Effect of silicone sound speed and intraocular lens thickness on pseudophakic axial length corrections

We compared the sound speeds of SLM-1/UV (990 M/sec at 35 degrees Celsius [degrees C]), SLM-2/UV (1090 M/sec at 35 degrees C), and Perspex CQ poly(methyl methacrylate)(2658 M/sec at 35 degrees C). Methods are presented to determine the correction of axial length (CAL) factors for axial length measurements made on pseudophakes with AMO PhacoFlex Si-18, Si-26 (SLM-1/UV), and AMO PhacoFlex II SI-20 or SI-30 (SLM-2/UV) silicone intraocular lenses (IOLs). A CAL is required to avoid potential errors with secondary IOL power predictions; CALs, which are strongly dependent on the material sound speed and less so on lens thickness, ranged from -0.65 mm to -1.20 mm for SLM-1/UV silicone IOLs and from -0.35 mm to -0.55 mm for SLM-2/UV silicone IOLs. The sound speeds of IOL materials varied insignificantly between ambient room temperature (23 degrees C) and intraocular temperature (35 degrees C).