Lea Hyvärinen, MD

Paper prepared for the WHO meeting on Classification of Visual Impairment
in September 2003

Infants and children with impaired vision are a small minority using low vision services in industrialized countries, whereas in many developing countries children are the largest group of clients with low vision. If visual impairment and disability are measured as years of life with disability, the impact on development, learning and activities is seen in correct perspective.

The group of infants and children range in age from birth to 16 or 18 years. Therefore the needs in terms of early intervention, assessment techniques and devices vary more than they vary in the care of adult clients. Multi-impairment is common among the visually impaired children in the western countries where more than 60% of visually impaired children have at least one additional impairment or chronic disease and many children have several impairments (1). Brain damage is the largest single cause of visual impairment in children in western countries.

The greatest difference between adults and children with impaired vision is related to its effect on development. Children are developing functions and concepts based on impaired vision whereas many adult persons with low vision have the background of normal visual experiences. The differences between adults and children should be mirrored in our definitions of impairment and disability and in the structure of services.

How should we define paediatric low vision as an impairment?

Visual acuity

The World Health Organization definition of low vision is based on measurement of distance visual acuity and the size of visual field. Visual acuity range is "less than 6/18 (0.3, 20/63) to light perception" and visual field "less than 10 degrees from the point of fixation".

The International Council of Ophthalmology specified in 1984 that visual acuity is measured with line tests at a distance of 4 meters when adult persons are examined (2). Well functioning school children can be examined like adult persons; younger children are tested at a distance of 3 meters. A great majority of visual impairments in children are congenital or occur during the first year of life, thus visual acuity and visual field cannot be assessed. Many children with multi-impairment can never be tested with line tests.

When a child cannot respond to line tests, single optotype tests are used. The values resulting from measurements with single optotypes are not comparable with results based on line tests. They may overestimate visual acuity by several lines and thus the definition of low vision is not the same as for adult persons. If single optotype tests are used for classification, the threshold values for the low vision categories for international reporting need to be defined. The present use of single optotype tests to define the degree of visual impairment and to make decisions on educational categories and low vision services is without foundation and prevents many children from having services that they need and deserve.

During infancy and in the examination of children at early developmental levels, grating acuity cards have been used to estimate visual acuity. The response in that test situation is detection of presence of more visual information in the grating compared with the equiluminant gray area. The task is to discern "where" the information is without identifying "what" it is. This response is possible up to the level of 5-6cpd in children and adult persons who have no measurable optotype acuity. They do not recognize the large optotypes by form but deduce the information from their eye movements while tracing along the edges of the optotypes. Thus in terms of optotype acuity they are profoundly visually impaired, in terms of grating acuity they are mildly impaired. The use of grating acuity values for classification of visual impairment is misleading and should not be allowed.

Children with severe motor impairments and children with profound intellectual disabilities may not have command of eye movements to respond in grating acuity tests or in test situations that require fixation of gaze on a target of certain size and contrast. Therefore classification of their visual impairment cannot be based on visual acuity.

Visual acuity measurements may overestimate visual functioning but they may also underestimate it. Visual acuity less than 0.3 (20/63, 6/18) does not always mean low vision. In Finland we have a mild form of x-linked retinoschisis with barely visible changes, folds in the central retinal. Visual acuity is often at the level of 0.2 (20/100, 6/30) and yet visual functioning is very close to normal. At pre-school and school age it is difficult to notice any effect of the lower than normal visual acuity on a boy's play or in sports. Several men with this mild form of retinoschisis have their driver's licenses and have driven their cars for more than a million miles without accidents and tickets. Careful recordings of eye movements and reactions to visual information in traffic scenes have shown good performance. Since their contrast sensitivity in the pericentral visual field and their flicker sensitivity are normal, these functions apparently depict the category of impairment better than visual acuity. Visual acuity measurements alone are thus not suitable for assessment of vision in children, even if the children are able to be tested.

Visual field

The WHO definition of low vision is also based on the size of the visual field, the limit of visual field size being 10 degrees from the point of fixation. Visual field measurements are equally difficult as testing of visual acuity during the examination of infants, young children and multihandicapped children.

However, not only the size of the visual field should be measured because small scotomas in the central visual field may interfere with reading and other demanding near vision tasks although the size of the visual field may be normal.

