Videokeratography, keratometry, and refraction after penetrating keratoplasty

To identify the correlation between videokeratography, autorefractometry, autokeratometry, and keratometry measurements and the subjective manifest refraction and spectacle-corrected visual acuity after penetrating keratoplasty.

We studied 100 eyes from 100 patients that had undergone penetrating keratoplasty. All eyes were examined by videokeratography (EyeSys 2000) (axial, tangential, and refractive power maps), autorefractometry, autokeratometry, and keratometry. Measurements were made at an an average of 19 +/- 9 months after surgery. Postoperative refractive astigmatism, spherical equivalent refraction, and spectacle-corrected visual acuity were studied by regression analysis.

Both the total topographic cylinder measured by the refractive power map and topographic cylinder measured by the axial power map showed the strongest correlation with the manifest refractive cylinder (rs = +0.89, P < .001). The axis of astigmatism determined by keratometry and autokeratometry showed the strongest correlation with the subjective manifest refraction axis (rs = +0.87, P < .001). The total topographic cylinder showed the strongest correlation with the spectacle-corrected visual acuity (rs = +0.38, P = .001); however the topographic indices of predicted corneal acuity, corneal acuity, corneal uniformity index, asphericity, and refractive power symmetry did not correlate with spectacle-corrected visual acuity.

Measurement of astigmatism after penetrating keratoplasty can be made more accurate by using videokeratographic measurements to supplement retinoscopic and manifest refraction. Other useful methods for predicting the axis of refractive astigmatism include keratometry, autokeratometry, and autorefractometry. In this study, indices designed to measure corneal surface irregularity failed to predict visual acuity after penetrating keratoplasty.