Comparison of measurements of the axial length of the eye using partial coherence interferometry and applanation ultrasound

Introduction
Accurate biometry is an essential component of cataract surgery. Preoperative measurement of axial eye length (AEL), rather than the corneal curvature, is the most critical factor for accurate calculation of the intraocular lens (IOL) power [].
Aim
The aim of this study was to compare axial eye length (AEL) measured by applanation ultrasound (U/S) biometry versus that measured by partial coherence interferometry in eyes with clear crystalline lenses and eyes with cataract.
Patients and methods
A prospective, nonrandomized study included 60 eyes which were divided into two groups. Group I: 30 eyes with clear crystalline lenses. Group II: 30 eyes with cataractous lenses. Each group is further subdivided into three groups: group a with short AEL (<22.00 mm), group b with average AEL (22.00–25.00 mm), and group c with long AEL (>25 mm). Complete ophthalmological examination was performed for every patient. AEL was assessed by applanation A-scan U/S and optical biometry using partial coherence interferometry.
Results
A total of 60 eyes were included in the study. In group I (clear crystalline lens group), the mean AEL by applantion U/S biometry was 24.23±3.73 mm which is shorter than the mean AEL measured by optical biometry which is 24.48±3.66 mm and the difference is statistically highly significant (=0.002). In group II (cataractous lens group), the mean AEL by applantion U/S biometry was 24.27±3.57 mm which is shorter than the mean AEL measured by optical biometry which is 24.46±3.43 mm and the difference between the two measurements was statistically nonsignificant (=0.077).
Conclusion
Optical biometry provides longer mean measurements than applanation U/S biometry in eyes with cataract or clear lens, which is represented by a negative difference of 0.05 mm in AEL measurements. These results suggest that applanation A-Scan U/S biometry underestimates AEL.