snell's law is applied at each refracting surface within the eye and the best focus position is compared with the position of the fovea.

Conclusions: Today, an increasing number of eyes that underwent refractive surgery previously are facing cataract surgery. Maybe even more important than adequate biometry of the human eye will be using appropriate calculation schemes in order to enhance post-cataract refractive outcomes or predictability.