Clinical evaluation of intraocular lens calculations

The DBR-300 A-Scan ultrasonic unit was used to evaluate 100 patients preoperatively. Intraocular lens power was calculated using the formula supplied with the instrument and the accuracy of the instrument was then evaluated. It was determined that 54% of our patients were within +/- 1.00 diopter of the calculated refractive error and that 85% of the patients were within +/- 2.00 diopters and that 97% were within +/- 3.00 diopters. Only 3% of our patients had greater than a 3.00-diopter difference between predicted and actual postoperative refractive error. A standard 3.2-mm anterior chamber depth was utilized for Choyce lenses and 3.4 mm ACD was utilized for Medallion lenses. No single factor could be found to account for the slight tendency toward myopia, although several were found to contribute. No single factor was found to contribute to large errors, though the 3% of patients with greater than three diopters variation from the predicted refractive error demonstrated high degrees of cylinder or corneal astigmatism postoperatively as compared to preoperatively. Though we are presently in the process of reviewing ACD postoperatively, one would not suggest any drastic changes in the values at this time due to the overall accuracy obtained. Certainly though small adjustments may be made in the Binkhorst formula in the future, this is yet to be proven clinically.