Visual competition for saccade target selection in the recovered field of hemianopia patients following visual restoration therapy.

Visual information processing is of critical importance in everyday life
activities. This becomes clear when part of the visual field gets damaged.
Visual field defects can arise due to post-chiasmatic lesions for example
caused by vasculaire incidents, carnio-cerebral trauma, hypoxia and
inflammatory processes. These patients, also called hemianopia patients, will
encounter problems in daily living due too limitations in reading, visual
navigation (cycling, driving a car) and visual identification (recognition of
objects and persons).

Spontaneous recovery of hemianopia patients occurs when the inflammations in
the damaged areas diminish. However, the chance of spontaneous recovery
decreases rapidly after the accident and become very rare after a couple of
months. Several studies show that intensive visual training, like visual
restoration therapy, can support this recovery to increase the change in extent
and depth of the visual field defect. This recovered visual field will
eventually improve the quality of daily living of these patients.

Certain patients report no improvements of daily living after the training.
Even though the standard perimetrical test show an enlarged visual field
including visual discrimination of letters, shapes and colours. Therefore, it
becomes important to find supplementary measurements to map the visual changes
caused by the training. The visual system is known to have several levels of
competition between different parts of the visual field. The standard
perceptual measures like perimetry give little insight about this aspect of the
recovery. It is very well possible that for some patients the recovered visual
field is no match for the competition in the visual attention with non-damaged
areas.

Our pilot study is designed to get insight about the contribution of the
recovered field in the visual decision-making process and in this way to get an
understanding of the recovery of competition abilities of the recovered field.
Previous studies in our group showed that in healthy participants the choice to
make an eye saccade between one of two identical goals, is based on a
competitive choice mechanism with feedback inhibition. Our goal is to map, if
this saccadic decision-making in the recovered visual field of hemianopia
patients comes about in a similar manner or shows deviations.
Any deviations in this saccadic decision-making would suggest an inferior role
of the recovered visual field with respect to the undamaged visual field.

To study the neurological changes that explains the recovering of visual field
defects after visual restoration therapy.

Each participant is his/her own control in a single-blind, randomised trial.

We will indirectly measure neural processes in the visual system using a
non-invasive, psychophysic task. The whole measurement will last up to 5 hours
including breaks. We divided the study into three sessions spread over the day
to limit the burden on the participants. This three sessions include; 1)
ophthalmological examination (Goldman perimetry and Humphrey perimetry), 2) a
first psychophysic session to determine the personal bias and 3) a second
psychophysic session which is the primary measurement.

Session 1 will determine if we will continue the experiment depending on the
results. Hereby, we will look if the participant still has a stable recovered
field measured with the Goldman and Humphrey perimetry. Throughout this session
the participant will be asked to concentrate, fixate and respond to a dot
light-stimuli presented in the visual defect and healthy part. No risks or
burdens are involved in both perimetrical tests.

Session 2 and 3 will last 0.5 and 1 hour, respectively and will involve
behavioural measurements using a computer-based task and an eye-tracker. During
this sessions, the participants will be asked to concentrate, fixate and
respond to a visual light-stimuli by performing a saccade towards to brightest
stimuli. We will use a bite board to ensure that the participant head position
throughout the both sessions.

There are no risks associated with the aforementioned technique. The
individually tailoring of the bite boards will take about 2 minutes and is
hardly uncomfortable. At this time, the study will not have direct benefits
for the participants. It does give however a possibility to 1) give insight
about the neurophysiological characteristics of the recovered field (including
the recovered visual field in normal or deviating networks of visual-motor
decision-making processes) or 2) if there is a correlation between the
deviations and the quality of daily life of patients.

Therefore, this experiment will give the first steps of understand the recovery
processes and a guide towards the development of improved (possible saccade
related) treatment which eventually will benefit patients.