Evaluation of different techniques of measurement of the axial length in silicone oil-filled eyes

Purpose To evaluate different techniques of axial length measurement in silicone oil-filled eyes and compare the results of each with the original axial length measured before pars plana vitrectomy and silicone oil injection for accurate measurement of intraocular lens calculation in these eyes. Patients and methods This retrospective observational cohort case series study included 30 eyes of 30 patients who underwent pars plana vitrectomy and silicone oil injection. The axial length of the silicone-filled eye was measured by A-scan ultrasonography using two different ultrasound velocities: the normal ultrasound wave velocity, an adjusted velocity and the correcting factor. The axial length was also measured by optical biometry and compared to the original actual axial length. Results The mean preoperative axial length by A-scan biometry was 23.33±1.37 mm. The postoperative axial length by standard velocity multiplied by the correcting factor of 0.71 was 23.21±1.25 mm. The postoperative axial length, using a slower velocity of 1000 m/sec, was 21.06±1.34 mm. The axial length measured by optical biometry using a standard program postoperatively was 24.27±1.2 mm, which had the highest intraclass correlation coefficient of 0.948 and Cronbach’s alpha 0.973. The postoperative axial length measured by optical biometry of the silicone-specialized program was 23.1±1.43 mm. The difference between measurements of postoperative axial length, compared to the preoperative value, was statistically significant ( P <0.001). Conclusion The axial length of the silicone oil-filled eye by the standard program of optical biometry was the most accurate method compared to the preoperative axial length measured by A-scan ultrasonography. It can also be accurately measured by the silicone-specialized program of optical biometry. A-scan ultrasonography of the silicone oil-filled eye using the standard ultrasound wave velocity (1548 m/sec) and the correcting factor gives results almost as accurate as the optical biometry using the silicone-specialized program.