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, co-ordination and fine tuning of the system occur. 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 our eyes to point in the right direction, then the eyes must be focussed and aligned on a 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. (An example is the millions of calculations and recalculations required 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 allows us to function effectively.
Behavioural optometrists are particularly interested in the appropriate development of children's visual systems. Of particular concern is how all the component systems operate once the child begins school. A delay in the development of any part of the visual system can have an impact upon the performance of the child at school. This can affect reading performance, concentration and behaviour in the classroom. Regular assessments of your child's vision by a Behavioural optometrist help ensure that all the different parts of the visual system are assessed thoroughly.
Some of the changes that occur in the first 6 months of life are:
Structure: 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.
Vision: 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 (20/20) by 4-6 months.
Focusing: 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 mother’s 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.
Visual guidance: 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.
Eye movement: 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 it to appear that there is a turned eye. 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.
Important Developmental Milestones
a. Birth to 6 weeks of age:
- Stares at surroundings when awake
- Momentarily holds gaze on bright light or bright object
- Blinks at camera flash
- Eyes and head move together
- One eye may seem turned in or out at times
b. 8 weeks to 24 weeks:
- Eyes begin to move more widely with less head movement
- Eyes begin to follow moving objects or people (8-12 weeks)
- Watches parent's face when being talked to (10-12 weeks)
- Begins to watch own hands (12-16 weeks)
- Eyes move in active inspection of surroundings (18-20) weeks
- While sitting, looks at hands, food, bottle (18-24 weeks)
- Now looking for, and watching more distant objects (20-28 weeks)
c. 30 weeks to 48 weeks:
- May turn eyes inward while inspecting hands or toy (28-32 weeks)
- Eyes more mobile and move with little head movement (30-36 weeks)
- Watches activities around him for longer periods of time (30-36 weeks)
- Looks for toy he drops (32-38 weeks)
- Visually inspects toys he can hold (38-40 weeks)
- Crawls after favourite toy when seen (40-44 weeks)
- Sweeps eyes around room to see what's happening (44 -48 weeks)
- Visually responds to smiles and voices of others (40-48 weeks)
- More and more visual inspection of objects and persons (46-52 weeks)
d. 12 months to 18 months:
- Now using both hands and visually steering hand activity (12-14 months)
- Visually interested in simple pictures (14-16 months)
- Often holds objects very close to eyes to inspect (14 -18 months)
- Points to objects or people using words "look" or "see" (14 - 18 months)
- Looks for and identifies pictures in books (16-18 months)
e. 24 months to 36 months:
- Occasionally visually inspects without needing to touch (20-24 months)
- Smiles, facial brightening when views favourite objects and people (20-24 months)
- Likes to watch movement of wheels, egg beater, etc (24 -28 months)
- Watches own hand while scribbling (26-30 months)
- Visually explores and steers own walking and climbing (30-36 months)
- Watches and imitates other children (30-36 months)
- Can now begin to keep colouring on the paper (34-38 months)
- "Reads" pictures in books (34-38 months)
f. 40 months to 48 months:
- Brings head and eyes close to page of book while inspecting (40-44 months)
- Draws and names circle and cross on paper (40-44 months)
- Can close eyes on request, and may be able to wink one eye (46-50 months)
g. 4 years to 5 years:
- Uses eyes and hands together well and with increasing skill
- Moves and rolls eyes in an expressive way
- Draws and names pictures
- Colours within lines
- Cuts and pastes quite well on simple pictures
- Copies simple forms and some letters
- Can place small objects in small openings
- Passes all the tests described on preceding pages
- Visually alert and observant of surroundings
- Tells about places, objects, or people seen elsewhere
- Shows increasing visual interest in new objects and places
