Changes in keratometric corneal power and refractive error after laser thermal keratoplasty

Abstract

Purpose: To evaluate the effect of laser thermal keratoplasty (LTK) on corneal power and refractive error to develop a logical approach to calculating accurate intraocular lens (IOL) power for cataract surgery. Setting: Department of Ophthalmology, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul, Korea. Methods: Laser thermal keratoplasty was performed in 27 eyes of 23 patients. Preoperatively and postoperatively, the refractive error was measured and the corneal power obtained by manual keratometry and topography. The changes in keratometric corneal power and refractive error after LTK were compared. Results: The mean age of the 15 women and 8 men was 45.0 years ± 4.6 (SD) (range 43 to 61 years). The mean preoperative refractive error was +1.43 ± 0.97 diopters (D) (range 0 to +3.63 D) at the spectacle plane and +1.46 ± 1.01 D (range 0 to +3.79 D) at the corneal plane. The mean postoperative refractive error was −0.44 ± 1.07 D (range −2.24 to +2.18 D) at the spectacle plane and −0.44 ± 1.08 D (range −2.18 to +2.23 D) at the corneal plane. After surgery, corneal powers measured by manual keratometry were significantly smaller than those measured by topography ( P<.001) and refractive error changes were significantly smaller than keratometric changes ( P<.001). Conclusions: After LTK, corneal power measured by manual keratometry was smaller than that measured by corneal topography and changes in corneal power measured by conventional keratometric instruments were greater than changes in refractive error. This difference should be considered in calculating IOL power in post-LTK eyes to prevent undesirable hyperopia after cataract surgery.