Strabismus
Encyclopedia
Strabismus is a condition in which the eye
s are not properly aligned with each other. It typically involves a lack of coordination between the extraocular muscle
s, which prevents bringing the gaze of each eye to the same point in space and preventing proper binocular vision
, which may adversely affect depth perception
.
Strabismus can be either a disorder of the brain in coordinating the eyes, or of one or more of the relevant muscles' power or direction of motion. Difficult strabismus problems are usually co-managed between orthoptists and ophthalmologists.
Strabismus is often mistakenly referred to as "lazy eye" or known as amblyopia; a result from constant unilateral strabismus. It is also referred to as "crossed eyes", “wandering eyes”, or having a “cast”. Other names include "squint", "crossed eye", "google eye", "boss eye", "cock eye", "wonk eye", "codeye", "wok eye", and "Derpy eyes".
"Cross-eyed" means that when a person with strabismus looks at an object, one eye fixes on the object and the other fixes with a convergence angle less than zero; the optic axes overconverge. "Wall-eyed" means that when a person with strabismus looks at an object, one eye fixes on the object and the other fixes with a convergence angle greater than zero; that is, the optic axes diverge from parallel
.
, IV (trochlear)
or VI (abducens) have a lesion. A strabismus caused by a lesion in either of these nerves results in the lack of innervation to eye muscles and results in a change of eye position. A strabismus may be a sign of increased intracranial pressure, as CN VI is particularly vulnerable to damage from brain swelling, as it runs between the clivus
and brain stem.
More commonly however, squints are termed concominant (i.e. non paralytic). This means the squint is not caused by a lesion reducing innervation. The squint in this example is caused by a refractive error in one or both eyes. This refractive error causes poor vision in one eye and so stops the brain from being able to use both eyes together.
s, orthoptists, ophthalmologists and optometrists typically use a cover test
to aid in the diagnosis of strabismus. If the eye being tested is the strabismic eye, then it will fixate on the object after the "straight" eye is covered, as long as the vision in this eye is good enough. If the "straight" eye is being tested, there will be no change in fixation, as it is already fixated. Depending on the direction that the strabismic eye deviates, the direction of deviation may be assessed. Exotropic
is outwards (away from the midline) and esotropic
is inwards (towards the nose); these are types of horizontal strabismus. "Hypertropia" is upward, and "Hypotropia" is downward; these are types of vertical strabismus, which are less common.
A simple screening test for strabismus is the Hirschberg test
. A flashlight is shone in the patient's eye. When the patient is looking at the light, a reflection can be seen on the front surface of the pupil. If the eyes are properly aligned with one another, then the reflection will be in the same spot of each eye. Therefore, if the reflection is not in the same place in each eye, then the eyes aren't properly aligned.
is the false appearance of strabismus. It generally occurs in infants and toddlers whose bridge of the nose is wide and flat, causing the appearance of strabismus. With age, the bridge of the child's nose narrows and the folds in the corner of the eyes go away. To detect the difference between pseudostrabismus and strabismus, a Hirschberg test
may be used.
Whereas amblyopia
(lazy eye), if minor and detected early, can often be corrected with use of an eyepatch
on the dominant eye and/or vision therapy
, the use of eyepatches is unlikely to change the angle of strabismus. Advanced strabismus is usually treated with a combination of eyeglasses or prism
s, vision therapy, and surgery
, depending on the underlying reason for the misalignment. Surgery does not change the vision; it attempts to align the eyes by shortening, lengthening, or changing the position of one or more of the extraocular eye muscles and is frequently the only way to achieve cosmetic improvement. The procedure can typically be performed in about an hour, and requires about a week for recovery. Double vision can result, and occasionally vision loss can occur. Glasses affect the position by changing the person's reaction to focusing. Prisms change the way light
, and therefore images, strike the eye, simulating a change in the eye position.
Early treatment of strabismus and/or amblyopia in infancy can reduce the chance of developing amblyopia and depth perception problems. Most children eventually recover from amblyopia by around age 10, if they have had the benefit of patches and corrective glasses.
Eyes that remain misaligned can still develop visual problems. Although not a cure for strabismus, prism lenses
can also be used to provide some comfort for sufferers and to prevent double vision from occurring.
Botulinum Toxin (Botox) may also be used in the treatment of strabismus, to improve cosmetic appearance. Most commonly used in adults, the toxin is injected in the stronger muscle, causing temporary paralysis. The treatment may need to be repeated 3–4 months later once the paralysis wears off. Common side effects are double vision, droopy eyelid, over correction and no effect. The side effects will resolve fairly quickly.
In adult
s with previously normal alignment, the onset of strabismus usually results in double vision (diplopia
).
