Immersion versus contact technique in the measurement of axial length by ultrasound.

The axial length was measured by A-scan in 60 cataractous patients using a non-contact (immersion) and a contact technique. The mean axial length was found to be 23.49 mm with the immersion technique and 23.35 mm with the contact technique, using the same Sonometrics transducer probe. The difference of 0.14 mm (+/- 0.19) was significant at the 0.01 level. The difference should be taken into account when evaluating the accuracy of IOL calculation, and may call for different empirical corrections of the axial length with different ultrasonic equipment.