Visual System Development

By Alice Montagner, Optometrist-optician

and student of the Expert Certificate in Vision Therapy

The visual system is the more complex sensory system, but functionally the least mature at birth[1]. Babies are not born with all the visual abilities they need in life. They need to learn how to focus, how to move eyes accurately and how use information their eyes send to the brain [5]. From early infancy, vision has also an important role in communication (even not verbal) and language, between the baby and the world or his/her parents. Eye and vision problems in infants can cause developmental delays. That’s why it’s so important to detect any problems early to ensure babies have the opportunity to develop the visual abilities needed to grow and learn. Parents play an important role in this, so communication to them must be effective.

 

To do this, it is important to know how the visual system develops and how it’s connected to the brain structures.

 

The first trimester [2]

 

The eyes begin to develop in the womb during the 17th day of pregnancy. Embryo’s eyes are like two tiny extensions from the developing brain.

 

At 6 weeks of pregnancy, the embryo’s eyes begin to fold inward and form two cup-like structures that stay connected to the brain by a stalk (which houses the optic nerve). This is the moment in which retina and lens begin to develop. By week 7 to 8 the lens grows to the size it will be at birth. The iris starts to develop at around week 4 to 5 and it will be fully developed within two weeks.

 

At 8 weeks the tear ducts start to develop and will become fully formed a few weeks after birth.

 

The second trimester:

 

Eyelids start to form at 12 weeks of pregnancy and remain close until 27 weeks of pregnancy, after which foetus’ eyes open up: he can blink.

 

The ciliary muscles do not develop until the 5th month of pregnancy and the constriction of pupil in response to light starts only at around the 8th month of pregnancy

 

The third trimester:

 

Between 28 and 30 weeks, the foetus begins to develop eye movements and sleep patterns; the pupils can react to light and he can focus large objects at about 20-25cm away.

 

Retina develops between 24 weeks of pregnancy and 3 to 4 months after birth and the myelination process of the optic nerve takes place.

 

From now to the 6th month after birth, macula develops. Connection between eyes and brain also starts to form and it takes about five months to complete.

 

After birth, the vision is fuzzy because the eyes can see but the brain isn’t ready to process all the visual information[3]. Significant improvement occurs during the first few months of life.

 

However, it is to remember that every child is different and some may reach certain milestones at different ages [5]. Also, there are several things parents can do to help with visual development.

 

AGE

VISUAL MILESTONES [2],[5]

WHAT PARENTS can do [5]

0-1 months

Blinks in response to light

VA is about 1/60
Able to stare at objects 10cm to 25cm away
Begins to follow moving objects

 

1-2 months

Clear vision at 25cm to 50cm away
Able to stare at faces and distinguish black & white images*. Eye movements are not coordinated yet.
Begins to develop tears

If an eye seems to turn in or out it must be checked

Keep reach-and-touch toys within the baby’s focus

2-4 months

Begins to notice familiar objects located 50cm away

VA is 6/60

Follows moving objects
Able to follows faces, objects, and light

 

4-8 months

Develops full colour vision

Develops eye movement and eye-body coordination
Able to turn the head to see objects

5th month: depth perception

8th month: starts crawling which lead to eye-head-foot-body coordination

Early walkers who did minimal crawling may not learn to use their eyes together as well as babies who crawl a lot.

So give the baby plenty of time to play and explore on the floor.

Objects for the baby to grab, pull and kick.

Provide plastic or wooden blocks that can be held in the hands.

Play games, moving the baby’s hands through the motions while saying the words aloud.

8-12 months

Develops independent eye movements
Able to notice smaller objects
Able to watch and follow fast moving objects

Pulls up to a standing position

Able to grasp objects with thumb and forefingers

Able to crawl well; try to walk

Encourage crawling and creeping.

Play hide and seek games with toys or their faces to develop visual memory.

Name objects when talking to encourage the baby’s word association and vocabulary development skills.

12-24 months

Clear distance vision
Able to perceive depth (depth perception) of objects
Able to do refined eye movements

Development of fine motor skills

Able to draw straight lines and circles

Roll a ball back and forth to help the child track objects with the eyes visually.

Give the child building blocks and balls of all shapes and sizes to play with to boost fine motor skills and small muscle development.

Read or tell stories to stimulate the child’s ability to visualize and pave the way for learning and reading skills.

2-3 years

Improvement of convergence and focusing abilities
Able to change focus from distant to near vision, as well as near to distant vision
Improvement of depth perception

 

3-4 years

Vision at far is about 20/20 or 6/6
Able to recognise complex visual shapes and letters

 

4-6 years

Clear vision at all distances

 

 

*At birth, rod cells are better developed so that colour recognition begins at 3 month of age when cone cells mature[2].

 

As far as behavioural and electrophysiological studies are concerned, pictures of the world may be interpreted thanks to the onset of functional binocular interaction in human visual cortex between 10 and 16 weeks of age[4],[6]. This is also when binocular vision, accommodation, depth and eye movements develop. The maturation of the eyes and optic pathways is directly related to the child’s visual and neuromotor development[7].

 

However, the best VA and the complete maturation of the visual cortex of the brain are achieved just before puberty [3].

 

All these information are referred to infants that were born at term and with normal development.

 

For what VA is concerned, it improves constantly thanks to a process called emmetropisation that completes at around 6 years of age. Hyperopia, myopia, astigmatism or disease can affect it.

 

Children are not just small adults and for their clinical examination a different approach is required[8]. Some tests are part of the routine eye examination, but depending on the single case, it could be necessary to use others more specific.

 

Case history is the starting point and its importance is sometimes underestimated.

 

The art of taking a patient’s case history is essential for a solid understanding of pertinent details before proceeding with an examination [9]. It’s at that point that we discover that knowing how the visual system develops is extremely important.

 

The clinician should ask question about birth history, developmental, educational and social history, while establishing rapport with the patients and parents. However, obtaining a detailed case history from the patients or the caregivers can be challenging at times [9]. It is known that parents are very good observers, but they are not so accurate on their observations. For example, they may refer that an eye deviates, but they don’t know exactly which one.

 

Talking about visual system development, it is known that understanding how it develops and how it works helps practitioner to work better: having clear what to expect in relation to the patient’s age, asking useful questions to parents, choosing the most appropriate tests for the eye exam.

[1] Glass, Penny PhD Development of the Visual System and Implications for Early Intervention, Infants & Young Children: July 2002 – Volume 15 – Issue 1 – p 1-10

 

[2] Development of the eye | Plano | Save sight. Empower lives.

 

[3] Warburg M. Synets udvikling [Development of sight]. Ugeskr Laeger. 1991 May 27;153(22):1571-5. Danish. PMID: 2058015.

 

[4] Braddick O. Binocularity in infancy. Eye (Lond). 1996;10 ( Pt 2):182-8. doi: 10.1038/eye.1996.45. PMID: 8776447.

 

[5] Infant Vision: Birth to 24 Months of Age | AOA

 

[6] Development of human visual function Oliver Braddick a, Janette Atkinson; Department of Experimental Psychology, University of Oxford, United Kingdom Visual Development Unit, Department of Developmental Science, University College London, United Kingdom

 

[7] Visual development in children aged 0 to 6; Anita Zimmermann, Keila Miriam Monteiro de Carvalho, Camila Atihe, Sara Martins Vieira Zimmermann, Valeriana Leme de Moura Ribeiro

 

[8] Optometry: Science, Techniques and Clinical Management E-Book, Mark Rosenfield, Nicola Logan

 

[9] The Pediatric Eye Exam Quick Reference Guide: Office and Emergency Room,  Zhu-Tam, Lily, Chung, Ida

 

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