This text was originally written for the book on assessment of vision, written by me and Namita Jacob. It was not used in the book in order to keep it concentrated on assessment problems. This information is important to keep available for young families and all people who teach or care for children. Workers of the basic health care and teachers and therapists have an important role in the detection of visual problems and disability in healthy looking infants and children. Infants’ parents should also know the main features of early visual development and require examination by a pediatric ophthalmologist if there is a delay in the infant’s development.
The first year
The first year of life is a period of great changes and development of the brain. It is also the period when many disabling conditions become apparent. Therefore knowing the development of vision during the first few weeks and months is crucial in the care of all infants and in the early diagnosis of deviations from the norm.
During the first month of life an infant starts looking at objects close to his face because his gaze is focused at the distance of about 30 cm (tonic accommodation). He is especially interested in the human face and looks intently into the eyes of adults as though he was peering through their head. At around the sixth week the child becomes interested in the complicated patterns in his surroundings and the focusing, accommodation starts to occur at different distances.
It is also at around six weeks that most healthy infants have eye contact; although in some infants it appears two or three weeks later. The photo to the left shows this infant communicating with both parents at the same time at the age of 8 weeks. The communicative expressions are first learned through imitation and later, when the smile becomes a happy social smile, through the functions of the mirror neuron networks that are active both during movements and also when we watch and copy movements of another person.
In a number of countries eye contact is one of the recorded developmental milestones of infants. If there is poor eye contact at eight weeks of age, infants should be referred to an ophthalmologist. If nothing abnormal is found in the eyes or visual functioning in general, infants are referred for further examination by a consulting pediatrician or a pediatric neurologist to rule out brain damage. Even if no cause is found for the “delayed visual maturation,” support of early development must be started because the parents need help in developing communication and interaction with their infant who does not respond in a usual way. If the baby does not see clearly enough or there is a loss of the special brain function to recognize facial features, human faces do not have the same value to the infant as they have to normally sighted infants. Parents describe their failure in interaction as “the baby is dreaming in his own world” and not responding with a social smile and body language when parents come close without saying something.
If a specific treatable disorder is diagnosed, early intervention is continued as a part of the therapy. There are countries where referral for further investigation is postponed to the age of three months, which means a long time of worrying for the parents and loss of precious intervention time for the infant.
By the age of three months, visual communication of a normally sighted infant creates an effective bonding; the infant and the adult person understand each other with no difficulty. This behavior is so regular that it can be used as a developmental milestone in all cultures and countries. During an assessment it is present if the infant is well awake.
Among young infants there are some groups that have a higher than usual risk of having problems in vision. The largest groups are infants who have brain damage causing delay in motor development; some of these infants had problems in blood circulation (asphyxia) before, during or soon after birth and are hypotonic, some have hypotonia related to Down syndrome. These infants should be examined for their visual functions and refractive errors early.
Development of eye-hand coordination and an enlarging visual world
A three-month old infant studies his hands and fingers for hours. At this age, ocular motor control, including accommodation and convergence are sufficiently developed for the infant to start studying his hands; first briefly when a hand happens to move in front of his eyes and then for long periods.
The hand-regard behavior is an important step in the development of eye-hand coordination. Through this activity, the infant begins to associate information from seeing his hands with the motor functions of hands and with tactile information when the hands meet at the mid-line and are brought to the mouth. As he reaches for and bats at toys, he learns about distances. He learns that toys are the same although he observes them from different angles and they look different. He also starts grasping toys learning more about texture and size. Through these activities he starts to develop the concept of visual space and visual orientation, which leads to awareness that sounds are related to things. Acting on objects in the environment and development of auditory orientation are often delayed in blind and severely visually impaired infants.
Between the ages of 3-4 months, most infants follow activities in their surroundings using all senses and have learned to vary their communicative expressions. Both eyes normally look at the same object. Squinting may occur only when the child becomes sleepy.
At five to six months of age, infants train eye-hand coordination in reaching for and grasping everything within reach. They observe their surroundings, look at toys that fall from their hands, and recognize favorite toys and the bottle or mug at a distance.
Visual information is central in communication and interaction during the first and second year of life. Infants enjoy watching other infants and children in different activities and learn by copying expressions and motor functions. Such activities as playing with water or eatable colors are fun for the infants and their parents. These “Infant Artists’ Clubs” have become popular in many countries.
Infants watch other infants’ artistic skills and techniques in a painting club for infants.
Development of the qualities of vision
From the age of 12 weeks many infants have their eyes “straight,” looking at same details but turning inwards or outwards may occur when the infant is sleepy. The normal position of eyes during sleep is turning outwards and upwards. Intermittent squint, brief turning of an eye may occur a few times and then disappear or occurs daily and requires consultation. In some countries health care nurses and pediatricians say that “the infant will grow out this problem with eye movements” and that it’s best to wait and see. But you shouldn’t wait for long, especially if the amount of time the eye stays turned is becoming longer because the infant may be losing binocularity, which can be difficult to get back. Loss of binocularity affects fine adjustment of hand movements.
