June 2015
Volume 56, Issue 7
Free
ARVO Annual Meeting Abstract  |   June 2015
Upper Limits of the Best Sphere Correction for Astigmatism in Threshold Visual Fields
Author Affiliations & Notes
  • Thomas Callan
    Clinical Affairs, Carl Zeiss Meditec Inc, Dublin, CA
  • Patricia Sha
    Clinical Affairs, Carl Zeiss Meditec Inc, Dublin, CA
  • Jennifer Luu
    Clinical Affairs, Carl Zeiss Meditec Inc, Dublin, CA
  • John G. Flanagan
    University of California, Berkeley, CA
  • Footnotes
    Commercial Relationships Thomas Callan, Carl Zeiss Meditec, Inc. (E); Patricia Sha, Carl Zeiss Meditec, Inc. (E); Jennifer Luu, Carl Zeiss Meditec, Inc. (E); John Flanagan, Carl Zeiss Meditec, Inc. (F)
  • Footnotes
    Support None
Investigative Ophthalmology & Visual Science June 2015, Vol.56, 1059. doi:
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    • Get Citation

      Thomas Callan, Patricia Sha, Jennifer Luu, John G. Flanagan; Upper Limits of the Best Sphere Correction for Astigmatism in Threshold Visual Fields. Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):1059.

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      © ARVO (1962-2015); The Authors (2016-present)

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Abstract
 
Purpose
 

To investigate the amount of spherical equivalent power that can be used in lieu of an astigmatic trial lens up to a decrease in mean deviation (MD) of 1 decibel (dB). The Humphrey Field Analyzer (HFA) advocates correction of astigmatism at 1.25 diopters of cylinder (DC).

 
Methods
 

Six normal subjects with previous perimetry experience and known spherical refractive errors were tested with the HFA 24-2 SITA Standard program. Two baseline visual fields were performed with the spherical refraction corrected for each subject. Additional visual fields were performed with myopic astigmatic refractive errors of 1.50, 2.00, 2.50, 3.00 and 3.50 DC induced using trial lenses. For these tests, the spherical equivalents of the refractive errors were corrected with the appropriate power spherical lens.

 
Results
 

The difference from the Baseline MD (average of the first two tests) was calculated for each visual field. The results of the different amounts of astigmatic blur corrected by utilizing the spherical equivalent and the effect on the MD are shown in Table 1. It was not until the astigmatic refractive error reached 3.50 D astigmatism did the mean deviation decrease by more than 1 dB.

 
Conclusions
 

Spherical equivalent lens correction of astigmatism is effective for refractive errors greater than the manufacturer’s recommendation of correction at 1.25 DC. In this study, astigmatic refractive errors up to 2 DC were corrected with the spherical equivalent before the mean deviation changed more than 0.5 dB, and 3DC for 1 dB.  

 
Table 1: Mean Deviation Difference for Each Astigmatism Amount (n=6)
 
Table 1: Mean Deviation Difference for Each Astigmatism Amount (n=6)

 
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