This document summarizes exotropia, an outward deviation of the eye. It discusses the different types of exotropia, including infantile exotropia characterized by a large angle constant exodeviation often first noticed before age 6 months. Intermittent exotropia, the most common type, involves occasional outward deviation that varies in frequency and duration. Evaluation of exotropia involves assessing visual acuity and eye alignment with cover tests. Treatment depends on the type but may include refractive correction, orthoptic exercises, patching, or strabismus surgery.
2. INTRODUCTION
Outward deviation of the eye
Visual axis deviated laterally and fovea is rotated nasally
Exodeviations=Divergent strabismus
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3. PREVALENCE
The estimated prevalence of any strabismus, exotropia, and esotropia
was 1.93% (1.64-2.21), 1.23% (1.00-1.46), and 0.77% (0.59-0.95),
respectively (1)
Intermittent exotropia is the most common type of exotropia, affecting
nearly 1% of the population
Exotropia has been reported to be more prevalent among Asian and
African American populations than among Caucasians women comprise
60 -70% of patients with exotropia (2)
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1. Hashemi H, Pakzad R, Heydarian S, Yekta A, Aghamirsalim M, Shokrollahzadeh F, Khoshhal F, Pakbin M, Ramin S, Khabazkhoob M. Global and regional
prevalence of strabismus: a comprehensive systematic review and meta-analysis. Strabismus. 2019
2. Azam P, Nausheen N, Fahim MF. Prevalence of Strabismus and its type in Pediatric age group 6-15 years in a tertiary eye care hospital, Karachi. Biom
Biostat Int J. 2019
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4. SYMPTOMS
Eyes turned outward some or all the time
Decreased vision in the deviated eye
Squinting
Eyestrain
Headaches
Double vision
Decreased depth perception
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Von Noorden, Binocular vision and ocular motility, sixth edition
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7. EVALUATION
Visual acuity
Cycloplegic refraction
Hirschberg test
Cover test
Prism bar cover test
Binocular vision test
Stereopsis
Fusional amplitudes
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8. PSEUDOEXOTROPIA
The term pseudoexotropia refers to a false appearance
of exodeviation when in fact the eyes are properly
aligned
Wide inter pupillary distance
Large angle positive kappa – hyperopia/ROP
Due to anatomical or mechanical factors within the orbit
Can be due to excessive tonic divergence
No treatment is required for pseudoexotropia.
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9. ESSENTIAL INFANTILE EXOTROPIA
Onset is before age 6 months and persists beyond this age
It is classified as primary infantile exotropia
Parents and other persons usually see the exodeviation because of the
large degree of deviation
early onset intermittent exotropia
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AAO. Strabismus: Infantile Exotropia. ByAlvina Pauline D. Santiago, MD.
2015
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10. Features:
• Large angle constant exodeviation is mostly more than 35PD
• Fusion will be poor
• It occurs in patients with craniofacial anomalies, cerebral palsy,
developmental delay
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11. 10/24/2023
AAO. Strabismus: Infantile Exotropia. ByAlvina Pauline D.
Santiago, MD. 2015
11
Infantile exotropia. A, This 10-month-old infant with
infantile exotropia also shows developmental
delay. B, Krimsky testing using 2 base-in prisms to
measure the large exotropia.
12. Amblyopia therapy should be started at the earliest possible.
Surgical treatment should be planned after six months of age and usually
better before 24 months.
There are few studies of infantile exotropia treated with botox
Bilateral lateral rectus recession or unilateral recession- resection
procedure may be preferred in the amblyopic or the non-dominant eye.
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13. INTERMITTENT EXOTROPIA
Intermittent exotropia is the most common type of strabismus
It is characterized by occasional outward deviation of one or alternate
eyes.
Frequency, duration of deviation, and control vary from individual to
individual
Manifest with attention, fatigue, end of the day (loose ability to convert)
Exposure to bright light cause reflex closure of one eye
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Kaur K, Gurnani B. Intermittent Exotropia. [Updated 2022 Dec 6]. In: StatPearls [Internet]. Treasure
Island (FL): StatPearls Publishing; 2022 Jan-.
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16. IDS-CONTROL SCORE
1. The Newcastle control score
It was developed by incorporating subjective (home control) and objective (clinic
control) criteria into a control rating scale. (1)
2. The PEDIG IXT score
Pediatric eye disease investigator group
This new scale for assessing control in children with intermittent exotropia can be
easily applied in the office setting and characterizes the wide range of control in this
disorder. (2)
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1. Haggerty H, Richardson S, Hrisos S, Strong NP, Clarke MP. The Newcastle Control Score: a new method of grading the severity of intermittent distance exotropia. Br
J Ophthalmol. 2004 Feb;88(2):233-5. doi: 10.1136/bjo.2003.027615. PMID: 14736781; PMCID: PMC1772020.
