The effect of viewing distance on responses to the pattern glare test

Background: We investigated whether symptoms of pattern glare were affected by viewing distance, as distinct from spatial frequency, because of an association between symptoms and anomalies of accommodation and vergence. Methods: One hundred young adults viewed gratings with spatial frequencies of 0.3, 2.3 and 9.4cycles per degree (cpd) at four test distances (0.4, 0.8, 1.6 and 3.2 metres). Participants were asked to grade the presence of 15 symptoms of visual perceptual distortions and discomfort, on a scale from zero (no symptoms) to 10 (maximum perceptual and somatic symptoms). Results: The viewing distance did not affect the nature and strength of symptoms, when viewing gratings with similar spatial frequencies. The symptoms increased with spatial frequency (p<0.008 for all comparisons). Conclusions: The symptoms from the Pattern Glare Test do not appear to be modulated by the changes in accommodation and vergence associated with viewing distance, at least in an unselected sample of students. The highest spatial frequency of the current Pattern Glare Test was 9.4cpd at 0.4 metre and this is insufficiently high to measure the reduction in symptoms at high spatial frequencies. If assessing relative aversion to gratings of different spatial frequencies, it may be useful to increase the testing distance to 0.6 metre so as to increase the spatial frequency of the third grating to 14.2cpd.