On the other hand, half field defects, hemianopias may be only partial. Even if there seems to be total hemianopia when measured with Goldmann perimetry or any of the automated perimetries, there may be normal or near normal perception and awareness of movement in the "blind" hemifield or there is no subjective awareness but yet useful vision in the "blind" hemifield, "blindsight". It is important to know that hemiplegic infants may have loss of only attention to a hemifield and, with training, may develop nearly normal function in the originally 'hemianopic' visual field. Training may still be effective several years after the original damage to the visual pathways even in adults (3).

The size of the visual field can be estimated even in infants by using confrontation techniques. However, when an infant is fixating the face of the examiner, attention to the face in the central vision may inhibit responses to peripheral stimuli so that the infant seems to have a constricted visual field, although the size of the visual field may be normal. Children with brain damage may have simultan agnosia and therefore may be unable to respond during perimetric tests.

In the assessment of visual field the effect on orientation and mobility should be assessed as one of the important functions. Half field defects, homonymous hemianopias, may or may not cause problems in mobility.

Central scotomas affect vision for communication because the child seems to be looking past the person (s)he looks at. Sighted persons in western countries expect normal eye contact during communication. Since a child with eccentric fixation seems to look past the person whom (s)he is talking to, the child is in danger of being assessed as "autistic" and "avoiding the eye contact". Eccentric fixation thus causes a social handicap in communication situations, especially in groups of pre-school children who are highly dependent on visual communication.

Visual acuity and visual field as classifiers of visual impairment

Based on the discussion above it can concluded that the two cardinal measurements for classification of visual impairment, visual acuity and visual field, cannot be properly measured in infants and children. Visual acuity, measured with a line test in examination of well functioning school children, can be used for classification of visual impairment for international reporting, but not in any other groups of children. For classification of visual impairment in infants and young children in general, in older children with brain damage and in children at early developmental levels, we need a classification that is not based on visual acuity. Similar difficulties of measurement are present in the measurement and interpretation of visual field and thus should be dealt with in the classification.

The WHO Bangkok meeting emphasised that "This working definition is solely designed for reporting purposes and SHOULD NOT be used for eligibility for services" (4). However, in many countries visual acuity value 0.3 (20/63, 6/18) is used as a pass/failure limit. If visual acuity, measured at any distance and with any visual acuity test is better than 0.3, the child is excluded from low vision services and special education. This is a serious misunderstanding that should be corrected. Eligibility for services should be evaluated based on the effect of visual impairment on the activities/functions, i.e. on the degree of disability. In children also developmental questions need to be considered.

How to assess paediatric low vision for activities and development?

Since the need for services is related to the effect of visual impairment on activities, to visual disability, it should be carefully assessed. During observation of an infant or a child in different play, therapy and communication situations it is possible to reveal the effect of visual impairment on the child's functioning. As background information we use the results from the assessment of visual acuity, visual field and all other measurable functions, not the measured values as such but to understand the effect of the decreased visual function on

  1. communication, in both person to person communication and group communication,

  2. orientation and mobility,

  3. sustained near vision tasks like reading and looking at pictures and

  4. eye-hand co-ordination and use of vision in daily living skills.

These activities vary at different developmental levels.

Since an infant and a child are in the phase of rapid development, two aspects need to be considered during each assessment:

  1. use of vision in the activities that the infant/child has now, and

  2. the effect of limited visual information on further development of all functions, including interaction/communication, motor development, development of spatial concepts, object permanence and language.

Since the development of an infant and a child is so dependent on parents and caretakers, it is important to also consider in each case, whether

3. the child is likely to get sufficient support or whether special intervention is required.

In the assessment of the infant's/ child's needs for services and school placement we need to understand which techniques of learning are available to the infant/ child. Since the effect of an impairment on the activities varies from activity to activity, following questions are answered in the assessment of each functional area: does the infant/ child have enough sight to perform a particular function

  1. like a child with normal or near normal vision, or

  2. using techniques that are typical to children with low vision, or

  3. is that particular function dependent on information from other senses than vision, i.e. is it performed using techniques typical to blind children.

Since the observations and their interpretation require understanding of techniques and processes of learning, each assessment should be based on a combination of medical and special educational knowledge. The present overrepresentation of medical expertise in the evaluation of children's needs of vision services is unfortunate because the effect of visual impairment on the different functions of a child is not known to most medical experts. They observe and assess children in an environment that is different from the normal environment of these children and the time used for the assessment is often too short to allow proper understanding of a child's vision for development. This is the more important, the younger the infant or the more multi-impaired the infant/ child is.

