Purpose: To study changes in astigmatism throughout a 20-year period using keratometry and refraction in patients who underwent penetrating keratoplasty (PKP) for keratoconus.
Methods: We reviewed the charts of patients who underwent PKP for keratoconus from 1975 to 1979 and recorded preoperative refraction, stage of keratoconus, laterality of surgery, graft size, suture technique, time of suture removal, keratometry, subjective refraction at 1, 3, 5, 7, 10, 15, 20, and 25 years after suture removal, and slit-lamp findings.
Results: Eighty eyes with a mean follow-up of 20 years (range, 15-25) were included in the study. Graft size, suture technique, and time of suture removal had no significant influence on the astigmatism at the last examination. We observed a stabilization of keratometric astigmatism in the first 7 years (4.05 +/- 2.29 D 1 year after suture removal, 3.90 +/- 2.28 D at year 3, 4.03 +/- 2.49 D at year 5, 4.39 +/- 2.48 D at year 7) followed by a progressive increase from 10 years after suture removal until the last follow-up visit (5.48 +/- 3.11 D at year 10, 6.43 +/- 4.11 D at year 15; 7.28 +/- 4.21 D at year 20, and 7.25 +/- 4.27 D at year 25). The mean absolute value of the difference vector (DV) calculated by vector analysis was 7.17 +/- 4.35 D (0-18.33). In 70% of cases, progression of the astigmatism was evident with mean absolute DV of 9.10 +/- 3.65 D. There was a significant correlation between the preoperative and final axis of astigmatism (Pearson r = 0.39, p = 0.0008). There was also a slight positive correlation coefficient between the DV of the eyes in bilateral cases, but it was not significant (Spearman's r = 0.2226, p = 0.34). The major late slit-lamp finding was a peripheral crescent-shaped thinning at the graft-host junction with absence of Bowman's layer on histopathology.
Conclusion: In spite of refractive stability obtained during the first years after PKP for keratoconus, increasing astigmatism thereafter suggests that there is a progression of the disease in the host cornea.