Meridional analysis for calculating the expected spherocylindrical refraction in eyes with toric intraocular lenses

To present a method of calculating the expected spherocylindrical refraction after toric intraocular lens (IOL) implantation and to compare it with the actual outcomes in a small group of patients.

Eye Institute, Tan Tock Seng Hospital, Singapore.

The expected refractions of the 2 principal meridians of the cornea (maximum keratometry and minimum keratometry) were calculated separately using the Holladay 1 formula with a modification to the data used for the effective lens position. The expected refraction was compared with the actual outcomes in 7 eyes that had phacoemulsification with toric IOL implantation.

The mean preoperative keratometric cylinder was 2.07 diopters (D) +/- 0.97 (SD) (range 1.25 to 3.75 D), and the mean postoperative cylinder by subjective refraction was 0.68 +/- 0.40 D (range 0.25 to 1.50 D). The mean expected cylindrical refraction was 0.62 +/- 0.46 D (range 0.30 to 1.60 D). Five eyes (71.4%) were within +/-0.25 D of the expected refraction, and all eyes were within +/-0.50 D. There was a significant reduction in cylinder after toric IOL implantation (P<.001, paired t test). There was no statistically significant difference between the magnitude of the expected cylindrical refraction and the actual postoperative cylinder by subjective refraction (P = .604).

Calculation of the expected spherocylindrical refraction with toric IOLs was achieved using meridional analysis.