Squint: overview, types, symptoms, causes, diagnosis and treatment

Squint or strabismus is a medical condition affecting the proper alignment of the eyes. The one eye is looking at the object while the other eye may be turned away in any direction away from the center. It can be present from birth or may be acquired later in life. If not treated, child may later develop amblyopia which is a serious vision threatening condition.

It occurs in approximately 2 to 4 percent of the population.

Types of squint or strabismus

Squint can be of various types on the basis of direction of misalignment of the eye ball as

• Horizontal: the eye is misaligned in horizontal plane. It may be turned inwards or outwards.
• Vertical: the eye may be turned upwards or downwards.
• Torsional: the eye is rotated on its axis such that the center of the both the eyes is same but the periphery is different. This condition is difficult to diagnose.

These conditions may occur in combinations too and with varying degree of misalignment.

Signs and symptoms

The misalignment is easily detectable gross sign of this disease. Apart from this there can be other symptoms which are not easily detectable as

• Defective vision: child may be having abnormality in vision which might be due to refractive errors or any other cause
• Diplopia: this is known as double vision. The child will be seeing two different images as the eyes are not focusing on the same thing.
• Lazy eye or amblyopia: It occurs as a complication of strabismus which can occur in as much of the half of children suffering from strabismus. Amblyopia is a condition in which the brain prefers images of one eye more as compared to the other eye. It takes considerable amount of time to treat this complication so it is better to detect and treat strabismus first.

Adults having squint may report following problems

• Overlapping or blurred images
• Difficulty in reading
• Loss of depth perception

Many adults with squints turn or tilt their heads to get the better focus of the image.

Causes

Movement of eyeballs in the socket is controlled by a group of muscles and nerves controlling them. The major causes of squint are related to the dysfunction of these muscles or injury to the nerves.

There are some conditions which causes an increased risk of developing strabismus though the cause is not much clear

• A positive family history: it is seen that children having squint are more likely to have family member who have already suffered from it.
• Low birth weight or premature birth: may be the improper maturity of organs or tissues is the reason behind it.
• Refractive errors: if the lens is not able to focus the light properly it is known as refractive error. Myopia, hypermetropia and astigmatism are the common refractive errors. A refractive error compels the affected eye to turn inwards in attempt to get the better focus of the image. It usually occurs around the age of 2 years or older
• Hydrocephalus: increase in the pressure inside brain can result in strabismus. Hydrocephalus is a medical condition in which there is increase in the fluid in which brain is suspended.
• Infections: some viral infections like measles are known to cause strabismus.

Squint can also begin in adulthood due to medical conditions like

• Graves’ disease
• Myasthenia gravis
• Diabetes
• Stroke
• Head trauma

It is seen that squint can be a presenting sign in some diseases such as retinoblastoma.

Diagnosis

It is important to differentiate between congenital and acquired strabismus because acquired strabismus can be caused by life threatening or vision threatening conditions. Squint can be easily detected with simple clinical tests. It is important to detect if child is developing amblyopia or not.

• History: the physician will ask questions to identify the underlying cause which may include questions regarding different signs, symptoms, duration, congenitally or acquired conditions, family history, history of trauma, injury, drug or medications, infections, double vision or any associated abnormalities
• Physical examination: the physician will perform a general checkup of the body which will include assessment of general health, developmental and neurological status as well as ophthalmologic examination. The ophthalmic examination can include assessment of seeing ability of eye, pupillary reaction, positions of eye lid, movement of eye ball in various planes. Tests like corneal reflex test, cover-uncover test can be performed to detect the squint.

Additional evaluation may be needed based upon the history and the physical examination which can include blood tests or imaging procedures.

Management

The management of squint is based on the treatment of underlying cause. The main aim of treatment is restoring the normal vision of the patient. General management principle of squint are as follows

Restoring vision: if the child is suffering from vision impairment due to any cause. It is treated first as vision impairment can cause amblyopia. It may include spectacles for refractive error. Surgical procedures for conditions like cataract can be needed in some patients suffering from it. If one has already developed amblyopia then the occlusion therapy may also need to be started which involves covering up of the normal eye so that brain is compelled to interpret images seen by the affected eye.

Correcting the misalignment: both surgical as well as nonsurgical options are available. Nonsurgical options include prescriptions of prism therapy, eye drops and visual training exercises. Botox injections are indicated to relax the muscles when no apparent cause is identified. Surgical treatment for the strabismus is the last approach when other management options fails to cure it. Muscles surrounding the eye are detached from the original positions and attached to different spot depending upon the degree and plane of misalignment.

References

• McManaway JW III, Frankel CA. Strabismus. In: Primary Pediatric Care, Hoekelman RA (Ed), Mosby, St. Louis 2001. p.1253.
• Williams C, Northstone K, Howard M, et al. Prevalence and risk factors for common vision problems in children: data from the ALSPAC study. Br J Ophthalmol 2008; 92:959.
• COMMITTEE ON PRACTICE AND AMBULATORY MEDICINE, SECTION ON OPHTHALMOLOGY, AMERICAN ASSOCIATION OF CERTIFIED ORTHOPTISTS, et al. Visual System Assessment in Infants, Children, and Young Adults by Pediatricians. Pediatrics 2016; 137:1.
• Joyce KE, Beyer F, Thomson RG, Clarke MP. A systematic review of the effectiveness of treatments in altering the natural history of intermittent exotropia. Br J Ophthalmol 2015; 99:440.