004 Binocular Vision

What is the importance of binocular vision test for children?

• BV problems can lead to permanent vision loss

• BV test require attention

What are the three key components that allow both eyes to work together?

• Alignment – proper positioning of both eyes

• Fusion – combining images into one

• Accommodation – focusing adjustment for clear vision

What is ocular alignment and what disorders are associated with it?

• Alignment: Eyes are properly directed at the same target

• Disorders:

  • Strabismus – manifest misalignment (eyes visibly not aligned)

  • Phoria – latent misalignment (only appears when fusion is disrupted)

What is fusion and what are its two components?

• Fusion: Brain combines images from both eyes into one

• Motor fusion: eye movements align images (vergence)

• Sensory fusion: cortical processing merges images

What is the epidemiology of strabismus in early childhood?

• Occurs in ~3.7% of children aged 6–72 months

• Infantile strabismus (6–12 months): ~1.1%

What are the major risk factors for strabismus?

• Prematurity (~8%)

• Smoking during pregnancy (~5.8%)

• Down syndrome (~6.3%)

• Cerebral palsy (~16.7%)

What are the common binocular vision disorders and their epidemiology by age?

• Convergence insufficiency (CI):

  • 5–7% in 6–18 year olds

  • 7.7% in college-age patients

• Convergence excess (CE):

  • 4–8% in 6–18 year olds

  • 1.5% in college-age patients

How does the prevalence of convergence insufficiency change with age?

Convergence insufficiency increases with age in this slide’s data:

• 5–7% in children/adolescents

• 7.7% in college-age patients

How does the prevalence of convergence excess change with age?

Convergence excess decreases with age in this slide’s data:

• 4-8% in children/adolescents

• 1.5% in college-age patients

What is the epidemiology of accommodative disorders by age?

• Accommodative disorders:

  • 6% in 6-18 year olds

  • 17% in college-age patients

• Suggests accommodative dysfunction is more common in college-age populations

How does the prevalence of convergence insufficiency change with age?

Convergence insufficiency increases with age in this slide’s data:

• 5-7% in children/adolescents

• 7.7% in college-age patients

How does the prevalence of convergence excess change with age?

Convergence excess decreases with age in this slide’s data:

• 4-8% in children/adolescents

• 1.5% in college-age patients

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What is the epidemiology of accommodative disorders by age?

• Accommodative disorders:

  • 6% in 6-18 year olds

  • 17% in college-age patients

• Suggests accommodative dysfunction is more common in college-age populations

What should be included in the examination when assessing binocular vision?

• Case history

• Visual acuity

• Binocular vision (if VA is adequate enough to assess BV)

• Refractive error

• Ocular health

How should significant refractive error be managed before a thorough binocular vision assessment?

• Prescribe the refractive correction first

• Allow the patient to adapt for ~1 month

• Then reassess binocular vision thoroughly

• A trial frame at the first visit usually will not show a large change in binocularity

Why should binocular vision not be fully assessed while the patient is cyclopleged?

• Do not assess fully while cyclopleged

• Cycloplegia is needed to find the correct prescription

• The refractive error itself may be contributing to the binocular vision problem

• BV assessment often requires follow-up after glasses wear

What is the key clinical sequence for evaluating binocular vision when refractive error is present?

• Cycloplege to determine accurate Rx

• Prescribe correction if significant refractive error is present

• Allow glasses adaptation

• Reassess binocular vision at follow-up

What abnormal head postures may be seen on direct observation during binocular vision assessment, and what do they suggest?

• Head turn

• Head tilt

• Chin tipping
  These may be compensatory postures used to maintain single binocular vision or reduce symptoms from ocular misalignment.

What is angle kappa?

• Angle kappa = the distance/angle between the center of the pupil and the corneal light reflex

• Important when interpreting apparent ocular alignment

What is the normal angle kappa/light reflex position?

• Average angle kappa ≈ ±5°

• In normal adult alignment, the light reflex is ~0.5 mm nasal to the center of the pupil

Why is angle kappa clinically important when assessing strabismus?

