Squint (Strabismus)

(Date of publication 30 July 2004)

It may seem unlikely, but Abraham Lincoln, Barbra Streisand, Ben Turpin and Marty Feldman have something in common; they all started life with a pronounced squint. This is not unusual: 2-3% of babies are born with eyes that point in different directions, due to either refractive abnormality or eye muscle imbalance, and in most cases this can be corrected if treated early. Older children and adults can also develop a squint, or strabismus; usually as a result of injury to the eye or brain, diabetes, stroke or infection.

Squints are subdivided according to the direction of the misaligned gaze. Esotropia (one or both eyes turning in toward the nose), exotropia (turning out toward the ear), hypertropia (turning vertically upward) and hypotropia (turning vertically downward) are all covered by the blanket term strabismus, as are phorias, where the brain is able to override a muscle imbalance and maintain normal vision except during periods of stress.

Strabismus resulting from paralysis of one or more ocular muscles is referred to as paralytic or nonconcomitant, whereas nonparalytic or concomitant strabismus is due to impaired muscle tone because of an abnormality in the central nervous system. These are described in detail here; both can result in eso-, exo-, hyper- or hypotropia. Occasionally, whether the squint is intermittent or constant, one eye will deviate at certain times, while the opposite eye will deviate at others; this is referred to as "alternating" strabismus.

Those in search of comprehensive information should go here, where a vast selection of in-depth articles on various permutations is available.

Often the precise cause is unknown, although the condition tends to run in families and is associated with several different disorders or syndromes, which are listed briefly here. Certain abnormalities, such as Duane’s Syndrome (where abnormal connections in the ocular nerves result in impaired eye movement) or Brown’s Syndrome (where the superior oblique muscle is unable to slide through its natural pulley system, preventing the eye looking up), are explained further here and illustrated in the Ocular Motility section of this site.

Strabismus is frequently a problem for young children, and one good parent-orientated guide is available by clicking here. The condition is particularly dangerous when left untreated at this age, because visual systems are not yet fully developed and any type of strabismus can lead to amblyopia, or ‘lazy eye’. Here, the brain persistently ignores images from the weaker eye, and binocular vision fails to develop properly, leading to blindness if left uncorrected. Before the age of four to six, amblyopia can usually be successfully eliminated with a combination of glasses and patching. Covering the dominant eye, either physically with a patch or by blurring its vision with atropine drops, forces the brain to rely on the weaker eye (for more information try here or here). By about nine years of age, however, the visual system is already fully established, and research continues into possible treatments for older children and adults.

Another frequent problem for infants is accommodative esotropia, where extreme farsightedness gives a cross-eyed appearance when the child attempts to focus on nearby objects. Most of the time glasses are all that is needed to correct this problem, and one appealing example as well as substantial further information can be found here. Occasionally even cases that have previously responded well to glasses can deteriorate, in which case corrective surgery may be necessary.

There is also a condition called pseudo-esotropia, where a flat nasal bridge or folds of skin either side of the nose give a deceptive appearance of squint. This is common in newborns, particularly those of Asian descent, and can usually be identified by thorough ocular examination. Although the majority of infants outgrow the condition, regular monitoring is usually considered necessary in case true strabismus develops at a later date. For more detail, plus interactive photographic illustrations, try clicking here.

There are several different clinical approaches to the treatment of strabismus. Children are usually much more responsive than their adult counterparts to non-invasive therapies such as patching or glasses. In later life, botulinum toxin injections are frequently used to paralyse the responsible muscles, and information on this process is available here. However, if these prove ineffective, the patient’s condition appears to be worsening, or binocular vision is lost, surgical intervention may be necessary to correct ocular alignment, particularly when imbalance results from an over- or under-acting muscle. This site provides a good basic diagram of the underlying principles, and the process is described in wince-inducing detail here, along with a rather unpleasant list of possible complications. An adjustable suture allows further modification to be carried out 4 to 24 hours after surgery, when the effects of anaesthesia have worn off and muscular alignment can be re-evaluated.

Should this tour have whetted your appetite for further research, a good place to start would be this site, where a lavishly illustrated and fully interactive ‘self-directed learning module’ awaits you. Any readers whose ambitions do not stretch that far can merely thank their lucky stars not to have been born in seventeenth-century Scotland, where anybody with a squint was believed to have ‘the evil eye’, and was therefore liable to be tortured, strangled and burned in a barrel of tar...

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A Tour around Squint (Strabismus)

A Tour around Squint (Strabismus)