ERGs and psychophysical thresholds in students with reading discomfort

Symptoms of reading discomfort include unpleasant somatic and perceptual effects, such as eye-strain, headache, and blurred text, despite normal visual acuity. Reading discomfort has been proposed to be the result of increased noise in the visual system. Several studies have suggested that the symptoms can be minimized by having the subject wear colored filters. Thus, there may be abnormal neural processing in the cone pathways. This study measured L- and M-cone isolating (1) ERGs and (2) psychophysical thresholds in normal and reading discomfort subjects to determine if cone processing was abnormal in the reading discomfort population.

Twenty-two normal and nineteen reading discomfort college students took part in this study. The normal subjects had Conlon survey scores within 0.5 SD of the mean and the reading discomfort subjects had scores >1.5 SD above the mean. ERGs were determined for a range (5 to 15%) of L- and M-cone contrasts. Slopes were determined for the L- and M-cone ERG amplitudes for each subject. Psychophysical thresholds were determined with a 2AFC technique combined with a 3-up and 1-down staircase procedure that terminated after 18 reversals occurred. The threshold was calculated as the average of the last 8 reversals.

The average ERG slopes were not significantly different between the normal and reading discomfort groups (L-Cone, p = 0.086; M-Cone, p = 0.47). The L/M cone ratios for the slopes were not significantly different (p = 0.55). The log of the color contrast thresholds were not significantly different between the normal and reading discomfort groups (L-Cone, p = 0.97; M-Cone, p = 0.92).

L- and M- cone ERG contrast gains and psychophysical estimates of color contrast thresholds were not significantly different. These results do not support the noisy visual system hypothesis of reading discomfort.