A normal angle kappa can make the eyes appear slightly misaligned, so it must be considered when interpreting the corneal light reflex and screening for strabismus/pseudostrabismus.

What is pseudostrabismus, and why is it clinically important?

• Pseudostrabismus = false appearance of ocular misalignment when true strabismus is not present

• Important because facial anatomy or abnormal angle kappa can mimic eso- or exotropia

What can cause a pseudoesotropia (esotropia appearance)?

• Epicanthal folds

• Narrow interpupillary distance (IPD)

• Deep-set eyes

• Negative angle kappa = corneal light reflex appears temporally

  • May occur if the fovea is dragged medially by a retinal condition

What can cause a pseudoexotropia (exotropia appearance)?

• Wide IPD / hypertelorism

• Positive angle kappa = corneal light reflex appears nasally

  • May occur if the fovea is dragged temporally, such as with:

    • ROP

    • High myopia

    • Congenital retinal folds

How is the Hirschberg test performed?

• Perform with the kappa test in mind

• Hirschberg should be done first

• Hold a transilluminator/bright penlight ~40 cm away

• Test is done binocularly

• Have the patient fixate on the light (or use a fixation target like a lighted puppet)

How do you interpret the Hirschberg test for strabismus?

• If the corneal light reflex position is the same in binocular and monocular viewing → no strabismus

• If the binocular reflex differs from the monocular reflex, the eye with the monocular difference is generally the strabismic eye

What are the limitations of the Hirschberg test?

• Must be interpreted with angle kappa

• Can be difficult/unreliable in:

  • Paralytic strabismus

  • Mechanical strabismus

How is the Krimsky test performed?

• Place a prism with the appropriate base orientation in front of the fixating eye

• Increase prism power until the corneal light reflex in the deviating eye matches the expected angle kappa position

What does the endpoint of the Krimsky test indicate?

When the deviating eye’s corneal reflex is aligned to the normal angle kappa position, the prism amount = magnitude of the tropia

What is the key principle behind the Krimsky test?

It is a prism-based modification of the Hirschberg test used to quantify a manifest deviation (tropia) by neutralizing the corneal light reflex asymmetry

What is the Brückner test used for?

• Used to detect the presence of strabismus

• Compares the red reflex brightness between the two eyes

How is the Brückner test performed?

• Child fixates on the direct ophthalmoscope in a dark room

• Examiner illuminates both eyes simultaneously with the direct ophthalmoscope

• Examiner stands about 1 meter from the child

How is the Brückner test interpreted in strabismus?

The brighter eye is the strabismic eye

What can cause false positives on the Brückner test?

• Media opacities

• Posterior pole abnormalities

• Anisocoria

• Anisometropia

What is the key limitation of the Brückner test?

• Unequal reflex brightness is not always due to strabismus

• Must consider other causes such as anisometropia, anisocoria, media opacity, or retinal/posterior pole disease

What are the age-related limitations of the Brückner test in infants?

• <2 months: infants do not show normal fundus reflex dimming with fixation

• 2-8 months: about 25% of children can have fundus reflex differences despite no strabismus

Why is the Brückner test less reliable in children younger than 8 months?

• Normal infants may show asymmetric fundus reflexes without true strabismus

• This creates a high false-positive rate, especially from 2-8 months

In what age group should the Brückner test generally not be used to detect strabismus?

Do not use in children younger than 8 months

What are the basic requirements for performing a cover test in a child?

• The child must be able to see the fixation target with both eyes

• Can be performed on any child who can fixate briefly

• Usually feasible in children older than ~1.5 years

• Unilateral cover test can be obtained on most children

What should be done before performing a cover test if the child has an abnormal head posture?

• Straighten the child’s head first if an anomalous posture is present

• A full sensorimotor exam includes cover testing in all directions of gaze

What are practical tips for performing a cover test in young children?

• Use engaging fixation targets

• Ask questions about the target to ensure attention stays on it

• If the child looks at the examiner instead, use the examiner’s face as the fixation target

How can prism use be adapted during cover testing in young children?

• Choose the prism wisely

• Loose prisms may work better early on because the child can look through them gradually

• A prism bar may be more intimidating and easier for the child to swat away

What is the key goal during pediatric cover testing?