, in which the brain
ignores input from the deviated eye. The appearance of strabismus may also be a cosmetic
problem. One study reported that 85% of adult strabismus patients "reported that they had problems with work, school
and sport
s because of their strabismus." The same study also reported that 70% said strabismus "had a negative effect on their self-image."
Human eye
The human eye is an organ which reacts to light for several purposes. As a conscious sense organ, the eye allows vision. Rod and cone cells in the retina allow conscious light perception and vision including color differentiation and the perception of depth...
s are not properly aligned with each other. It typically involves a lack of coordination between the extraocular muscle
Muscles of orbit
The muscles of the orbit are a group of six muscles that control movement of the eye. Four of the muscles control the movement of the eye in the four cardinal directions: up, down, left and right...
s, which prevents bringing the gaze of each eye to the same point in space and preventing proper binocular vision
Binocular vision
Binocular vision is vision in which both eyes are used together. The word binocular comes from two Latin roots, bini for double, and oculus for eye. Having two eyes confers at least four advantages over having one. First, it gives a creature a spare eye in case one is damaged. Second, it gives a...
, which may adversely affect depth perception
Depth perception
Depth perception is the visual ability to perceive the world in three dimensions and the distance of an object. Depth sensation is the ability to move accurately, or to respond consistently, based on the distances of objects in an environment....
.
Strabismus can be either a disorder of the brain in coordinating the eyes, or of one or more of the relevant muscles' power or direction of motion. Difficult strabismus problems are usually co-managed between orthoptists and ophthalmologists.
Paralytic strabismus
Forms of paralytic strabismus include- Third (oculomotor) nerve palsy
- Fourth (trochlear) nerve palsy
- Congenital fourth nerve palsyCongenital fourth nerve palsyCongenital fourth nerve palsy is a condition present at birth characterized by a vertical misalignment of the eyes due to a weakness or paralysis of the superior oblique muscle....
- Congenital fourth nerve palsy
- Sixth (abducent) nerve palsy
- Total (external) ophthalmoplegia
- Progressive external ophthalmoplegia
- Other
- Kearns-Sayre syndromeKearns-Sayre syndromeKearns–Sayre syndrome also known as oculocraniosomatic disease or Oculocraniosomatic neuromuscular disease with ragged red fibers is a mitochondrial myopathy with a typical onset before 20 years of age...
- Kearns-Sayre syndrome
Other strabismus
Other forms of strabismus include:- Convergent concomitant/Divergent concomitant
- EsotropiaEsotropiaEsotropia is a form of strabismus, or "squint", in which one or both eyes turns inward. The condition can be constantly present, or occur intermittently, and can give the affected individual a "cross-eyed" appearance...
- ExotropiaExotropiaExotropia is a form of strabismus where the eyes are deviated outward. It is the opposite of esotropia. People with exotropia often experience crossed diplopia. Intermittent exotropia is a fairly common condition. "Sensory exotropia" occurs in the presence of poor vision...
- Esotropia
- Vertical strabismus
- HypertropiaHypertropiaHypertropia is a condition of misalignment of the eyes , whereby the visual axis of one eye is higher than the fellow fixating eye.Hypotropia is the similar condition, focus being on the eye with the visual axis lower than the fellow fixating eye....
- Hypotropia
- Hypertropia
- Other and unspecified heterotropia
- Microtropia
- Monofixation syndromeMonofixation syndromeMonofixation syndrome is an eye condition defined by less than perfect binocular vision. It is defined by a small angle deviation with suppression of the deviated eye and binocular peripheral fusion. It often results post surgical treatment of congenital esotropia....
- HeterophoriaHeterophoriaHeterophoria is a type of eye condition in which the directions that the eyes are pointing are not consistent with each other. A person with two normal eyes has single vision because of the combined use of the sensory and motor systems. The motor system acts to point both eyes at the target of...
- EsophoriaEsophoriaEsophoria is characterised by inward deviation of the eye usually due to extra-ocular muscle imbalance.Causes include:*refractive errors*divergence insufficiency*convergence excess, these can be due to nerve, muscle, congenital or mechanical anomalies....
- ExophoriaExophoriaExophoria is a form of heterophoria in which there is a tendency of the eyes to deviate outward. During examination, when the eyes are dissociated by prisms, the visual axes will appear to diverge away from one another.-Prevalence:...
- Esophoria
- Mechanical strabismus
- Brown's sheath syndrome
- Other
- Duane syndromeDuane syndromeDuane syndrome is a rare, congenital eye movement disorder most commonly characterized by the inability of the eye to abduct or move outwards...
