Optical and ultrasound measurement of axial length and anterior chamber depth for intraocular lens power calculation.

PURPOSE

To evaluate the precision, reproducibility, and applicability of an optical method based on partial coherence interferometry for intraocular lens (IOL) power calculation.

SETTING

Ultrasound laboratory of a university eye hospital.

METHODS

A prospective comparison of measurements made by the IOLMaster optical instrument (Carl Zeiss) and Ultrascan Digital 2000 contact ultrasound A-scan (Alcon) for IOL calculations was performed. Examined were 255 eyes of 134 persons (204 phakic, 47 pseudophakic, and 4 aphakic). The mean age of the patients was 67.9 years (range 7 to 94 years).

RESULTS

The IOLMaster measurements were successful in more than 80% of cases: in 82%, 99%, and 99% for axial length (AL), anterior chamber depth (ACD), and keratometry measurements, respectively. The reproducibility of the AL and ACD measurements was very high (coefficient of variation 0.13% and 2.20%, respectively). The AL and ACD values were significantly larger with the IOLMaster (P <.001) than with the Ultrascan Digital 2000. The correlation between ultrasound and optical AL measurements was high (r = 0.985; P <.001); however, there was no correlation between ACD measurements (r = 0.079; P =.397). The corneal refractive power measurements of a Javal-type keratometer and the IOLMaster were highly correlated (r = 0.955; P <.001), with a mean difference of 0.2 diopter.

CONCLUSIONS

The results show that measurements for IOL calculation are easy and precise with the optical method. It is a noncontact method, so no anesthesia is needed and there is no risk of infection.