Strabismus

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Strabismus
Other namesHeterotropia, crossed eyes, squint [1]
StrabismusVL2.jpg
A person with exotropia, an outward deviated eye
Pronunciation
Specialty Ophthalmology, optometry
Symptoms Nonaligned eyes [2]
Complications Amblyopia, double vision [3]
Types Esotropia (eyes crossed); exotropia (eyes diverge); hypertropia (eyes vertically misaligned) [3]
CausesMuscle dysfunction, farsightedness, problems in the brain, trauma, infections [3]
Risk factors Premature birth, cerebral palsy, family history [3]
Diagnostic method Observing light reflected from the pupil [3]
Differential diagnosis Cranial nerve disease, [3] convergence insufficiency
Treatment Glasses, surgery [3]
Frequency~2% (children) [3]

Strabismus is an eye disorder in which the eyes do not properly align with each other when looking at an object. [2] The eye that is pointed at an object can alternate. [3] The condition may be present occasionally or constantly. [3] If present during a large part of childhood, it may result in amblyopia, or lazy eyes, and loss of depth perception. [3] If onset is during adulthood, it is more likely to result in double vision. [3]

Contents

Strabismus can occur due to muscle dysfunction (e.g., myasthenia gravis [4] [5] ), farsightedness, problems in the brain, trauma, or infections. [3] Risk factors include premature birth, cerebral palsy, and a family history of the condition. [3] Types include esotropia, where the eyes are crossed ("cross eyed"); exotropia, where the eyes diverge ("lazy eyed" or "wall eyed"); and hypertropia or hypotropia where they are vertically misaligned. [3] They can also be classified by whether the problem is present in all directions a person looks (comitant) or varies by direction (incomitant). [3] Diagnosis may be made by observing the light reflecting from the person's eyes and finding that it is not centered on the pupil. [3] This is known as the Hirschberg reflex. Another condition that produces similar symptoms is a cranial nerve disease. [3]

Treatment depends on the type of strabismus and the underlying cause. [3] This may include the use of glasses and possibly surgery. [3] Some types benefit from early surgery. [3] Strabismus occurs in about 2% of children. [3] The term comes from the Ancient Greek word στραβισμός (strabismós), meaning 'a squinting'. [6] Other terms for the condition include "squint" and "cast of the eye". [7] [8] [9]

Signs and symptoms

Autostereogram normal vergence.svg
Aligned  vergence
Autostereogram cross-eyed vergence.svg
Esotropia
Autostereogram wall-eyed vergence.svg
Exotropia

When observing a person with strabismus, the misalignment of the eyes may be quite apparent. A person with a constant eye turn of significant magnitude is very easy to notice. However, a small magnitude or intermittent strabismus can easily be missed upon casual observation. In any case, an eye care professional can conduct various tests, such as cover testing, to determine the full extent of the strabismus.[ citation needed ]

Symptoms of strabismus include double vision and eye strain. To avoid double vision, the brain may adapt by ignoring one eye. In this case, often no noticeable symptoms are seen other than a minor loss of depth perception. This deficit may not be noticeable in someone who has had strabismus since birth or early childhood, as they have likely learned to judge depth and distances using monocular cues. However, a constant unilateral strabismus causing constant suppression is a risk for amblyopia in children. Small-angle and intermittent strabismus are more likely to cause disruptive visual symptoms. In addition to headaches and eye strain, symptoms may include an inability to read comfortably, fatigue when reading, and unstable or "jittery" vision.

Psychosocial effects

Fayum mummy portrait, c. 150-200 AD Fayum-40.jpg
Fayum mummy portrait, c. 150–200 AD
Tommaso Inghirami Inghirami Raphael.jpg
Tommaso Inghirami
Norma Shearer Norma Shearer 1926.jpg
Norma Shearer
Alger Hiss Alger Hiss (1950).jpg
Alger Hiss
Jean-Paul Sartre Sartre 1967 crop.jpg
Jean-Paul Sartre
Marty Feldman Marty Feldman 1972.JPG
Marty Feldman
Chelsea goalkeeper Hannah Hampton has strabismus. Hannah-Hampton.jpg
Chelsea goalkeeper Hannah Hampton has strabismus.

