12. TYPICAL FEATURES AND ASSESSMENT OF VISION DEVELOPMENT IN VISUALLY IMPAIRED INFANTS

Functional assessment of vision is based on the findings during clinical examination that is made for diagnostic purposes and enlarges to cover many neuropsychological test situations that need to be modified for paediatric evaluation. The most important findings of the clinical examination are following:

• structure of the eye and the optic nerve,

• structure of the visual pathways if it has been investigated with echography, CT or MRI,

• refractive error of both eyes and - if glasses or contact lenses have been prescribed - whether the correction is equal to the measured refraction or there is under- or overcorrection,

• whether the infant seems to use eyes together, i.e. binocularly, or alternatingly or uses only one eye

• oculomotor functions, alignment or nonalignment of the eyes and what nonalignment may mean functionally, type of fxation, visual anticipation

• all values that have been measured during the clinical examination: grating acuity, contrast sensitivity, size of the visual field and electrophysiological findings. Grating acuity can be measured with Teller Acuity Cards or LEA GRATINGS. Binocular value is the functionally important value but also the monocular values should have been measured. During the first few weeks it is difficult to diagnose deviations from normal binocular development if the eyes look normal and eye movements develop normally, as often is the case in infants with brain damage related vision impairment.

In our functional assessment we use as background information the normal developmental milestones of sighted children and our knowledge on variations in the development of visual functions in children with different degrees of vision impairment and multi-impairment.

Vision has an important organising role in early communication and learning. It gives an effective overview of many situations. Visual information can be looked at repeatedly, objects can be visually explored from different angles and the environment observed thousands of times during each day. In contrast, auditory information is heard once and disappears: its relation to the sound source is detected through vision, sometimes from vibration of the surface of the source. Visual information is constantly combined with information from the other modalities and its use requires development of numerous brain functions that thus need to be assessed as a part of thorough assessment of a visually impaired infant who is likely to have at least one other impairment or chronic illness in more than 60% of cases.

When we observe and assess an infant's visual development we need to assess both the peripheral visual functions and the central visual functions:

• the peripheral pathways develop rapidly during the first year and although there is variation in the speed of myelinisation of the pathways and in the development of individual visual functions, this variation is known;

• use of vision requires development of attention, which may show great individual variation and often is a greater problem in children with brain damage,

• use of vision requires also oculomotor functions although it is possible to see with a totally immobile eye.

• integration of visual information with information from other modalities and use of vision for motor functions are critical for the child's development.

Development of vision of visually impaired infants differs from normal development of a sighted infant. Although development of visual functions is generally well known and is briefly covered in the Information for Parents in the "What I Have Seen" a short table might be helpful. This table is from my book "Vision in Children" and my article "Assessment of Visually Impaired Infants" in the Ophthalmology Clinics of North America, June 1994: