Development of the Visual Field

The visual field is defined as the area that can be seen when the eye is directed forward and
steadily fixating, including that which is seen with peripheral vision. The visual field is almost
always tested one eye at the time, and there are several methods and more or less advanced
equipments for visual field testing (also called perimetry). This chapter describes visual field
testing in children and factors influencing the visual field development and the test results.
Methods for testing the visual field in children
A simple, although quite informative way of testing the extent of the visual field is ad modum
Donders, when you use your own hands as stimuli, and your own visual field as reference.
This method is used in adults to detect large constrictions and when no equipment is
available. For quantitative testing of the sensitivity within the visual field, computer assisted
techniques are preferred. Since most of the diseases affecting the visual system first affects in
the central part of the visual field (although not necessarily affecting the area for reading
ability; the fovea), most computerized perimeters test the central 30° area. In children,
however, it is sometimes interesting also to test the extent of the visual field, and then
different manual methods, possible to adapt to the children’s age and ability to co-operate,
have to be used.
In small children, testing the visual field is a challenging task. A number of different methods
have been developed but only a few of them have been adequately evaluated. In very young
children a variant of “preferential -looking” is used, in which the examiner observes if the
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infant shifts gaze when a stimulus is presented. In toddlers the so called ball-on-a-stick can be
used. Pre-school children are able to co-operate in a manual Goldmann examination and
school children can perform computerized perimetry (Fig 1).
Figure 1. Different techniques for visual field testing. Goldmann perimetry (Courtesy of
Luisa Mayer) (Left), Computerized perimetry: Rarebit perimetry (Right)
The Normal Visual Field in Children
Measuring the visual field in young children; infants and toddlers, is complicated. Yet, several
studies have provided knowledge about the extent of and sensitivity in the visual field in the
growing child, even if different reports give somewhat varying results. The extent of the
visual field in small children is also depending of the method used; kinetic or static, the size
of the stimulus and, in children at 1-2 years of age, also on the presentation of competing
stimulus in the fixation area.
The effective visual field has been shown to expand between 2 and 4 months of age and the
ability to respond to peripheral objects more distant than the fixation object develops after 3
months. Visual field extent corresponding to adult levels has been reported to be present at 17
and 30 months of age, measured with kinetic and static perimetry, respectively (Dobson et al
1998), see figure 2.
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Figure 2. Visual field extent in different ages measured a with 6° stimulus (Goldmann III –
IV). Thin continous blue line = newborn, dashedd blue line = 3.5 months, thick continous
blue line = 7 months, red dash/dot line = 4 years, blue dash/dot line = adult (adapted from
Dobson et al 1998).
Regarding the standard tests, routinely used in adults, it is well known that the child has to
reach an age of 5-7 years before reliable visual field results can be expected. Using the most
common computerized methods the extent and sensitivity values, equal to those from adults,
can be obtained at the age of 10-12 (Martin 2005, Martin & Lundvall 2007; 2009).
Attention
One main reason for the different results in children and adults, especially regarding static and
moving stimuli, may relate to differences in peripheral summation areas or to differences in
attention between infants and adults. The visual field in pre-school children is affected by non
visual factors, such as vigilance and cognitive processes (Tschopp et al 1998). From the age
of 5 to 7, the child is able maintain steady fixation on a target and to respond to a stimulus
presented in the periphery by pressing a button. But in younger children and infants, the
examiner has to rely on the fixation eye movements of the child. However, infants between
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approximately 1 and 4 months of age were reported to have difficulty with disengagement,
i.e. looking away from a stimulus, once their attention has been engaged (Hunnius 2007).
The eccentricity to which infants move their gaze to locate a target has been found to increase
rapidly during the first 4 months of age (Harris & MacFarlane, 1974; Lewis & Maurer1992).
Despite this fast early development, several studies report that an adult-like performance is
not attained before the end of infancy or even the school-age years. Other authors have
reported that from the age of approximately 6 months, infants’ performance when shifting
gaze between two stimuli is comparable to that of adults (Atkinson et al, 1992).