People of all ages who have noticeable strabismus may experience psychosocial difficulties. [10] [11] [12] Attention has also been drawn to potential socioeconomic impact resulting from cases of detectable strabismus. A socioeconomic consideration exists as well in the context of decisions regarding strabismus treatment, [10] [11] [12] including efforts to re-establish binocular vision and the possibility of stereopsis recovery. [13]

One study has shown that strabismic children commonly exhibit behaviors marked by higher degrees of inhibition, anxiety, and emotional distress, often leading to outright emotional disorders. These disorders are often related to a negative perception of the child by peers. This is due not only to an altered aesthetic appearance but also because of the inherent symbolic nature of the eye and gaze and the vitally important role they play in an individual's life as social components. For some, these issues improved dramatically following strabismus surgery. [14] Notably, strabismus interferes with normal eye contact, often causing embarrassment, anger, and feelings of awkwardness, thereby affecting social communication in a fundamental way, with a possible negative effect on self esteem. [15] [16]

Children with strabismus, particularly those with exotropia, an outward turn, may be more likely to develop a mental health disorder than normal-sighted children. Researchers have theorized that esotropia (an inward turn) was not found to be linked to a higher propensity for mental illness due to the age range of the participants, as well as the shorter follow-up time period; esotropic children were monitored to a mean age of 15.8 years, compared with 20.3 years for the exotropic group. [17] [18]

Investigations have highlighted the impact that strabismus may typically have on quality of life. [19] Studies in which subjects were shown images of strabismic and non-strabismic persons showed a strong negative bias towards those visibly displaying the condition, clearly demonstrating the potential for future socioeconomic implications with regard to employability, as well as other psychosocial effects related to an individual's overall happiness. [20] [21]

Adult and child observers perceived a right heterotropia as more disturbing than a left heterotropia, and child observers perceived an esotropia as "worse" than an exotropia. [22] Successful surgical correction of strabismus, for adult as well as children, has been shown to have a significantly positive effect on psychological well-being. [23] [24]

Very little research exists regarding coping strategies employed by adult strabismics. One study categorized coping methods into three subcategories: avoidance (refraining from participation in an activity), distraction (deflecting attention from the condition), and adjustment (approaching an activity differently). The authors of the study suggested that individuals with strabismus may benefit from psychosocial support such as interpersonal skills training. [25] No studies have evaluated whether psychosocial interventions have had any benefits on individuals undergoing strabismus surgery. [26]

Pathophysiology

The extraocular muscles control the position of the eyes. Thus, a problem with the muscles or the nerves controlling them can cause paralytic strabismus. The extraocular muscles are controlled by cranial nerves III, IV, and VI. An impairment of cranial nerve III causes the associated eye to deviate down and out and may or may not affect the size of the pupil. Impairment of cranial nerve IV, which can be congenital, causes the associated eye to drift up and perhaps slightly inward. Sixth nerve palsy causes the associated eye to deviate inward and has many causes due to the relatively long path of the nerve. Increased cranial pressure can compress the nerve as it runs between the clivus and brain stem. [27] [ page needed ] [28] [29] [30]

Evidence indicates a cause for strabismus may lie with the input provided to the visual cortex. [31]

Amblyopia may also cause strabismus. If a great difference in clarity occurs between the images from the right and left eyes, input may be insufficient to correctly reposition the eyes. Other causes of a visual difference between right and left eyes, such as asymmetrical cataracts, refractive error, or other eye disease, can also cause or worsen strabismus. [27] [ page needed ]

Diagnosis

During an eye examination, a test such as cover testing or the Hirschberg test is used in the diagnosis and measurement of strabismus and its impact on vision. Retinal birefringence scanning can be used for screening of young children for eye misalignment. A Cochrane review to examine different types of diagnosis test found only one study. This study used a photoscreener which was found to have high specificity (accurate in identifying those without the condition) but low sensitivity (inaccurate in identifying those with the condition). [32]

Several classifications are made when diagnosing strabismus.

Latency

Strabismus can be manifest (-tropia) or latent (-phoria). A manifest deviation, or heterotropia (which may be eso-, exo-, hyper-, hypo-, cyclotropia or a combination of these), is present while the person views a target binocularly, with no occlusion of either eye. The person is unable to align the gaze of each eye to achieve fusion. A latent deviation, or heterophoria (eso-, exo-, hyper-, hypo-, cyclophoria or a combination of these), is only present after binocular vision has been interrupted, typically by covering one eye. This type of person can typically maintain fusion despite the misalignment that occurs when the positioning system is relaxed. Intermittent strabismus is a combination of both of these types, where the person can achieve fusion, but occasionally or frequently falters to the point of a manifest deviation.

