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Multicenter Study
. 2017 May 1;58(6):BIO268-BIO276.
doi: 10.1167/iovs.17-21710.

Metrics and Acquisition Modes for Fixation Stability as a Visual Function Biomarker

Etienne M Schönbach  1 , Mohamed A Ibrahim  1 , Xiangrong Kong  1   2 , Rupert W Strauss  1   3   4   5   6 , Beatriz Muñoz  1 , David G Birch  7 , Janet S Sunness  8 , Sheila K West  1 , Hendrik P N Scholl  1   6
Affiliations
Multicenter Study

Metrics and Acquisition Modes for Fixation Stability as a Visual Function Biomarker

Etienne M Schönbach et al. Invest Ophthalmol Vis Sci. .

Abstract

Purpose: To compare different metrics and acquisition modes of fixation stability as a new visual function biomarker in a large cohort of patients with ABCA4-related Stargardt disease from the multicenter prospective ProgStar study.

Methods: Fixation was tested during a separate fixation exam and also dynamically during a sensitivity exam, using fundus-tracking microperimetry (Nidek MP-1). Fixation data were analyzed using the bivariate contour ellipse area (BCEA), the 2/4 degree method, and the Fujii classification.

Results: In a total of 235 patients, the mean BCEA was larger when measured during the sensitivity exam (418 eyes; 12.5 vs. 4.6 deg2 during the fixation task in 427 eyes). Correlations between the two tests were generally weak. Fixation stability during the sensitivity test was significantly correlated with visual acuity. Comparing the BCEA values and the corresponding Fujii categories for these eyes revealed ranges of overlap where an eye with one defined BCEA value can fall into each of the three Fujii categories.

Conclusions: Patients may have limited ability to fixate over defined time periods, which leads to significant differences between shorter and longer measurements of fixation stability. The most appropriate way to use this functional biomarker appears to be using continuous metrics for fixation stability, such as the BCEA, during a macular sensitivity test.

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Figures

Figure 1
Figure 1
Fixation was tested during a separate fixation task (A) where the patient was instructed to focus on the center of a red cross. Blue dots represent the recorded fixation events. Afterward, fixation was determined during a sensitivity exam (B). Here, a higher number of fixation points is available as a result of the longer test duration. Fixation events also seem to be more widely scattered during the sensitivity exam.
Figure 2
Figure 2
Correlation of the bivariate contour ellipse area with the percentage of fixation points within 2° (A, B) and 4° (C, D) during a separate fixation test (A, C) and the macular sensitivity test (B, D).
Figure 3
Figure 3
Box plots showing the distribution of different bivariate contour ellipse areas across different Fujii categories. 1SD-BCEA, bivariate contour ellipse area with one standard deviation.
Figure 4
Figure 4
Correlation of the bivariate contour ellipse area as measured during the fixation (A) and sensitivity (B) test with visual acuity. BCVA, best-corrected visual acuity; 1SD-BCEA, bivariate contour ellipse area of one standard deviation.
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