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Lecture 31: Visual Development, Strabismus and Amblyopia
Timothy Beer (Modified by Dave Reilly 2013)
Strabismus: misalignment of the visual axes of the eyes due to the eyes not working together
STRABISMUS
TYPE
DEFINITION
Comitant Strabismus
 Deviation size increases when the gaze is in the
direction of the involved muscle
 Causes include CN palsy, thyroid eye disease, MG
NO known neuromuscular etiology
and mechanical obstruction
 Less common than comitant strabismus. RED
Common in children
FLAG!!
 CN3 Palsy
o Patient presents with ptosis, eye pointed down
Congenital Esotropia
o Seen in infants in the first few months of life
and out and dilated pupil (“blown wall eye”)
o Unknown mechanism
o Levator muscle weakness  ptosis (droopy
eyelid)
o Amblyopia is common
o Treatment is surgery
o CN3-innervated EOM weakness  eye
o May require additional surgery or glasses
pointed “down and out”
before age 5
o Pupillary fibers weakness  dilated pupil
o Mechanism may be congenital, trauma, MS or
Accommodative Esotropia
o Develops between ages 1-4
aneurysm
o Occurs in children who are very hyperopic
o Very difficult to treat, but some patients do
(farsighted)
well with surgery
o Intermittent at first, but increases over time
 CN4 Palsy
o Patient presents with vertical diplopia and a
o Amblyopia is common
o Excess accommodation  excess
head-tilt away from bad side
convergence (esotropia)
o Involves the superior oblique muscle
o Treatment is glasses (reduces excess
o Vertical diplopia is worse in downgaze
accommodation)
opposite the superior oblique
o Many children can wean off of glasses by
o Patients often use a head-tilt to manage their
teenage years (eye lengthens with time)
vertical diplopia
o Outcome is extremely good
o Mechanism may be congenital or trauma
o Treatment for mild vertical diplopia is glasses
Sensory Esotropia
o Occurs in eye with poor vision (eye wanders,
with a prism
o Treatment for severe vertical diplopia is
tends to wander in)
o Treatment is with surgery
surgery. Managable.
o Surgery straightens eye, but does NOT
 CN6 Palsy
o Patient presents with horizontal diplopia and
improve vision!!!
o Surgery often needs to be repeated within 15
face-turn toward bad side
years (vision is not improved… eye wanders
o Involves the lateral rectus muscle
again)
o Horizontal diplopia is worse in gazes toward
the lateral rectus
Idiopathic Exotropia
o Begins intermittently, but increases in
o Patients often use a face-turn to manage their
frequency and duration
horizontal diplopia
o Usually more severe at distance
o Mechanism may be trauma, tumor, viral
o Amblyopia is common but not usually as
(lyme disease) or microvascular
o Initial treatment is glasses with a prism
severe.
o Treatment is observation +/- eventual
(almost always works)
strabismus surgery
o For refractory cases, surgical correction may
be indicated
Sensory Exotropia
o Occurs in eye with poor vision
o Many cases resolve on their own without
o Treatment is with surgery
treatment
o Surgery straightens eye, but does NOT
 Mechanical Limitation
o Causes include blowout fractures and masses
improve vision
o Surgery often needs to be repeated within 15
within the orbit
years
 Thyroid Eye Disease (Grave’s Disease)
o Discussed in preceding lecture (no details
 Deviation is consistent, regardless of gaze
ETIOLOGY

EPIDEMIOLOGY
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SUBTYPES
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Incomitant Strabismus
PHYSICAL 
EXAM 
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
provided in this lecture)
 Myasthenia Gravis
o Discussed in preceding lecture (no details
provided in this lecture)
Check light reflex (to determine where the light falls on each eye) +/- cover test
Check vision
Check stereopsis (depth perception)
Check rotations
Measure deviation in different gaze positions (helps determine etiology and plan surgery)
Amblyopia: impairment of vision without any detectable organic lesion of the eye
ETIOLOGIES  Refractive (49%): one eye has more far-sightedness, more near-sightedness or more astigmatism than the
other eye (rarely, the cause may be bilateral abnormalities). More difficult to pick up.
 Strabismus (49%): alignment of the eyes such that the image does not fall on one (or both) of the maculas
 Ocular Pathology (2%): cataract, glaucoma or corneal anomaly
MANAGEMENT ****CORRECT THE AMBLYOPIA BEFORE YOU WORRY ABOUT FIXING THE
STRABISMUS. When vision improves the brain will work harder to keep eyes in line!
 Eliminate the cause (e.g. correct the strabismus, provide correct glasses, remove organic cause such as
cataract)
 Force patient to use weaker eye, with one of the following measures:
o Patch over the stronger eye (gold standard)
 Must be a sticky, bandaid-like patch
 Amount of time patient needs to wear patch to improve vision is related to two things:
 Degree of initial visual impairment
 Age at time of first noticing amblyopia (the younger the age, the less patch time needed)
 Once vision is improved, patient must continue to wear patch 1 hour per day until age 8-9
o Atropine dilating drops (less common) – not the best.
 Paralyzes the ability of the stronger eye to focus
OUTCOMES  After the age of 8, amblyopia treatment is rarely successfully
Miscellaneous Points on Visual Development
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Introduction
o Vision is a learned process, we are not born with good vision
o If we don’t have a clear image focused on the retina, we simply won’t develop good visual acuity
Neonatal Vision
o At birth, vision is approximately 20/200 (10% of normal adult vision)
Requirements for the Development of Normal Vision
o Images must be clearly focused onto the retinas, which requires the following:
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Symmetric refractive error (one eye can NOT be more near-sided or far-sided that the other eye)
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Straight eyes
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No organic pathology obstructing a clear visual axis
Two Functions Served by Binocular Vision and Stereoacuity (equal acuity in both eyes)
o Permanency of eye alignment over time
o Depth perception (stereopsis) – important, but not as important as eye alignment
Definitions Associated with Strabismus
o Esotropia: eye turns inward

Be careful not to mistake children with epicanthal folds (especially Asians) for having esotropia (pseudoesotropia)

These children can be distinguished by the fact that the light will fall in the middle of each of their pupils
o Exotropia: eye turns outward
o Hypertropia: one eye is higher than the other eye (here “the other eye” refers to the “normal” eye)
o Hypotropia: one eye is lower than the other eye (here “the other eye” refers to the “normal” eye)
Miscellaneous Points Regarding Amblyopia
o Until the age of 7, poor vision will result if a clear image is not focused onto the fovea of each eye
o This is a CNS problem, and will occur even if the eye is structurally completely normal
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D/t failure of the neural pathways to develop correclty
o The earlier the onset of amblyopia, the worse the prognosis
Additional Important Notes
o If the problem is caused by an eye muscle that does not work, the solution (treatment) will NOT involve trying to get that eye to work better
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Instead, the treatment will be targeted at making adjustments to other structures and muscles to improve the functional problem
o MUST BE CORRECTED BY AGE 8 OR VISION LOSS IS PERMANENT. THE LONGER YOU WAIT THE WORSE THE OUTCOMES.