Motion perception in early glaucoma

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Abstract

Purpose

The aim was to underline changes in the motion perception for early glaucoma. Our hypothesis consisted in inquiring if the impairment of the magnocellular pathway may modify the motion perception.

Methods

We included 14 healthy subjects and 14 patients with early primary open angle glaucoma. A moving target was presented on a semicircular screen; participants were asked to localize the Ending Point (EP) of each motion. A stimulus consisted in a white dot moving horizontally. Two different laws of motion were displayed: a “biological” motion, consisting in a bell-shaped velocity profile, and a “non-biological” motion corresponding to a constant velocity profile. EP may be displayed in the peri-central or peripheral visual field. The experiment was constituted by 192 trials. 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 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).

Conclusion

The unexpected lack of difference between normal subjects and patients in localizing a moving stimulus suggested that the visual deficiency could be partly compensated by endogenous informations.

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