Evaluation of Immersion Ultrasound Biometry in Eyes That Cannot Be Measured by Partial Coherence Interferometry

Purpose: To compare the axial length (AL) measurements by immersion and applanation ultrasound biometry in eyes with preoperative AL that could not be measured by partial coherence interferometry.<BR>Subjects and Methods: Subjects were 36 pseudophakic eyes of 28 patients whose AL could not be measured by partial coherence interferometry (IOL Master^®, Carl Zeiss Meditec, Germany) before cataract surgery but 3 months after surgery. All the subjects underwent ultrasound biometry preoperatively with both immersion (A-Scan Plus^®, Acuttome) and applanation (US-4000, NIDEK) techniques. We compared the preoperative AL measurements by these two methods with the measurement by IOL Master^® at 3 months after surgery. The Wilcoxon signed-rank test was performed and a p-value less than 5% was considered statistically significant. <BR>Results: The mean preoperative ALs by immersion and applanation techniques were 24.06 ± 1.50 mm and 23.88 ± 1.40 mm, respectively. The mean AL by immersion technique was significantly longer than that by applanation technique (P < 0.0001). The mean postoperative AL by IOL Master^® (24.00 ± 1.40 mm) did not significantly differ from the mean AL by immersion technique (P = 0.44) but from the mean AL by applanation technique (P = 0.002). In addition, 92.0% and 84.0% of the eyes with standard AL (22.0 mm to 24.5 mm) measured by immersion and applanation techniques respectively had a difference within ± 0.2mm from the IOL Master^® measurements. In the eyes with long AL (> 24.5 mm), the corresponding percentages were 33.3% and 44.4% for immersion and applanation techniques, respectively.<BR>Conclusion: The current study suggested that in the eyes with standard AL, the AL measurement by immersion ultrasound biometry could be used with the same IOL Master^® parameters for the intraocular lens power calculation even if the eyes could not be measured by partial coherence interferometry preoperatively. However, in the eyes with long AL, the measurements by immersion and applanation techniques all varied widely and better proficiency would be required.