Slower saccadic reading in Parkinson’s disease

Abstract

Idiopathic Parkinson’s Disease (PD) is characterized by degeneration of dopaminergic and other neurons, leading to motor and non-motor deficits. Abnormal eye movements in PD, including fixations, saccades, and convergence, are well described. However, saccadic reading, which requires serial and alternating saccades and fixations, is not well studied, despite its obvious impact on the quality of life. In this study, we assessed saccadic reading using variations of the King-Devick (KD) test, a rapid single digit number naming test, as a way to assess the ability to make serial left-to-right ocular motor movements necessary for reading. We recruited 42 treated PD patients and 80 age-matched controls and compared their reading times with a variety of measures, including age, duration of disease, Unified Parkinson’s Disease Rating Scale (UPDRS), the National Eye Institute 25-Item Visual Functioning Questionnaire 25 (VFQ-25), and Montreal Cognitive assessment (MoCA) test. The subjects performed 4 trials of reading 120 single digit numbers aloud as fast as possible without making errors. In each trial, they read 3 pages (KD1, KD2, and KD3), and each page contained 40 numbers per page in 8 lines with 5 numbers/line. We found that PD patients read about 20% slower than controls on all tests (KD1, 2, and 3 tests) (p < 0.02), and both groups read irregularly spaced numbers slower than regularly spaced numbers. Having lines between numbers to guide reading (KD1 tests) did not impact reading time in both PD and controls, but increased visual crowding as a result of decreased spacing between numbers (KD3 tests) was associated with significantly slower reading times in both PD and control groups. Our study revealed that saccadic reading is slower in PD, but controls and PD patients are both impacted by visuospatial planning challenges posed by increased visual crowding and irregularity of number spacing. Reading time did not correlate with UPDRS or MoCA scores in PD patients but significantly correlated with age, duration of disease, and VFQ-25 scores. The presence of convergence insufficiency did not significantly correlate with reading time in PD patients, although on average there was slower reading time in those with convergence insufficiency by 8 s (p = 0.2613). We propose that a simple reading task using 120 single-digit numbers can be used as a screening tool in the clinical setting to assess functional ocular motor difficulties in Parkinson’s disease that can have a profound impact on quality of life.

A simple saccadic reading test to assess ocular motor function in cerebellar ataxia

“…Because improved reading has been reported as the number one goal or complaint in patients with vision difficulties [ 51 – 53 ], assessment of reading should be more routinely performed in the clinical setting. Simple number reading tests such as regularly (this study, [ 54 ]) or irregularly spaced (King-Devick test, [ 37 , 39 – 41 ]) number reading tests can rapidly and accurately quantify reading speed in patients with different neurological conditions in the clinic. A regularly spaced task involving small saccades like the one used in this study may be particularly suitable for measuring patients with cerebellar ataxia, since patients with cerebellar ataxia tend to have difficulty making precise, small saccades as well as performing repetitive tasks.…”

“…Compared with controls, patients with cerebellar ataxia had the greatest decrease in reading speed by 44% while performing the easiest, simplest task—the 120 regularly spaced numbers. This is because reading regularly spaced single-digit numbers is easier and faster than irregularly spaced numbers in controls [ 54 ]. In contrast, patients with cerebellar ataxia have great difficulty making precise, regular patterns of small eye movement, and our data provide support for the utility of this simple saccadic reading task as a way to differentiate the ocular motor abilities in those with cerebellar ataxia from that of controls, to identify difficulties in reading performance in patients with cerebellar ataxia, and to monitor ataxia patients over time in the clinical setting.…”

Ocular manifestations of Parkinson disease

“…Saccadic reading in PD is slower. The reading time was slower in PD with CI by 8 s [35]. In a study, PD patients developed vertical gaze abnormalities, while the diagnosis was changed from PD to progressive supranuclear palsy-Parkinsonism during a 4-year follow-up [36].…”

“…Moreover, binocular vision tests, such as positive fusional vergence (PFV) and NPC, are required for CI diagnosis. It has been emphasized that simple reading tasks using 120 single-digit numbers can play the role of a screening tool in clinical practice to assess functional ocular motor difficulties in PD, which can have a considerable effect on the quality of life [35] and electrophysiological recordings such as electrooculogram, flash, pattern and multifocal electroretinogram, or visual evoked potential. An anterior segment slit-lamp examination is needed for dry eyes and cataracts.…”

Management of Visual Dysfunction in Patients with Parkinson’s Disease

“…Oculomotor abnormalities however are not as prominent as in other Parkinson’s-related disorders, such as progressive supranuclear palsy [ 19 ] and their clinical relevance is unclear. It has been shown, however, that saccadic reading assessed by the King-Devick test in PD patients is 20% slower than controls [ 20 ] suggesting a potential role for abnormal extraocular movements in clinical impairment.…”