A B C D E F G H I J K L M N O P R S T U V W

SQUINT AND DOUBLE VISION

What is Squint and Double Vision ?

Squint (strabismus) is the term used for the condition when the eyes are misaligned and not looking at the same thing. The common forms are when one eye either turns in or outwards. Vertical (up or down) misalignment is less common. Squint is a term also used when one squeezes the eyelid partly closed to see more clearly or against bright sunlight. When misalignment occurs each eye is directed at a different image and generally results in double vision (diplopia). However when squint occurs in childhood double vision generally does not occur.

How does Squint and Double Vision occur ?

Childhood squint often runs in families. Infants may be born with a squint. Usually the eye turns in (infantile esotropia) for the first week or two after birth. The eyes are often occasionally misaligned and this is normal and should stabilise within a month. Pseudo squint is a common condition in infancy and early childhood. The appearance of apparent squint is due to the structure of the tissue around the middle part of the face. This is known as the epicanthic fold and is on the inner aspect of each eyelid. It gives the impression that the eye is turning in as the white of the eye disappears underneath the epicanthal fold when the child looks either to one side or the other. Infants with true esotropia (convergent squint) usually squint with either eye. They often have an associated upward movement intermittently. Divergent squint is rare in infants and can mean there is a defect within the eye or neurological problem.

Convergent squint developing between the age of 18 months and four years is usually due to the child being very long sighted. The child will squint when looking at close objects as the child has had to focus hard to see clearly. Divergent squint (exotropia) often develops after four years and is usually intermittent occurring when the child is tired. The squint may become more obvious and occur more frequently as the child gets older. The child may experience double vision. Children with a congenital vertical squint may adopt a tilted head position to keep the eyes correctly aligned.

There are many other different types of squint. In neurological squint, one of the three different nerves supplying the muscles which adjust the eye movement positions is affected. Disturbance of nerve function has many causes but the end result of disturbance is misalignment and onset of double vision. The double vision usually occurs suddenly and neurological examination is necessary. Paretic squint means the nerve is not functioning and is either partly or completely paralysed. Paretic squint may result from damaged blood supply to the nerve. This is often associated with diabetes or hypertension. The defect may recover over time. Head injury can cause nerve damage by stretching the nerve inside the brain. There are many neurological causes of double vision including multiple sclerosis, inflammation (meningitis) and tumours. The condition of myasthenia (chemical transmission defect) can be localised to the eye causing episodes of variable and intermittent double vision. A mechanical squint is caused by a restriction to the eye muscles. The eye muscles can be affected by restriction of their movement in the orbit (the bony compartment enclosing the eye) or by inflammation and scarring of the muscles. Inflammation within the orbit or swellings or tumours within the orbital tissue can cause this condition. The double vision usually then develops slowly. Thyroid disorder usually associated with over active thyroid and can cause inflammation of eye muscles. The eye is often also pushed out (proptosis). Trauma directly to the eye causes a "blow out fracture" of the orbital floor or the inner wall. This can result in entrapment of orbital tissue causing the muscle function to be restricted.

Treatment involved for Squint and Double Vision

Childhood squint. Infantile esotropia is generally operated on when the child is about 1 year to 18 months old. An operation on both eyes is usual. A convergent squint associated with the child being very longsighted (accommodative squint) can usually be corrected by correcting the long-sightedness with glasses. The child still squints when the glasses are removed and some children require a corrective operation and to wear glasses. It is very important that the vision is considered in treatment of squint. A permanently squinting eye in childhood will result in amblyopia or "lazy eye". Patching (occlusion therapy) is used to cover the good non squinting eye to stimulate the lazy eye. This may be recommended to be done full time initially and then reduced up to on average one hour a day when the vision has improved. When the child is eight years old the visual system is stable and patching discontinued. For childhood squint more than one corrective operation may be necessary.

Mechanical and paretic squints. Treatment of the underlying cause if present is important. Double vision can in many cases be corrected with prismatic glasses. Surgery may be possible to improve the condition in some cases.

If Squint and Double Vision are left untreated

In childhood squint the squinting eye is very likely to become lazy and have poor vision permanently. Sudden onset squint in adult life needs investigation as there may be a serious underlying cause.