Onset

Strabismus may also be classified based on time of onset, either congenital, acquired, or secondary to another pathological process. Many infants are born with their eyes slightly misaligned, and this is typically outgrown by six to 12 months of age. [33] Acquired and secondary strabismus develop later. The onset of accommodative esotropia, an overconvergence of the eyes due to the effort of accommodation, is mostly in early childhood. Acquired non-accommodative strabismus and secondary strabismus are developed after normal binocular vision has developed. In adults with previously normal alignment, the onset of strabismus usually results in double vision.

A child with accommodative esotropia affecting the right eye Esotropia.jpg
A child with accommodative esotropia affecting the right eye

Any disease that causes vision loss may also cause strabismus, [34] but it can also result from any severe and/or traumatic injury to the affected eye. Sensory strabismus is strabismus due to vision loss or impairment, leading to horizontal, vertical or torsional misalignment or to a combination thereof, with the eye with poorer vision drifting slightly over time. Most often, the outcome is horizontal misalignment. Its direction depends on the person's age at which the damage occurs: people whose vision is lost or impaired at birth are more likely to develop esotropia, whereas people with acquired vision loss or impairment mostly develop exotropia. [35] [36] [37] In the extreme, complete blindness in one eye generally leads to the blind eye reverting to an anatomical position of rest. [38]

Although many possible causes of strabismus are known, among them severe and/or traumatic injuries to the affected eye, in many cases no specific cause can be identified. This last is typically the case when strabismus is present since early childhood. [39]

Results of a U.S. cohort study indicate that the incidence of adult-onset strabismus increases with age, especially after the sixth decade of life, and peaks in the eighth decade of life, and that the lifetime risk of being diagnosed with adult-onset strabismus is approximately 4%. [40]

Laterality

Strabismus may be classified as unilateral if the one eye consistently deviates, or alternating if either of the eyes can be seen to deviate. Alternation of the strabismus may occur spontaneously, with or without subjective awareness of the alternation. Alternation may also be triggered by various tests during an eye exam. [41] [ page needed ] Unilateral strabismus has been observed to result from a severe or traumatic injury to the affected eye. [35]

Direction and latency

Horizontal deviations are classified into two varieties, using prefixes: eso- describes inward or convergent deviations towards the midline, while exo- describes outward or divergent misalignment. Vertical deviations are also classified into two varieties, using prefixes: hyper- is the term for an eye whose gaze is directed higher than the fellow eye, while hypo- refers to an eye whose gaze is directed lower. Finally, the prefix cyclo- refers to torsional strabismus, which occurs when the eyes rotate around the anterior–posterior axis to become misaligned and is quite rare.

These five directional prefixes are combined with -tropia (if manifest) or -phoria (if latent) to describe various types of strabismus. For example, a constant left hypertropia exists when a person's left eye is always aimed higher than the right. A person with an intermittent right esotropia has a right eye that occasionally drifts toward the person's nose, but at other times is able to align with the gaze of the left eye. A person with a mild exophoria can maintain fusion during normal circumstances, but when the system is disrupted, the relaxed posture of the eyes is slightly divergent.

Other considerations

Strabismus can be further classified as follows:

Nonparetic strabismus is generally concomitant. [42] Most types of infant and childhood strabismus are comitant. [43] Paretic strabismus can be either comitant or noncomitant. Incomitant strabismus is almost always caused by a limitation of ocular rotations that is due to a restriction of extraocular eye movement (ocular restriction) or due to extraocular muscle paresis. [43] Incomitant strabismus cannot be fully corrected by prism glasses, because the eyes would require different degrees of prismatic correction dependent on the direction of the gaze. [44] Incomitant strabismus of the eso- or exo-type are classified as "alphabet patterns": they are denoted as A- or V- or more rarely λ-, Y- or X-pattern depending on the extent of convergence or divergence when the gaze moves upward or downward. These letters of the alphabet denote ocular motility pattern that have a similarity to the respective letter: in the A-pattern there is (relatively speaking) more convergence when the gaze is directed upwards and more divergence when it is directed downwards, in the V-pattern it is the contrary, in the λ-, Y- and X-patterns there is little or no strabismus in the middle position but relatively more divergence in one or both of the upward and downward positions, depending on the "shape" of the letter. [45]

Types of incomitant strabismus include: Duane syndrome, horizontal gaze palsy, and congenital fibrosis of the extraocular muscles. [46]

When the misalignment of the eyes is large and obvious, the strabismus is called large-angle, referring to the angle of deviation between the lines of sight of the eyes. Less severe eye turns are called small-angle strabismus. The degree of strabismus can vary based on whether the person is viewing a distant or near target.

