The effect of static scanning and mobility training on mobility in people with hemianopia after stroke: A randomized controlled trial comparing standardized versus non-standardized treatment protocols

Stroke is a leading cause of disability [1], and approximately 30-35% of people with stroke have a homonymous hemianopia [2]. Hemianopia is described as "blindness in one half the field of vision in one or both eyes" [3]. Literature suggests that natural recovery occurs in 50% of people, mostly in the first month with minimal recovery taking place after 6 months [2]. Visual loss, following a stroke can be temporary or permanent, and interfere with an individual's ability to perform daily living activities and live independently [4].

Visual training in homonymous hemianopia post stroke is recognized as an important part of rehabilitation [5]. The project described in this manuscript is comparing the effects of two approaches to treating visual field loss in the subacute rehabilitation phase (week two - six months) following a stroke. Currently rehabilitation employs three key strategies including optical devices, compensatory training and visual restitution therapy [6]. The first strategy is to use optical devices, such as prism glasses, to displace the visual image. The efficacy of prisms has not been demonstrated due to the lacking of a standardized methodology and few controlled studies [7].

The second strategy is compensatory and aimed at enhancing eye movements and/or head movements. This takes a number of different forms including the training of oculomotor or saccadic movements, on a standardised computer screen, or devices such as the Dynavision [8], which incorporates a larger visual area, where head movements are required. Oculomotor scanning performance, thus only requiring eye movement, has been linked to subjects reported visual difficulties in everyday life [9]. Training of oculomotor or saccadic movements has been demonstrated to lead to an improved visual search field and reading ability [10‐12]. No large scale randomized controlled trials have been performed to date to validate this intervention [13]. Dynavision training has been demonstrated to lead to improvement in visual scanning in a single case study [14], and in a descriptive study of driving [15], but not in a small controlled study of driving in stroke [16].

The third strategy uses visual restitution therapy and aims to enhance neuroplasticity [17]. This method involves the stimulation of the 'borderzone' or 'transition zone' between the area of visual loss and the intact area of vision [18]. A systematic review found [13] inconclusive evidence to support visual restitution based therapy as a means of restoring visual fields following brain damage.

In Australia, most visual training employs compensatory eye and head movement based therapy but current delivery of vision rehabilitation is recommended by treating therapists and is thus subjective [19]. Therapies can vary from a comprehensive combined static and mobility training to the prescription of magnifiers to help with reading with minimal instruction of their use. Due to the wide variability in type and dosage of therapy received by an individual patient, the benefits of visual training in terms of compensation and improved performance in functional tasks are uncertain [20].

In response to the need for a structured therapy program of visual training in homonymous hemianopia post stroke, the Neuro Vision Technology (NVT) program has been developed which is a standardized therapy and involves both a static scanning training and a dynamic mobility component. The static scanning component uses the NVT device, (see figure 1) to assess for the presence of neurological vision impairment, such as a homonymous hemianopia and/or visual spatial neglect. A standardized presentation of colored lights (LEDs) is displayed on a horizontal panel, placed at eye level approximately 30 cms from the patient. The panel of lights extends approximately 80 cms either side of central fixation, with the lights at the ends of the panel subtending an angle of approximately 70 degrees from midline. In the presence of a homonymous hemianopia the patient is required to use both head movement and eye movement towards the affected visual field to detect the light stimulus.

The NVT scanning device is used in rehabilitation to teach a pattern of systematic visual search strategies from the perimeter of the affected visual field towards the intact visual field. It aims to improve the patient's awareness and understanding of the nature of their vision impairment. The NVT training program then transfers visual scanning strategies, established using the NVT scanning device, into tasks that are mobility based. This developed NVT training differs from the other compensatory techniques as it involves a larger real visual world, whereas other compensatory training is aimed at rehabilitating reading abilities using a computer screen. NVT training has not been evaluated in terms of its effectiveness in rehabilitation for people with hemianopia.

To determine the most effective rehabilitation for people who have a hemianopia after stroke, it is necessary to examine the effects of the standardized and non-standardized rehabilitation strategies on performance in daily activities. We aim to compare the effectiveness of the standardized NVT program versus current individualized therapy as recommended by treating clinicians in patients with homonymous hemianopia post stroke.

The study design is a single-blind randomized, controlled trial in Adelaide, Australia, which will be conducted over 12 months. The intervention design is summarised in Figure 2.

Visual rehabilitation training is routinely provided for people with hemianopia following stroke however the benefits of visual rehabilitation training on functional outcomes have not been well evaluated. Despite us knowing it is important to rehabilitation as it impacts negatively on independence following stroke [4].

The goal of visual rehabilitation involves making the most of a person's residual vision, specifically to try to overcome the visual disabilities that are most troublesome to them. Part of the difficulty in evaluating the effectiveness of vision rehabilitation in homonymous hemianopia is the varied type of strategies used by therapists. At the moment the details of the rehabilitation program are negotiated between each patient and their rehabilitation therapist. No robust evidence currently exists to identify the most effective way to deliver vision rehabilitation in people with homonymous hemianopia after a stroke or the optimum time required [13].

There is evidence that providing more exercise therapy early after stroke improves peoples' ability to recover [29] but the effects of additional therapy in vision rehabilitation are unclear. No large scale randomized controlled trials have been performed to establish the effectiveness of visual rehabilitation following brain damage [13].

This project will compare the effectiveness of current visual rehabilitation protocols which vary in type and dosage according to individual clinicians' recommendations, to a new standardized technology (NVT). Functional outcome measures, such as performance on a mobility assessment course and scanning ability will be employed as well as patient reported outcomes such as, vision specific health related quality of life to allow a meaningful assessment of this rehabilitation intervention.

A debate exists around the mechanisms which underlie the remedial approach in visual rehabilitation following stroke, that is compensatory or neuroplasticity [7]. The outcome of our proposed study will contribute to the knowledge of the mechanisms behind the compensatory approaches, currently used in clinical practice. Furthermore, the results of the trial will provide information that will inform the allocation of resources in visual rehabilitation post stroke. This is in terms of dosage and type of therapy provided.

As in many areas of rehabilitation more rigorous research is needed to identify which remedial approaches should be included in clinical practice for visual loss following stroke.