Refractive versus keratometric astigmatism postkeratoplasty

In patients who had undergone penetrating keratoplasty, we compared the relationship between keratometric astigmatism and actual refractive cylinder required for visual correction in 115 eyes postoperatively. The average time from surgery to refraction was 49.5 months and from surgery to keratometry 50.3 months. Sixty-five eyes retaining their running 10-0 nylon sutures had an average of 5.43 diopters of keratometric cylinder and 2.95 D of refractive cylinder. The difference was highly statistically significant (P less than .001). This significant difference was true in eyes with keratoconus and Fuchs' endothelial dystrophy. In 50 eyes with all sutures removed, the average keratometry reading revealed 4.27 D of astigmatism while the cylindrical refraction required in spectacles averaged 3.70 D. The difference was not statistically significant (P = .018). The significant difference between astigmatism as measured by keratometry and by refraction in eyes with the sutures still in place should be taken into consideration when using suture removal or adjusting techniques after keratoplasty.