Neural origin of slow vision: contributions of the central and peripheral nervous system.

A number of patients who seek help at the Department of Ophthalmology
Radboudumc experience problems of delayed or slow processing of visual
information at home, school, work or in traffic. For example, patients can
complain about their inability to read subtitles before they disappear from the
screen. Although these patients face substantial hamper in daily life, they do
not meet current diagnostic criteria of any known ocular or neurological
disorder or of visual impairment. In fact, the source of their problems is
still unknown. There is also no current treatment option for these patients. To
fill this gap, we want to investigate their visual and attentional systems to
learn more about the origin of their symptoms thereby providing information
necessary for the development of diagnostic criteria and treatment.

To study neuronal and ophthalmological characteristics of a newly detected
clinical entity called slow vision which hampers visual perception and
attention of the affected patients.

Observational case-control study.

We will measure processing throughout the visual system using a number of
non-invasive measurements. The measurements will last about 8 hours in total.
To limit the burden on participants, we have divided the study into three
sessions: 1) ophthalmological examination (routine ophthalmological examination
and cognitive VEP, mERG ) and psychophysics, 2) fMRI session and 3) MEG
session. The sessions will be carried out separately. Sessions 2 and 3 will
only be done if results of session 1 show differences between patients and
controls on the main psychophysical tasks (computer based attentional and
perception tasks) or on the cognitive VEP. Session 1 will last approximately 5
hours including breaks. Although all measurements will be easy to perform,
participants will have to concentrate, fixate and sometimes respond to visual
stimuli. Some of the measurements could be experienced as somewhat
uncomfortable by the participant. mERG measurements require eye drops (1%
tropicamide or 2.5% phenylephrine in case of allergies) to increase signal to
noise ratio (SNR). Additional eye drops consisting of 4 mg/ml oxibuprocaine are
used to locally anaesthetize the eyes. This is part of a routine procedure
applied in electrophysiology measurements at the ophthalmology department of
Radboudumc and in accordance with ISCEV standards (Hood et al., 2012).
Subjects should not rub their eyes for at least one hour after administration
of the oxibuprocaine drops, and they are not allowed to drive until the effects
of the drops have worn off (i.e. 2-4 hours after installation).
Sessions 2 and 3 will each last about 1.5 hours and will involve measuring
brain activity using MRI and MEG, respectively. During these sessions,
participants will have to sit or lie very still while performing psychophysical
tasks similar to those used in session 1.
Risks associated with the aforementioned techniques are minimal if procedures
are followed carefully. No significant risks are to be expected for cognitive
VEP. There is a minimal risk of corneal erosion caused by the mERG electrode.
However, this type of damage rarely occurs and is known to heal quickly and
completely. Risks associated with MRI and MEG mainly revolve around metals and
electromagnetic implants. We will therefore thoroughly screen participants
beforehand with a standard screening questionnaire provided by the Donders
Centre for Cognitive Neuroimaging. If a patient reports contraindications for
MRI and/or MEG, he will be excluded from session 2 and/or 3. Controls will be
screened before inclusion and again before session 2 and 3. If they report any
contraindications for MRI and/or MEG, they will be excluded from the study.
At the time of this study, participants will not benefit. However, it will
raise awareness of the existence of SV, describe its neurophysiological and
behavioural characteristics, provide the first steps in elucidating its causes,
and guide development of diagnostic criteria and treatment which will
eventually benefit the patients.