The accuracy of ultrasonography in 5 500 mPas silicone-tamponade eyes

Abstract

Background The ultrasonography for silicone tamponade eye is a problem in diagnosis and treatment of eye diseases, especially for the calculation of intraocular lens (IOL) power.IOL Master is usually used to the biometric measurement of the silicone tamponade eye in well-equipped hospital, but it is still disabled in serious cataractous eyes.Corrective B or A-type ultrasound methods have been used for a fewer years, but these measured results are incomparable probably due to the difference of viscosity of silicone oils. Objective This study attempted to investigate the accuracy of B-type ultrasonography for ocular axial length (AL) measurement in silicone tamponade eyes. Methods The transmitting speed of ultrasonic wave in the silicone oil was determined by comparing the outcomes between balance solution mesuring and 5 500 mPas silicone oil, and a calculating formula for corrective ocular AL in 5 500 mPas silicone filled eyes was further established.Thirty-two eyes of 30 patients who received 5 500 mPas silicone oil tamponade due to complex retinal detachment were enrolled in Qingdao Hiser Medical Group from May 2012 to March 2014.The eyes were assigned to the AL<26 mm group (18 eyes of 16 patients) and AL≥26 mm group (14 eyes of 14 patients). B-scan ultrasound and IOL Master were used to measure the AL before the removal of the silicone oil, and the Als were measured again using A-scan ultrasound and B-scan ultrasound 3 months after the removal of the silicone oil.The outcomes were compared and the correlations were evaluated among different measuring methods.The vitrous length values before and after removal of the oils, and the diopters before and after intraocular pressure (IOP) implantation were compared to varify the results of B-type sonography for 5 500 mPas silicone-tamponade eyes. Results The transmitting speed of sound wave in 5 500 mPas silicone oil was 1 023 m/second with the conversion factor 0.668 between silicon oil eyes and vitreous cavity, and the corrected formula for AL measurement was: the length form cornea apex to the posterior pole of lens or the center of the capsular membrane+ 0.668×the length form posterior pole of lens or the center of the capsular membrane to the macular area.No significnant differences were found in the AL values among the corrective-B scan, IOL Master method, postoperative B-scan method and A-scan method both in the AL<26 mm group and the AL≥26 mm group (AL<26 mm: F=0.108, P=0.955; AL≥26 mm: F=0.011, P=0.998), and the AL values by corrective B-scan was significantly correlated with that by IOL Master, postoperative B-scan and A-scan, respectively (AL<26 mm group: r=0.876, 0.921, 0.809, all at P<0.01; AL≥26 mm group: r=0.943, 0.956, 0.955, all at P<0.01). The vitreous cavity depth was (20.78±2.13)mm by corrective B-scan in 1 day before the removal of silicone, and that in 3 months after removal of silicone was (20.89±2.16)mm, without statistical diference between them (t=0.795, P=0.219). The actual postoperative refraction in 16 eyes with IOL was (-1.25±1.69)D, and preoperative refrection was (-1.50±0.00)D, the difference was not statistically significant (t=0.585, P=0.284). Conclusions The biometry of B-scan ultrasonography for silicone-tamponade eye is accurate and simple, with a good feasibility in clinical measurement. Key words: Biometry/methods; Eye/ultrasonography; Lenses, intraocular; Silicone oils/therapeutic use; Viscosity; Axial length, ocular; Diagnostic techniques, ophthalmological/instrumentation; Humans