Small and Large Field Blur Adaptation: Foveal and Peripheral Contrast Sensitivity Changes

Abstract

 

Purpose

 

The effect of blur adaptation is known from earlier reports as increased acuity and improved contrast sensitivity after prolonged exposure to optical blur. However, both the stimulus and the effects studied were limited to fovea. The aim of this study was to evaluate the changes in contrast sensitivity function (CSF) in fovea and periphery following small and large field blur adaptation.

 

Methods

 

The CSF was measured for resolution with oblique gratings. Foveal measurements were done with a quick method, qCSF (Lesmes et al., Journal of Vision 2010) and a modified qCSF procedure was used for the periphery. Measurements were made prior to and following adaptation in 3 locations; in fovea and 10° nasal field of the adapting right eye and in fovea of the fellow eye, with refractive correction, if any. Three subjects participated in the study. Adaptation stimulus was a 30 minutes video of forest scenery projected on a screen, viewed by the adapting eye. Two different stimuli were used for adaptation: small field stimulus (SFS) i.e. a video frame occupying the central 7.5° visual field and a large field stimulus (LFS) i.e. 7-tiles of the 7.5° video frame stacked horizontally. Tiling was done to have the same spatial contents. Four conditions were tested in random order: SFS and LFS adaptation with and without +2.00 D blur.

 

Results

 

The difference in log contrast sensitivity (log CS) was analyzed. Foveal CS in the adapting eye improved for SFS-blur adaptation in the region of spatial frequencies between 2 to 5 cpd (p<0.05, Figure 1a). On contrary, for LFS-blur adaptation, there was a small but significant decrease for 3.5 to 5 cpd (p<0.05, Figure 1b). This suggests that the presence of peripheral blur stimulus can affect adaptational effects in fovea. The only other change seen was in SFS-Clear adaptation, where the CS in 10° visual field decreased significantly for 1.2 to 2.4 cpd, possibly due to the absence of stimuli in the field of interest. The fact that no changes were seen in the fellow eye ruled out learning effects.

 

Conclusions

 

A difference in trend was noted in foveal adaptational effects when the stimulus extent was varied. The changes were confined to spatial frequencies that were present in the defocused adaptation stimulus.

 

 

Figure 1: Foveal logCS change following adaptation to +2.00 D blur for (1a) small field and (1b) large field stimulus. * indicates regions with significant difference

 

Keywords: 406 adaptation: blur • 478 contrast sensitivity