Measuring intraocular lens power within the eye

Abstract

Although various methods exist for confirming the power of an intraocular lens (IOL) prior to implantation, few clinicians perform this step due to the improved quality control by manufacturers, 5, 6, 7, the risk of contamination and the increased surgical time. After the lens has been implanted, however, there has been no method described for directly measuring the power. We present a method using slit lamp photography which measures with an average error of only 0.25 D the IOL power within the eye.

A method is described for determining the power of an intraocular lens (IOL) within the eye by measuring the horizontal dimension of the corneal reflected image (Purkinje-Sanson I) and the anterior IOL reflected image (Purkinje-Sanson III) as seen through a standard slit lamp with a target approximately 68 mm in front of the cornea. The horizontal K-reading (180 degrees) and the anterior chamber depth are the two other parameters necessary to calculate the exact power of the IOL. Seven tables have been provided which utilize these four measurements, eliminating the need for complex calculations.

To determine the accuracy of his technique, ten implanted IOL’s ranging from 9 D to 27 D were chosen, their power calculated and compared to the actual IOL power. The largest error was 0.5 D and the average error was 0.25D.