The human visual system is our most dynamic sense. At birth, many of the components of the visual system are in place, such as the eyes, optic nerve and brain, but it is after birth that growth, development, coordination and fine tuning of the system occurs. The visual system requires light, movement and change in environment to make these developmental processes occur.
Vision is generally thought of as what we can see. There are, however, many systems involved before we are able to see things and analyse the information. First we need to have the eyes point in the right direction and then get the eyes focussed and aligned on the target to make it single and clear. The information must then be captured on the retina, processed, and sent to the brain for further processing and assessment. The brain must then make judgements about the information and begin to put actions into place. In this regard, vision is our most important sense, allowing us to move through space, interpret our surroundings and provide feedback over a period of time, eg. It takes millions of calculations and recalculations to accurately catch or hit a ball in sport.
It is the normal development of the visual system that allows all the individual systems to coordinate and allow us to function effectively. Some of the changes that occur in the first 6 months of life are:
The newborn eye is remarkably close to its full adult size. At birth the length of the eye is around 17mm, growing to full adult size of 23mm. The power of the cornea is around 50 dioptres at birth, reducing to 43 dioptres as an adult.
The visual acuity of an infant develops rapidly from birth. At 1 month, the child has a visual acuity of 6/180, improving to 6/30 at 2 months and to adult levels of 6/6 by 4-6 months.
Focusing, like visual acuity appears to develop to full adult levels by around 4-6 months. At 1 month the infant has a fixed focus at around 20 cm, which is the perfect distance to see the mothers face while feeding. At 2 months there is some flexibility, while at 4 months there is adult capacity to vary focus and to fixate on objects at different distances.
At birth, a primitive reflex called the tonic neck reflex exists. This reflex has the head and eyes pointing at the outstretched hand when the head is turned to the side. At 4 months, the child exhibits “swiping” behaviour, where it sees an object and tries to grasp it, but doesn’t have the required coordination. At 6 months, the child is able to grasp an object they see.
At birth, the child’s eyes generally point in the same direction, but they do not work together as a team. This is why it is common for an apparent turned eye to be present. The eyes generally move together, but only one eye fixates a target. By 8 weeks, the child is generally able to use both eyes as a team.