Abstract
Purpose
The ability to smoothly pursue a moving target with eye movements is known to be impacted in macular degeneration (MD). Specifically, smooth pursuit gain is lower and more variable in MD than in age-matched controls (Shanidze et al, 2016). Here we examine whether the addition of a dynamic acuity task modulates pursuit gain in macular degeneration.
Methods
Ten participants (6 MD, 4 age-matched Controls) were tested in the confocal scanning laser ophthalmoscope (Rodenstock SLO-101), which allows for direct visualization of the moving target on the retina. Participants were asked to acquire and track a target for the entirety of the trial. The target was an annulus that changed briefly to a Landolt C and moved horizontally to the left or the right in a modified step-ramp (Rashbass, 1961), at 5 degrees/s. Participants were asked to identify the orientation of the Landolt C, which had one of 4 possible orientations and appeared for 300 ms at 4 different time points in the trial.. Target size was adjusted to achieve an accuracy of 75% during static presentation, and ranged from 0.5 to 5.3 degrees.
Results
Pursuit gains during the presentation of the Landolt C target were significantly lower for MD participants, compared to controls (p = 0.022). More importantly, across 10 eyes of MD participants (4 with bilateral scotomata, 2 with unilateral scotoma), the ability to identify the target orientation (d’) was significantly correlated with pursuit gain (Pearson correlation, r = 0.645). Although the distance of the preferred retinal locus to the target was much larger in MD participants than in controls, there was no systematic relation between d’ and distance to the target, indicating that low pursuit gain rather than increased distance to the target determines dynamic visual acuity in MD. As for catch-up saccades that are characteristic of lower pursuit gains, participants with MD had significantly fewer catch-up saccades than controls (p = 0.0025), perhaps because their pursuit is not foveal (Heinen et al., 2016).
Conclusions
Our results indicate that the failure to stabilize the target on the eye due to low pursuit gain impairs the ability to discriminate a moving target, and thus impacts dynamic visual acuity in MD.