Pseudostrabismus

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

Agarwal Amar. Handbook of Ophthalmology. Slack Incorporated 2006. P 144- 145.

Basak Samar K. Atlas of Clinical Ophthalmology Second Edition. Jaypee Brothers Medical Publishers (P) Ltd. 2013. P 430.

Coats David K, Olitsky Scott E. Strabismus Surgery and its Complications. Springer-Verlag Berlin Heidelberg 2007. P 5- 6.

Garg Ashok, Aliό Jorge L, Prost Ewa Oleszczynska, Sharma Pradeep, Pajic-Eggspuehler Brigitte, Dhull CS, Saxena Rohit. Surgical Techniques in Ophthalmology- Strabismus Surgery. Jaypee Brothers Medical Publishers (P) Ltd. 2010. P 100.

Rowe Fiona J. Clinical Orthoptics Third Edition. Wiley-Blackwell 2012. P 174- 175.

Ansons Alec M, Davis Helen. Diagnosis and Management of Ocular Motility Disorders Fourth Edition. John Wiley & Sons, Ltd 2014.

Bowling Brad, Kanski's Clinical Ophthalmology- A Systematic Approach. Eighth Edition. Elsevier, 2016. P 755- 756.

Kanski Jack J, Bowling Brad. Clinical Ophthalmology- A Systematic Approach Seventh Edition. Elsevier Saunders 2011. P 755.

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

• 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).
• Interpupillary distance (IPD): Patients with small interpupillary distance (IPD) may also appear to be esotropic.
• 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.
• Enophthalmos: Enophthalmos gives the appearance of convergent deviation.

II. Pseudoexotropia: Pseudoexotropia may result due to

• 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.
• Interpupillary distance (IPD): Patients with wide interpupillary distance (IPD) give the appearance of divergent deviation.
• 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.
• Exophthalmos: Exophthalmos gives the appearance of divergent deviation.

III. Pseudohypertropia: Pseudohypertropia may be due to

• Facial asymmetry: Facial asymmetry which produces an appearance of vertically misaligned eyes where one eye appears to be higher than the other.
• Orbital tumours: Certain orbital tumours of the orbital floor may produce hypoglobus (downward displacement of eyeball) simulating vertical misalignment.
• Trauma: Trauma to the orbital floor may also produce hypoglobus simulating vertical misalignment.

IV. Miscellaneous causes:

• Ptosis may give appearance of vertical deviation.
• Facial asymmetry.
• Palpebral fissure asymmetry.
• Dermatochalasis (lax eyelid skin and muscle).
• Abnormal head posture.
• Ill-fitting spectacles.
• Heterochromia iridis (a difference in colour of iris of an eye).
• Coloboma of iris (a fissure or gap in the iris).
• Anisocoria (a difference in size of the pupils).

Risk factors:

• Prematurity: Prematurity may cause retinopathy of prematurity which may result in temporal dragging of macula producing positive angle kappa and pseudoexotropia.
• Facial morphology: Prominent epicanthal folds in asian children results in pseudoesotropia.
• Orbital tumours: Certain orbital tumours may result in pseudohypertropia.
• Orbital trauma: It may produce hypoglobus resulting in pseudohypertropia in some patients.
• 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

• Hirschberg’s light reflex test: This gives a rough objective estimate of the angle of manifest strabismus and is especially useful when fixation in the deviating eye is poor.

-       A pen-torch is shown in to the eyes from a distance of about one arm and the patient is asked to fixate the light. The corneal reflection of the light is more or less in the center of pupil of the fixating eye, but will be decentered in the squinting eye, in the direction opposite to that of deviation.

-       The distance of the corneal light reflection, if any, is noted. In orthotropic eyes (eyes without squint), there is no decentering of the light reflex.

• Cover-uncover test:

Cover test: This is done to detect heterotropia. It is good to begin the near test first by using light and then the accommodative target. Then the test is done for distance as follows

-       The patient fixates a straight-ahead target.

-       If a right deviation is suspected, the examiner covers the fixing left eye and notes any movement of the right eye to take up fixation.

-       No movement indicates orthotropia or left heterotropia.

-       Adduction of the right eye to take up fixation indicates right exotropia and abduction indicates right esotropia.

-       Vertical movement indicates vertical hyper- or hypotropia.

-       The test is repeated in the opposite eye.

Uncover test: It detects heterophoria. It is performed both for near and far.

Most examiners perform cover and uncover test sequentially, hence the term cover-uncover test.

• Alternate cover test: It is a dissociation test which reveals the total deviation when fusion is suspended. It is performed after the cover-uncover test. The occluder is shifted quickly back and forth from one eye to other, several times. After the cover is removed, the speed and smoothness of recovery is noted as the eyes return to their pre- dissociated state. A patient with well compensated heterophoria will have straight eyes before and after the test has been performed, whereas a patient with poor control may decompensate to manifest deviation.
• Ocular movements: It is necessary to test the function of each extra-ocular muscle by testing uniocular and binocular movements.

III. Sensory evaluation: Complete sensory evaluation may give clue to sensory development. Detection of fixation preference for one eye may be performed by vertical prism test.

Differential diagnosis

True strabismus should be ruled out by conducting thorough examination before reaching to the conclusion of pseudostrabismus.

Patient should be followed-up with re-evaluation every 6 months because true strabismus may sometimes develop in patients with pseudostrabismus.

Factors causing pseudostrabismus may be present when there is a true strabismus and may mask or accentuate its presence. Doubtful cases should be followed up. Certain findings are strong indicators that a child should be observed even though no convincing evidence of strabismus is found. These include

-       Family history of strabismus or refractive error.

-       Presence of significant heterophoria. Even a small esophoria when present is significant.

-       A tendency to squeeze eye in sunlight indicates a possible intermittent childhood exotropia.

Once a pseudostrabismus is diagnosed, the parents should be explained the reason for the apparent deviation and reassured.

Orthoptic investigation establishes the presence of binocular single vision and fusion control in cases of pseudostrabismus.

For the common pseudoesotropia, since the nasal sclera part is being covered by the epicanthus, the orthotropic appearance may be demonstrated by pinching the nasal bridge slightly and revealing the nasal sclera. As the flat nasal bridge develops, this excessive epicanthal skin is raised and the condition corrects by itself. Hence, no treatment is required except for follow-up for disappearance of pseudoesotropia.

However, true manifest squint is treated if it is associated with pseudostrabismus. 

Prognosis

The natural course of pseudostrabismus is variable. Most of the cases of pseudoesotropia resolve usually by the age of two to three years, because the epicanthal folds diminish as the bridge of the nose enlarges.

Pseudostrabismus secondary to positive or negative angle kappa typically persists in adulthood.