Comparative Analysis of Contact and Immersion Technique in Ultrasonographic Biometry

ABSTRACT

PURPOSE: To establish the accuracy of the newly released biometer Ocuscan RxP(R) (Alcon, USA) by comparison with the established Ultrasonic Biometer Model 820(R) (Allergan Humphrey, USA), and to compare the accuracy of contact and immersion biometries. METHODS: This is a prospective study involving 27 patients (40 eyes) who were scheduled for cataract surgery and had axial lengths measured with an Ocuscan RxP(R) biometer using both contact (Method 1) and immersion (Method 2) techniques. As a reference, a contact type Ultrasonic biometer 820(R) (Method 3) was also used. IOL(Intraocular Lens) power for the cataract surgery was calculated using this result. An axial length which would have caused no post-operative refractive error was reversely calculated from the difference of target diopter and post-operative refractive error. This length was compared with the axial lengths obtained via Methods 1, 2 and 3. RESULTS: The means and standard deviations for the measurement sets were compared. Methods 1 and 2 showed no significant difference (23.22+/-0.68, 23.24+/-0.69 mm, p=0.55). The axial length measured by Method 3 was 23.32+/-0.67 mm. The difference between the target refraction and post-operative refractive error was 0.29+/-0.60D. The axial length was reversely calculated from the difference (23.07+/-0.84 mm). The differences between the reversely calculated axial lengths and those of Methods 1, 2 and 3 were 0.15+/-0.31, 0.17+/-0.31 and 0.24+/-0.28 mm, respectively. CONCLUSIONS: Biometric results from Methods 1 and 2 caused less refractive error than did Method 3. The contact and immersion methods are both accurate for IOL power calculation if performed by a well-skilled examiner.