The ability to fixate and follow an object can be used to assess the development of visual functioning. Small balls are rolled on the floor in front of the infant or balls are attached on thin rods and moved against a contrasting background. The child’s eye movements are observed and the size of the smallest ball that the child notices is recorded. Pictures of face and high contrast geometric patterns interest infants and are therefore interesting as fixation targets. Toys coming from behind the infant are used to measure the outer limits of an infant’s visual field. A good stimulus is a flickering light, which at 10Hz gives the largest visual field in young infants.
Young infants tend to look at stripes if they can see them as a pattern, i.e. as long as they can see the difference between the stripes and an equally large gray area. By presenting the infant patterns with thinner and thinner lines simultaneously with a gray surface (a preferential-looking situation) the observer can usually see the change in the child’s behavior when he no longer sees the stripes. Grating acuity can be used to follow development of detection acuity during the first year.
When infant responds with a social smile to the picture of a smiling face of the Hiding Heidi test (produced by Good-Lite), he has shown ability to 1) follow the moving picture with a combined eye and head movement, 2) perceive the picture, 3) recognize it as a smiling face and 4) has responded with a normal social smile, in a few seconds.
Responses to visual information at low contrast can be assessed with low contrast pictures of face, the Hiding Heidi pictures. This is important information for communication because shadows on faces are faint, low contrast information in motion, especially on the fair Nordic faces and on very dark faces. Facial expressions are also fast movements and therefore infants’ ability to perceive movements should be assessed. Simple test situations are not yet available except the Pepi-test, which can be downloaded from www.lea-test.fi and then click on GAMES on the left side panel.
Reaching and grasping
Around five or six months, infants’ hitting and touching objects develops to reaching for objects. First it is a swift reflex like movement as soon as the infant’s gaze notices something interesting. During the following weeks it becomes more selective but it takes months before the inhibitory functions to regulate this motor activity are fully developed and the movement becomes a slower, well controlled reaching for grasping objects.
When the awareness of visual space has developed and the child has learned to coordinate the movements of his limbs, he is ready to reach for and move towards visually interesting objects. From this stage onwards, the child enjoys playing in small spaces. He experiences space visually, tactily, as echoes and with his own body, which facilitates the further development of the concept of space.
The normal milestones of the development of vision
Vision has a central role in the development of many functions. The most important functions affected during the first year are:
– communication and early interaction,
– motor development,
– body awareness,
– development of spatial concepts and orientation in space,
– object permanence, and
Visual functions and main structures of the eyes are recorded at birth and eye contact at 6 or 8 weeks. Ocular motor development is important to follow so that strabismus is noticed early, preferably when it is still occurs only now and then (is intermittent) so that the need of treatment can be evaluated and started early.
The stages of the early development of visual functions that are easy to observe is summarized in Table 1.
|0–1||• turns eyes and head to look at light sources
• horizontal eye tracking, tonic focusing
|2–3||• intense eye contact at 6-8 weeks
• vertical and circular tracking
• interested in mobiles
• interested in lip movements
|3–6||• watches own hands
• reaches toward, later grasps hanging objects
• observes toys falling and rolling away
• shifts fixation across mid-line
• visual sphere of attention widens gradually
• very active in visual interaction
|7–10||• notices small bread crumbs, touches them
• adjusts the grasp to the size of the objects
• interested in pictures, also stereo images
• recognizes partially hidden objects
• recognizes family members by facial features
|11–12||• knows places at home
• looks through window and recognizes people
• recognizes pictures, plays hide-and-seek
• can predict adult’s goals of motor actions
Table 1 summarizes the main steps of the visual development. These milestones are used in many countries in the follow-up of normal development of visual functions and in detecting symptoms and signs of deviations from the norm.
At the age of 9 months, infants start to respond to the Lang stereo picture although some infants shift fixation from the location of one picture to another on the Lang stereo card already at the age of 4–5 months. In experimental laboratories stereovision has been measured a few weeks earlier as a sign of development of binocular vision.
Infants with normal looking eyes and visual functions may have some significant losses in visual functions, like loss of recognition of facial features of the family members. This group of children is increasing. The largest group of these children are infants who were born prematurely and had some circulatory problems at or soon after birth. These infants and children as well as all hypotonic, even slightly hypotonic infants and all infants with communication difficulties should be assessed by an ophthalmologist who is accustomed in the follow-up of development of infants and children.
Children’s interest in books and pictures is individual and is related to their exposure to these materials. Infants often copy the behaviors of their parents. If the parents read newspapers and magazines, the infant may grasp a magazine or book placed suitably low. Development of the concepts of similarity and differences will be influenced by selection of toys and play materials.
Our brains are built to attune with the emotions and motor functions of people whom we find interesting even during the first contact. Infants start to respond to the direction of an adult person’s gaze and turn their gaze to watch the same object at the age of 3 months, which becomes an important ability to show sharing of interest. By the age of one, infants are able to anticipate adults’ intentions by watching their movements (Falc-Ytter et al 2006).
Infants start to notice the difference between family members and other people at the age of 5-7 months and recognition of the faces of family members is well developed at the age of 10-11 months. If an infant does not respond with recognition when a family member comes close to the infant but responds as soon as the person says something, this is a “red flag”, a symptom requiring assessment: whether the infant has a specific loss of face recognition. This problem is especially important if the infant is raised in an environment where he interacts with many people.