Strabismus that sets in after eye alignment had been surgically corrected is called consecutive strabismus.

Differential diagnosis

Pseudostrabismus 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 esotropia due to less sclera being visible nasally. With age, the bridge of the child's nose narrows and the folds in the corner of the eyes become less prominent.

Retinoblastoma may also result in abnormal light reflection from the eye.

Strabismus correction surgery US Navy 090707-F-7923S-026 Navy Capt. Kristen Zeller and Hospital Corpsman 3rd Class Michael Peterson perform surgery to correct strabismus, or cross-eye, on an eight-month-old Nicaraguan infant.jpg
Strabismus correction surgery

Management

Strabismus is usually treated with a combination of eyeglasses, vision therapy, and surgery, depending on the underlying reason for the misalignment. As with other binocular vision disorders, the primary goal is comfortable, single, clear, normal binocular vision at all distances and directions of gaze. [47]

Glasses

In cases of accommodative esotropia, the eyes turn inward due to the effort of focusing far-sighted eyes, and the treatment of this type of strabismus necessarily involves refractive correction, which is usually done via corrective glasses or contact lenses, and in these cases surgical alignment is considered only if such correction does not resolve the eye turn.[ citation needed ]

In case of strong anisometropia, contact lenses may be preferable to spectacles because they avoid the problem of visual disparities due to size differences (aniseikonia) which is otherwise caused by spectacles in which the refractive power is very different for the two eyes. In a few cases of strabismic children with anisometropic amblyopia, a balancing of the refractive error eyes via refractive surgery has been performed before strabismus surgery was undertaken. [48]

Early treatment of strabismus when the person is a baby may reduce the chance of developing amblyopia and depth perception problems. However, a review of randomized controlled trials concluded that the use of corrective glasses to prevent strabismus is not supported by existing research. [49] Amblyopia has long been considered to remain permanent if not treated within a critical period, namely before the age of about seven years. [33]

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. [34]

Surgery

Strabismus surgery does not remove the need for a child to wear glasses. Currently it is unknown whether there are any differences for completing strabismus surgery before or after amblyopia therapy in children. [50]

Strabismus surgery attempts to align the eyes by shortening, lengthening, or changing the position of one or more of the extraocular eye muscles. The procedure can typically be performed in about an hour, and requires about six to eight weeks for recovery. Adjustable sutures may be used to permit refinement of the eye alignment in the early postoperative period. [51] It is unclear if there are differences between adjustable versus non-adjustable sutures as it has not been sufficiently studied. [52] An alternative to the classical procedure is minimally invasive strabismus surgery (MISS) that uses smaller incisions than usual.

Medication

Medication is used for strabismus in certain circumstances. In 1989, the US FDA approved botulinum toxin therapy for strabismus in people over 12 years old. [53] [54] Most commonly used in adults, the technique is also used for treating children, in particular children affected by infantile esotropia. [55] [56] [57] The toxin is injected in the stronger muscle, causing temporary and partial paralysis. The treatment may need to be repeated three to four months later once the paralysis wears off. Common side effects are double vision, droopy eyelid, overcorrection, and no effect. The side effects typically resolve also within three to four months. Botulinum toxin therapy has been reported to be similarly successful as strabismus surgery for people with binocular vision and less successful than surgery for those who have no binocular vision. [58]

Prognosis

When strabismus is congenital or develops in infancy, it can cause amblyopia, in which the brain ignores input from the deviated eye. Even with therapy for amblyopia, stereoblindness may occur. The appearance of strabismus may also be a cosmetic problem. One study reported 85% of adults with strabismus "reported that they had problems with work, school, and sports because of their strabismus." The same study also reported 70% said strabismus "had a negative effect on their self-image." [59] [ unreliable medical source ] A second operation is sometimes required to straighten the eyes. [27] [ page needed ]

In other animals

A Balinese cat exhibiting esotropia Siam Strabismus.jpg
A Balinese cat exhibiting esotropia

Siamese cats and related breeds are prone to having crossed eyes. Research suggests this is a behavioral compensation for developmental abnormalities in the routing of nerves in the optic chiasm. [60]

Strabismus may also occur in dogs, most often due to imbalanced muscle tone of the muscles surrounding the eye. Some breeds such as the Shar Pei are genetically predisposed to the condition. Treatment may involve surgery or therapy to strengthen the muscles. [61]

