Probing the mechanism of saccade-associated head movements through observations of head movement propensity and cognition in the elderly

Head and Gaze Behavior in Retinitis Pigmentosa

Purpose

Peripheral visual field loss (PVFL) due to retinitis pigmentosa (RP) decreases saccades to areas of visual defect, leading to a habitually confined range of eye movement. We investigated the relative contributions of head and eye movement in RP patients and normal-sighted controls to determine whether this reduced eye movement is offset by increased head movement.

Methods

Eye-head coordination was examined in 18 early-moderate RP patients, 4 late-stage RP patients, and 19 normal-sighted controls. Three metrics were extracted: the extent of eye, head, and total gaze (eye+head) movement while viewing a naturalistic scene; head gain, the ratio of head movement to total gaze movement during smooth pursuit; and the customary oculomotor range (COMR), the orbital range within which the eye is preferentially maintained during a pro-saccade task.

Results

The late-stage RP group had minimal gaze movement and could not discern the naturalistic scene. Variance in head position in early-moderate RP was significantly greater than in controls, whereas variance in total gaze was similar. Head gain was greater in early-moderate RP than in controls, whereas COMR was smaller. Across groups, visual field extent was negatively correlated with head gain and positively correlated with COMR. Accounting for age effects, these results demonstrate increased head movement at the expense of eye movement in participants with PVFL.

Conclusions

RP is associated with an increased propensity for head movement during gaze shifts, and the magnitude of this effect is dependent on the severity of visual field loss.

Head-Eye Coordination Increases with Age and Varies across Countries

Purpose

Head movements in older people may contribute to their dizziness and equilibrium problems. Head gain is the ratio of head movement to total movement (head + eye) when executing a saccade to an eccentric target. Two studies have investigated the relationship between head gain and age but have provided conflicting results.

Methods

We report head gain data collected from research laboratories and optician stores. Our sample sizes are much larger (n = 657 for laboratory, n = 64,458 for optician stores), permitting more detailed analyses.

Results

The head-eye coefficient, expressed as 100 times the square root of head gain, was bimodal with one mode of primarily eye movers and one mode of eye-and-head movers. Head-eye coefficient increased with age and was invariant with eye correction and gender. We also found an effect of nation that seemed associated with gross domestic product or by latitude (in the northern hemisphere) and log population density.

Discussion

Assuming that head movements and visual distortions contribute to dizziness and equilibrium problems, our study suggests that customizing eyewear based on age and country may help in reducing the prevalence of problems associated with head and/or eye movements.