The College of Optometrists

  

Purpose:           

 

Previous studies have shown how visual information affects prehensile  movements, such as reaching and grasping. However, to date no study has investigated the effect of simulated visual impairment on reach-to-grasp movements. This study will explore how simulated visual impairment affects  these movements.

 

Methods:   

 

Ten volunteers with normal vision (mean age 24.1 years) took part. Participants were asked to pick up a cylindrical object under normal viewing conditions and in conditions were vision was reduced (+3.00DS and +6.00DS lenses placed in front of both eyes). A motion analysis system (Vicon 460) was used to record and reconstruct 3D hand and fingers movements.  The Reach or Transport component was defined by Maximum Wrist Velocity, Time to Maximum Velocity and Total Movement Time. The Grasp component was measured by Maximum Grip Aperture and Time to Maximum Grip Aperture.

 

Results:    

 

Repeated measures analysis of variance (between subjects) revealed that as the level of blur increased Maximum Velocity decreased (p=0.0005). However, the overall organisation of the movement was similar because the percentage of time taken to reach Maximum Velocity did not change with the defocus conditions. The Maximum Grip Aperture increased with increasing levels of blur (p=0.0001). Time to Maximum Grip aperture occurred earlier in blur conditions (+6.00DS) than in normal conditions.

 

Conclusion:

 

Both reaching and grasping were affected by decreased vision. These results have important implications in visually impaired participants. In daily activities, low vision patients may show slower hand movements with an inaccurate scaling of the size of the object. Data are examined in terms of modelling the effects of different levels of vision loss to measured motor impairment.