- Duane syndrome
Signs and symptoms
One eye moves normally, while the other points in (esotropia or "crossed eyes"), out (exotropia), up (hypertropia) or down (hypotropia).Strabismus is often mistakenly referred to as "lazy eye" or known as amblyopia; a result from constant unilateral strabismus. It is also referred to as "crossed eyes", “wandering eyes”, or having a “cast”. Other names include "squint", "crossed eye", "google eye", "boss eye", "cock eye", "wonk eye", "codeye", "wok eye", and "Derpy eyes".
"Cross-eyed" means that when a person with strabismus looks at an object, one eye fixes on the object and the other fixes with a convergence angle less than zero; the optic axes overconverge. "Wall-eyed" means that when a person with strabismus looks at an object, one eye fixes on the object and the other fixes with a convergence angle greater than zero; that is, the optic axes diverge from parallel
Parallel (geometry)
Parallelism is a term in geometry and in everyday life that refers to a property in Euclidean space of two or more lines or planes, or a combination of these. The assumed existence and properties of parallel lines are the basis of Euclid's parallel postulate. Two lines in a plane that do not...
.
Pathophysiology
Strabismus can be caused when the cranial nerves III (oculomotor)Oculomotor nerve
The oculomotor nerve is the 3rd of 12 paired cranial nerves. It enters the orbit via the superior orbital fissure and controls most of the eye's movements, including constriction of the pupil and maintaining an open eyelid by innervating the Levator palpebrae superiors muscle. The optic nerve is...
, IV (trochlear)
Trochlear nerve
The trochlear nerve is a motor nerve that innervates a single muscle: the superior oblique muscle of the eye....
or VI (abducens) have a lesion. A strabismus caused by a lesion in either of these nerves results in the lack of innervation to eye muscles and results in a change of eye position. A strabismus may be a sign of increased intracranial pressure, as CN VI is particularly vulnerable to damage from brain swelling, as it runs between the clivus
Clivus (anatomy)
The clivus is a part of the cranium, a shallow depression behind the dorsum sellæ that slopes obliquely backward. It forms a gradual sloping process at the anterior most portion of the basilar occipital bone at its junction with the sphenoid bone. On axial planes, it sits just posterior to the...
and brain stem.
More commonly however, squints are termed concominant (i.e. non paralytic). This means the squint is not caused by a lesion reducing innervation. The squint in this example is caused by a refractive error in one or both eyes. This refractive error causes poor vision in one eye and so stops the brain from being able to use both eyes together.
Diagnosis
During eye examinationEye examination
An eye examination is a battery of tests performed by an ophthalmologist, optometrist, or orthoptist assessing vision and ability to focus on and discern objects, as well as other tests and examinations pertaining to the eyes....
s, orthoptists, ophthalmologists and optometrists typically use a cover test
Cover test
A cover test is an objective determination of the presence and amount of ocular deviation. It is typically performed by orthoptists, ophthalmologists and optometrists during eye examinations....
to aid in the diagnosis of strabismus. If the eye being tested is the strabismic eye, then it will fixate on the object after the "straight" eye is covered, as long as the vision in this eye is good enough. If the "straight" eye is being tested, there will be no change in fixation, as it is already fixated. Depending on the direction that the strabismic eye deviates, the direction of deviation may be assessed. Exotropic
Exotropia
Exotropia is a form of strabismus where the eyes are deviated outward. It is the opposite of esotropia. People with exotropia often experience crossed diplopia. Intermittent exotropia is a fairly common condition. "Sensory exotropia" occurs in the presence of poor vision...
is outwards (away from the midline) and esotropic
Esotropia
Esotropia is a form of strabismus, or "squint", in which one or both eyes turns inward. The condition can be constantly present, or occur intermittently, and can give the affected individual a "cross-eyed" appearance...
is inwards (towards the nose); these are types of horizontal strabismus. "Hypertropia" is upward, and "Hypotropia" is downward; these are types of vertical strabismus, which are less common.
A simple screening test for strabismus is the Hirschberg test
Hirschberg test
In the fields of optometry and ophthalmology, the Hirschberg test, also Hirschberg corneal reflex test, is a screening test that can be used to assess whether a person has strabismus ....
. A flashlight is shone in the patient's eye. When the patient is looking at the light, a reflection can be seen on the front surface of the pupil. If the eyes are properly aligned with one another, then the reflection will be in the same spot of each eye. Therefore, if the reflection is not in the same place in each eye, then the eyes aren't properly aligned.
