Compensatory approaches to rehabilitation of vision loss as a result of brain injury are aimed at improving the efficacy of eye movements, enabling patients to bring the otherwise unseen stimuli into their sighted field. Eye movement training has shown promise in a large number of studies in small clinical populations. Nevertheless, there remain two problems; standardisation and wide accessibility. NeuroEyeCoach™ (NEC) has been developed to address both. The therapy is based on the visual search approach and is adaptive to the patient’s level of disability and the task difficulty is varied systematically through a combination of set-size and target/distractor similarity. Importantly, the therapy can be accessed online or in clinical settings, to enhance accessibility. Here we have reported on the findings from the first 296 consecutive cases who have accessed and completed NEC online, the largest cohort of patients studied to date. Patients’ performance on two objective (visual search times and errors) and one subjective (self-reported disability) measures of performance were assessed before and after therapy. The findings showed that patients improved in search time, had less errors and improved disability scores in 87% (255/294), 80% (236/294) and 66% (167/254) of all cases respectively. We examined factors age, sex, side of blindness, age at the onset of brain injury, and time elapsed between the brain injury and start of therapy as predictors of both objective and subjective measures of improvements. Age was a significant predictor of improved search errors with older patients showing larger improvements. Time between brain injury and intervention negatively influenced search reaction time, however, none of the factors could predict improved subjective reports of disability.
Areas of blindness in the visual field could arise as a result of lesions along the visual pathways. Stroke is the main cause of brain injury, although trauma and elective surgery may also affect the visual pathways. There is a high incidence (60%) of visual impairments in stroke survivors (Rowe, Hepworth, Hanna, & Howard, 2016), with as many as half of those have been reported to have visual field loss (Fujino et al., 1986, Zhang et al., 2006a). In post chiasmatic lesions, the resultant blindness is similar in extent within the same hemifield in both eyes, hence referred to as homonymous. Homonymous hemianopia is therefore blindness covering the entire one hemifield in both eyes.
The leading causes of sight loss such as age-related macular degeneration, cataracts, diabetic retinopathy and glaucoma, characteristically affect an individual over an extended period of time typically ranging from weeks to years (Groeneveld et al., 2019, Rudnicka et al., 2015). Although the blindness is debilitating, there is scope for a period of adjustments to the gradual visual impairment. Sight loss due to brain injury on the other hand is sudden and often occurs over few hours and without prior warning. Some spontaneous recovery may take place in the acute stage of injury, but the probability of recovery diminishes rapidly with time and very little recovery of sight is expected 3–6 months post injury (de Haan et al., 2014, Zhang et al., 2006b).
There are three main approaches to rehabilitation of hemianopic patients, namely substitution, restitution or compensatory approaches. Substitution refers to methods where the damaged field is imaged onto a portion of the sighted field using spectacle prisms to enable patients to see the otherwise undetected objects (Bowers, Keeney, & Peli, 2008). The method can expand the field of vision, nevertheless a number of studies have shown low compliance (Bowers et al., 2008, Bowers et al., 2014). This may in parts be due to the reported difficulties that patients experience with the required shifts in attention and the distraction caused by rival information in the two eyes (Raz & Levin, 2017). Also, the benefits are of course contingent upon the use of optical devices. Hence the substitution techniques have not been widely adopted in clinical practice.
Restitution techniques are aimed at improving the visual sensitivity within the field defect. Post-geniculate lesions along the optic radiation and early cortical processing may lead to lack of conscious visual experience. However, there are numerous projections of visual information to subcortical and cortical sites that by-pass the usual retino-geniculo-striate route (Cowey, 2004, Sahraie and Trevethan, 2014). The premise of restitution techniques relies on the residual capabilities of the remaining pathways enhanced through perceptual learning. That is, with repeated simulation over an extended period of time, learning can take place. Thus, associating visual stimulation with residual neuronal activity (Huxlin, 2008, Sahraie, 2007). The fact that neuronal activity associated with visual stimuli, confined to the blind visual fields, can influence behaviour in forced-choice paradigms and in the absence of conscious perception is well established and is termed blindsight (Weiskrantz, 1986). Whilst there is an absence of any conscious experience in type I blindsight, some rudimentary awareness may be experienced in type II blindsight, often reported as a feeling that a visual event had taken place (Weiskrantz, 1998). Conscious visual experience lies on a continuous spectrum and systematic and repeated stimulation can lead behavioural performance from no detection ability to blindsight type I, type II, and eventually conscious vision (Sahraie, Trevethan, Macleod, Weiskrantz, & Hunt, 2013). Over the past two decades, a number of restitution techniques based on systematic stimulation have been developed. These include utilising repeated stimulation of the light flux channel in Vision Restoration Therapy (Kasten and Sabel, 1995, Poggel et al., 2008, Romano et al., 2008). Active stimulation of motion sensitivity (Huxlin et al., 2009), spatial vision (Sahraie et al., 2006) and flicker sensitivity (Raninen, Vanni, Hyvärinen, & Näsänen, 2007) have also been used in restoration approaches. The time commitment for patients using restitution techniques is significant, often requiring adherence to the daily use of an intervention over a number of months.