Maintain steady fixation on a visible target with both eyes long enough to detect ocular misalignment accurately

What are the two main components of fusion, and what does each represent?

• Sensory fusion = cortical combination of images from both eyes into one percept

  • Includes stereopsis

• Motor fusion = eye movement response that maintains alignment

  • Includes fusional vergence

What is stereopsis, and why is it clinically important?

• Stereopsis = depth perception from binocular disparity

• It is a form of sensory fusion

• Clinically, it is an indirect indicator of strabismus

What is the difference between global and local stereoacuity?

• Global stereoacuity = random dot stereopsis

  • Requires bifoveal fixation

• Local stereoacuity = contour stereopsis

  • May still be present in some patients with small-angle strabismus

Which type of stereopsis is more sensitive to binocular misalignment?

• Global stereoacuity is more sensitive because it requires bifoveal fixation

• Local stereoacuity may still show gross stereopsis even with small-angle strabismus

What do vectographic stereopsis tests measure, and what type of stereopsis do they assess?

• They assess stereopsis as part of sensory fusion

• These slides focus on global stereopsis

• Global stereopsis is tested with random dot targets

Which vectographic stereopsis test uses preferential looking?

• Stereo Smile

• It is a global stereopsis / random dot test

• Response is based on preferential looking, making it useful for very young children

Which vectographic global stereopsis tests use a 2-alternative fixed-choice format?

• PASS Test

• Random Dot E

• Both are random dot global stereopsis tests using a 2-alternative fixed-choice response style

What is Preschool Randot used for?

• A vectographic global stereopsis test

• Uses random dot stereopsis

• Designed for preschool-age children, typically with child-friendly picture/shape targets

What are the key features of the Frisby stereotest?

• Real depth stereopsis test

• Assesses global stereopsis

• No glasses required

• Uses plates of different thicknesses to create disparity

What stereoacuity levels are tested with the Frisby stereotest on this slide?

• 340 arcsec

• 170 arcsec

• 55 arcsec
  These represent progressively finer stereoacuity.

What are the key features of the Lang stereotest?

• Prism stereopsis test

• Assesses global stereopsis

• No glasses required

• Turn the test 90° to eliminate disparity and help check for non-stereo cues

What is the difference between Lang I and Lang II stereotests?

• Lang I: no monocular target

• Lang II: the star is a monocular target

How is the 10Δ base-out (BO) reflex fusion test performed, and what is the normal response?

• Place 10Δ BO prism over the preferred eye while the patient looks at a near target

• Normal response in the non-preferred eye:

  1. Abducts

  2. Then adducts

• If both phases occur, fusion is present

How is the 10Δ BO reflex fusion test interpreted?

• Abduction then adduction of the non-preferred eye = fusion present

• Abduction only = no fusion

How can fusional vergence be assessed in children who cannot describe blur/break/recovery?

• Use prism bar vergence ranges in children with steady fixation

• If the child cannot report blur / break / recovery, observe the eyes directly for the response

How is near point of convergence (NPC) tested in younger vs older children?

• Older children: test the same as adults

• Younger children: perform similarly, but watch for an eye to drift instead of asking about diplopia

• Very young children: move a small target toward the patient and watch for a convergence response

What are the 3 main aspects of accommodation that should be assessed?

• Magnitude – how much accommodation the patient can produce

• Accuracy – how accurately the accommodative response matches demand

• Flexibility – how quickly/easily focus can change

How is accommodative magnitude tested, and what does it measure?

• Measures amplitude of accommodation

• Tested with push-up or pull-away methods

• Assesses the maximum accommodative ability

What does MEM retinoscopy assess, and how is it performed?

• Assesses accommodative accuracy

• Performed on each eye

• Done at 40 cm or Harmen distance (forearm length)

What is a normal MEM lag of accommodation?

• Normal lag is +0.50 to +0.75 D

• More plus = greater lag of accommodation

What test is used to assess accommodative flexibility?

• Accommodative facility testing

• Evaluates how quickly/easily the patient can change focus