Intraocular Lens Power Determination Research Articles

A simple BASIC computer program to individualize the SRK formula.

A computer program written in BASIC language that calculates, updates, and stores the A value used in the formula for the determination of intraocular lens power is presented. It has the structure of a subroutine, and can either be easily integrated into an already existing larger program or it can function independently of another program.

The clinical use, accuracy, and reliability of the Veri-Vu lensometer.

One hundred forty-six lenses from 11 manufactures were tested with the Veri-Vu lensometer and optical power plus resolution compared with results from an optical bench. Accuracy was found to be +/- 0.2 diopter in 95% of the lenses tested. The greatest error was 0.37 D. The lensometer correctly identified 125 of 128 lenses that were greater than 160 line pairs per millimeter (LP/mm) resolution and correctly identified nine lenses that had less than 100-LP/mm resolution. All other important optical aberrations were identified with the lensometer. The greatest problem was the variation from company to company in terms of the calculated power in aqueous as determined from the back focal length in air. This, however, was felt to be an asset for those doing A-scan intraocular lens power determination in giving one simple reliable power for all lens companies.

An inexpensive ultrasonic device for intraocular lens power determination

The Echo-oculometer is a relatively inexpensive ultrasonic device for measuring anterior chamber depth and axial length prior to lens implantation. It is uncomplicated, easy to use and functioned very well in this limited study, giving an average error of 0.98 D when preoperative measurements were compared to postoperative refraction.

Pitfalls in the Determination of Intraocular Lens Power Without Ultrasound

The rule is simple: An 18 diopter intraocular lens tends to restore the basic refraction. For each diopter of basic refraction to be corrected add or subtract 1.25 diopters. To determine the basic refraction a careful history and an examination of old glasses and past refraction records is necessary. When the basic refraction cannot be ascertained, capital errors may occur. Given the basic refraction, errors or several diopters are still apt to occur. Calculation of intraocular lens power based on K-readings and ultrasonic measurements is therefore always advisable and a must when there is doubt about the basic refraction.