2. Mohney BG, Holmes JM. An office-based scale for assessing control in intermittent exotropia. Strabismus. 2006 Sep;14(3):147-50. doi: 10.1080/09273970600894716.
PMID: 16950743; PMCID: PMC2699414
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PBCT (N) 20PD
PBCT (D) 35 PD
remeasure
Yes
PBCT (N) 30PD
PBCT (D)35 PD
No
PBCT (N) becomes
higher-pseudo
divergence excess
True
divergence
excess
PBCT (N)
same after +3
lens – normal
AC/A
PBCT (N)
higher after +3
lens – high
AC/A
Monocular
patch test
(45 min)
Change in findings?
20. Refractive error: overcorrecting minus lens
Orthoptics: These may be used to improve the control of the deviation
Part-time occlusion of the non-deviating eye may improve control in some
patients
Base in prisms
Unilateral lateral rectus recession and medial rectus resection
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Kaur K, Gurnani B. Exotropia. [Updated 2023 Feb 13]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls
Publishing; 2023 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK578185/
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21. SENSORY EXOTROPIA
Secondary (sensory) exotropia is the result of monocular
or binocular visual impairment by acquired lesions, such
as cataract or other media opacity
Treatment consists of correction of the visual deficit, if
possible, followed by surgery if appropriate
A minority of patients develop intractable diplopia due to
loss of fusion
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22. CONSECUTIVE EXOTROPIA
This occurs when a person who was
formerly esotropic becomes exotropic.
In most cases this occurs from a surgical
overcorrection of the esotropia (beyond 3-4
weeks)
Treatment is correction of refractive error if
present. Surgery can be done for cosmetic
purposes.
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23. INCOMITANT EXOTROPIA
Incomitant deviation implies that the divergent deviation of the visual axis
is variable in different gazes.
These are often associated with the limitation of extraocular movements
resulting either from paralytic or a restrictive etiology.
Incomitant Exotropia Differentials
• Third nerve palsy
• Duane retraction syndrome
• Crouzon syndrome
• Restrictive pathologies (thyroid eye disease, medial wall blowout
fracture, myositis, myasthenia gravis)
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Kaur K, Gurnani B. Exotropia. [Updated 2023 Feb 13]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls
Publishing; 2023 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK578185/
Concomitant deviation means that the divergent deviation of the visual axis remains the same in all positions of gaze. Incomitant deviation implies that the divergent deviation of the visual axis is variable in different gazes.
A patient with exotropia should undergo a detailed physical and ocular examination. The crucial clinical evaluation points in any patient with exotropia should include the following:
Visual acuity – It is imperative to record the visual acuity or fixation patterns using age-appropriate methods. Any anisometropia or amblyopia should always be ruled out.
Cycloplegic refraction - should ideally be repeated every six months in any patient presenting squinting eyes.
Corneal reflex/Hirschberg test should assess the ocular alignment at 1/3 meter, 6 meters, and far distance.
Cover test – should be done to assess eyes' alignment following breakage of fusion. This also needs to be done at 1/3 meter, 6 meters, and far distance.
Prism cover test – prism bar cover test should be performed in all cardinal positions of gaze and for both near and distance. It is essential to look for lateral gaze incomitance or any associated A or V pattern. Lateral gaze incomitance is diagnosed when there is a 20% reduction in squint angle in the lateral gazes.
Measurement of squint should also be done at a far distance beyond 6 meters. At times a larger angle of deviation may be detected when tested at a far distance.
Binocular single vision (BSV) – Should be assessed for distance and near separately with worth four dots test. BSV should be repeated at each visit and documented, as it might worsen over time.
Stereopsis – Should be tested during the phoric phase. A progressive decline significantly in the distance stereopsis is an early indication for surgical intervention.
An occlusion test is essential when the patient presents with an intermittent exotropia that is present only for distance or a distance deviation that exceeds near deviation by 15 prism diopters or more. In this test, one eye is occluded for a minimum of 45 minutes duration, and the squint measurements are repeated using the prism bar cover test. 18929306 If the post occlusion near the angle of deviation increases markedly, this is labeled as simulated divergence excess exotropia. If the near deviation remains unchanged, this is labeled as true divergence excess exotropia. This helps in differentiating between true and simulated divergence excess.
+3 diopter spherical lens test – In this test, the exodeviations for near are measured with and without a +3 diopter spherical lens placed in front of the exotropic eye while using an accommodative target, and the AC/A ratio can be estimated. The AC/A ratio predicts how a patient will respond to plus lenses should a surgical overcorrection result.[19]
Fusional amplitudes – Convergence and divergence amplitudes should be measured. Most patients with intermittent exotropia have good convergence amplitudes for near and poor to good amplitudes for distance. Divergence amplitudes are normal in these patients.
