Patients with Parkinson disease (PD) exhibit different visual searching behaviors depending on disease severity, and they vary from those of healthy control individuals, according to a study published in the Journal of the Neurological Sciences.
Researchers recruited 13 patients with PD (mean age 67±9.2 years, 12 men, average disease duration 11.38±5.39 years) and 7 age-matched controls (mean age 64.29±7.54 years, 4 men) for the analysis. They evaluated participants’ eye movement during gaze holding tasks, while viewing a blank scene, and while performing visual search tasks. The gaze holding task involved monocular and binocular fixation on a target for 45 s. The blank screen activity required participants to click on randomly appearing objects on a 50% gray screen. Visual search analysis involved searching for items in a cluttered environment. Researchers assessed motor function through the Unified Parkinson’s Disease Rating Scale (UPDRS-III).
Investigators determined that participants with PD had fewer correct responses than control individuals during the visual search task (F[1,37], 10.873; P =.002), even when given extra time (F[1,37], 6.813; P =.013). They scored lower when researchers placed the targets in unexpected positions (t, 2.904; P =.009) and had longer response time durations. The team noted that a longer duration to the first response was negatively correlated with success in identifying the target (r, −0.891; P <.001).
Investigators observed higher fixational saccade frequencies (F[1,14], 13.948; P =.002), lower non-fixational saccade frequencies (F[1,14], 7.993; P =.013), larger fixational saccade amplitudes (F[1,1362.64], 18.235; P <.001), and smaller non-fixational saccade amplitudes (F[1,1349.4], 20.563; P <.001) in individuals with PD compared with the control group.
When the team placed targets in an unexpected location, final score, first score, and time to first response correlated with age. Total UPDRS-III scores correlated with reaction time and time to initial response when investigators placed targets in expected locations.
“Our results suggest that during visual search tasks, compared to their healthy counterparts, the PD participants spend a long time reaching the [region of interest],” according to the investigators. “In addition, PD participants make more fixational saccades with larger amplitudes and fewer non-fixational saccades with smaller amplitudes while gazing at the blank screen. The trend reverses while viewing complex images depicting a natural visual scene. There is a strong correlation between the matrix of visuomotor behavior during visual search tasks and the overall clinical severity of the disease.”
Study limitations include a small sample size and the overrepresentation of men among participants with PD.
Beylergil SB, Kilbane C, Shaikh AG, Ghasia FF. Eye movements in Parkinson’s disease during visual search. J Neurological Sci. Published online May 28, 2022. doi:10.1016/j.jns.2022.120299