Michael Goggin, Ben LaHood
Purpose: Current lens formulae and calculators incorporating an estimate of the posterior cornea assume it is steepest vertically in all cases. The IOL- Master 700 is a widely used biometry device that uses swept source optical coherence tomography (OCT). We present the ftrst description of its ability to measure the posterior cornea.
Methods: 1098 eyes were analysed from two sites over a period of 8 months including eyes that had undergone various surgeries and those with pathol- ogies including keratoconus. The anterior or poste- rior cornea could not be accurately measured in 88 eyes.
Results: The majority of eyes (73.32%) had verti- cally steep posterior corneas with oblique (16.79%) and horizontal (9.89%) less common. In anterior ?with-the-rule? (WTR) eyes, the posterior cornea was steep vertically in 91.75%. Mean T Standard Deviation (SD) posterior corneal astigmatism was 0.24D 0.15D. There was a positive correlation between magnitude of anterior and posterior corneal astigmatism (Pearson r(1096) = 0.45) which was sta- tistically signiftcant (p <0.01). Conclusions: The IOLMaster 700 emphasises that not all posterior corneas are steep vertically and actually found a lower proportion (73.32%) com- pared to ftndings of Koch et al (86.6%). This implies that we are risking making incorrect lens choices by using current lens formulae and calculators which assume posterior corneas are always steep vertically. The ability of such a commonly used device to mea- sure posterior corneal astigmatism accurately could improve surgical outcomes and render current for- mulae and nomograms which estimate posterior cor- neal astigmatism obsolete.