Pseudo axial length increase after silicone lens implantation as determined by ultrasonic scans.

Repeat A-scans of 45 patients who had silicone intraocular lens (IOL) implantation indicated an apparent increase in the axial length of the eyes. The average increase of 1.045 mm over the original axial length was noted when using the pseudophakic mode for the axial length determination. The actual velocity of sound in eyes with a silicone IOL is 1,486 M/sec compared to 1,548 M/sec in an eye with a polymethylmethacrylate implant. This finding is clinically significant when one is comparing the axial length of two eyes, one of which is pseudophakic. A 1 mm difference in axial length can cause serious doubts about the validity of one or the other of the scans if the type of implant is not known. The velocity of RMX-3 silicone was determined to be 1,049 M/sec.