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Antonio Modarelli, Luca Mario Rossetti, Laura Ottobelli, Paolo Fogagnolo, David P Crabb, Giovanni Montesano; Spontaneous and evoked gaze movements in fundus perimetry. Invest. Ophthalmol. Vis. Sci. 2018;59(9):5131. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
To develop a novel method to distinguish and analyse spontaneous gaze movements and those evoked by stimulus projections in fundus perimetry.
31 glaucoma and 17 normal subjects performed a 10-2 visual field test with a Compass fundus perimeter (CenterVue, Padua) with ZEST threshold strategy. Individual stimulus presentations (dB) and fixation displacement tracks (degrees) were extracted.For each presentation, we calculated the Concordant Displacement (CD) as the orthogonal projection of the maximum gaze displacement on the direction of the presented stimulus (Figure 1 A). We estimated noise amplitude from negative CDs (gaze movements away from the stimulus), likely due to random gaze wandering. The 95% limit for negative CDs was used as noise cut-off and reflected around zero to detect significant gaze attractions (positive CDs). Projection intensities are expressed as Difference from the Final Threshold estimate (DFT) for each location. Two cut-offs were calculated for projections below or above threshold (Figure 1 B).We modelled the rate of significant CDs as a function of the DFT with a logistic model. From cut-off definition, we expected 2.5% false positive rate (FPR).Significant CDs were identified in the fixation tracks and the 95% Bivariate Contour Ellipse Area (BCEA) was used to assess their contribution to fixation stability estimate (Figure 2).
We detected a significant increase (p < 0.05) of significant CD rate with reducing DFT in 13 glaucoma and 6 normal subjects. In these subjects, on average, the significant CD rate reached above 5% (twice the FPR) at 4.5 ± 5.2 dB (Mean ± SD, p < 0.01) below the final threshold, indicating gaze attraction at intensities below measured sensitivity.In all subjects, BCEA was reduced removing evoked gaze movements (16% reduction in normals, 24% in glaucomas, p < 0.001, Figure 2).
Projections can evoke gaze attraction and influence estimates for fixation stability. Significant gaze attraction at lower-than-threshold sensitivities might help refine threshold estimation and reliability assessment.
This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.
Figure1. Example from one test: A) Calculation of CD for a presentation (red segment); B) Detection of significant CDs above noise cut-offs (red dots); the frequency of significant CDs (gaze attraction) starts to increase before reaching the estimated thresholds (all set at 0).
Figure2. BCEA reduction removing evoked gaze attractions
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