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.
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.
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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
II. Pseudoexotropia: Pseudoexotropia may result due to
III. Pseudohypertropia: Pseudohypertropia may be due to
IV. Miscellaneous causes:
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.
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
- 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 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.
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.
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.
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.