Measurement of corneal curvature after corneal transplantation and radial keratotomy using standard and automated keratometry.

Keratometry readings obtained with a standard Bausch & Lomb keratometer were compared to readings obtained with a Humphrey automated keratometer in 50 eyes that had undergone radial keratotomy and 40 eyes that had undergone corneal transplantation. Both instruments recorded similar results for the flat, steep, and mean keratometry meridians, but they produced significantly different results in determination of keratometry-measured astigmatism and axis of astigmatism. Differences in readings were greater (with the automated keratometer recording more astigmatism than the Bausch & Lomb keratometer) following corneal transplantation than radial keratotomy. It is suggested that only one or the other instrument be used for a clinical study because of the potential differences that can occur when measuring postsurgical astigmatism.