The claim that medical doctors may be unable to make proper diagnosis on children's visual disability, does not mean that the medical assessment would be without value. It gives necessary information

  • on the anatomy and physiology of the disorder that cause the impairment,

  • on refractive errors and accommodation capacity of the visual system and

  • from the clinical tests.

For the assessment of the needs of low vision services, the use of vision in each area of functioning is then evaluated during therapies, play situations and specific functional tests that measure the use of vision. The low vision services are best planned when based on this functional assessment.

Among the functional areas that should be considered in the evaluation of needs for low vision services, communication is the most important function in all age groups but especially in infancy. Even if infants skilfully use smell and auditory information to recognise significant adult persons, visual information is their most important avenue of information in early interaction and learning.

Since visual communication is the dominant mode in the interaction with a baby, lack of eye contact and delay in the development of social smile negatively affect interactions between the infant and the parents. If the unusual visual behaviour of the infant is allowed to affect early bonding there will be decrease in communication with the infant and thus increase in deprivation. A visually impaired infant needs more communication and a skilfully planned introduction to the environment than a sighted infant to learn about the world and about interaction with adults and children. The need for services means early support and guidance to the parents and caregivers in communication through other modalities. Everyone needs to accept the close communication distance and to increase contrast of the communicative information so that it is seen by the infant.

Visual information in communication and interaction is at low contrast levels if not specifically enhanced. When we communicate with a hard-of-hearing person, we do not whisper because it would be an impolite and strange behaviour. When we communicate with visually impaired persons, we use low contrast information in motion without asking whether it is seen! The distance within which the infant/ child can get sufficient visual information for communication may be very limited. The communication space or sphere should be determined for each child. Measurement of an infant's/ a child's contrast sensitivity with the Hiding Heidi test is a good demonstration of the child's capability to use visual communication.

Lack of accommodation and problems in fixation of gaze may disturb communication and should therefore be examined in each case and combined with training using near correction lenses, "reading glasses", to give the infant/ child a clear image on the retina.

If contrast sensitivity and visual acuity are so poor that the child cannot properly discern facial expressions, the expressions can and need to be taught as a part of early intervention using high contrast pictures of expressions, by making visuotactile pictures of expressions together with the child and by studying expressions using magnifying mirrors and strong make-up on both the child, the therapist and the parent or care giver.

Special education in communication skills seems to be neglected in many countries. It is not appreciated that communication skills of children with low vision need to be trained through the pre-school and school age, especially in the teens when communication is as strongly visual as in the interaction between toddlers.

The negative effect of visual impairment on motor development is important to notice early. Supportive motor training should be instituted before marked delays have occurred. With skilful training an infant and child with visual impairment may have normal motor development.

As a prerequisite of motor learning, the infant needs experiences of spaces of different size and with different surfaces to develop spatial concepts and orientation in space using the visual, auditory and tactile cues available. Training auditory functions requires knowledge of the child's hearing and thus testing of hearing should be an integral part of each low vision assessment. The compensatory functions are equally important to assess as the impaired function, especially hearing.

Although orientation and mobility instruction is a well known part of special skills of visually impaired persons, orientation and mobility skills of children with low vision do not get similar attention as those of blind children. However, learning visual orientation techniques and combining them with the use of auditory and all other cues from the environment is a special area of learning that should be included in early intervention and as a special skill to be trained during school age. To plan training to meet the needs of each child, vision for orientation and mobility is assessed and reported as a separate entity.

A visually impaired child does not learn about every day activities the same way as a sighted child. Different activities need to be demonstrated at close distances and the use of other modalities is often necessary also in this area of learning. Therefore vision for incidental learning and for learning daily living skills should be evaluated and reported to the early intervention specialists for further assessment in practical learning situations.

How could we classify paediatric low vision?

There is need for classification of paediatric low vision for international reporting, for administration of low vision services and for planning special education. A classification based on the effect on activities would also depict visual impairment, depict which visual functions are involved.

Traditionally the reasoning has been that since the impairment causes a disability it should also depict it. From the work with and for the visually impaired we know now that impairment, at least when defined as at present, does not depict disability in children. If we assess the child's disability we learn which visual functions are impaired.

In the definition of 'visual impairment' we need to look at both words.

What is vision? Vision consists of three basic functions:

We see forms, colours and movement.

The forms are seen both with colours and as achromatic forms, in different shades of grey, and they are perceived also in motion. They are forms in the environment or drawings or characters related to written information.

