光学的方法による眼軸長測定法

Abstract

In IOL power prediction, an error of axial length significantly affects the accuracy of implant power calculation. For the purpose of improving the accuracy of axial length measurement, a noncontact optical method for axial length measurement in cataract surgery was developed. Using a newly developed portable infrared autorefractometer (GR-M3) and a contact lens, the author measured refractive states of aphakia just before IOL implantation in 54 cases. Ten measurements could easily be taken within 2 minutes. Using the ray tracing technique and a portable computer, refractive errors were converted into axial length immediately. Then IOL power calculation and IOL implantation were performed. The data of axial length acquired by this method are compared with data obtained from the conventional ultrasonic method. Between them, good correlation was obtained (r=0.981). In 51 cases (94%), differences between the new method and the ultrasonic method were smaller than 0.35 mm. In 3 cases, differences were larger than 0.36 mm. In these cases, the axial length obtained with the ultrasonic measurements were shorter than results obtained with the optical method. The measured results were converted into calculated values based on ray tracing and were compared with refraction data after operation, revealing that the axial length acquired by the optical method was more accurately measured than by the ultrasonic method. This method may contribute greatly to measuring axial length at cataract surgery.