Prevalence of amblyopia, strabismus and refractive errors amongst children of the 7th grade and influence of spectacle correction of hypermetropia on reading ability

In The Netherlands, eye screening of children is being performed during visits
to the maternity service (consultatiebureau) and school physician (schoolarts),
using the VOV protocol (Vroegtijdige Onderkenning Visuele stoornissen). This
protocol aims at the detection of strabismus (squint), amblyopia (lazy eye) and
refractive errors (need for spectacle correction). This screening stops before
the age of 7. The rationale for this cessation of screening is that strabismus
and amblyopia are usually present before the age of 7 and refractive errors do
not affect the health of the eye. This point of view is disputable since vision
disorders may affect intellectual development at any age during childhood. Any
motivated judgement about (the need for) vision screening is hampered by the
fact that the prevalence of vision disorders (before as well as beyond the age
of 7) is unknown. Moreover, it is not known whether the disorders that have
been detected in the screening programme, are indeed adequately treated and
managed.
As reported above, vision abnormalities may affect intellectual development.
There are many reports about the association between refractive errors and
reading capacity: hypermetropia (farsightedness) is associated with lesser
reading capacity; myopia (nearsightedness) with higher reading capacity.
However the nature of this association is not known. It is unknown whether
correction of hypermetropia by means of spectacles will indeed improve reading
capacity.

Main objectives:
1. to investigate the prevalence of vision abnormalities in 9- and 10 year old
children;
2. to investigate the percentage of these vision abnormalities that were
detected the VOV screening programme;
3. to investigate whether these detected vision abnormalities were adequately
managed / treated;
4. to investigate whether correction hypermetropic refractive errors can
improve reading capacity;

The objectives (1, 2 and 3) will be investigated in a cross sectional
observational study. The objective (4) will be investigated in a double blind
randomized controlled interventional study (intervention: prescription of
glasses).

For the objective (4) glasses will be provided to those subjects who have
relevant hyperopia, on a random basis. The effect of these glasses on the
reading capacity will be investigated by repeating the reading tests after 4
months.

The risks of the study are negligible. The burden consists of one eye
investigation of 8 minutes performed at the school, possibly a second
investigation of 75 minutes hours (in case of suspected abnormalities) and the
possibility of wearing glasses during 4 months (only in case of relevant
hypermetropia, hence likely to benefit the subject).
The possible benefits consist of a thorough eye examination, revealing
treatable abnormalities, correction of refractive errors (improving visual
acuity) and possibly improving reading capacity.