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Strabismus

Key points ⚡
Succinct notes to superpower your revision
Strabismus\: eyes misaligned when focusing on an object, can be occasional or constant; often onset in childhood.
Consequences\: can cause amblyopia (lazy eye), leading to decreased or loss of vision in one eye; a
development.
Detection and management\: early referral to an ophthalmologist is essential; treatment includes observation, optical
correction, therapy, and surgery.
Types of strabismus\:
Tropia\: manifest disorder of ocular alignment.
Phoria\: latent disorder of ocular alignment.
Esotropia/Esophoria\: inward deviation.
Exotropia/Exophoria\: outward deviation.
Hypertropia/Hyperphoria\: upward deviation.
Hypotropia/Hypophoria\: downward deviation.
Aetiology\:
Primary\: idiopathic, congenital.
Secondary\: cranial nerve palsies, intracranial infection, trauma, myopathies, endocrine conditions.
Risk factors\: family history, low birth weight, premature birth, maternal smoking.
Red
History-taking\: onset, visual acuity, diplopia, asthenopia, performance changes, socialisation issues, behavioural problems,
walking di
Clinical examination\:
Light re
Brückner test\: uses ophthalmoscope to compare red re
Cover test\: identi
Cover–uncover test\: identi
Prism cover test\: measures angle of small-angle tropia.
Alternate prism cover test\: measures angle of phoria.
Further examination\: includes stereopsis testing for depth perception.
Article 🔍
A comprehensive topic overview
Strabismus (a.k.a. squint) is an ophthalmic condition in which the eyes do not properly align with each other when focusing
to look at an object (i.e. poor fusion). The misalignment may be present occasionally or constantly, commonly with onset
from childhood or, less commonly, from adulthood. Strabismus can be subtle, particularly those that are latent (phorias). A
patient may present with slight angulation of the head on the visually weaker side to compensate for strabismus.
Strabismus can cause permanent functional disability, psychosocial distress and signi
psychological development, particularly if persistent throughout childhood. This functional disability may manifest as
(strabismic) amblyopia, or lazy eye, in which the brain is unable to process inputs from one eye and over time favours the
other eye, causing structural changes in the visual pathway and cortex. This ultimately results in decreased or complete
loss of vision in an eye that otherwise appears normal.
1,2
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Early detection and management of strabismus are essential to reduce the risk of functional disability and mitigate the
amblyogenic burden. 3
This requires all medical practitioners, particularly those working with children, to be competent in
recognising potential strabismus so early referral to an ophthalmologist is possible. Treatment options can include
observation, optical correction, overminus therapy, prisms, occlusion therapy, vision therapy and surgery.
Table 1. Nomenclature of strabismus
Term Meaning
2-line di
amblyopia
healthy eye
tropia / -
tropia
Manifest (i.e. always present) disorder of ocular alignment; from
Greek,
'place'
phoria / -
phoria
Latent disorder of ocular alignment when binocular fusion is
suspended or interrupted; from Greek,
'to bear'
ortho- Right; correct; straight
hetero- Other; di
heterotropia Same as 'tropia'
eso- Inwards (i.e. nasal horizontal) deviating;
exo- Outwards (i.e. temporal horizontally) deviating;
hyper- Upwards-deviating
hypo- Downwards-deviating
cyclo- Tilted or torsed about an eye's visual axis

Aetiology and epidemiology of strabismus

Aetiology

Common aetiologies of strabismus are described below in Table 2.
Table 2. Aetiologies of strabismus.
Primary aetiologies
of strabismus
Secondary aetiologies of strabismus
Idiopathic
Congenital
Cranial nerve palsies, particularly of those of
nerves innervating the extraocular muscles
Intracranial infection
Intracranial, intraorbital and intraocular masses
Orbital fracture or other trauma
Myopathies (e.g. myasthenia gravis)
Endocrinological conditions (e.g. diabetes mellitus,
Graves’ disease)
Heavy metals and toxins
Interestingly, although amblyopia is a known sequela of long-standing, established strabismus, it itself can be a cause of
strabismus. Lower visual experience (sensation, cognition and processing and perception) in an eye can result in that eye
drifting out of correct alignment.
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Note that pseudostrabismus (i.e. false strabismus), where an eye may appear turned, often in children, may be due to
structural causes that generally resolve with time, as the individual grows. These causes include a broad,
hypo- or hypertelorism (i.e. abnormally reduced or abnormally increased distance between the eyes) or extraneous skin
that covers the medial canthus.
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Triggers for intermittent strabismus can include fatigue and stress.

