Purpose: Parkinson’s Disease(PD) is the second most common neurodegenerative disease globally. As many as 78% of PD patients report difficulty with vision and reading, but few studies have directly examined reading in PD patients. The goal of this study is to better assess visual disability and reading difficulties in PD patients.
Methods: We recruited 112 subjects (59 PD, 53 age-matched controls) per approved protocol at a single academic institution. All subjects were assessed using the Visual Function Questionnaire (VFQ-25), Neuro-Ophthalmic(NO-10) supplement, and King-Devick (KD) rapid number naming test. We performed 500-Hz 2D infrared oculography (RED500, SMI, Germany) on a subset of subjects (21 PD and 14 controls) during reading (8 pages of single digit numbers at 40/page and 14 pages of words, 3-8 lines/page). Statistical analysis was performed using Mann-Whitney U test.
Results: Per vision disability questionnaire, PD patients experienced greater self-reported visual dysfunction (VFQ-25: PD:62.7±3.1, Ctrl=88.7±1.7, P<0.00001; NO-10: PD:62.5±3.2, Ctrl=85.2±2.7, P=0.00002). The largest differences were observed in the near activities, computer use, and mental health subscores (P<0.0001). On the KD test, PD patients read slower by 24% (PD:1 20.5±5.6 #/min, control: 158.3±6.1 #/min, P=0.00002), which correlated with VFQ-25 scores (P=0.0009) but not with Unified Parkinson’s Disease Rating Scale (P=0.14). Infrared oculography confirmed that PD patients exhibited slower number (PD: 107.0±5.3 #/min, Ctrl:148.3±8.8 #/min, P=0.001) and word reading (PD: 200.2±12.0 words/min, control: 246.2±13.4 words/min, P=0.024). PD patients made greater number of saccades/line (PD: 9.0±0.9, Ctrl: 4.9±0.1, P=0.08) and fixations/line (PD: 8.6±0.8, Ctrl: 6.0±0.28, p= 0.025), smaller saccade amplitudes (PD: 3.50±0.05deg, Ctrl: 4.36±0.30deg, p=0.035), longer
fixations, and greater fixation dispersion.
Conclusions: Our study is the largest so far to systematically assess reading in PD. Visual disability and reading difficulty are common and likely directly impact mental health. Eye movement
recording revealed that fixation and saccade measurements are both significantly affected during reading, with some patients exhibiting poor oculomotor planning and backtracking. The etiology of reading difficulty in PD patients is likely multifactorial in origin, and neuro-ophthalmic assessments of PD patients should include examination of reading.
- Eye movements during reading are significantly affected in Parkinson’s disease.
- K-D Test performance is significantly worse in Parkinson’s patients compared to normal controls, specifically, PD patients were 24% slower.
- K-D Test performance correlates with vision related disability measures.