Compensatory techniques rely on the patient’s intact visual field for processing the otherwise unseen stimuli, by using eye movements to bring their image onto the intact field. Although such compensatory approach is intuitive, spontaneous adaptation and development of an effective eye movement pattern is seen in only 40% of hemianopic patients (Zihl, 1995) and the majority of cases shows inefficient eye movements years after the injury. The pattern of eye movements in affected cases can be characterised as having smaller amplitude saccades, leading to requiring a larger number of eye movements to explore a given portion of the field, hence slowing down in time to explore and identify targets within the field defect (Zihl, 2011). There is also a more disorganised search strategy in that patients make more frequent between hemifield saccades. Disturbances of eye movement patterns extend to both sighted and blind hemifields (Chokron et al., 2016, Zihl, 1995, Zihl and Hebel, 1997). In a pioneering study (Zihl, 1988), demonstrated that hemianopic patients that undertook a visual search training (involving detection of a target item amongst distractors) had improved search times. These studies were extended by the use of computerised visual search paradigms in the same lab (Zihl, 1995, Zihl, 2011) as well as others (Kerkhoff et al., 1992, Mannan et al., 2010, Nelles et al., 2009, Nelles et al., 2001, Pambakian et al., 2004, Roth et al., 2009); showing an overall improvement in detection time, a reduced scanpath and a smaller number of fixations prior to target detection (for a review see Sahraie, Smania, & Zihl, 2016). It is important to note that the improvements following compensatory therapies are domain specific. For example, reading disorders are also common following stroke and online therapies such as Read-Right (Ong et al., 2012, Woodhead et al., 2015) can lead to improvements in reading abilities. However, performance improvements following specific training for eye movement scanning behaviour and those for reading do not transfer (Schuett, Heywood, Kentridge, Dauner, & Zihl, 2012).
As eye movements play a crucial role in visual perception and in the interaction of an individual with their environment, it is assumed that improved eye movement efficiency could lead to a reduction in self-reported level of disability. Indeed, assessment of improvements in self-reported ratings of perceived disability, introduced by (Nelles et al., 2001) has been implemented and extended in a number of studies (Aimola et al., 2014, Lane et al., 2010, Mannan et al., 2010, Pambakian et al., 2004). Evaluation of the functional improvement in quality of life and interaction with the environment after visual rehabilitation interventions has not been carried out in any large scale studies to date, and the reported subjective ratings in Activities of Daily Living (ADL) questionnaires remain the most widespread method for such assessments.
Recent systematic reviews of the evidence for the effects of visual rehabilitation interventions (Pollock et al., 2011, Pollock et al., 2019) have suggested eye movement training to be the most promising approach to vision rehabilitation in stroke patients. There are however, two major issues that needs to be addressed if any eye movement-based intervention is to become the standard care. These include standardisation of approach and ease of access (Pollock et al., 2019). In a collaborative approach Sahraie et al. (2016) reported on development of NeuroEyeCoach™ (NEC), an eye movement intervention that was based on the original visual search task that had shown to be effective in improving search performance in hemianopia (Zihl, 1995) (also described below). NEC is a Class I CE marked medical device in the EU and is registered as an FDA 510(K) exempt medical device in the US. For the patient sample described in this paper, the cost of accessing NEC was approximately $400US. The intervention was self-administered with in-built algorithms to adapt to the patient’s level of disability and systematically train the affected individual to make effective eye movements. In addition, the intervention was deliverable over the internet, thus it could be accessed at home or in clinical settings. To further illustrate the stages involved in NEC, a demo version can be accessed here (https://novavision.com/download-neuroeyecoach-demo/).
Here, we report for the first time, on changes in performance of a large group of hemianopic patients who undertook NEC outside a clinic environment. We have obtained pre- and post-intervention self-reported assessment of ADL (referred to as disability score DS) as well as reaction time (RT) and errors (ER) on a specific search task. Improvements in RT, ER and DS have been analysed in relation to age, sex, side of blindness, age at the onset of brain injury, and time elapsed between the brain injury and start of therapy.