What is Squint (Strabismus)

Squint, also known as strabismus is a condition in which the eyes do not align properly, one of them turns inwards, upwards, downwards, or outwards while the other one focuses at one spot. Typically, the extraocular muscles are not working in coordination, resulting in each eye unable to gaze at the same spot at the same time. If both eyes are not completely aligned, binocular vision is not possible, making it harder for the person to appreciate depth perception.

Strabismus can also be caused by a disorder in the brain which cannot coordinate the eyes correctly.

According to the data available, squints affect approximately 5% of children and usually develop during their first 36 months of life (sometimes later). Squints are sometimes identified in infants a few days after they are born.

Types of squints:

1. Non-paralytic –Commonly seen during childhood where nerves are normal.
2. Paralytic Squint – Damage to one or more of the three cranial nerves that supply the eye muscles, as a result of poor blood supply to the nerve, pressure on the nerve or inflammation will cause limited eye movements and strabismus.
   1. Superior Oblique Palsy
   2. Lateral Rectus Palsy
   3. IIIrd Nerve Palsy

3. People can also have intermittent or latent squint which is known as phoria

 

Classification of squints:

1. The eye turns inwards – Esotropia (less common)
2. The eye turns outwards – Exotropia (less common)
3. The eye turns upwards – Hypertropia
4. The eye turns downwards – Hypotropia

Lazy Eye (Amblyopia)

The earlier in life a squint can be identified and treated, the more effective that treatment is likely to be. Squint, if left untreated, can eventually develop into lazy eye (amblyopia), in which the brain starts ignoring input from one of the eyes. The brain ignores one of the eyes to avoid double vision.

If a child has poor vision in the squinting eye, wearing a patch over the other eye might help the squinting eye’s proper development.

Sometimes a squint comes back later in adulthood, even though it had been successfully treated when the patient was a child. In such cases the adult may have double vision, because by that time the brain is trained to gather data from both eyes, it cannot ignore one of them.

 

Signs and symptoms of Squint (Strabismus)

The sign of squint is fairly obvious – one of the eyes does not look straight ahead, but veers. Some people may have minor squints that are less noticeable.

Infants (newborns) may go cross-eyed, especially if they are tired. This does not mean they have a squint. Concerned parents should check with their doctor.

If you notice that your child has one eye closed, or turns his/her head when looking at you, this could be a sign of double vision, and a squint is possible. Check with your doctor.

 

What your doctor looks for

Your doctor would like to know whether

• the Squint was congenital (you are born with it)
• it runs in the family
• it is related to any long term illness
• because of asymmetrical refractive error i.e.myopia (short-sightedness), hypermetropia (long-sightedeness), or astigmatism (the cornea is not curved properly)
• it can also be a sign that a cranial nerve has a lesion.
• Hydrocephalus, a condition in which too much CSF (cerebrospinal fluid) has built up in and around the brain, can cause squints to develop.
• Some viral infections, such as measles can cause strabismus.
• Noonan syndrome, and some other genetic conditions can cause squints

 

Diagnosis

Parent should bring their children for routine eye check-ups at birth, 6 months and at 3 years so that squint can be diagnosed easily.

The Hirschberg test, also known as the Hirschberg corneal reflex test is used to assess whether the patient has strabismus. The ophthalmologist shines a light in the child’s eye and observes where the light reflects off the corneas. In a person with well-aligned eyes, the light goes to the center of both corneas. If it does not, the tester can determine whether the patient has exotropia, hypertropia, esotropia or hypotropia.

Some people may suffer from more than one tropia at the same time.

 

Treatment

A diagnosed squint needs prompt treatment; otherwise there is a serious risk of complications, such as amblyopia (lazy eye). The younger the patient is, the more effective treatment is likely to be.

1. Glasses – if the child is found to have hypermetropia (long-sightedness), they will be prescribed glasses which usually solve the squint.
2. Eye patch – this is worn over the good eye to get the other eye, the one with the squint, to work better.
3. Botulinum toxin injection (botox) – this is injected into a muscle on the surface of the eye. The doctor may recommend this treatment if no underlying cause can be identified, and if signs and symptoms come on suddenly. The injected muscle is weakened temporarily, which often helps the eyes to align properly.

The doctor may also prescribe eye drops, and get the patient to do specific eye exercises.

1. Surgery – surgery is only used when other treatments have not been effective. Surgery can restore binocular vision, as well as realign the eyes. The surgeon moves the muscle that connects to the eye to a new position – sometimes both eyes need to be operated on to get the right balance.

 

Prognosis

a. Need for glasses after surgery :

A critical factor that determines why a child’s eye becomes misaligned in the 1st place, and may squint post-surgery as well is because of decreased or less vision in the squinting eye.

The aim of surgery is to give well aligned eyes, capable of working together with binocular vision and often stereo vision, and if the child needed glasses before the operation they will still be required afterwards (and some children are given glasses only after surgery). To ensure good results of surgery you must always assume that your child should keep wearing glasses.

The extent of muscle resection during surgery is matched to the maximum turn of the child’s eyes while wearing their glasses before surgery. Thus after surgery the eyes should be well aligned with glasses on, but will often have a turn if they are off.

b. Need for more than one operation

In children with misaligned eyes some neurological deficit might be present because of which even after surgical correction the eyes might not align completely. This may require another surgery at a later stage.

In some children the neurological pathways may respond very well to surgery initially with the both eyes working together. When eyes are not locked in this alignment it may be necessary to reposition muscles again.

c. Need for operating on both eyes when only one eye is turning

The key is to realize that the both eyes move synchronously, and they work to balance each other. Shifting the muscles of an eye which is “straight” will allow the turned eye to move into it’s correct alignment..

d. Risks of surgery

In alternating squint where both eyes have good / equal vision then surgery on either eyes can produce good results, regardless of which eye appears to be ‘turned’.

In unilateral squint or one eye predominantly squinting with poor vision, the desired result can be achieved by surgery on that eye only.

Risk of losing vision because of squint surgery is very low i.e. approximately 1 in 20,000.

e. Can surgical correction for a squint also correct a lazy eye?

Surgical correction, for squint corrects the misalignment of the two eyes so that both eyes look in the same direction. If your child has developed a lazy eye as a result of his or her squint, surgery alone won’t correct it. Your child will need additional treatment.