Related Research Articles

<span class="mw-page-title-main">Esotropia</span> Form of strabismus in which the eyes turn inward

Esotropia is a form of strabismus in which one or both eyes turn inward. The condition can be constantly present, or occur intermittently, and can give the affected individual a "cross-eyed" appearance. It is the opposite of exotropia and usually involves more severe axis deviation than esophoria. Esotropia is sometimes erroneously called "lazy eye", which describes the condition of amblyopia; a reduction in vision of one or both eyes that is not the result of any pathology of the eye and cannot be resolved by the use of corrective lenses. Amblyopia can, however, arise as a result of esotropia occurring in childhood: In order to relieve symptoms of diplopia or double vision, the child's brain will ignore or "suppress" the image from the esotropic eye, which when allowed to continue untreated will lead to the development of amblyopia. Treatment options for esotropia include glasses to correct refractive errors, the use of prisms, orthoptic exercises, or eye muscle surgery.

Orthoptics is a profession allied to the eye care profession. Orthoptists are the experts in diagnosing and treating defects in eye movements and problems with how the eyes work together, called binocular vision. These can be caused by issues with the muscles around the eyes or defects in the nerves enabling the brain to communicate with the eyes. Orthoptists are responsible for the diagnosis and non-surgical management of strabismus (cross-eyed), amblyopia and eye movement disorders. The word orthoptics comes from the Greek words ὀρθός orthos, "straight" and ὀπτικός optikοs, "relating to sight" and much of the practice of orthoptists concerns disorders of binocular vision and defects of eye movement. Orthoptists are trained professionals who specialize in orthoptic treatment, such as eye patches, eye exercises, prisms or glasses. They commonly work with paediatric patients and also adult patients with neurological conditions such as stroke, brain tumours or multiple sclerosis. With specific training, in some countries orthoptists may be involved in monitoring of some forms of eye disease, such as glaucoma, cataract screening and diabetic retinopathy.

<span class="mw-page-title-main">Amblyopia</span> Failure of the brain to process input from one eye

Amblyopia, also called lazy eye, is a disorder of sight in which the brain fails to fully process input from one eye and over time favors the other eye. It results in decreased vision in an eye that typically appears normal in other aspects. Amblyopia is the most common cause of decreased vision in a single eye among children and younger adults.

Anisometropia is a condition in which a person's eyes have substantially differing refractive power. Generally, a difference in power of one diopter (1D) is the threshold for diagnosis of the condition. Patients may have up to 3D of anisometropia before the condition becomes clinically significant due to headache, eye strain, double vision or photophobia.

<span class="mw-page-title-main">Diplopia</span> Double vision

Diplopia is the simultaneous perception of two images of a single object that may be displaced horizontally or vertically in relation to each other. Also called double vision, it is a loss of visual focus under regular conditions, and is often voluntary. However, when occurring involuntarily, it results from impaired function of the extraocular muscles, where both eyes are still functional, but they cannot turn to target the desired object. Problems with these muscles may be due to mechanical problems, disorders of the neuromuscular junction, disorders of the cranial nerves that innervate the muscles, and occasionally disorders involving the supranuclear oculomotor pathways or ingestion of toxins.

<span class="mw-page-title-main">Medial rectus muscle</span> Extraocular muscle that rotates the eye medially

The medial rectus muscle is a muscle in the orbit near the eye. It is one of the extraocular muscles. It originates from the common tendinous ring, and inserts into the anteromedial surface of the eye. It is supplied by the inferior division of the oculomotor nerve (III). It rotates the eye medially (adduction).

Vision therapy (VT), or behavioral optometry, is an umbrella term for alternative medicine treatments using eye exercises, based around the pseudoscientific claim that vision problems are the true underlying cause of learning difficulties, particularly in children. Vision therapy has not been shown to be effective using scientific studies, except for helping with convergence insufficiency. Most claims—for example that the therapy can address neurological, educational, and spatial difficulties—lack supporting evidence. Neither the American Academy of Pediatrics nor the American Academy of Ophthalmology support the use of vision therapy.

<span class="mw-page-title-main">Exotropia</span> Visual disorder where eyes work independently

Exotropia is a form of strabismus where the eyes are deviated outward. It is the opposite of esotropia and usually involves more severe axis deviation than exophoria. People with exotropia often experience crossed diplopia. Intermittent exotropia is a fairly common condition. "Sensory exotropia" occurs in the presence of poor vision in one eye. Infantile exotropia is seen during the first year of life, and is less common than "essential exotropia" which usually becomes apparent several years later.

