Crowding in children with visual impairment: The effect of a magnifier on near visual acuity

Crowding is a phenomenon in which symbols are less accurately identified in
the proximity of other symbols. This phenomenon is present in everyone at some
point, but normally disappears between the age of five to seven and is then no
longer disturbing. Children with a visual impairment experience more crowding
than normally sighted children. Research has shown that an impressive number of
adults with a visual impairment still experience disturbing amounts of
crowding. Crowding has a big influence on reading and learning to read.
Children with a visual impairment have more problems with reading and learning
to read than normally sighted children. They show poorer reading speed, which
indicates that the process of decoding the letter symbols takes more time.
The visual system is more capable of identifying symbols when they are larger
and the space between symbols is larger. A magnifier also reduces the amount of
symbols in the field of view. The combination of these two factors suggests
that a child who experiences difficulties in identifying closely-spaced symbols
because of crowding will benifit from the use of a magnifier. The development
of fine motor skills and eye movements are essential for magnifier use.
The recent study proposal is focussed on exploring the effects of the use of a
magnifier on mechanisms that underlie learning to read, viewing behaviour and
stimulating near visual acuity. Fine motor skills and eye movements which are
required for magnifier use will also be assessed.

This study has two major goals. The first goal of this study is to evaluate
whether the disabilitating effects of crowding can be reduced by the use of a
magnifier early in life. The second goal is to investigate motor and visual
development of visually impaired children in order to apply low vision aids
more successfully.

Children will be assessed in terms of fine motor skill development, mental
developmental level and ophthalmologic research (acuity, near visual acuity,
visual field). These are the prime measures of the project. Within the crowding
project, two research moments will take place.
In september and october 2010 Part 1 and Part 2 of the study will be performed.
Part 1 consists of measuring the amount of crowding with a crowding test
without using a magnifier. In Part 2 the same test will be administrated, but
this time a magnifier is used. Additionaly, fine motor skills and eye movements
will be assessed through experiments. These measures are premeasures. In
november and december 2010, a part of he group will follow a magnifier
training. Half of the youngest, visually impaired group will practice the task
with a magnifier and the other half will practice the task without a magnifier.
In january and february postmeasures will be taken (crowding test with and
without magnifier use and the experiments that measure fine motor skills and
eye movements).
In september and october 2011 a new dynamic crowding task will be developed.
Also pilots will be used to test the adequacy of the new instrument. In
september and october 2012, this training will be performed and task
performance will be measured before and after the new training. Only the young,
visually impaired group follows this intervention. Finally, experiments will
measure integration of action and perception.

In november and december 2010 the young, visually impaired children will
receive an intervention. This interventions will take course over 6 weeks.
Children will be visited at home by a trainer. During 6 weeks, 12 half hour
sessions will be take place.
The dynamic crowding training will be constructed in 2011.

The burden includes an ophthalmologic, fine motor and developmental assessment.
These are standard procedures for a child's first visit to Bartimeus.
Additionally, fine motor skills and eye movements are measured. The burden for
the participant is reasonable. The young children with a visual impairment will
be trained with a evidence-based intervention. Stimulating fine motor skills
and reducing crowding are the fundamental goals of this study.