Overview
This lecture covers pseudostrabismus, its causes, distinguishing features from true strabismus, and the key clinical tests for diagnosis.
Definitions and Types
- True strabismus is a real misalignment of the visual axes.
- Pseudostrabismus is a false or apparent eye deviation without real misalignment.
- Types include pseudoesotropia (inward), pseudoexotropia (outward), pseudohypertropia (upward), and pseudohypotropia (downward).
Causes of Pseudostrabismus
- Epicanthus: A crescent-shaped skin fold near the nose that hides the inner sclera, mimicking esotropia.
- Narrow palpebral fissures: Make eyes appear turned in (pseudoesotropia).
- Enophthalmos: Backward displacement of the eyeball gives a false esotropia appearance.
- Wide palpebral fissures or exophthalmos (proptosis): Eyes appear turned out (pseudoexotropia).
- Interpupillary distance (IPD): Narrow IPD causes pseudoesotropia; wide IPD causes pseudoexotropia.
- Orbital or facial asymmetry: Displaced orbits from congenital or acquired causes can simulate squint.
- Angle Kappa anomalies: Positive angle Kappa causes pseudoexotropia; negative causes pseudoesotropia.
- Eyelid positions: Ptosis (drooping upper lid) causes pseudohypertropia; inverse ptosis (high lower lid) causes pseudohypotropia.
Diagnostic Tests
- Pinch Test: Lifting the epicanthus skin eliminates pseudoesotropia but not true esotropia.
- Hirschberg’s Corneal Reflex Test: Centered light reflexes indicate pseudostrabismus; displaced reflexes indicate true strabismus.
- Cover Test: No eye movement in pseudostrabismus; movement occurs in true strabismus.
- Stereopsis/Random Dot Test: Normal in pseudostrabismus; reduced in true squint.
- Base-Out Prism Test: Normal motor fusion in pseudostrabismus; sometimes abnormal in true strabismus.
- Visual acuity is usually normal in pseudostrabismus if no other eye issues.
Key Terms & Definitions
- Strabismus — true misalignment of the eyes' visual axes.
- Pseudostrabismus — false appearance of eye deviation without actual misalignment.
- Epicanthus — crescent fold of skin covering inner canthus, simulating esotropia.
- Interpupillary distance (IPD) — distance between pupil centers; affects apparent deviation.
- Angle Kappa — angle between visual and pupillary axes; anomalies can simulate deviation.
- Hirschberg Test — exam of corneal light reflex to assess alignment.
- Stereopsis — depth perception; reduced in true strabismus.
Action Items / Next Steps
- Review videos on Hirschberg’s Corneal Reflex Test and angle Kappa for deeper understanding.
- Be cautious with patients who have a family history of strabismus, significant heterophoria, or close one eye in sunlight.