When the human eye looks at an object, light rays pass through the lens and fall on the retina that is located at the back of the eyeball. The retina has two types of specialized nerve cells that are called rods and cones. Rods are more sensitive to light. These cells are located more peripherally on the retina. Since they are sensitive to light and are placed peripherally on the retina, rods play an important role in night vision and peripheral vision.
The other type of cells on the retina, called the cones, are placed along the central part of the retina. These cells are responsible for color vision and primarily recognize blue, green, and red color. The visual system can blend these colors in varying proportions, and can recognize a wide spectrum of many other colors from this basic color bank.
The first optic tissue in the fetus appears as two tiny little blobs placed on the sides and at the front end of the neural tube. This happens as early as 22 days after conception. During the first five weeks, these blobs change into cup-shaped structures, and also get differentiated into the lens and retina of the eye.
These blobs then migrate toward the mid-line by about eight weeks of fetal life. The retina or the image-capturing screen located at the back of the eye is developed between the 6th and the 20th week of gestation.
The nerve that transmits light from the eye to the brain is called the optic nerve. It is formed by the eighth week of gestation. By the 27th week of gestation, the fetal brain starts responding to stimulation by light.
Once the retina has perceived an image, the message is carried by the optic nerve, and reaches the primary visual cortex in the brain. The primary visual cortex is the place where all information about an image is processed. It is located at the rear of the brain.
The visual cortex undergoes massive growth between 14 and 28 weeks of gestation. Because of the complexity of the visual system and the amount of information to be processed, such as depth, dimensions, movements and color, it is not surprising that the brain devotes more area to the visual sense than to all the other senses combined together.
In a newborn, the eye is about one-third of its adult size. The basic elements of the visual system are present but not fully matured. The lens and the central part of the retina where the receptors are located are still immature, and the movements of the eyes are also not very well coordinated.
Visual acuity in an adult is 20/20. The visual acuity of 20/20 in an adult means that he can see and clearly identify an object, 20 feet away from him. If an individual has a visual acuity of 20/50, which is not normal, it means that he can see an object clearly from a distance of 20 feet compared to a person with normal visual acuity who will be able to see the same object clearly from a distance of 50 feet.
By the end of the first year the visual acuity of the baby is the same as that of an adult
At birth, the infant’s acuity is about 20/400, but starts to improve very quickly during the first year of life as a result of changes in the brain and the neural connections. By one year of age, most infants reach a level of 20/20 which means it is now as good as that of an adult.
For the first few weeks of life, infants best see black and white. By two months of age, the ability to distinguish between different colors is developing rapidly, but color vision is still in a rudimentary stage. As weeks go by, they can see farther and farther, and by three months, babies can easily see objects within a distance of 10 feet.
Despite the ability to focus at only a short distance at birth, newborns actively scan their surroundings. Newborns like to look at different geometric shapes, and enjoy looking at complex patterns, such as checkerboards, concentric circles and stripes rather than plain patterns. They seem to concentrate more on black and white and three-dimensional objects, and like to look and concentrate on areas of high contrast and at the edges between the shapes and the background.
Newborns also have an affinity for human faces or even portraits of human faces drawn on a white background. A newborn has the ability to identify and recognize the mother’s face as early as two days after birth.
There is a major spurt of activity in the visual system between four to eight months of the infant’s life. This is what is called the “critical window of opportunity” for vision.
The critical window of opportunity for visual development is between four to eight months of age
Visual stimulation should be carried out to the maximum during this phase of life, in order to create and strengthen as many connections as possible between the eye and the brain, both in terms of quality and quantity.
Due to this early spurt of activity, the child’s early visual experiences will leave a strong and a long-lasting impression as far as visual perception is concerned. Heredity does play a role in the quality of vision, but it is critical to remember that early visual stimulation and visual experiences play a major role in the child’s eventual visual capabilities.
By four months of age, the special areas responsible for processing the color vision in the cortex are fully mature.
Normal development of vision requires that both the eyes function together. This is called binocular vision. On average, binocular vision develops around three and a half months of age. Anything that prevents a child from using both the eyes together increases the risk of permanent visual defects, which may not be corrected later on. It is therefore important that babies who are showing signs of cross-eyes should be examined promptly.
Besides a problem occurring in the binocular vision, the other one that could occur is the lack of clarity in vision. This may happen because of some opacity in the lens of the eye, which is known as congenital cataract. If the opacity is not removed or corrected in time, it can lead to permanent visual disability.
This happens because the eye-brain connection has not been stimulated at the right time, and the critical window of opportunity for visual development has been missed out.
It is essential that congenital cataracts be removed as soon as they are detected. If left untreated, and not removed by the age of six months, chances of achieving a reasonable amount of visual acuity in the future are slim. It is now a common procedure to remove cataracts as early as two months of age.
The attention span of a newborn can be increased from a few seconds to more than a minute by offering him visual stimulation in sharp contrasting black and white flash cards, and with black and white toys. This ability of the newborn to gaze attentively at these patterns is called fixation.
The process of following a moving object within the visual field is called tracking. If a newborn is offered an object of interesting shape in black and white color, he will track the object with a lot of interest.
The ability to track in the first few weeks of life is not very well developed but increases rapidly by the third month. Using highly contrasting colors and interesting complex shapes as stimulation tools can greatly enhance the tracking ability of a newborn.
When an infant is presented with several different objects within his visual field, his eyes will show small jumping movements from one object to the other until they finally settle on the object of his choice. This is called scanning.
Scanning, tracking, and fixation are all important components in the development and enhancement of visual abilities. The human eye and the visual pathway are indeed one of the most fascinating areas of research in the medical field.
Now that we know about the timing of visual pathway development and the critical periods of eye/brain connection, every opportunity should be taken to provide the infant with rich experiences to stimulate vision. It not only enhances the visual pathway, but also at the same time stimulates and nurtures the other vital senses as well.
"Every Second is Important, And Every Second Counts"