Motion perception in early glaucoma

Purpose: The aim of our study was to underline the changes in the movement perception for early glaucoma. Our working hypothesis consisted in inquiring if the impairment of the magnocellular pathway may modify the movement perception capabilities in the visual field, more particularly in its peripheral area.Methods: We included 14 healthy subjects and 14 patients with early primary open angle glaucoma. A moving target was presented on a semicircular screen (1.8 m diameter); participants were asked to localize the Ending Point (EP) of each movement. Each stimulus consisted in a white dot (0,72° of diameter) moving horizontally with the imposed velocity profile. Two different laws of motion were displayed: a “biological” motion corresponding to the recording of an arm pointing movement, consisting in a bell-shaped velocity profile, and a “non-biological” motion corresponding to a constant velocity profile. The study field was divided into 4 quadrants and 2 eccentricities: EP may be displayed in the “peri-central” (10° from the foveal axis) or peripheral (20° from the foveal axis) visual field. Two trajectories length were presented (10° and 20°). Each stimulus with same characteristics was displayed two times. Thus the experiment was constituted by 192 trials, presented in a random order. For every participant we calculated the PCE (Position Constant Error) which was defined as the average difference between the estimation of the EP indicated by the participant versus the true location of the same target. The PVE (Position Variable Error) was defined as the standard deviation of the responses of each participant.Results: All the participants overestimated the EP (13.23 ± 8.87 mm for healthy subjects and 17.06 ± 13.07 mm for glaucoma patients, p = 0.2518). The PVE was 28.14 ± 6.86 mm for healthy subjects and 40.95 ± 9.83 mm for glaucoma patients (p = 0.0004). There was a significant difference in the PVE for both groups when stimulus moved accordingly to the “non-biological” velocity profile (p = 0.0001). Glaucoma patients had substantial PVE increase when the target image had a “non-biological” speed profile (p = 0.0388).Conclusions: This study desrcibed disorders in movement perception and localization in patients with early glaucoma.Particularly, the unexpected lack of difference between normal subjects and patients in localizing a moving stimulus strongly suggested that the visual deficiency could be partly compensated by endogenous informations