History and exam
Key diagnostic factors
common
diplopia
In strabismus, the diplopia is binocular (i.e., present only when both eyes are open).
If diplopia is present when one eye is closed, it is most likely not caused by strabismus.
Horizontal diplopia is indicative of esotropia or exotropia, while vertical diplopia is indicative of hypertropia or hypotropia.
May be absent in children with strabismus, as a result of suppression.
eye misalignment
Inspection of the eyes may reveal a manifest strabismus; however, this examination finding should be interpreted with caution, as epicanthal folds, a wide nasal bridge, or eyelid abnormalities may falsely convey the impression of ocular misalignment, particularly in young children and in the Asian population.
amblyopia
Strabismus in children may cause suppression (active process of the central nervous system by which the visual input of one eye is ignored) of the image created by the non-fixating eye, resulting in amblyopia (decreased vision in an anatomically normal eye) and irreversible loss of vision if not adequately treated.[22]
Although amblyopia generally develops in children below the age of 7 years, there is no universally accepted upper age limit and it can occur at any age prior to the development of visual maturity.
Amblyopia does not usually occur in visually mature patients.
Other diagnostic factors
common
abnormal eye movements
May be present in children and noted by parents and close contacts.
visual confusion
The phenomenon where images of 2 different objects are seen superimposed. It is rarely reported, and is usually a transient symptom.
asthenopia
Although not specific for strabismus, some patients complain of asthenopia (ocular discomfort) with 'eye strain' or headaches in certain situations. They may also note a 'pulling sensation' and be aware of when the eyes are misaligned.
uncommon
intermittent closure of one eye
Some children (particularly those with intermittent exotropia) intermittently close one eye, especially when outside in the sunlight.
cranial nerve palsy
Acquired paralytic strabismus is related to malfunction of one or more of the 3 cranial nerves (oculomotor, trochlear, abducens) providing motor supply to the extraocular muscles. This can be determined through a detailed examination of the cranial nerves.
Oculomotor nerve (cranial nerve III) palsy is characterised by exotropia, hypotropia, ptosis, and possible mydriasis (pupil dilation). Abducens nerve (cranial nerve VI) palsy is characterised by esotropia, and decreased abduction of the involved eye. Trochlear nerve (cranial nerve IV) palsy is characterised by hypertropia, elevation in adduction, and possible excyclotorsion of the involved eye.
Risk factors
strong
family history of strabismus
There is evidence that comitant strabismus is heritable, although multiple genes seem to be involved.[14]
Studies have found that approximately 30% of patients with strabismus have a relative who is affected, and most families are concordant for the type of strabismus (e.g., esotropia or exotropia).[13]
prematurity
Preterm birth increases the risk of developing strabismus. One study found that in a group of children born prematurely without retinopathy of prematurity (ROP), strabismus was present in 12% at age 11 years.[15] Another study found that strabismus was present in 13.5% of premature babies, with esotropia (77.6%) more common than exotropia (22.4%).[16]
The frequency of strabismus is higher in patients with a history of ROP - a condition of the retina in preterm babies that affects the development of the retinal vasculature, potentially resulting in poor structural and visual outcome. Increasing severity of ROP is a further risk factor for strabismus, with even higher frequencies observed in patients who required cryotreatment for the condition.[8]
The presence of neurological complications in preterm babies also increases the risk of strabismus. One study found the frequency of strabismus in children who had experienced neurological complications to be 34%, compared with only 9.4% in those without such complications.[16]
low birth weight
maternal smoking during pregnancy
Studies have found that maternal smoking throughout pregnancy is associated with development of strabismus in the child, probably as a consequence of fetal hypoxia. This association is not observed if maternal smoking is limited to the early stages of pregnancy.[14]
weak
refractive error
The presence of uncorrected hyperopia is a risk factor for the development of accommodative esotropia. In hyperopia, accommodation enables a clear image to be created on the retina. Accommodation is associated with ocular convergence (eyes turning inwards); compensatory mechanisms may be overwhelmed if large amounts of accommodation are required, and esotropia can develop.
Poor vision in one eye because of uncorrected refractive errors may result in disruption of fusional mechanisms designed to keep the eyes aligned. This most often leads to exotropia in older children and adults, and to esotropia in young children.
Refractive errors are not considered to be a risk factor for infantile forms of strabismus.
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