Binocularity, strabismus, visual orientation in space
At the age of three months eyes of normally developing children are usually working together although strabismus still occurs, especially when the infant is tired. Visually impaired children may develop binocularity but it is rare. In many cases one of the eyes sees better that the other and thus functional amblyopia may develop on top of the structural amblyopia in the more poorly sighted eye. Training of amblyopia needs to consider the role of vision in the functions of the baby. If the amblyopic eye has very little vision, the better eye cannot be covered for more than 10-15 minutes at a time or even less, to observe whether the infant is able to use the more impaired eye well enough to play and to communicate. If not, then brief stimulation with very strong stimuli can be tried (see Stimulation). To learn to use an eye the infant must be interested in looking with that eye. If patching makes the infant's world disappear, it may be too difficult a situation. Some infants protest by screaming, other infants by falling asleep and thus patching is useless. Therapy situations are important for diagnostic observations and assessment of amblyopia training.
Oculomotor functions, tracking and saccades are trained as a part of therapies by using high contrast toys to attract the infant's attention. Sometimes toys that the infant moves himself elicit better following movements than toys shown to the infant.
In the interaction between the infant and the parents 'visual sharing' starts normally at this age; the infant sees something interesting, looks at it, looks at the parent and then at the interesting object, the parent responds to the cue, looks at the object and tells the child what the object is and may ask, whether the infant might like to play with it. Sharing may also start from the adult looking at something. Baby notices it, looks at the same object that then is described to the infant when the adult person notices the child's interest. Sharing interest is an important part of interaction and thus we need to observe whether it is possible to the visually impaired infant. This kind of incidental learning and communication is not available to most visually impaired infants. Their world is smaller than that of their peers and they cannot see objects or facial expressions well enough to initiate visual sharing. It can be trained by showing objects that the infant knows and by telling the infant: 'I have a soft brush. Would you like to have it for a while?' Or, 'Are you looking at your mug, would you like to drink?' Infants start to understand this kind of questions quite early, not word by word but the intention to share a common interest and learn to initiate interaction by looking at objects.
Refractive errors develop toward emmetropia in healthy children. Among the visually impaired children this development is rare and thus large refractive errors typical to the early part of the first year may remain. If accommodation does not develop, an infant's vision for communication is disturbed. Thus accommodation needs to be measured at least every other month during the first year as a part of assessment of visual functioning until it appears. When insufficient accommodation is diagnosed 'reading lenses' of +2.0 to +4.o are prescribed for near vision tasks (see Accommodation). This near correction needs to be used during all tests at near, also grating acuity and Hiding Heidi tests,
Visual information stimulates infants to reach for and to move toward interesting objects. If an infant's visual sphere is limited, motor development is slow but it can be kept within normal milestones with physiotherapy (occupational therapy in the US), preferably by a therapist with training in neurodevelopmental therapy (NDT). Even short periods of useful vision support motor development, as was seen in the infant who had clear cornea in one eye for a few weeks. Her motor behaviour became that of a sighted child and remained so even when form perception was again lost. When she kicked ball at the age of two years her balance and motor skills were age appropriate.
Orientation in space requires stronger contrasts if a child's vision is impaired. The usual pastel colours are not good in the crib or as the colours of the playmat and toys. If the mother or someone else has time to sew a playmat with high contrast details, it becomes a useful plaything for development of orientation in space.
Playmats for training orientation in space. The ends of the playmat are clearly different both visually and tactily. The dark surfaces are smooth and the light surfaces are rough (this design is chosen because most dark materials with rough surface do not keep their colours well when washed). This kind of surface stimulates both tactile and visual exploration and helps to combine the information from the two modalities because the edge between two different surfaces coincides in visual and tactile information.
Another play situation that activates the infant to explore space is the resonance board with clear visuotactile markings on it.
In the assessment of vision: remember to assess vision for balance, for communication and for reaching, i.e. peripheral visual field, contrast sensitivity and visual sphere. Make sure that the infants refraction and accommodation have been measured. When in doubt about accommodation use plus lenses (basic refraction + reading addition +3.0) in near communication.