Laterality
Strabismus may be classified as unilateral if the same eye consistently 'wanders', or alternating if either of the eyes can be seen to 'wander'. Alternation of the strabismus may occur spontaneously, with or without subjective awareness of the alternation. Alternation may also be seen following the cover test, with the previously 'wandering' eye remaining straight while the previously straight eye is now seen to be 'wandering' on removal of the cover. The cover-uncover test is used to diagnose the type of strabismus (also known as tropia) present.Onset
Strabismus may also be classified based on time of onset, either congenital, acquired or secondary to another pathological process, such as cataract. Many infants are born with their eyes slightly misaligned. The best time for physicians to assess this is between ages 3 and 6 months.Differential diagnosis
PseudostrabismusPseudostrabismus
Pseudostrabismus is the false appearance of crossed eyes. When the eyes are actually crossed or not completely aligned with one another it is called strabismus. Pseudostrabimus generally occurs in infants and toddlers whose facial features are not fully developed. The bridge of their nose is...
is the false appearance of strabismus. It generally occurs in infants and toddlers whose bridge of the nose is wide and flat, causing the appearance of strabismus. With age, the bridge of the child's nose narrows and the folds in the corner of the eyes go away. To detect the difference between pseudostrabismus and strabismus, a Hirschberg test
Hirschberg test
In the fields of optometry and ophthalmology, the Hirschberg test, also Hirschberg corneal reflex test, is a screening test that can be used to assess whether a person has strabismus ....
may be used.
Management
As with other binocular vision disorders, the primary therapeutic goal for those with strabismus is comfortable, single, clear, normal binocular vision at all distances and directions of gaze.Whereas amblyopia
Amblyopia
Amblyopia, also known as lazy eye, is a disorder of the visual system that is characterized by a vision deficiency in an eye that is otherwise physically normal, or out of proportion to associated structural abnormalities of the eye...
(lazy eye), if minor and detected early, can often be corrected with use of an eyepatch
Eyepatch
An eyepatch or eye pad is a small patch that is worn in front of one eye. It may be a cloth patch attached around the head by an elastic band or by a string, or an adhesive bandage. It is often worn by people to cover a lost or injured eye, but it also has a therapeutic use in children for the...
on the dominant eye and/or vision therapy
Vision therapy
Vision therapy, also known as visual training, vision training, or visual therapy, is a broad group of techniques aimed at correcting and improving binocular, oculomotor, visual processing, and perceptual disorders."-Historical development:...
, the use of eyepatches is unlikely to change the angle of strabismus. Advanced strabismus is usually treated with a combination of eyeglasses or prism
Prism (optics)
In optics, a prism is a transparent optical element with flat, polished surfaces that refract light. The exact angles between the surfaces depend on the application. The traditional geometrical shape is that of a triangular prism with a triangular base and rectangular sides, and in colloquial use...
s, vision therapy, and surgery
Eye surgery
Eye surgery, also known as orogolomistician surgery or ocular surgery, is surgery performed on the eye or its adnexa, typically by an ophthalmologist.-Preparation and precautions:...
, depending on the underlying reason for the misalignment. Surgery does not change the vision; it attempts to align the eyes by shortening, lengthening, or changing the position of one or more of the extraocular eye muscles and is frequently the only way to achieve cosmetic improvement. The procedure can typically be performed in about an hour, and requires about a week for recovery. Double vision can result, and occasionally vision loss can occur. Glasses affect the position by changing the person's reaction to focusing. Prisms change the way light
Light
Light or visible light is electromagnetic radiation that is visible to the human eye, and is responsible for the sense of sight. Visible light has wavelength in a range from about 380 nanometres to about 740 nm, with a frequency range of about 405 THz to 790 THz...
, and therefore images, strike the eye, simulating a change in the eye position.
Early treatment of strabismus and/or amblyopia in infancy can reduce the chance of developing amblyopia and depth perception problems. Most children eventually recover from amblyopia by around age 10, if they have had the benefit of patches and corrective glasses.
Eyes that remain misaligned can still develop visual problems. Although not a cure for strabismus, prism lenses
Lens (optics)
A lens is an optical device with perfect or approximate axial symmetry which transmits and refracts light, converging or diverging the beam. A simple lens consists of a single optical element...
can also be used to provide some comfort for sufferers and to prevent double vision from occurring.
Botulinum Toxin (Botox) may also be used in the treatment of strabismus, to improve cosmetic appearance. Most commonly used in adults, the toxin is injected in the stronger muscle, causing temporary paralysis. The treatment may need to be repeated 3–4 months later once the paralysis wears off. Common side effects are double vision, droopy eyelid, over correction and no effect. The side effects will resolve fairly quickly.
