To establish the accuracy of the newly released biometer Ocuscan RxP® (Alcon, USA) by comparison with the established Ultrasonic Biometer Model 820® (Allergan Humphrey, USA), and to compare the accuracy of contact and immersion biometries.

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® biometer using both contact (Method 1) and immersion (Method 2) techniques. As a reference, a contact type Ultrasonic biometer 820® (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.

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.

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.