Effects of Optokinetic Stimulation Without a Reading Task in Patients With Hemianopic Alexia

Stroke can cause a visual field defect known as homonymous hemianopia (HH). When this visual field loss involves the macula, the central area of vision, it may result in reading difficulties known as hemianopic alexia (HA).

The literature reports improved reading performance in these patients after repeated induction of horizontal optokinetic nystagmus (i.e., an oculomotor reflex consisting of horizontal saccades). To induce this nystagmus, previous studies have used a reading task involving text scrolling from right to left.

However, this type of exercise, which relies on reading, is cognitively demanding and may lead to frustration due to reading difficulties, fatigue, and reduced motivation and potentially the impact of rehabilitation. Therefore, the use of a non-reading task could help overcome these limitations.

The present study aims to compare the efficacy of optokinetic stimulation with reading to optokinetic stimulation without reading in patients with HA.

• Optokinetic stimulation without reading task (Other): Participants are exposed to a horizontally moving optokinetic visual stimulus on a computer screen for 40 minutes per session. The task consists of viewing random sequences of letters scrolling from right to left. The sessions are spread out over 4 weeks, with 3 or 4 sessions per week, to achieve 10 hours (15 sessions) of optokinetic rehabilitation.
• Optokinetic stimulation with reading task (Other): Participants are exposed to a horizontally moving optokinetic visual stimulus on a computer screen for 40 minutes per session. The task consists of reading aloud sentences scrolling from right to left. The sessions are spread out over 4 weeks, with 3 or 4 sessions per week, to achieve 10 hours (15 sessions) of optokinetic rehabilitation. The scrolling speed ranges from 85 to 275 words per minute, depending on the participant's reading accuracy.

Primary outcomes

• Change in reading speed on paper [Baseline and end of each 4-week rehabilitation period: Week 0, Week 4, and Week 8]: Change in the number of correctly read words per minute, assessed using the International Reading Speed Texts (IReST). For each participant, the change in reading speed will be calculated separately for the optokinetic rehabilitation condition with a reading task and for the optokinetic rehabilitation condition without a reading task. The within-participant changes obtained after each 4-week period will be pooled across the two randomized sequences and compared between conditions. A higher reading speed indicates better reading performance.

Secondary outcomes

• Change in reading accuracy on paper [Baseline and end of each 4-week rehabilitation period: Week 0, Week 4, and Week 8]: Change in the number and type of errors (paralexias, omissions) assessed using the International Reading Speed Texts (IReST).
• Change in reading speed on screen [Baseline and end of each 4-week rehabilitation period: Week 0, Week 4, and Week 8]: Change in the number of correctly read words per minute, assessed using a screen-based reading task
• Change in reading accuracy on screen [Baseline and end of each 4-week rehabilitation period: Week 0, Week 4, and Week 8]: Change in the number and type of errors (paralexias, omissions), assessed during a screen-based reading task
• Change in subjective reading abilities [Baseline and end of each 4-week rehabilitation period: Week 0, Week 4, and Week 8]: Change in the score on the Hemianopia Reading Questionnaire (HRQ)
• Change in ocular fixations during reading [Baseline and end of each 4-week rehabilitation period: Week 0, Week 4, and Week 8]: Change in the number of fixations and in the mean fixation duration (in ms) during the screen-based reading task, assessed with an eyetracker
• Change in ocular saccades during reading [Baseline and end of each 4-week rehabilitation period: Week 0, Week 4, and Week 8]: Change in the number and in the mean amplitude of saccades (in degrees) during the screen-based reading task, assessed with an eyetracker
• Change in optokinetic nystagmus [Baseline and at the end of both rehabilitation: Week 0 and Week 8]: Change of saccade amplitude and frequency during optokinetic stimulation
• Change in visual detection during standard perimetry [Baseline and end of each 4-week rehabilitation period: Week 0, Week 4, and Week 8]: Change in visual sensitivity (in dB) at each tested visual field location on automated static perimetry (Humphrey or Octopus)
• Change in visual detection during screen-based perimetry [Baseline and end of each 4-week rehabilitation period: Week 0, Week 4, and Week 8]: Change in number of correctly detected targets and mean reaction time (in ms) at each tested visual field location on screen-based perimetry
• Tolerability of rehabilitation [Before and after each rehabilitation session]: Score of fatigue, stress, and mood induced by the treatment, self-assessed using a numbered visual analogue scale
• Motivation for rehabilitation [End of each 4-week rehabilitation period: Week 4 and Week 8]: Score obtained on the Situational Motivation Scale

Sex: All, ages: 18 Years to any

Inclusion Criteria:

* Time since lesion > 1 month
* Diagnosis of homonymous hemianopia post-stroke without macular sparing
* Reading complaint and/or reading impairment
* Proficiency in reading French
* Agreed to give informed consent
* Afiliated with national health insurance

Exclusion Criteria:

* History of neurological or psychiatric disorders
* Visual impairment of peripheral origin (i.e., related to damage to the structures of the eye or the optic nerve)
* Uncorrected visual acuity deficit
* Reading disorder prior to the stroke (dyslexia)
* Instability of reading impairment
* Instability of homonymous hemianopia
* Major cognitive that would limit the ability of the patient to participate in the study (unilateral spatial neglect, simultanagnosia, comprehension disorder, oral expression disorder)

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• Christophe Duret, Principal investigator, Clinique Les Trois Soleils, Boissise-le-Roi, France