Positive angle kappa without other ocular abnormalities.
Positive angle kappa together with other abnormalities such as temporal dragging of the macula in ROP.
No treatment is required for pseudoexotropia. Parents can be reassured that their child most likely will outgrow the condition. Infants should be observed and reevaluated every 6 months
It is classified as primary infantile exotropia, where patients are healthy with no evidence of systemic or ocular disease
Parents and other persons who have regular contact with the patient usually reliably see the exodeviation because of the large degree of deviation: it almost always exceeds 30 prism diopters (pd), and may be a large as 90pd
Those who improve with occlusion therapy of the dominant eye are more likely to have early onset intermittent exotropia than true infantile exotropia
Botulinum toxin injection to the lateral rectus (LR) muscle, typically 2.5-5.0 units to both lateral rectus muscles, can be offered as an alternative to surgery. This technique minimizes secondary vertical deviation and ptosis that sometimes accompany higher doses or unilateral injections.18 The experience with botulinum is obtained mostly from the more common intermittent exotropia, and is fraught with recurrence.19 There are few studies of infantile exotropia treated with botox. Fewer than 50% of patients with constant exotropia responded to botulinum toxin injection of one LR muscle.20
To differentiate between true and pseudo:
Do monocular occlusion for 45 min. if near PD did not change. It is true DXT.
If near PBCT gets higher (difference between N and D >10PD) it is pseudo DXT
After the patch test with eyes being still dissociated, the measurements are repeated for near with a +3D add
Add bilateral +3.00 lens. If near PD gets higher about 20PD after +3 then it is true with high AC/A ratio.
If near PD didn’t change, it is true with normal AC/A ratio
Refractive error: overcorrecting minus lens, This is based on the principle of stimulating accommodative convergence and thus reducing an exodeviation. Full correction.
Orthoptics: These may be used to improve the control of the deviation. The aim is to make the patient aware of the manifest deviation
Part-time occlusion of the non-deviating eye may improve control in some patients. Alternate patching if no visual preference
Base in prisms
Unilateral lateral rectus recession and medial rectus resection are generally preferred except in true distance exotropia when bilateral lateral rectus recessions are more usual
Refractive error correction – Cycloplegic refraction should be done to assess any underlying myopia, hyperopia, astigmatism, or anisometropia. If refractive errors are not rectified, they can impair fusion and thus lead to a manifest deviation. Minus lenses, in particular, helps in regaining the fusion control. These patients need to be followed up closely at a gap of 3 months to check compliance and improvement in control after spectacle usage.
Over minus therapy – Minus lenses work by stimulating the accommodative convergence. This is particularly useful in patients with a high AC/A ratio.[21]
Antisuppression exercises – In the form of part-time occlusion, are particularly beneficial for very young children who cannot perform active orthoptic exercises. This may help in improving the stage of intermittent exotropia to exophoria. Occlusion can be advised for either the dominant eye or an alternate eye occlusion in patients with alternating exotropia t prevent amblyopia. These passive antisupression exercises are also helpful during waiting periods before surgical correction or in young children until accurate measurements are recorded.
Prismotherapy – Prisms have a limited role in patients with intermittent exotropia. These are used to promote fusional convergence. Base in prisms are used to promote bifoveal stimulation. Prims might also be useful in the immediate postoperative period as a temporary measure if patients complaint of transient disturbing diplopia.[22]
Orthoptics – Active anti-suppression exercises and diplopia awareness exercises like bar reading, cheiroscope, or synaptophore help make the patient aware whenever the deviation becomes manifest.[23] This helps in promoting the fusional convergence amplitudes. The aim is to obtain a near-normal point of convergence.
Surgical intervention might be needed when the exodeviation occurs for more than 50% of the waking hours, and there is a recorded gradual loss of fusional control, progressive increase of primary deviation, asthenopic symptoms not relieved by convergence, or fusional exercises, development of suppression or gradual deterioration of distance stereopsis.
This often results from poor visual acuity in one eye. Sensory exotropia is more common when unilateral vision loss occurs in infancy or adulthood. It may appear secondary to anisometropia, unilateral medial opacity secondary to corneal opacity or lenticular changes, unilateral aphakia, optic atrophy, or macular pathology.
A minority of patients develop intractable diplopia due to loss of fusion, even when good visual acuity is restored to both eyes and the eyes are realigned
Consecutive exotropia may result from a surgical overcorrection of esotropia or a spontaneous change of esotropia to exotropia
Incomitant exotropia is divided into paralytic (third nerve paralysis, isolated medial rectus paralysis, paralysis of convergence), A, V, or X pattern, or restrictive (Duane retraction syndrome, thyroid myopathy, restriction due to trauma or following surgery).
