Abstract
Purpose :
To investigate the effect of stimulus presentation duration and visibility (i.e. seen or unseen) on fixation stability in observers with age-related macular degeneration (AMD) and healthy controls, under the adaptation conditions of Standard Automated Perimetry (SAP).
Methods :
Fixation behaviour was measured with a high-speed eye-tracker (1000 Hz, EyeLink 1000-plus) in 11 participants with early-intermediate AMD (mean age: 74.2 years, range: 65-90) and 20 healthy observers (mean age: 67.8 years, range: 55-80) whilst performing a gaze-contingent perimetry test. Achromatic contrast thresholds were measured for a Goldmann III stimulus (0.43°) with six different presentation durations (range: 3.7-190ms) at eight test locations (four each at 2.5° and 5° eccentricity). Fixation stability was quantified by calculating the bivariate contour ellipse area (BCEA) for each stimulus presentation period (incorporating stimulus presentation and inter-stimulus interval) in all tests. A four-way ANOVA with the fixed-effects of disease status, stimulus duration, test location and stimulus visibility was used to identify factors influencing BCEA.
Results :
Statistically significant interaction effects were observed between disease status and stimulus visibility (F(1,9765)=9.8, P=0.002), in addition to disease status and stimulus duration (F(5,9765)=10.4, P<0.001) on BCEA. Main effect analysis demonstrated fixation stability to be lower for visible stimuli and longer stimulus durations across all observers, with BCEA values also being larger in AMD participants (all P<0.001). Post-hoc analysis revealed fixation stability in healthy observers to be lower with visible stimuli (P<0.001), with the 190ms stimulus also producing larger BCEA values compared to stimuli <190ms (all P<0.001). In the AMD group stimulus visibility had no significant effect on BCEA (P=0.07), but values were significantly larger for the 120 and 190ms stimuli compared to the 3.7ms stimulus (all P<0.05).
Conclusions :
Fixation behaviour under the conditions of SAP is influenced by stimulus visibility and presentation duration, with the relative effect of altering such parameters differing with disease status. Fixation stability may be improved in SAP through the use of stimuli <120ms, possibly due such stimuli being shorter than the minimum velocity of voluntary saccadic eye movements.
This is a 2020 ARVO Annual Meeting abstract.