Audit on A-scan use prior to cataract surgery in Mater Dei Hospital

Abstract

The A-scan is a method of measurement of the ocular axial length (L). It is coupled with corneal curvature keratometry (K) readings so that one can measure the required power (P) of an intraocular lens (IOL) used for cataract surgery. The Sanders, Retzlaff and Kraft (SRK) formula calculates the required P of the IOL as P = A − 2.5L − 0.9K where A is the specific IOL constant. The power of the lens determines the refraction of the image onto the retina and thus determines the visual acuity of the eye. The axial length of the eye is measured by the time a signal takes to be reflected back to the source, like ultrasound or light. Distance is calculated by the velocity formula, depending on the speed of the signal. In Mater Dei hospital, two methods are used to determine the axial length of the eye prior to cataract surgery, namely an ultrasound method and an optical method.