Comparison of contact and immersion techniques for axial length measurement and implant power calculation

The contact technique for ultrasound biometry was compared to the immersion technique. One hundred eyes were measured by both methods. Two groups were created based upon the axial length measurement: a group of 46 short eyes (axial length less than 23.3 mm) and a group of 54 long eyes (axial length greater than 23.3 mm). In each group the different types of measurement influenced the results obtained for the anterior chamber depth and the axial length of these eyes such that the contact technique yielded shorter measuring values than the immersion technique. In considering both methods, the difference in the anterior chamber depth and the axial length was smaller in the first group. Shorter measurements produced stronger intraocular lens power, which is equivalent to the axial length shortening by using the contact technique. The effect on the implant power calculation and the postoperative deviation of the pseudophakos refraction is shown by comparing the theoretical formula with the SRK formula. This prospective study describes the greater range of refractive pseudophakos deviation when using the contact method.