Normal visual field development
As has been stated above, there are numerous studies using manual perimetry for examining
the visual field in children and for evaluation of the extent of the visual field. We have been
interested in evaluating new computerized perimetric methods in children for evaluation the
sensitivity of the central visual field, both in healthy children and pediatric patients. Two
methods have been used, both developed in Sweden; the high-pass resolution perimeter (HRP
(Frisén 1993; Martin et al 2008a) and Rarebit perimetry (Frisén 2002; Martin 2005).
Especially the latter was found to be suitable for children of at least 6 year of age. The method
is sensitive to low-degree damage, very patient-friendly, requires short examination time and
is preferred by the children, when compared to other techniques (Martin et al 2004).
Figure 3 shows a summary of five of our studies of healthy children of different ages,
evaluating the normal values established with Rarebit perimetry (Martin et al 2004; Martin
2005; Martin & Lundvall 2007; Martin et al et al 2008b; Hellgren et al 2009).
Abnormal visual field development
There are several factors that can disturb the normal development of the visual field. In
several studies we have described the effect of intrauterine incidents, intrauterine growth
restriction, premature birth, treatments for side effects of premature birth (retinopathy of
prematurity) and other hinders for the normal visual development such as ametropia,
strabismus and congenital cataract.
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Figure 3. Results from computerized perimetry (Rarebit perimetry), expressed as a
percentage of stimuli seen (hit rate) from age 7 to 20 (healthy subjects). Note the low increase
in hit rate from age 7 to 12 and the somewhat larger variability in examination results in
younger children (Martin & Lundvall, submitted).
Prematurity and co-morbidity
Prematurity influences the visual system in several ways. In a follow-up study of 11-year old
children, born prematurely, we could confirm findings in previous studies, i.e. that children
treated for retinopathy of prematurity have somewhat constricted visual fields compared to
age-matched controls. But we could also show that prematurity per se reduced the sensitivity
in the central visual field (outside the fovea), presumably reflecting a reduced density of
retino-cortical neural channels (Larsson et al 2004). This was true also for children born small
for gestational age due to intrauterine growth restriction (Martin et al 2004).
Approximately one third of the children born prematurely and/or with very low birth weight
have cerebral sequelae, such as white brain matter damage (Olsén et al. 1997). Studies
regarding visual outcome, especially the visual field are sparse, due to the wide-spread
misunderstanding that quantitative perimetry is not possible in these children. However, using
a combination of the manual kinetic Goldmann perimetry for examination of the extent of the
visual field, and one of two computerized techniques for examining the central visual field,
we were able to carefully examine a number of prematurely born teenagers and young adults
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with visual dysfunction due to white matter damage of immaturity of pre- or perinatal origin.
They all had subnormal visual field function, although the depth and extension of the defects
differed between subjects. Typically, the inferior field function was more impaired than the
superior. We could also show that, as in adults, the static computerized techniques revealed a
slightly higher frequency of abnormality (Jacobson et al. 2006) compared to Goldmann
perimetry.
In a separate study of adolescents with very low birth weight (<1500 g) we found that the
subjects are at a disadvantage regarding visual outcome compared to subjects with normal
birth weight (Hellgren et al 2007). Almost one fifth of all VLBW children, and 40% of those
with white matter damage, had subnormal visual fields (Hellgren et al. 2009).
Congenital cataract
It is well known that dense cataract, even when surgically treated early in infancy, causes
persistent impairment of visual acuity. Recently we have shown that not only the extent of
the visual field, but also the sensitivity in the 30-degree visual field is affected, although less
pronounced than visual acuity (Martin et al. 2008a). This finding has to be taken into account
when evaluating visual field results in for example in the diagnosis of glaucoma, a frequent
complication after cataract surgery in early infancy.
Glaucoma
Computerized visual field examinations are gold standard in the diagnosis and follow-up of
glaucoma. Nevertheless, not many studies are published using computerized perimetry in
pediatric glaucoma. We have found that the Rarebit perimetry is well suited for glaucoma
management in children (Martin & Lundvall 2007). Recently we could show that the visual
fields remained essentially unchanged during 5 years of follow-up in children and
adolescents, carefully treated for glaucoma (Martin & Lundvall 2009).
Conclusions
Visual fields develop rapidly during early infancy as shown in studies with tests appropriate
for the age of the child. However, conventional perimetric techniques are less suitable for
children below the age of 7 to 12 years. Recent developments in perimetric methods may
improve the ability to detect visual field abnormalities in even younger children.
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