Astigmatic Keratotomy for the Correction of Astigmatism Workup

Updated: Apr 06, 2017
  • Author: James Hays, MD, MBA, MHA; Chief Editor: Douglas R Lazzaro, MD, FAAO, FACS  more...
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Imaging Studies

In order to produce accurate arcuate incisions, the use of corneal topographers and/or corneal tomographers is essential when visualizing the corneal landscape. Elevation maps can identify regular versus irregular astigmatism, the magnitude of the astigmatism, and its relationship with the overall contour of the anterior corneal surface. Fortunately, over the past ten years, both topographers and tomographers have become commonplace in ophthalmic practices, allowing for better preoperative and postoperative assessment of corneal contour.

Combined elevation and thickness measurements can be obtained from machines such as the Orbscan and Pentacam. Both technologies offer an added advantage over standard topographers: mapping the posterior corneal curvature, an area whose relevance had been overlooked for many years. Recently, some ophthalmic investigators have attributed improved refractive results when considering the contribution of the posterior corneal curvature to total corneal power. [18]

Since traditional astigmatic keratotomy (AK) nomograms are based on ultrasonic pachymetry measurements, one must correlate corneal thickness values measured with the Orbscan or Pentacam with those obtained from a standard ultrasonic pachymeter. Statistical differences between thickness readings from these machines have been reported. [19]