Computerized Topography to Rule-Out Keratoconus Prior to LASIK

Dr Raymond Stein of the Bochner Eye Institute wrote the following clinical update. We hope you find it of interest.

Keratoconus is a well-recognized contraindication to LASIK. The creation of a corneal flap and removal of tissue by an excimer laser can weaken a cornea making it structurally compromised. This can lead to corneal instability with progressive ectasia characterized by steepening and thinning. Although there are a variety of clinical signs of keratoconus the use of computerized topography and pachymetry usually allows for the detection of the earliest stages of keratoconus. The most advanced topography units measure both curvature, elevation, and pachymetry. The Pentacam is our unit of choice at Bochner.

We typically make the diagnosis of keratoconus when one or more findings are present:

1. Inferior steepening of greater than 1.5 Diopters compared to superior cornea.

2. Elevation of the posterior cornea of greater than 17 microns compared to a best-fit sphere.

3. Elevation of the anterior cornea of greater than 21 microns compared to a best-fit sphere.

4. Central steepening of greater than 49 Diopters.

5. Steepest corneal location associated with thinning of less than 500 microns.

6. Advanced clinical signs include corneal iron deposition at the base of the cone, Vogt’s striae or stress lines, and apical scarring.

In addition to the clinical findings above we are reluctant to perform LASIK if there is an immediate family history of keratoconus.

Careful preoperative evaluation prior to laser vision correction can greatly reduce the risk of corneal ectasia.

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