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Rethinking the optimal methods for vector analysis of astigmatism
Douglas D Koch1, Li Wang, Adi Abulafia
1From the Cullen Eye Institute, Department of Ophthalmology, Baylor College of Medicine (Koch, Wang, Holladay), Houston, Texas, USA; Department of Ophthalmology, Shaare Zedek Medical Center, Affiliated to Hadasa Faculty of Medicine, The Hebrew University (Abulafia); Jerusalem, Israel, East Valley Ophthalmology (Hill), Mesa, Arizona, USA.
Purpose:
To evaluate the accuracy and usefulness of certain methods of analyzing astigmatic vectors.
Setting:
Cullen Eye Institute, Baylor College of Medicine, Houston, Texas.
Design:
Case samples.
Methods:
Using 2 sample cases for analysis of corneal surgically induced astigmatism and an actual toric intraocular lens (IOL) case, univariate analyses from the ASSORT program were compared to double-angle plots of preoperative and postoperative astigmatism and prediction errors.
Results:
Certain univariate figures for analyzing the 2 sample cases were misleading. For the toric IOL case, some of the key outcome vectors were inaccurate.
Conclusions:
ASSORT's univariate analysis of astigmatic vectors can be unpredictably erroneous and misleading. Recommended vector analyses should include double-angle plots with centroids and confidence ellipses of preoperative and postoperative astigmatism and the prediction errors, along with means and standard deviations of these vector magnitudes.
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