Already at birth, the visual function of a child displays some unconditioned visual reflexes – the direct and consensual reaction of the pupils to light, a short-term reflex for the turn of the eyes and head toward the source of light, an attempt to follow a moving object. As the child grows, all the other visual functions gradually develop and improve.
Sensitivity to light
Sensitivity to light appears immediately following birth. From the very first days of the child’s life, light has a stimulating effect on the development of the entire visual system and serves as a basis for the formation of all its functions. Light does not create visual images in the new-born child’s eyes, but mainly provokes inadequate protective reactions. The sensitivity to light of new-born children is very low. In conditions of dark adaptation, it is 100 times higher than in the course of light adaptation. By the end of the first six months of life, the light sensitivity of the child grows considerably and reaches 2/3 of that of an adult. By the age of 12-14, it comes to normal. The low light sensitivity of new-born children is explained by the insufficient development of the visual system, particularly the retina. The expansion of the pupil in darkness is slower than its narrowing in light. By the second and third weeks of life, the development of conditioned-reflex ties begins to lead to a more sophisticated activity of the visual system, the development and upgrading of the functions of object, colour, and solid vision.
The central vision of a child appears only in the second or third months of life. Later it undergoes gradual improvement – from an ability of discerning an object to an ability of distinguishing and identifying it. The potential to discern simple objects is based on the corresponding level of the development of the visual system, whereas recognition of complex objects is associated with the development of intellect.
At the fourth or sixth month of life, the child reacts to the close appearance of faces, and earlier – on the second or third month of life - recognizes mother’s breasts. On the seventh to tenth months of life, the child is able to discern geometric forms (cubes, pyramids, cones, balls), while recognition of drawn images begins on the second or third year of life. It is only by the time of schooling, when the child acquires full perception of object forms and normal acuity of vision.
According to medical studies the vision acuity of new-born children is low and ranges from 0.005 to 0.015. During the first few months of life, the vision acuity grows to 0.01 – 0.03 D. By the age of 2, there is an increase up to 0.2 – 0.3; and it is only by the age of 6-7 years (according to some reports by the age of 10-11) when acuity reaches 0.8 – 1.0.
The development of vision acuity goes hand in hand with formation of colour perception. It has been discovered in the course of medical studies that a child is able to recognize colours for the first time at the age of 2-6 months. The perception of colours begins first and foremost with red. Later the child is able to discern colours of the short-wave section of the spectrum (green, blue). By the age of 4-5 years, the colour vision is well-developed but continues its improvement further. Colour perception anomalies are approximately same (in terms of occurrence and sex-relation) as they are in adults.
Field of vision
The field of vision in children of pre-school age is about 10% narrower than in adults. By the time of schooling, the field of vision reaches normal dimensions. The blind spot in vertical and horizontal directions, as estimated from a distance of 1 meter, is 2-3 cm greater than in adults.
The binocular vision develops later than the other visual functions. The main feature of binocular vision is its ability to provide a more accurate evaluation of the third spatial measurement – the depth of the space. There are three basic stages in the development of spatial vision in children:
- At birth, the child has no cognitive vision. Bright light causes the pupil to get narrow, the eyelids close, and the head jerks back, while the eyes roam aimlessly and independently from each other.
- Two or five weeks after birth, bright light stimulates the child to keep eyes stable and watch the bright surface intently.
- By the end of the first month of life, the optical irritation of the peripheral zone of the cornea causes a reflex movement of the eye; as a result, a light object is perceived by the centre of the retina. This central fixation is initially done fleetingly and only by one eye, but gradually due to repeated occurrences, the fixation stabilizes on a bilateral basis and the aimless movement of the eyes are replaced by coordinated movement of both eyes. Thus, physiological basis for binocular vision is developed.
The binocular system develops despite the obvious inferiority of monocular vision systems and it develops faster with the goal to ensure spatial perception which best facilitates the adaptation of the organism to the environment.
During the second month of life, the child begins to make himself familiar with the nearest space. Initially, the child sees the nearest objects in two dimensions (height and width), but thanks to the sense of touch begins to perceive them in three dimensions (height, width and depth). Foundations are laid for the first notions on the extensionality of objects.
On the fourth month of life, the child develops a grasp reflex. Most of children identify the direction correctly but mistake the distance. They also make mistakes in identifying the extensionality of objects and attempt to grasp flecks of sunlight and moving shadows.
After six months, the child begins to master distant space. Crawling and walking come in place of touching. The child is able to compare distances of movement against the changing size of the images on the retina and the tone of the eye movement muscles, thus creating visual perception of distance. This function ensures three-dimensional perception of space and is combined only with the complete coordination of the movements of the eyeballs and their symmetric position. The mechanism of spatial orientation goes out beyond the framework of the visual system and is the product of complex activity of the brain. In this connection, the further improvement of spatial perception is closely associated with the cognitive activity of the child.
There occur substantial and qualitative changes in spatial perception at the age of 2-7 years when the child masters speech and develops abstract thinking. The visual assessment of space is improved at a more advanced age.
The further development of visual sensations of a child incorporates both innate mechanisms and mechanisms acquired in the process of accumulating life experience.