Purpose: To evaluate the refractive outcome of cataract patients 3 months postoperatively using optical biometry obtained with a prototype version (axial length measurement, ALM, Carl Zeiss Jena) of the commercial partial coherence interferometry (PCI) instrument (IOLMaster, Carl Zeiss Jena).
Setting: Department of Ophthalmology, Vienna General Hospital, and Institute of Medical Physics, University of Vienna, Austria.
Methods: Forty-five patients with age-related cataract in both eyes were scheduled for bilateral cataract surgery. Axial length was measured preoperatively with a prototype (ALM) of the commercial PCI instrument as well as with immersion ultrasound (IUS). Immersion US was performed by a single experienced investigator. In each patient, the first eye was randomly assigned to receive an intraocular lens (IOL) using the Holladay IOL power formula based on ALM or IUS biometry. The other biometric technique was used in the contralateral eye. Subjective refractive outcome was assessed 3 months postoperatively.
Results: Refractive outcomes with the 2 techniques did not differ significantly (P = .28). The mean numerical error (MNE) (the difference between the refractive outcome 3 months postoperatively and the predicted spherical equivalent) was 0.13 diopter (D) and 0.03 D for the ALM and IUS, respectively. The mean absolute error (MAE) (the absolute value of MNE) was 0.48 D (range 0.00 to 1.58 D) and 0.46 D (range 0.01 to 1.92 D) with the ALM and IUS, respectively. By recalculating the surgeon factor retrospectively to correct the Holladay formula to obtain a postoperative MNE of zero, a theoretical MAE of 0.46 D was obtained with both biometry techniques.
Conclusions: Refractive outcome in cataract patients using PCI biometry was as good as that achieved with optimized IUS. However, the difference in axial length measured by the ALM compared to that measured by IUS must be considered when using the IOL A-constants supplied by the manufacturers.