STRABISMUS
 
PEDBASE.org - The Pediatric Database - Detailed information of STRABISMUS

 

STRABISMUS

 

DEFINITION:

Abnormal ocular alignment in any field of gaze, constant or intermittent, and occurring at distant and/or near fixation.

EPIDEMIOLOGY:

  • incidence: 2-5% of preschool children

PATHOGENESIS:

1. Background

  • because of oculomotor instability during the 1st month of life, adequate assessment of alignment is usually not made until 3 months of age, i.e. conjugate gaze is not established until 3 months of age
  • other features established by 3 months of age:
    • final eye colour
    • trichromatism established - red, green, yellow
    • binocularity established - depth perception
    • infant enjoys looking at human mouth and eyes and simple coloured toys
  • by 6 months of age, full visual fields have been established

2. Consequences of Uncorrected Strabismus

  • 1. amblyopia - loss of visual acuity
  • 2. loss of fusion - depth perception

    • 3. Esotropia

    • account for >75% of all childhood cases of strabismus
    • differential diagnosis:

    1. Pseudostrabimus

    • distinguished from a true strabismus by observing symmetrically placed corneal reflexes and a negative cover test

    2. Infantile Esotropia

    • age of onset: <12 months
    • types of fixation:
      • alternate - both eyes affected
        • amblyopia less likely
      • constant - one eye affected -> constant suppression
        • amblyopia more likely
      • cross - fixes L side with R eye and visa versa
        • both eyes simultaneously turned inward
        • amblyopia less likely

    3. Congenital Sixth Nerve Palsy

    • lateral rectus weakness manifest by poor abduction
    • spinning infant will not produce abduction nystagmus

    4. Duane Retraction Syndrome

    • marked limitation of abduction of affected eye due to a congenital agenesis of the 6th nerve nucleus & paradoxical innervation of the lateral rectus by the 3rd nerve

    5. Accomodative Esotropia

    • age of onset: 1-7 years
    • usually accompanied by hyperopia (image behind retina)
    • to correct the hyperopia, one eye turns in
    • initially intermittent & for near fixation and eventully constant for both near and distance fixation

    6. Sensory Deprivation Esotropia

    • ocular deviation usually seen due to visual loss is esotropia, i.e., retinoblastoma
    • sensory strabismus results from any primary cause of visual loss, if vision is poor in one eye, fusion cannot occur and ocular alignment is lost

    7. Others

    • Mobius Syndrome
    • Nystagmus Blockage Syndrome

    CLINICAL FEATURES:

    1. Ocular Manifestations

    1. Symptoms

    • amblyopia/blindness
    • diplopia
    • photophobia
    • tearing

    2. Signs (O/E)

    • head tilt/turn
    • facial features - epicanthal folds, asymmetry (hemangioma, lymphangioma)
    • eyes - ptosis, proptosis, palpebral fissures, hypertelorism, photophobia
    • lacrimal duct obstruction
    • movement - strabismus, nystagmus
    • ophthalmoscope - coloboma, cataracts, leukocoria, glaucoma

    2. Eye Position

    1. Tropia (eye deviation is manifest)

    • esotropia - inward deviation of eyes (convergent strabismus)
    • exotropia - outward deviation of eyes (divergent strabismus)
    • hypertropia - upward deviation of eyes
    • hypotropia - downward deviation of eyes
    • heterotropia - misalignment of the eyes all of the time

    2. Phoria (eye deviation is latent)

    • orthophoria - perfect ocular alignment
    • heterophoria - latent tendency to drift from perfect alignment
    • exophoria - latent tendency to drift from outward alignment
    • esophoria - latent tendency to drift from inward alignment
      • since a phoria is kept latent by fusion, anything that disrupts fusion may elicit a phoria, i.e., covering eye
      • the eye deviates only under certain circumstances: stress, illness, fatique

    INVESTIGATIONS:

    1. Strabismus

    1. Corneal Light Reflex

    • screening test
    • if tropia is present, the light reflex will be displaced in the deviating eye
    • esotropia - light reflex lateral to pupil
    • exotropia - light reflex medial to pupil

    2. Cover Test

    • diagnostic test:

    1. For Tropia (upon covering the unaffected eye):

    • constant fixation:
      • esotropia - eye makes an outward fixation movement
      • exotropia - eye makes an inward fixation movement
    • alternate fixation:
      • refixation movement by both eyes

    2. For Phoria (upon covering the affected eye):

    • the affected eye will deviate under the cover as the cover is brought over one eye
    • when the cover is removed and binocularity is re-established there is a quick refixation movement of the affected eye

    2. Visual Acuity

    1. Infant

    • follow face test
    • follow red yarn (on Denver II Test)
    • optokinetic nystagmus
    • fixation behaviour pattern (central, steady, maintained)

    2. Preschool (test each eye separately)

    • Allen Charts (2.5-3 years of age)
    • "E" Game (4-5 years of age)
    • "HOTV" Chart (3-5 years of age) - perform at 10 feet

    3. School Age

    • Snellen Letter Chart

    3. Others

    1. Spinning

    • use in infants
    • assesses extraocular movements and nerves (lacteral rectus, 3rd cranial nerve)
    • eyes should deviate in the direction of the turn

    2. Fusion

    1. Worth 4 Dot Test

    • with the child wearing a pair of glasses with 1 green and 1 red lens, this tests for fusion and suppression of the right and left eyes

    MANAGEMENT:

    1. Patching

    • the preferred eye forcing the amblyopic eye to work

    2. Glasses

    • for accommodative esotropia, i.e., treat hyperopia

    3. Surgery

    REFERENCES:

    • Pediatrics in Review 13(1): 7-14 (1992)

     

     

    Pediatric Database - STRABISMUS

     

    Pediatric Organization - Pedbase [at] Gmail.com

     
    1994 -2007 Pedbase.org 

    Powered by Database of Pediatrics- STRABISMUS