My child does not react when moving from shade to light

Have you noticed that your child does not react when you move from a dark to a bright environment? He does not squint or blink. 

The fact that a child does not react when moving from shade to light does not necessarily mean a visual problem. It is important, however, to check that other symptoms do not come into play, which could be the sign of an eye disorder.

The role of the pupil in adapting to changes in light

The pupil is the black part of the eye that is in the centre of the iris. It plays a crucial role in vision by regulating the amount of light that enters the eye. The pupil is like a diaphragm that opens or closes to allow more or less light to enter.

How does the eye react when in a shaded space?

When the eye is exposed to shade, the pupils dilate to allow more light to penetrate, allowing better vision in low-light conditions. 

This reaction is known as the pupillary reflex of accommodation to darkness.

How does the eye react when exposed to light?

When the eye is exposed to strong light, the pupils shrink to limit the amount of light that enters the eye. 

This reaction is known as the miosis or the pupillary reflex to light. This protects the eye from damage caused by excessive exposure to light and also helps to maintain good visual acuity.

The role of the retina in adapting the eyes to light

The retina is the part of the eye that converts light into electrical impulses. They are then transmitted to the brain to be interpreted as an image. The retina adapts to changes in light thanks to the presence of two types of light-sensitive cells, cones and rods. The cones are sensitive to bright light and allow the vision of details and colours, while the rods are sensitive to weak light and allow night vision.

When switching from darkness to light, and vice versa, the rods disconnect temporarily to avoid overstimulation and allow the cones to take over. 

This adaptation to different brightness levels is called “retinal adaptation”.

It is important to note that it can take several minutes to occur

The role of the iris in regulating the amount of light that enters the eye

The iris is the coloured part of the eye that surrounds the pupil. It plays a key role in adapting to light changes by regulating the amount of light that enters the eye. 

When the environment is bright, the sphincter muscle of the iris contracts. This shrinks the pupil and limits the amount of light that enters the eye.

When the environment is dark, the dilator muscle of the iris allows the pupil to dilate and allow more light to enter.

When to worry if your child does not react to light changes

Children react differently to changes in brightness. This does not necessarily mean that they have an eye disorder.

However, this finding can be associated with other signs suggestive of poor vision, such as:

• looking at objects very close-up, 
• an absence of ocular fixation or tracking, 
• abnormal spontaneous movements of the eyes, 
• an absence of the blink reflex to a threat, 
• excessive rubbing of the eyes, 
• stereotyped movements.

This constellation of signs may then be suggestive of poor vision in children and requires an ophthalmological assessment.

Some medical conditions, such as visual impairment, may not cause obvious symptoms in children. It is therefore important to have them monitored regularly. If in doubt, talk to your paediatrician, who can refer you to an ophthalmologist if necessary.

Find out more about children’s visual disorders

You now know when it is necessary to carry out an eye examination if your child does not react when moving from shade to light. 

Do you want to learn more about children’s visual defects? Our ophthalmologists explain different pathologies such as strabismus, myopia, congenital glaucoma, hyperopia, astigmatism or amblyopia.