[Echographic measurement of eyeball length in pseudophakic eyes]

Refraction affects ultrasound as it passes obliquely through tissues or materials with different propagation speeds. Therefore, the accuracy of axial length measurements might theoretically be influenced after implantation of an IOL, which has a propagation speed exceeding those of the ocular humors by a factor of 1.8 (2718 m/s-1 vs. 1532 m/s-1). The in vitro studies of the present paper clearly demonstrate that ultrasound length measurements were not affected significantly by inclination of the lens up to 25 degrees or variation of the transducer-lens distance from 0 to 25 mm. Axial lengths measured in 26 patients were found to be virtually the same after IOL implantation. The authors conclude from these data that accurate ultrasound axial length measurements of the eye can be obtained after IOL implantation if the different propagation speed in PMMA and the thickness of the IOL are taken into account in the calculation.