Strabismus (Squint)

What is strabismus?

Strabismus (commonly known as a squint) is a visual defect in which the eyes are misaligned and point in different directions. One eye may look straight ahead, while the other eye turns inward, outward, upward or downward. 

About 3-4% of all children are born with strabismus, making it a common condition in New Zealand. Strabismus occurs equally in males and females. They may run in families however, many people with strabismus have no relatives with the condition.

What causes strabismus?

The exact cause is not fully understood. Any factors influencing the brain’s control of binocular vision or the eye muscle functions can cause it. Occasionally children with Down Syndrome, brain tumours or infections can present with strabismus.

What are the indications of strabismus?

The main indication is that an eye is not straight. Sometimes the child may squint an eye to see or tilt their head to see. Favouring one eye over the other can lead to amblyopia (lazy eye) which will lead to long term poor sight in that eye. 

What is pseudoesotropia?

This is when the eye of an infant appears to be crossed, though they actually are not.  This is often due to a wide, flat nose, or a fold of skin in the inner lids making the eyes appear crossed. Children often grow out of pseudoesotropia but they never grow out of a true esotropia.

Common types of strabismus?

Infantile esotropia

Infantile esotropia, where the eye turns inward, is the most common type of strabismus in infants and it usually occurs between 3-6 months of age. The correct treatment for infantile esotropia is early intervention with surgery. This restores the eyes to their normal alignment and it also gives the child a better chance to develop the ability to use two eyes together (3D vision).

Accommodative esotropia

Accommodative esotropia is a common form of strabismus and often occurs in children two years of age or older. The eye turns inward due to excessive use of accommodative effort for better vision.  It can present when the child is looking at distant or near objects. Often children with this condition are farsighted – wearing appropriate corrective glasses helps with the control of misalignment. Sometimes children will need eye muscle surgery to correct the misalignment.

Exotropia

Exotropia refers to the outward turning of the eye. This type of strabismus more often occurs when the child is looking at far (distance) objects though it can occur for any distance visual fixation. It becomes more noticable when the child is tired or sick. Exotropia often needs surgical correction if it becomes constant or noticeable for majority of the time during the day.

How is strabismus treated in children?

After a complete medical eye examination the child may be prescribed glasses as a treatment for the strabismus and also more importantly to improve the child’s vision.

If glasses cannot control the strabismus or are not needed, then eye muscle surgery will be recommended to restore normal alignment and binocular vision.

How is strabismus surgery performed on children?

Strabismus surgery on children is carried out as a day stay procedure performed under a general anaesthetic. The eye muscle causing the eye to turn inward or outward is ‘loosened’ or ‘tightened’ as required. The eyes are not normally patched and recovery is fast so the child can resume normal activities within a few days.

Educational Implications

Behaviours or conditions that might indicate strabismus

• Turning inward, outward, upward or downward or one or both eyes.
• Complaining of seeing double vision.
• Challenges to depth and distance judgement (bumping into doorframes, table corners or other objects or obstacles underfoot; stumbling or tripping. hesitancy around unfamiliar steps or kerb cut-aways; using the toe or foot as a guide to judge changing surfaces (footpath to grass, carpet to lino).

What to do

• The young person should visit an ophthalmologist to determine diagnosis.
• Parents, whānau and caregivers will need to review treatment options depending on the type of strabismus (glasses or surgery).
• When using glasses with corrective lenses, persevere. Try to engage the young person with something interesting and diverting to become more accustomed with the corrective view through the lenses.  This can be a visual activity or it can include activities that use the young person’s hearing such as listening to music or audiobooks or someone reading.
• If the young person finds it challenging to wear glasses, review whether the issue is one of comfort along the nose or behind the ears or whether the lenses may no longer be beneficial. When a young person chooses not to wear prescription glasses and comfort has been ruled out, it might indicate that the prescription is no longer helpful and may need to be reviewed or that the young person is not experiencing any consistent, obvious and functional benefit from the correct prescription lenses and a review may be required.
• If strabismus persists or has gone undiagnosed and/or untreated, the young person will typically discover strategies, such as using an abnormal head turn, to assist visual access, particularly in the area of depth and distance judgement.
• Darker lines on writing paper can assist depth perception when it comes to handwriting (placement of letters, spacing and formation).
• Familiarity of the environment and activities will need to be reviewed, particularly if they are unfamiliar places and activities that involve judgement of depth and distance.
• Safety moving around the environment may require an environmental audit to review steps, ramps, kerb-cutaways and any changes to surfaces. Judging distances of on-coming traffic and moving playground equipment may also be affected.  Highlighting the edges of steps or changes in surfaces can help practice depth judgement and incorporate visual ‘hooks’ to build familiarity.
• Following or tracking fast moving objects like balls may be challenging to maintain visual contact and to judge where in space it is in relation to the young person. Having opportunities to view and practice with slower moving objects can build familiarity with how objects move through space.