Prospective corneal topographic analysis in surgery for postkeratoplasty astigmatism

Computer-assisted photokeratoscopy was used to evaluate the topographic characteristics of corneas preoperatively and postoperatively in seven patients who underwent surgery for correction of postkeratoplasty astigmatism. The steep hemimeridians were typically separated by an angle other than 180 degrees (mean, 162.5 degrees) and the flat hemimeridians were often not orthogonal to the steep hemimeridians. Asymmetry of power (1.5 or more diopters) between these two major hemimeridians was also observed in three patients. Relaxing incisions were placed in the two steep hemimeridians and compression sutures were placed in the flat hemimeridians. The mean percent of reduction of astigmatism (vector-corrected) was 81.1%. The amount of keratometric astigmatism, and the degree of asymmetry of the hemimeridians were not correlated with the percent of reduction of astigmatism after placement of the relaxing and compression sutures. Computer-assisted topographic analysis may prove useful in planning transverse keratotomies centered on the steep hemimeridians and in placement of compression sutures in flat hemimeridians.