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Paul A. Wetzel, George T. Gitchel, Mark S. Baron; Effect of Parkinson’s Disease on Eye Movements During Reading. Invest. Ophthalmol. Vis. Sci. 2011;52(14):4697.
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Reading requires accurate eye movement control and stability during fixation. Parkinson’s disease patients (PDs) often report difficulty with reading or have altogether stopped. To investigate these reports, the eye movements of PDs and aged matched controls were compared during reading.
Eye movements of 36 medication confirmed PDs from 57 to 88 years old (mean 68 ± 7.5 yrs) and 20 similarly age-matched controls from 49 to 81 years old (62.9 ± 6.9 yrs) were recorded during reading. Patients with dementia (Mini-Mental State Exam scores <24) were excluded. On the day of testing, PDs were evaluated using the Unified Parkinson’s Disease Rating Scale (mean score 12.1 ± 9.7). Each subject read 10 out of 35 available texts ranging from easiest to most difficult and of equivalent difficulties. All texts were of equal line number, character style, character width with nearly equal numbers of total characters. From the reading distance, text boundaries were ±10° H by ±6° V. Texts were presented in a randomized order on a computer display while binocular eye movements were measured at 500 Hz from a two-dimensional eye tracking system (SR Research). Head movement was not restricted, but showed no measurable changes in position or orientation while reading. Eye position subject data were analyzed for the number of forward saccades and regressions including their respective amplitudes and durations, the number of fixations, their duration and stability, reading speed measured in characters/sec and the number of lines read.
Statistically significant differences between PDs and controls were found in nearly all eye measurement parameters except in the number of regressions and saccadic durations. PDs produced a greater number of smaller amplitude saccades than controls. Main sequence data for both groups appeared normal and similar to each other. The fixation durations of PDs were longer and less stable compared to controls. The visual span during reading was significantly less for PDs compared to the control group. For controls, reading speed was unaffected by text difficulty level compared to a downward slowing trend among PDs.
PD negatively affects nearly all aspects of normal reading behavior related to eye movements primarily through reduced visual span and increased instability during fixation.
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