Accuracy of Total Corneal Astigmatism Measurements With a Scheimpflug Imager and a Color Light-Emitting Diode Corneal Topographer

PURPOSE: To determine the accuracy of total corneal astigmatism measurements with a Scheimpflug imager and a color light-emitting diode corneal topographer, and to compare the accuracy of total corneal astigmatism measurements with the accuracy of measurements that are based only on the anterior corneal surface.

DESIGN: Prospective validity assessment.

METHODS: This study was conducted at the Rotterdam Ophthalmic Institute, Rotterdam, Netherlands. The study population consisted of 91 eyes of 91 patients with monofocal, non-toric intraocular lenses (IOLs). Refractive astigmatism was measured with the ARK-530A autorefractor (Nidek, Gamagori, Japan). Anterior and total corneal astigmatism were measured with the Pentacam HR (Oculus, Wetzlar, Germany) and the Cassini (i-Optics, The Hague, Netherlands). Under the assumption that refractive astigmatism must equal total corneal astigmatism in these patients, accuracy of the corneal astigmatism measurements was defined as the vectorial difference with the refractive astigmatism, with lower vector differences denoting higher accuracy.

RESULTS: The median refractive astigmatic magnitude was 0.84 diopter (D). The mean difference vector lengths were 0.61 D, 0.58 D, 0.49 D, and 0.45 D for Pentacam anterior, Cassini anterior, Pentacam total, and Cassini total corneal astigmatism, respectively. The mean difference vector length decreased by 0.12 and 0.13 D for Pentacam and Cassini, respectively, if the total instead of anterior corneal astigmatism was measured. These decreases were statistically significant (P < .001).

CONCLUSIONS: With Pentacam as well as with Cassini, the accuracy of total corneal astigmatism measurements was higher than that of anterior corneal astigmatism measurements. Measuring total instead of anterior corneal astigmatism may therefore decrease the residual astigmatism in toric IOL implantation.