EVALUATION OF INTRAOCULAR-LENS POWER CALCULATION FORMULAS IN THE TRIPLE PROCEDURE

Purpose: To determine whether the choice of intraocular lens (IOL) pow er formula improves IOL power predictions and whether personalized con stants within the IOL power formula are critical factors in improving refractive predictions after combined penetrating keratoplasty, catara ct extraction, and IOL implantation. Methods: Records of 46 patients w ho had the triple procedure between January 1988 and December 1992 wer e evaluated using the SRK II, SRK/T, Holladay, and Hoffer Q formulas t o predict the postoperative spherical equivalent refractions for impla nted lens power. Calculations were carried out with and without the us e of personalized constants. The predictive accuracy of each formula w as assessed by comparing the actual postoperative spherical equivalent refractive error with that predicted by the formulas. The predictive error and the distribution of predictive errors were used to assess pr edictive accuracy. Results: There was no difference in the mean absolu te predictive errors and the distribution of predictive errors for the four formulas evaluated (P > .05). The use of personalized formula co nstants significantly reduced the mean absolute predictive error for t he SRK II, SRK/T, and Holladay formulas (P < .05) and approached signi ficance for the Hoffer Q formula. Conclusion: The findings suggest tha t the choice of IOL power formula does not affect IOL power prediction s in the corneal triple procedure; however, personalized constants wit hin a formula appears to be a critical factor in improving postoperati ve refractive predictions.