Pseudostrabismus gives an appearance of strabismus (squint) when no manifest deviation of the visual axis is actually present. This apparent misalignment of the eyes is created by certain morphological features of the face, although it may be associated with certain ocular or orbital conditions. The most common form of pseudostrabismus is pseudoesotropia where the eyes appear crossed. There may be pseudoexotropia, where eyes appear to be deviated outwards and pseudohypertropia where eyes appear to be misaligned vertically.
Patients with pseudostrabismus require full investigation as the prevalence of strabismus is higher in those diagnosed with pseudostrabismus as compared to general population and especially those with developmental delay.
References
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http://eyewiki.aao.org/Pseudostrabismus
http://emedicine.medscape.com/article/1199610-overview
Pritchard C, Ellis GS Jr. Manifest strabismus following pseudostrabismus diagnosis. American Orthoptic Journal 2007; 57: 111- 117.
Usually parents notice squint in the eyes of young child. The deviation is more noticeable when the child turns head and the eyes are in lateral gaze, especially in pseudoesotropia because nasal sclera appears buried in the epicanthal fold.
Parents may bring pictures of the baby with eyes in pseudoeso- or pseudoexodeviation.
I. Pseudoesotropia: Pseudoesotropia is the most common type of pseudostrabismus and may be seen due to
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Morphological features: Morphological features such as orientation, shape and size of the orbits, shape and size of globes, and volume of retro-bulbar tissue may create an impression of misaligned eyes. Commonly this is seen in infants who have wide nasal bridge with prominent epicanthal folds (semi-lunar folds of skin near medial canthus).
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Interpupillary distance (IPD): Patients with small interpupillary distance (IPD) may also appear to be esotropic.
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Negative angle kappa: A negative angle kappa (angle formed between visual axis and pupillary axis at the pupil), where corneal light reflex appears to be on the temporal side of the center of pupil, may simulate esodeviation.
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Enophthalmos: Enophthalmos gives the appearance of convergent deviation.
II. Pseudoexotropia: Pseudoexotropia may result due to
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Morphological features: Morphological features of the face may result in false appearance of eyes to be divergent. Most commonly hypertelorism (widely set eyes) may result in pseudoexotropia.
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Interpupillary distance (IPD): Patients with wide interpupillary distance (IPD) give the appearance of divergent deviation.
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Positive angle kappa: Pathologic ectopia of the macula temporally due to traction of retina may produce a positive angle kappa. Positive angle kappa results in nasal displacement of the light reflex on the cornea simulating exotropia. Pseudoexotropia due to positive angle kappa is mostly seen in retinopathy of prematurity, which results in temporal dragging of the macula. It may also be seen in ectopic macula resulting from high myopia, toxocara retinal scars or congenital retinal folds.
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Exophthalmos: Exophthalmos gives the appearance of divergent deviation.
III. Pseudohypertropia: Pseudohypertropia may be due to
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Facial asymmetry: Facial asymmetry which produces an appearance of vertically misaligned eyes where one eye appears to be higher than the other.
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Orbital tumours: Certain orbital tumours of the orbital floor may produce hypoglobus (downward displacement of eyeball) simulating vertical misalignment.
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Trauma: Trauma to the orbital floor may also produce hypoglobus simulating vertical misalignment.
IV. Miscellaneous causes:
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Ptosis may give appearance of vertical deviation.
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Facial asymmetry.
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Palpebral fissure asymmetry.
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Dermatochalasis (lax eyelid skin and muscle).
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Abnormal head posture.
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Ill-fitting spectacles.
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Heterochromia iridis (a difference in colour of iris of an eye).
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Coloboma of iris (a fissure or gap in the iris).
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Anisocoria (a difference in size of the pupils).
Risk factors:
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Prematurity: Prematurity may cause retinopathy of prematurity which may result in temporal dragging of macula producing positive angle kappa and pseudoexotropia.
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Facial morphology: Prominent epicanthal folds in asian children results in pseudoesotropia.
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Orbital tumours: Certain orbital tumours may result in pseudohypertropia.
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Orbital trauma: It may produce hypoglobus resulting in pseudohypertropia in some patients.
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Chorioretinal infections: These may produce chorioretinal scarring with temporal dragging of macula resulting in pseudoexotropia.
Clinical diagnosis of pseudostrabismus requires ruling out the presence of true intermittent or constant strabismus.
Patients with pseudostrabismus require full investigation as the prevalence of strabismus is higher in those diagnosed with pseudostrabismus.
Diagnosis depends upon clinical history, physical examination and certain diagnostic tests.
Detailed history regarding weight at birth, gestational age, health of child, any procedure for retinopathy of prematurity may give diagnostic clues. History of initial presentation aided by photographs of the child may assist in documenting the onset, detecting the stability of the condition and confirming the diagnosis.
A good physical examination comprises of inspection of eye and adnexal morphology.
Both normal and pathologic variations in palpebral fissure may produce the appearance of strabismus, despite normal alignment of the visual axis of two eyes. Diagnosis of pseudoesotropia in infants with large epicanthal folds is probably the most common reason. Family members may believe that strabismus is present because they do not see much of white sclera on the nasal aspect of the eye compared to the temporal aspect. After careful examination, most parents may often be convinced that the position and shape of the eyelids and ocular adnexal structures may produce the appearance of strabismus. Doubting parents may be convinced by tightening the epicanthal fold by pinching the bridge of the nose.
Similarly, abnormalities involving the lateral canthal area may create impression of exotropia.
Diagnostic tests
I. Visual acuity evaluation: Every patient presenting with pseudostrabismus should have complete evaluation of visual acuity.
II. Motor evaluation: It comprises of tests such as