When we assess, how much vision is impaired, we should assess form vision more broadly than we do at present. Recognition of characters is one of several specific forms of recognition. Recognition of facial features and expressions is socially more important than recognition of letters and numbers. Recognition of landmarks is necessary for visual orientation in space. Recognition is based on memory functions; recognition tests are not purely visual tasks. The complex connections of vision and memory are often clearly demonstrated by visually impaired children with brain damage who may be able to handle visual information in working memory but cannot store it or cannot retrieve it from memory later.

Colour vision is not routinely tested as a part of low vision assessment in most low vision services. It is easy to the brain functions to recognise colour information and colour recognition is often spared when pathways to form recognition are damaged. Colour matching is thus possible but colour naming may be lost. Since colours are important in play and in education, colour vision should be routinely assessed using quantitative tests.

Motion perception may be spared when form perception is lost in certain brain lesions. Investigations at the Vision Laboratory at the University of Helsinki have shown that stimulation with flickering patterns may improve vision in 'blind' hemifield years after the loss of vision. Motion perception should be evaluated as a part of low vision assessment but the techniques for clinical testing are not yet simple enough to be widely used.

Visual functioning is more than a mere sum of its components because there are numerous cognitive functions related to the use of vision. Therefore measurement of individual visual functions is useful in evaluating the quality of visual image, not its use.

Visual disability or the effect of impaired vision on the activities is usually evaluated in four main areas (4, 5):

  • communication,

  • orientation and mobility,

  • activities of daily life and

  • sustained near vision tasks.

In each of these four areas a person uses either techniques typical to sighted people or typical to persons with low vision or those typical to the blind. When the four main functional areas are assessed it is possible to classify children and adults with low vision as profoundly, severely, moderately and mildly visually disabled for the reporting purposes.

The boarders between the different groups are not clear cut because a person may use techniques typical to a blind person in one function, for example: use long cane because of tunnel vision, but techniques of normally sighted people in another function, for example, read without the help of any optical devices at a normal reading distance. In young children ADL and sustained near vision tasks can be combined to one functional area. If each functional area receives 1-3 points:

  • blind techniques 1 point

  • low vision techniques 2 points

  • sighted techniques 3 points,

and ADL and sustained near vision task are combined as one functional area in the assessment of young children, we would have a variation between 3 and 9 points.

Three points would mean functional blindness, four points profound low vision, 5 - 6 points severe low vision, 7 points moderate low vision and 8 points mild low vision. With 9 points there would not be any reportable visual impairment although the child may have problems caused by a visual impairment and need for services or for modification of some learning techniques etc, especially if the child has another disability.

In the assessment of school children the variation would be between 3 and 12 points.

In special education, children can be reported also based on their learning medium and need of optical devices. In terms of learning medium they are either Braille readers or use print, some children, however, use both. In terms of low vision devices they either use them or use geometric magnification by holding the book at a close distance.

For administration of low vision services and for the decisions on specific therapies and education each functional area needs to be evaluated separately. This follows usual reasoning in medicine; we do not treat intraocular pressure or blood pressure because a certain level in repeated measurements is reached but because of their effect on the health. However, if a measured value is very high, we know that therapy is necessary. Similarly, in profound low vision the need for special services is apparent. It is in the group if mild low vision where the decisions may be difficult. Even if a child needs to use low vision techniques in one functional area only, the need should be recognised and proper devices and training given.

In the low vision care of children there is one important additional aspect - future. If a child has a progressive disorder, retinitis pigmentosa being the most common disorder of this type, future needs must be considered as well. For example a child with Usher Syndrome needs special training in written language if sign language is the first language, because sign language will be impossible to use if the child loses vision 20-40 years later. In paediatric low vision services we need to constantly look both into the past to understand where the child comes from and into the future to make correct plans. We also need to consider the other impairments, especially brain damage, and chronic diseases that affect visual functioning to choose the best intervention to support each child's development.


1. Rosenberg T, Flage T, Hansen E, Riise R, Rudanko SL, Viggosson G, Tornqvist K. Incidence of registered visual impairment in the Nordic child population. Br J Ophthalmol. 1996 Jan;80(1):49-53.

2. Visual Acuity Measurement Standard (1984) Consilium Ophthalmologicum Universale, Visual Function Committee.

3. Hyvärinen L, Raninen AN, Näsänen RE. (2002) Vision rehabilitation in homonymous hemianopia. Neuro-Ophthalmology 27(1-3): 97-102.

4. Management of Low Vision in Children, Bangkok July 1992. WHO Publication 93.27.

5. Hyvärinen L (1985) Classification of visual impairment and disability. Bull.Soc.belge Ophtal 215:1-16.