[Comparison of contact and immersion techniques of ultrasound biometry]

Biometry, i. e. the measurement of the eye axial length, is performed in patients before cataract surgery. Together with keratometry, it serves for the calculation of the intraocular lens refractive (dioptric) power. The purpose of our study was to determine whether contact and immersion A-scan ultrasound techniques produce comparable measurements of the eye axial length. The axial length of 120 non-paired eyes was measured, using both contact and immersion techniques. The measurements were performed by means of an Alcon Ocuscan machine. The mean eye axial length using the contact technique was 23.28 mm (min. 19.31 mm, max. 31.25 mm), compared to the mean of 23.38 mm (min. 19.38 mm, max. 31.36 mm) gained by the immersion technique. The standard deviation of the measurements using both techniques was less than 0.1 mm. A statistically significant difference was proved between the contact and the immersion techniques (p < 0.01). There is significant correlation between both methods (p < 0.01). The eye axial length gained by means of the immersion technique was on average 0.1 mm longer than that obtained by the contact technique. Biometry is of great importance for achieving accurate postoperative target refraction in cataract surgery that is a part of refractive surgery today. It will be necessary to carry out another retrospective study with a special focus on the target postoperative refraction in order to verify the accuracy of both the biometric techniques.