Partial coherence laser interferometry vs conventional ultrasound biometry in intraocular lens power calculations

Abstract

Aims. The purpose of the study was to compare optical biometry based on partial coherence laser interferometry (PCLI) principle to conventional ultrasound biometry in the accuracy of intraocular lens (IOL) power calculations. The role of partial coherence laser interferometry in pseudophakic axial length measurement was analysed in the study. Methods. In a prospective randomised clinical trial, 100 patients undergoing phacoemulsification cataract surgery were randomised to undergo biometry by either partial coherence laser interferometry (IOL Master) or the applanation ultrasound technique. The IOL material, design and the IOL formula were standardized. The mean error and mean absolute error were calculated and compared using paired t-tests. Results. One hundred patients were included in this prospective randomised trial, of whom 50 patients underwent optical biometry and 50 patients had biometry by applanation ultrasound. The mean age of patients in the PCLI group was 67 ± 6 yrs as compared to 71 ± 8 yrs in the ultrasound group (P > 0.05). The preoperative mean axial length was 23.47 ± 1.1 mm in the PCLI group (range 20-27.6 mm) and 23.43 ± 1.2 mm in the ultrasound group with a range of 20.1-27 mm (P > 0.05). The mean absolute error (MAE) in the PCLI group was 0.52 ± 0.32 D (upper and lower 95% CI 0.62 and 0.42 respectively). The MAE in the ultrasound group was 0.62 ± 0.4 D (upper and lower CI 0.73 and 0.50 D respectively). Eighty-seven per cent of patients were within ± 1 D in the PCLI group as compared to 80% in the ultrasound group (P = 0.24). The MAE of axial length difference with optical biometry was 0.13 mm ± 0.13 SD (range -0.42 to 0.78 mm) in the PCLI group and 0.19 ± 0.13 mm in the ultrasound group. There was a mean shortening of the eye length in the PCLI group postoperatively. Optical biometry improved the post op refraction by 16% on retrospective IOL power calculations. Eight per cent failed biometry with IOL Master (dense cataracts (4%) and fixation instability due to macular degeneration (4%)). Conclusion. The non contact optical biometry using the partial coherence laser interferometry principle improves the predictive value for postoperative refraction and is a reliable tool in the measurement of intraocular distances in pseudophakic eyes.