Risk factors

Risk factors for primary strabismus include a family history of strabismus , low birth weight 4 5,6 7
, premature birth maternal smoking.
7,8
and

Clinical features of strabismus

History-taking

Red
Recent trauma
Symptoms of raised intracranial pressure (e.g. morning headaches, vomiting)
New strabismus in a school-age child
History of presenting complaint
Onset (e.g. dependent on the direction of gaze or time of day)
Reduced visual acuity
Diplopia
Asthenopia (i.e. eye strain, fatigue or pain), particularly in the afternoon or at the end of the day
Decreased academic and/or work performance
Decreased socialisation
Behavioural problems
Maladjustment at home or school
Walking di
Other important topics
Obstetric and developmental history
Previous medical history, including any history of head or ophthalmic trauma, autoimmune or neoplastic conditions, toxin
exposure
Previous visual acuity or ophthalmic testing results

Clinical examination

The physical examination of potential strabismus requires a penlight or other light source and an occluder. The basic
physical examination involves the light re
Brückner screening test as well as the prism cover and alternate prism cover tests are also described below. Others such as
the Parks–Bielschowski 3-step test can be found in other literature. Factors a
abnormal head posture, should be noted.
The following elements should be described when characterising a tropia\:
direction;
laterality (unilateral or alternating, specifying the deviating eye);
frequency (constant or intermittent);
comitant or noncomitant (i.e. whether or not the amount of deviation varies according to the direction of the tropia and
re
Light re
1. Ask the patient to focus on a target approximately half a metre away whilst you shine a pen torch towards both eyes.
2. Inspect the corneal light re
If the ocular alignment is normal, the light re
De
Brückner test
The Brückner test is useful for identifying the presence of small-angle strabismus. At approximately 50 cm away from the
patient, the examiner uses a direct ophthalmoscope (DO) with the largest diameter of light to view both of the patient’s red
re
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skin around the eyes is in focus. Asymmetry of the red re
ocular disorder, including strabismus, anisometropia (i.e. imbalance of refractive error) or media opacity that is obstructing
the visual axis (e.g. cataract, anterior-chamber or vitreous disorder, coloboma, retinal tumour).
Cover test (a.k.a. single-cover test)
The cover test is used to determine if a heterotropia (i.e. manifest strabismus) is present.
1. Ask the patient to
2. Occlude one of the patient's eyes and observe the contralateral eye for a shift in
If there is no shift in
alignment).
If there is a shift in
3. Repeat the cover test on the other eye.
The direction of the shift in
Table 3. Interpretation of direction at rest and directions of shifts in
Direction of eye at rest
Temporally (i.e. laterally or outwards) Nasally (i.e. medially or inwards) The direction of shift in
unoccluded eye when the opposite eye is
occluded
Type of tropia present
Nasally (i.e. medially or inwards) Exotropia
Temporally (i.e. laterally or outwards) Esotropia
Superiorly (i.e. upwards) Inferiorly (i.e. downwards) Hypertropia
Inferiorly (i.e. downwards) Superiorly (i.e. upwards) Hypotropia
C o v e r t e s t
Cover–uncover test (a.k.a. alternate cover test)
The cover–uncover test is used to di
demonstrates no tropia, it is used to determine if a phoria (i.e. latent strabismus) is present. Large ones can be associated
with asthenopia (i.e. eye strain) and diplopia. Note, small, subtly perceptible phorias are common and non-pathological.
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The examiner occludes one eye for approximately 1-2 seconds, then quickly removes the occluder to restore binocular
vision. The eye that was previously occluded is observed (rather than the unoccluded eye, as in the cover test) for re
movement. If a phoria is present, this eye will shift back to being orthotropic (i.e. straight-looking) to re-establish sensory
fusion with the other eye.
The speed and smoothness of re
14
Table 4. Interpretation of directions of re
The direction of the re
occluded eye when occluded and then
unoccluded
Type of phoria present
Nasally (i.e. medially or inwards) Exophoria
Temporally (i.e. laterally or outwards) Esophoria
Inferiorly (i.e. downwards) Hyperphoria
Superiorly (i.e. upwards) Hypophoria
Prism cover test (a.k.a. simultaneous prism cover test)
The prism cover test is used to measure the angle of deviation of a small-angle tropia. The magnitude of the tropia is
estimated from the cover and cover–uncover test. A prism (by itself or in a prism bar) underestimating the magnitude is
selected.
This prism is placed over the non-
for an exo- deviation, the prism should be base-in or temporally
for an eso- deviation, the prism should be base-out or nasally
for an hypo- deviation, the prism should be base-up
for a hyper- deviation, the prism should be base-down
Simultaneously, this prism should occlude the
until there is no shift in
suspending binocular fusion, which can make the deviation of a tropia larger due to any imposition of the e
phoria.
Alternate prism cover test
An alternate prism cover test is the alternate cover test performed with the prism placed as above. This is used to
measure the angle of deviation of a phoria. The prism should decrease the magnitude of re
compared with when no prism is used. The strength of the prism is increased until no re
this point, the magnitude of the phoria is equal to the strength of the prism.
To con
the re
there is no re
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Prism bar and
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Further examination
Further examination should include stereopsis, which is the perception of depth and 3-dimensional structure from
visual information obtained from both eyes simultaneously. However, as a basic screen by a medic, this usually
requires special images called random-dot stereograms and is seldom performed.

