Comparison of immersion ultrasound biometry and partial coherence interferometry for intraocular lens calculation according to Haigis

Background: The precision of intraocular lens (IOL) calculation is essentia lly determined by the accuracy of the measurement of axial length. In addit ion to classical ultrasound biometry, partial coherence interferometry serv es as a new optical method for axial length determination. A functional pro totype from Carl Zeiss Jena implementing this principle was compared with i mmersion ultrasound biometry in our laboratory. Patients and methods: In 10 8 patients attending the biometry laboratory for planning of cataract surge ry, axial lengths were addition ally measured optically. Whereas surgical d ecisions were based on ultrasound data, we used postoperative refraction me asurements to calculate retrospectively what results would have been obtain ed if optical axial length data had been used for IOL calculation. For the translation of optical to geometrical lengths, five different conversion fo rmulas were used, among them the relation which is built into the Zeiss IOL -Master. IOL calculation was carried out according to Haigis with and witho ut optimization of constants. Results: On the basis of ultrasound immersion data from our Grieshaber Biometric System (GBS), postoperative refraction after implantation of a Rayner IOL type 755 U was predicted correctly withi n +/- 1 D in 85.7% and within +/- 2 D in 99% of all cases. An analogous res ult was achieved with optical axial length data after suitable transformati on of optical path lengths into geometrical distances. Conclusions: Partial coherence interferometry is a noncontact, user- and patient-friendly metho d for axial length determination and IOL planning with an accuracy comparab le to that of high-precision immersion ultrasound.