Placebo Effect in Visual Restitution Training: No Stimulated Neuroplasticity after Stroke

Background: Restitution Training (RT) promises patients suffering from visual field loss after stroke partial restoration of blind areas. RT is supposed to activate neuronal (re)connection by repeated bright light stimulation of the transition area between patients’ intact and defect visual field. However, the effectiveness of RT is discussed controversially both in science and clinical practice. Main reasons are (1) unreliable perimetry due to compensatory eye movements and (2) inhomogeneous patient samples.

Methods: With the help of our newly developed Virtual Reality goggles Salzburg Visual Field Trainer (SVFT) 16 stroke patients performed RT on a regular basis for five months. By utilizing our also newly developed and validated Eye Tracking Based Visual Field Analysis (EFA), we conducted a first-time full eye-movement-controlled perimetric study on potential changes in visual field functionality before and after rehabilitation with RT. Additionally, patients subjectively rated the functionality of their visual field.

Findings: Patients' mean self-assessment of their subjective visual field functionality indicated statistically significant improvement of 11·5% - increasing from 51·0% (SD = 21·2) before RT to 62·4% (SD = 17·9) after RT (t(15) = -2·356, 95% CI [-0·215, -0·011], p = 0·032, r = 0·520). In contrast, eye tracking controlled perimetric results revealed no statistically significant improvement.

Interpretation: RT solely induces a placebo effect and does not ameliorate the visual field functionality of stroke patients. Improvements - as reported in other studies - can be explained by (1) patients’ compensatory eye movements during perimetry and (2) inclusion of patients with lesions in higher cortical areas associated with attention. Our findings are supported by recent work, suggesting that RT may lead to actual visual field enlargement in patients suffering from neglect.