Refractive error after triple and non-simultaneous procedures: is the application of a standard constant keratometry value in IOL power calculation advisable?

Purpose: The purpose of this investigation was to determine whether or not the use of a standard constant keratometry value in cases of preoperative abnormal keratometry values in biometry for triple procedures is advisable.

Methods: Cataract surgery and penetrating keratoplasty were performed in 82 eyes; 53 eyes underwent triple procedures and 29 eyes underwent non-simultaneous procedures. A standard constant keratometry value of 42.50 D was applied in 18 triple-procedure eyes because the preoperative measured keratometry values were outwith the normal range (41-47 D). The spherical equivalent and expected values were compared after a mean follow-up of 20.5 months.

Results: Cases in the triple-procedure group that achieved spherical equivalent within +/- 2.0 D of expected values included nine of 18 eyes (50%) in which a standard constant keratometry value of 42.50 D was applied, three of 17 eyes (18%) in which keratometry values outwith the normal range were applied (p = 0.044), and eight of 18 eyes (45%) in which keratometry values within the normal range were applied (p = 0.862). Cases in the non-simultaneous procedure group that achieved spherical equivalent within +/- 2.0 D of expected values included 22 of 24 eyes (92%) in which keratometry values within the normal range were applied (p = 0.0025), and five of five eyes (100%) in which a standard constant keratometry value was applied.

Conclusions: The application of a standard constant keratometry value of 42.50 D for intraocular lens power calculation in triple procedures can be recommended if abnormal keratometry values were measured previously. If possible, non-simultaneous procedures should take priority.