Rehabilitative effect of the patterned stimulation with MP1 microperimeter in homonymous hemianopia

Homonymous visual field (VF) defects are a common complication of stroke, cranial trauma and brain tumors. Among them, the homonymous hemianopia (HH) is the one found most frequently. Because this impairment can affect a variety of cognitive visual functions, including visual search, safe navigation through changing environments and reading, and given the poor rate of spontaneous recovery, several rehabilitative programs have been proposed to help patients recover. Three main different approaches have been developed to treat patients with HH: (1) substitution, including special devices such as optical

This last approach is based on the concept of brain plasticity. Just as plasticity after brain damage is well recognized in other functional systems (motor, somatosensory), plasticity of the visual system has been recognized as a useful mechanism whereby the brain compensates for its functional loss, either spontaneously or by repetitive visual stimulation (Safran, 1988; Sabel et al., 2005; Schofield and Leff, 2009; Matteo et al., 2016).

About visual stimulation aimed to restore the VF in HH patients, 2 major kinds of behavioural stimulation were applied: the blindsight training and the border-field training. The blindsight training accomplishes goals by training pathways left intact after the damage, which project directly or indirectly to higher cortical regions, the border-field training by strengthening the function of partially damaged regions at the VF border or in islands of residual vision inside the blind field (Sabel et al., 2011).

For the VF border training, different visual rehabilitative programs were used, including repetitive VF testing (Zihl and von Cramon, 1979; Zihl and von Cramon, 1985), reaction perimetry treatment (Zihl & Werth, 1984) and the vision restoration therapy (VRT) (Sabel et al., 2005; Kasten et al., 1998; Julkunen et al., 2003; Julkunen et al., 2006; Marshall et al., 2008; Mueller et al., 2008; Poggel et al., 2008; Romano et al., 2008; Sabel and Kasten, 2000; Widdig et al., 2003; Werth, 2008); moreover Bergsma and van der Wildt found an enlargement of the VF in their patients which was independent of the type of stimulus-set used during training (Bergsma and van der Wildt, 2010).

Since September 2009, is possible to perform repetitive visual stimulation also by the MP-1 microperimeter (NIDEK Technologies, Padua, Italy), using a program of visual pattern with structured stimuli. The MP-1 is a diagnostic and rehabilitative device, currently used to train patients with central vision loss. It is equipped with a visual rehabilitation tool consisting of flickering pattern, which allows patients with unstable fixation to develop a new preferred retinal locus (PRL). The patterned stimulation has highly significant recognition shape that increase inner retina integration processes and optimize stimulus processing and recognition and brain transmission and it was suggested that it can involve residual surviving cells, as well as amplify and integrate retinal and brain cor- tical plasticity (Verboschi et al., 2013; Markowitz and Reyes, 2013). For these characteristics, this photostimulation program might activate surviving neurons in areas of residual vision in patients with VF defects as well as other behavioral stimulation. Moreover, thanks to its eye-tracking module, the MP1 allows the operator to observe eye movements throughout the training session. In our study we want to verify the possibility to rehabilitate patients with VF defects and central vision preserved, using the MP1 patterned stimulation. based practices that have yielded positive results for their students, which we will share here. After describing the challenges that people who have restricted visual fields or visual acuity loss may have with horizontal lateral scanning for vehicles at uncontrolled crossings, we will explain the accommodative strategies that were found to help them address those difficulties, and a procedure that

Brain injuries (stroke, cerebral hemorrhage, cerebral trauma or brain surgery outcomes) are the most common causes of the damage of the retrochiasmal visual pathways, resulting in homonymous VF defects, as quadrant defects or complete hemianopia or more. The HH presents a spontaneous improvement in the first month in 50% of cases, many cases continue this process up to the 3rd month, only rarely up to the 6th. The spontaneous recovery is complete in 38% of cases (Zhang et al., 2006). During the last decade, the traditional view that visual system damage is permanent has given way to a more optimistic view, because visual loss does not remain unchanged, but it can recover spontaneously to some extent. Even when the period of spontaneous recovery has ended, there is still additional potential of plasticity and regeneration. The neuroplasticity approach has shown that residual structures can be reactivated by repetitive stimulation. This can be achieved by different means: visual experience, visual training or electrical brain stimulation (Sabel et al., 2011). Concerning the visual training, several kinds of visual stimulation have already been used in ophthalmology for the treatment of hemianopic patients with the aim to restore the VF (Kasten and Sabel, 1995; Polat et al., 2004; Sahraie et al., 2006; Henriksson et al., 2007; Raninen et al., 2007; Jobke et al., 2009; Hayes et al., 2012). The border-field training is the most frequently used method and is based on exercises specifically targeting the transition zone between intact and damaged VF (Kasten et al., 1998; Schmielau and Wong, 2007). According with Residual Vision Activation Theory (Sabel et al., 2011), clinically relevant plasticity occurs not primarily in regions of “absolute blindness” but in “areas of residual vision”, known also as “relative defects”, typically located at the VF borders. It is hypothesized that repeated stimulation (training) of the transition zone induces a synaptic plasticity of the partially damaged structures and downstream areas, stabilizing their synchronous firing, even after the treatment period. This improved or stabilized synchronization is one of the proposed neurophysiological mechanism of vision restoration. Previous studies have demonstrated the efficacy of LV rehabilitation by means of microperimeter MP1 biofeedback in patients with central LV, reporting improvements in visual acuity, fixation behavior, retinal sensitivity and reading speed (Melillo et al., 2020; Vingolo et al., 2009). The MP1 is an automated retina scotometry and sensitivity measuring system, which monitors the fundus image at the same time, and thanks to the biofeedback tool, it can be used as a rehabilitating device. Training with a visual target or a pattern, connected to an acoustic signal that measured the best fixation position, leads to improve unconscious functions (fixation and visual acuity). This kind of procedure was ideated for the LV patients who have lost fovea fixation capabilities, to increase their fixation stability or to train to relocate their PRL into a different region, called trained retinal locus. On the other hand, for the intrinsic characteristics of the flickering stimulation pattern, we thought to use the MP1, for the first time, to rehabilitate patients with VF defect and we obtained hopeful results. Thanks to the eye-tracker system, we can guarantee that the fixation was stable in all patients during all examinations and that the VF enlargement was not due to saccadic movements (Sabel & Trauzettel-Klosinksi, 2005). In conclusion, our results indicate that MP1 pattern stimulation induces a little improvement of the VF in hemianopic patients, restoring areas of residual visual function. So the MP1 can be dedicated to rehabilitate also patients with peripheral defects, even in longstanding cases of cerebral accident. Since to the best of our knowledge there are no studies exploring the effect of MP1 patterned stimulation for the rehabilitation of the peripheral LV, considering the easy availability of the MP1 device in the LV Centers, we wanted to make our preliminary findings known, although the absolute change is low, to encourage the study of the applications of the MP1 also for the rehabilitation of the VF defects and to contribute to the best possible rehabilitative care for LV patients.

Large-scale studies are necessary to confirm our preliminary findings and to investigate the effects on visual exploration performance. Other limits of the current study are the lack of the long-term follow-up after treatment period and the lack of a control group (which was excluded from the training or was treated with a placebo training), although spontaneous recovery can be excluded. Compared with the baseline time point, all patients showed a statistically significant reduction of the VF Mean Deviation (VFMD) and scotoma points (VFSP), consequently an improvement in the VF (Figure 1,2). Before stimulation the mean of the VFMD