<span class="mw-page-title-main">Sixth nerve palsy</span> Inability to turn out the eye due to dysfunction of the abducens nerve

Sixth nerve palsy, or abducens nerve palsy, is a disorder associated with dysfunction of cranial nerve VI, which is responsible for causing contraction of the lateral rectus muscle to abduct the eye. The inability of an eye to turn outward, results in a convergent strabismus or esotropia of which the primary symptom is diplopia in which the two images appear side-by-side. Thus, the diplopia is horizontal and worse in the distance. Diplopia is also increased on looking to the affected side and is partly caused by overaction of the medial rectus on the unaffected side as it tries to provide the extra innervation to the affected lateral rectus. These two muscles are synergists or "yoke muscles" as both attempt to move the eye over to the left or right. The condition is commonly unilateral but can also occur bilaterally.

Suppression of an eye is a subconscious adaptation by a person's brain to eliminate the symptoms of disorders of binocular vision such as strabismus, convergence insufficiency and aniseikonia. The brain can eliminate double vision by ignoring all or part of the image of one of the eyes. The area of a person's visual field that is suppressed is called the suppression scotoma. Suppression can lead to amblyopia.

<span class="mw-page-title-main">Hypertropia</span> Condition of misalignment of the eyes

Hypertropia is a condition of misalignment of the eyes (strabismus), 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. Dissociated vertical deviation is a special type of hypertropia leading to slow upward drift of one or rarely both eyes, usually when the patient is inattentive.

<span class="mw-page-title-main">Strabismus surgery</span> Surgery to correct strabismus

Strabismus surgery is surgery on the extraocular muscles to correct strabismus, the misalignment of the eyes. Strabismus surgery is a one-day procedure that is usually performed under general anesthesia most commonly by either a neuro- or pediatric ophthalmologist. The patient spends only a few hours in the hospital with minimal preoperative preparation. After surgery, the patient should expect soreness and redness but is generally free to return home.

Burt Kushner is an American pediatric ophthalmologist specializing in the diagnosis and treatment of strabismus. Kushner's contributions include demonstration of improved visual fields of patients following strabismus surgery, elucidation of torsional contribution to patients with diplopia, corticosteroid treatment of periocular capillary hemangioma, and novel hypotheses on the mechanism of "overacting" extraocular muscles.

Infantile esotropia is an ocular condition of early onset in which one or either eye turns inward. It is a specific sub-type of esotropia and has been a subject of much debate amongst ophthalmologists with regard to its naming, diagnostic features, and treatment.

Cyclotropia is a form of strabismus in which, compared to the correct positioning of the eyes, there is a torsion of one eye about the eye's visual axis. Consequently, the visual fields of the two eyes appear tilted relative to each other. The corresponding latent condition – a condition in which torsion occurs only in the absence of appropriate visual stimuli – is called cyclophoria.

<span class="mw-page-title-main">Stereopsis recovery</span> Medical phenomenon

Stereopsis recovery, also recovery from stereoblindness, is the phenomenon of a stereoblind person gaining partial or full ability of stereo vision (stereopsis).

Botulinum toxin therapy of strabismus is a medical technique used sometimes in the management of strabismus, in which botulinum toxin is injected into selected extraocular muscles in order to reduce the misalignment of the eyes. The injection of the toxin to treat strabismus, reported upon in 1981, is considered to be the first ever use of botulinum toxin for therapeutic purposes. Today, the injection of botulinum toxin into the muscles that surround the eyes is one of the available options in the management of strabismus. Other options for strabismus management are vision therapy and occlusion therapy, corrective glasses and prism glasses, and strabismus surgery.

The management of strabismus may include the use of drugs or surgery to correct the strabismus. Agents used include paralytic agents such as botox used on extraocular muscles, topical autonomic nervous system agents to alter the refractive index in the eyes, and agents that act in the central nervous system to correct amblyopia.

Daniel Mojon is a Swiss ophthalmologist and ophthalmic surgeon who is considered to be the inventor of minimally invasive strabismus surgery (MISS), a method of surgically correcting squinting that uses only very small incisions of two to three millimeters and is supposed to lead to quicker rehabilitation and wound healing. Daniel Mojon is president of the program committee of the Swiss Academy of Ophthalmology (SAoO).

Alan Brown Scott was an American ophthalmologist specializing in eye muscles and their disorders, such as strabismus. He is best known for his work in developing and manufacturing the drug that became known as Botox, research described as "groundbreaking" by the ASCRS.

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