Optokinetic Therapy for Hemianopic Alexia
July 1, 2007
Optokinetic Therapy for Hemianopic Alexia
Abstract & Commentary
By Erik J. Kobylarz, MD, Ph.D, Assistant Professor of Neurology and Neuroscience, Weill Cornell Medical College, Cornell University. Dr. Kobylarz reports no financial relationship relevant to this field of study.
Synopsis: Improved reading skills in patients with hemianopic alexia can be achieved by having patients practice reading a right-to-left scrolling text.
Source: Spitzyna GA, et al. Optokinetic therapy improves text reading in patients with hemianopic alexia: a controlled trial. Neurology. 2007 May 29;68(22):1922-1930.
Spitzyna and colleagues evaluated the efficacy of optokinetic therapy for alexia in patients with right-sided homonymous hemianopia. Essential visual information required for efficient reading to help guide reading fixations is lacking in patients with acquired right-sided homonymous hemianopia, particularly that involving foveal or peri-foveal vision. Patients with hemianopic alexia (HA) saccade more frequently when reading a line of text than do normal subjects, but utilize an inefficient ocular motor strategy when doing so. Two hypotheses were tested in this study: 1) Practice with a visual rehabilitation method that induced small-field optokinetic nystagmus (OKN) would improve reading speeds in patients with HA when compared to sham visual rehabilitation therapy. 2) OKN-inducing therapy would preferentially affect reading saccades into the blind hemifield.
Dr. Alexander Leff at the National Hospital for Neurology and Neurosurgery in London, England, and colleagues designed a physical rehabilitation method which induces small-field optokinetic nystagmus (OKN) by using horizontally scrolling text moving from right to left (so-called "Times Square presentation"). This technique has been shown to increase text reading speeds in normal subjects. The authors wished to compare the efficacy of this method, which induces OKN eye movements, versus a non-reading task that also induces saccadic eye movements for the treatment of HA. An additional objective was to identify if any therapy-induced effects on reading saccades were direction-specific.
Nineteen patients with hemianopic alexia were entered into this study. In most of the patients a posterior cerebral artery territory stroke (infarct or hemorrhage) was the causative lesion, but some patients had head injuries or tumors. All of the patients had a fixed homonymous field defect for a period of at least 3 months. This was a two-armed study with two therapy blocks in each arm. Group 1 practiced reading right-to-left moving text (MT) every day for 2 4-week blocks. Group 2 had sham therapy, consisting of "spot-the-difference" non-reading tasks (viewing children's puzzles), for the first four weeks, followed by MT for the second 4 weeks.
Group 1 showed significant improvements in mean reading speed (18%) following each of the two therapy blocks. However for Group 2 there was no significant improvement (5%) during the first block, but after crossing over to MT therapy, they subsequently demonstrated a 23% improvement. Spitzyna et al also report that MT therapy was associated with a direction-specific effect on saccadic amplitude for rightward, but not leftward reading saccades. The authors conclude that OKN-inducing therapy preferentially affects reading saccades in the direction of the induced (involuntary) saccadic component. They do not propose a neurophysiologic mechanism for this effect, but observed that after OKN therapy patients are able to make larger amplitude reading saccades into their blind field, which can improve their reading ability.
Commentary
A variety of visual search and navigation tasks have been utilized in an attempt to improve ocular motor efficiency (Pambakian et al. 2005). Only a few groups have focused on using such methods for the treatment of reading difficulties associated with HA (Kerkhoff, 2000). This study is novel in that it is the first to demonstrate the effectiveness of specific eye movement based therapy in patients with hemianopic alexia in the context of a therapy controlled trial; they compared the treatment group with patients receiving sham therapy to induce saccadic eye movements. These results indicate that moving text therapy for inducing rightward optokinetic nystagmus can help reading efficiency in patients with hemianopic alexia.
Although rehabilitation for static visual defects is a controversial topic in the field of neuro-ophthalmology, to their credit, this group has utilized saccade training by means of OKN therapy in an attempt to train HA patients to read more effectively, thus improving their quality of life. It appears that MT therapy improves the reading ability in HA patients by augmenting the saccade amplitude towards the blind right hemifield. However, further studies are warranted to determine the exact neurophysiologic mechanism(s) by which the improvement in reading with OKN therapy occurs, as well as how to optimize its therapeutic effect (e.g., text movement velocity and direction, frequency and duration of therapy). The authors have made a Web-based version of this therapy available without cost on-line, which is certainly commendable.
Additional Reading
Kerkhoff G. J Neurol Neurosurg Psychiatry. 2000 Jun;68(6):691-706.
Pambakian A, et al. Rehabilitation strategies for patients with homonymous visual field defects. J Neuroophthalmol. 2005 Jun;25(2):136-142. Review.
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