Abstract
Purpose :
Eccentric viewing is a common strategy used by patients with central vision loss (CVL) to direct the eye such that the image falls onto healthy peripheral retina, known as the preferred retinal locus (PRL). Typically, fixation tests are used to determine the location of the PRL. It has been long acknowledged that we do not know whether the PRL used in a fixation test is also used when performing tasks. There is some evidence of multiple PRLs and the PRL moving depending on the conditions. We present an innovative method to determine whether the same PRL observed during fixation task was used to watch videos.
Methods :
The gaze of a group of 60 normal vision (NV) observers was used to define a democratic center of interest (COI) of video clips from movies and television. This democratic COI approach takes into account that people look at the same objects most of the time (Dorr et al. 2010; Goldstein et al. 2007). People with CVL are expected to look at the COI, but with less ability, due to reduced resolution (identifying objects of interest), unstable fixation, and poor eye movement control. For each participant, we computed the gaze offsets from the COI across the video clips. The distribution of gaze offsets of the NV subjects was used to define the limits of NV behavior. If the gaze offset was within this 95% degree confidence interval, then the same PRL was used for fixation and video watching.
Results :
As expected, CVL patients had wider gaze-offset distributions than NV subjects (p<0.00005) indicating worse eye movement control. The largest gaze offset of a CVL patient was ~13 degrees. Gaze offsets of 13/20 CVL patients were outside the NV confidence interval (further from the COI than expected). Further, none of 15 NV subjects watching the same videos with spherical defocus blur had a gaze offset that was decentered (outside the NV confidence interval), suggesting that resolution was not the problem.
Conclusions :
This indicates that many CVL subjects are using a PRL to view videos that differs from that found with a fixation task. The relationship between these locations needs further investigation.
This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.