References

Adams GGW, Sloper JJ. Update on squaint and amblyopia. J R Soc Med. 2003;96(1)\:3-6.
Niechwiej-Szwedo E, Goltz HC, Chandrakumar M, Wong AMF. E
Amblyopia on Visuomotor Behavior\: III. Temporal Eye–Hand Coordination During Reaching. Investigative Ophthalmology &
Visual Science. 2014;55\:7831-7838.
Webber AL, Camuglia JE. A pragmatic approach to amblyopia diagnosis\: evidence into practice. Clinical and Experimental
Optometry. 2018;101(4)\:451-459.
Maconachie GDE, Gottlob I, McLean RJ. Risk Factors and Genetics in Common Comitant Strabismus\: A Systemic Review of
the Literature. JAMA Ophthalmology. 2013;131(9)\:1179-1186.
O'Connor AR, Stephenson TJ, Johnson A, Tobin MJ, Ratib S, Fielder AR. Strabismus in Children of Birth Weight Less Than
1701 g. Arch Ophthalmol. 2002;120(6)\:767–773.
Gulati S, Andrews CA, Apkarian AO, Musch DC, Lee PP, Stein JD. E
Strabismus Among Premature Infants. JAMA Pediatr. 2014;168(9)\:850–856.
Cotter SA, Varma R, Tarczy-Hornoch K, et al. Risk factors associated with childhood strabismus\: the multi-ethnic pediatric
eye disease and Baltimore pediatric eye disease studies. Ophthalmology. 2011;118(11)\:2251–2261.
Hakim RB, Tielsch JM. Maternal Cigarette Smoking During Pregnancy\: A Risk Factor for Childhood Strabismus. A r c h
O p h t h a l m o l . 1992;110(10)\:1459–1462.
Matsuo T, Yamane T, Ohtsuki H. Heredity Versus Abnormalities in Pregnancy and Delivery as Risk Factors for Di
of Comitant Strabismus. Journal of Pediatric Ophthalmology and Strabimus. 2001;38(2)\:78-82.
Berk AT, Oner FH, Saatci AO. Underlying pathologies in secondary strabimus. Strabismus. 2009;8(2)\:69-75.
Capó H, Roth E, Johnson T, Muñoz M, Siatkowski RM. Vertical strabimus after cataract surgery. Ophthalmology.
1996;103(6)\:918-21.
Xia Q, Huang Z, Shen DA, Dai H. [Clinical analysis of the diplpia and strabismus after ophthalmic surgeries]. [Zhonghua yan
ke za Zhi] Chinese Journal of Ophthalmology, 2003;39(12)\:727-730.
Quah BL, Tay MTH, Chew SJ, Lee LKH. A study amblyopia in 18–19 year old males. Singapore Med J. 1991;32\:126-129.
https\://app.geekymedics.com/notebook/2579/ 6/711/14/24, 10\:43 AM Strabismus
Kanski JJ. Clinical Ophthalmology\: A systemic approach. 6th ed. Edinburgh\: Elsevier Butterworth–Heinemann; 2007.
TeamE PFR. Prism bar and CC BY-SA. Available from\: [LINK].

Related notes

Acute Angle-Closure Glaucoma
Age-related Macular Degeneration (ARMD)
Amblyopia
Ametropia
Anisocoria

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