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W.H. Ridder, III, E. Borsting, C. Chase; L– and M–Cone Isolating ERGs and Psychophysical Thresholds in College Age Students With Reading Discomfort . Invest. Ophthalmol. Vis. Sci. 2006;47(13):3696.
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Symptoms of reading discomfort include unpleasant somatic and perceptual effects, such as eye–strain, headache, and blurred text, despite normal visual acuity. Reading discomfort is 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) psycophysical thresholds in normal and reading discomfort subjects to determine if cone color processing was abnormal in the reading discomfort population.
ERGs and psychophysically determined detection thresholds of L– and M–cone color contrast stimuli were measured in 22 normal and 19 reading discomfort college students. The normal subjects had Conlon survey scores within 0.5 SD of the mean and the reading discomfort subjects had scores greater than 1.5 SD above the mean. The stimuli (30 Hz flicker) were displayed on a CRT monitor. ERGs were determined for a range (5 – 15%) of L– and M–cone contrasts. ERG data were acquired and analyzed with a Biopac Lab PRO System. Slopes were determined for the L– and M–cone ERG amplitudes for each subject. A G4 was interfaced with a CRT monitor to produce the stimuli and analyze the results of the psychophysical experiments. Threshold was determined with a 2AFC technique combined with a 3 up 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 for the reading discomfort group were 0.62 ± 0.390 (L–cone) and 0.76 ± 0.708 (M–cone). The slopes for the normal subjects were 0.83 ± 0.380 (L–cone) and 0.93 ± 0.725 (M–cone). There were no significant differences between the normal and reading discomfort groups in the slopes (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 color contrast thresholds for the reading discomfort group were –1.16 ± 0.243 (L–cone) and –0.88 ± 0.156 (M–cone). The color contrast thresholds for the normal subjects were –1.12 ± 0.212 (L–cone) and –0.87 ± 0.167 (M–cone). There were no significant differences between the normal and reading discomfort groups in their color contrast thresholds (L–Cone, P = 0.66; M–Cone, P = 0.85).
L– and M– cone isolating ERG slopes and psychophysical estimates of color contrast thresholds were not significantly different. These results do not support the noisy visual system hypothesis of reading discomfort.
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