In adult
Adult
An adult is a human being or living organism that is of relatively mature age, typically associated with sexual maturity and the attainment of reproductive age....
s with previously normal alignment, the onset of strabismus usually results in double vision (diplopia
Diplopia
Diplopia, commonly known as double vision, is the simultaneous perception of two images of a single object that may be displaced horizontally, vertically, or diagonally in relation to each other...
).
Prognosis
When strabismus is congenital or develops in infancy, it can cause amblyopiaAmblyopia
Amblyopia, also known as lazy eye, is a disorder of the visual system that is characterized by a vision deficiency in an eye that is otherwise physically normal, or out of proportion to associated structural abnormalities of the eye...
, in which the brain
Brain
The brain is the center of the nervous system in all vertebrate and most invertebrate animals—only a few primitive invertebrates such as sponges, jellyfish, sea squirts and starfishes do not have one. It is located in the head, usually close to primary sensory apparatus such as vision, hearing,...
ignores input from the deviated eye. The appearance of strabismus may also be a cosmetic
Beauty
Beauty is a characteristic of a person, animal, place, object, or idea that provides a perceptual experience of pleasure, meaning, or satisfaction. Beauty is studied as part of aesthetics, sociology, social psychology, and culture...
problem. One study reported that 85% of adult strabismus patients "reported that they had problems with work, school
School
A school is an institution designed for the teaching of students under the direction of teachers. Most countries have systems of formal education, which is commonly compulsory. In these systems, students progress through a series of schools...
and sport
Sport
A Sport is all forms of physical activity which, through casual or organised participation, aim to use, maintain or improve physical fitness and provide entertainment to participants. Sport may be competitive, where a winner or winners can be identified by objective means, and may require a degree...
s because of their strabismus." The same study also reported that 70% said strabismus "had a negative effect on their self-image."
See also
- Orthoptist
- Duane syndromeDuane syndromeDuane syndrome is a rare, congenital eye movement disorder most commonly characterized by the inability of the eye to abduct or move outwards...
- Möbius syndromeMobius syndromeMöbius syndrome is an extremely rare congenital neurological disorder which is characterized by facial paralysis and the inability to move the eyes from side to side. Most people with Möbius syndrome are born with complete facial paralysis and cannot close their eyes or form facial expressions...
- Orthoptics
- International Orthoptic AssociationInternational Orthoptic AssociationThe International Orthoptic Association represents over 20,000 orthoptists, in over 20 countries.- History :The International Orthoptic Association was formed in 1967 after the first International Orthoptic Congress. The British Orthoptic Association were the founding members. - Registration and...
- Pediatric ophthalmologyPediatric ophthalmologyPediatric ophthalmology is a sub-speciality of ophthalmology concerned with eye diseases, visual development, and vision care in children.-Training:...
- RetinoblastomaRetinoblastomaRetinoblastoma is a rapidly developing cancer that develops in the cells of retina, the light-detecting tissue of the eye. In the developed world, Rb has one of the best cure rates of all childhood cancers , with more than nine out of every ten sufferers surviving into...
- PalsyCranial nerve diseaseCranial nerve disease is a term used to describe an impaired functioning of one of the twelve cranial nerves.Although it could theoretically be considered a mononeuropathy, it is not considered as such under MeSH....
of cranial nerve III (oculomotor)Oculomotor nerve palsyOculomotor nerve palsy is an eye condition resulting from damage to the third cranial nerve or a branch thereof. As the name suggests, the oculomotor nerve supplies the majority of the muscles controlling eye movements. Thus, damage to this nerve will result in the affected individual being unable...
, IV (trochlear)Fourth nerve palsyFourth nerve palsy is a condition caused by weakness or paralysis of the superior oblique muscle. This condition often causes double vision as the weakened muscle prevents the eyes from moving in the same direction....
, VI (abducens)Sixth nerve palsySixth nerve palsy, or abducens nerve palsy, is a disorder associated with dysfunction of cranial nerve VI , which is responsible for contracting the lateral rectus muscle to abduct the eye... - Strabismus surgeryStrabismus surgeryStrabismus surgery is surgery on the extraocular muscles to correct the misalignment of the eyes. With approximately 1.2 million procedures each year, extraocular muscle surgery is the third most common eye surgery in the United States.-Types:...
- AmblyopiaAmblyopiaAmblyopia, also known as lazy eye, is a disorder of the visual system that is characterized by a vision deficiency in an eye that is otherwise physically normal, or out of proportion to associated structural abnormalities of the eye...
- Bates methodBates MethodThe Bates method is an alternative therapy aimed at improving eyesight. Eye-care physician William Horatio Bates attributed nearly all sight problems to habitual strain of the eyes, and felt that glasses were harmful and never necessary...