Optokinetic therapy improves text reading in patients with hemianopic alexia: a controlled trial

Abstract

Objective: An acquired right-sided homonymous hemianopia can result in slowed left-to-right text reading, called hemianopic alexia (HA). Patients with HA lack essential visual information to help guide ensuing reading fixations. We tested two hypotheses: first, that practice with a visual rehabilitation method that induced small-field optokinetic nystagmus (OKN) would improve reading speeds in patients with HA when compared to a sham visual rehabilitation therapy; second, that this therapy would preferentially affect reading saccades into the blind field.

Methods: Nineteen patients with HA were entered into a two-armed study with two therapy blocks in each arm: one group practiced reading moving text (MT) that scrolled from right to left daily for two 4-week blocks (Group1), while the other had sham therapy (spot the difference) for the first block and then crossed over to MT for the second.

Results: Group 1 showed significant improvements in static text reading speed over both therapy blocks (18% improvement), while Group 2 did not significantly improve over the first block (5% improvement) but did when they crossed over to the MT block (23% improvement). MT therapy was associated with a direction-specific effect on saccadic amplitude for rightward but not leftward reading saccades.

Conclusion: Optokinetic nystagmus inducing therapy preferentially affects reading saccades in the direction of the induced (involuntary) saccadic component. This is the first study to demonstrate the effectiveness of a specific eye movement based therapy in patients with hemianopic alexia (HA) in the context of a therapy-controlled trial. A free Web-based version of the therapy used in this study is available online to suitable patients with HA.

Figure 1

Timeline for the two groups: G1 = group 1; G2 = group 2. The treatment blocks were either moving text (MT) or the sham therapy, spot-the-difference (StD). T1-5 are the five time points that data were collected. Text reading speeds were averaged over T1 and T2 to provide a baseline (B) measure.

Figure 2

Text reading times (y-axis, in words per minute) for both group 1 and group 2 at three time points (Baseline (B), T3 and T4). The group averages are shown in filled circles for group 1 (A) and filled squares for group 2 (B) with SEM error bars. Analysis was on the individual subjects’ reading times (open circles in both graphs). The average percentage increase is shown for both groups (C) across all four time points (B, T3, T4 and T5 (post-rehabilitation)).

Figure 3

Eye movement data: spatial characteristics. Average spatial saccadic measures across three time points (B, T3 and T4/T5) for both group 1 (filled circles) and group 2 (filled squares), and associated SEM (error bars) for the following reading measures: progressive (rightward) saccadic amplitude (A); regressive (leftward) saccadic amplitude (B); incoming saccadic amplitude (C). Y-axis shows amplitude in number of pixels. The average word-box widths for the 3-7 letter words in the materials were 93, 120, 142, 171, and 198 pixels respectively, and the average letter width was 25 pixels.

Figure 4

Eye movement data: temporal characteristics. Average temporal saccadic measures across three time points (B, T3 and T4/T5) for both group 1 (filled circles) and group 2 (filled squares), and associated SEM (error bars) for the following reading measures: mean fixation rate, Y-axis = fixations per 100 words (A); refixation proportion, Y-axis = proportion through word (B); mean fixation duration, Y-axis = time in ms (C).

Figure 5

Average single word reading times and reading slopes pre and post rehabilitation with associated SEM (error bars). Y-axis is in milliseconds, note truncated scale. NB: data collapsed across both groups.

Figure 6

Eye movements recorded from a normal subject reading both static text (left panel) and scrolling text (right panel). The static text consisted of three rows of four words that did not make a sentence in order to force the reader to fixate each word. The OKN inducing scrolling text also consisted of 12 words; the rate of motion was set to match the time it took to read the static text (3000 milliseconds, x-axis). The y-axis is in pixels. Declining values = eye movement to the right, ascending values = eye movement to the left. Note that the OKN induced saccades are of more uniform amplitude than the voluntary ones (near-vertical components of both scanpath traces).