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

https://doi.org/10.1016/j.ajo.2016.04.011Get rights and content

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.

Section snippets

Subjects

This prospective validity assessment was conducted at the Rotterdam Ophthalmic Institute, Rotterdam, Netherlands. Ninety-one eyes of 91 patients who underwent cataract surgery with implantation of a monofocal, non-toric IOL were enrolled. If both eyes of a patient were eligible for inclusion, the eye that was operated most recently was selected. Exclusion criteria were corneal diseases (eg, keratoconus, corneal scarring, pterygium), pseudoexfoliation syndrome, previous corneal or refractive

Results

Mean patient age was 69.4 ± 8.4 years (range 45.9–90.0). Forty-one patients (45%) were men, and 50 eyes (55%) were right eyes. The mean preoperative axial length was 23.92 ± 1.39 mm (range, 20.89–27.63), and the mean preoperative corneal power was 43.64 ± 1.48 D (range, 40.30–47.44). Measurements of acceptable quality could be obtained for the Pentacam and Cassini in 78 (86%) and 60 eyes (66%), respectively. An overview of the astigmatism magnitudes as measured with the different devices is

Discussion

The main outcome variable in this study was the accuracy of corneal astigmatism measurements, expressed as the vectorial difference between the corneal measurements and the refractive astigmatism. With mean values of 0.61 and 0.58 D for the Pentacam and Cassini, respectively, the accuracy for measurements of the anterior corneal surface of these devices was similar (independent-samples t test, P = .59). When measurements of the total instead of only anterior corneal astigmatism were performed,

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