W15 Binocular Vision and Paediatrics

What is the definition of binocular single vision?

The ability to use the 2 eyes together simultaneously such that each eye contributes to a single perception

What does binocular single vision depend on?

Sensory fusion in the brain and motor fusion- the physical act of moving the eyes

What are the FIVE requirements for binocular vision?

• 2 eyes

• Visual fields of both eyes must overlap

• Coordinated eye movements must ensure that fields of fixation of both eyes overlap

• Neural transmission of light impulses from both eyes must reach the same area of the brain

• Perceptual blending of the impulses from both eyes must take place in higher levels of the brain

What happens if the requirements for binocular vision are not met?

Can cause deterioration in vision for patients

What is stereopsis?

Difference of vision between the 2 eyes can judge the distance of vision between us- depth perception/3D imaging

What are the benefits of binocular vision?

Stereopsis, larger visual field, binocular summation, “extra” eye

How does binocular vision enhance visual performance?

Space perception, hand-eye coordination, more comfortable reading

What are disadvantages of binocular vision?

Neurophysiology needed to fuse the input from each eye is complex, problems may cause eye strain, problems with close work

What are causes of binocular stress?

• Incorrect refractive balance

• Over/under convergence

• Conflict between accommodation and convergence

• Dissimilar images between the 2 eyes caused by anisometropia or retinal disease

What are the 3 positions of gaze?

• Primary- gazing straight ahead at distant object

• Secondary- Movign eyes in horizontal or vertical direction

• Tertiary- moving eyes in oblique direction

How are eye movements controlled?

By the extra-ocular muscles (EOM)

What are the 6 EoM’s?

• Medial rectus - Lateral rectus

• Superior rectus - Inferior rectus

• Inferior oblique - Superior oblique

What are the antagonistic muscle pairs?

They do opposite action: LR-MR, IO-SO, IR-SR

Which cranial nerves are EOM’s innervated by?

CN VI supplies lateral rectus

CN IV supplies superior oblique

CN II supplies medial rectus, inferior oblique, superior rectus, inferior rectus

What is Sherrington’s Law of reciprocal innervation?

When one of the extraocular muscles contracts, the other one will relax at the same amount

What is Hering’s law of equal innervation?

Innervation to the EOM is equal to both eyes- thus, all movements of the 2 eyes are equal and symmetrical

What are the involved muscles in Hering’s law?

Yoke muscles

Why can we not only move one eye?

For yolk muscle pairs, when there’s an impulse to perform an eye movement, both eyes will get the same amount of innervation

What’s are the SIX yolk muscle pairs?

• LSR - RIO

• LLR - RMR

• LIR - RSO

• RIR - LSO

• RLR - LMR

• RSR - LIO

What is contralateral synergists?

The EOM work together to move the eye in a certain direction

What is Worth’s classification of binocular vision?

Simultaneous perception and superimposition occurs 1-3 months

Fusion occurs 3 months

Stereoscopic vision occurs 3-5 months

What is neonatal misalignment?

Abnormal ocular alignment- it’s alternating, unilateral, intermittent (few secs at a time)

What is critical period?

Flexibility of the visual system and it can be adapted by its visual experience- mostly where treatment of binocular vision problems occur as neural connections can be modified (4 months - 8/9 years)

What is amblyopia?

Lazy eye- reduces visual acuity in one eye but cannot be corrected with spectacles/lenses, happens as px experiences abnormal visual stimulation during the critical period, interfering with normal visual development and can be permanent

What is stimulus deprivation amblyopia?

Something is blocking the stimulus from reaching the eye

What is strabismic amblyopia?

Caused by a eye muscle imbalance (strabismus), making one eye turned forward

What is anisometropic amblyopia?

Caused by difference in unequal refractive power between the 2 eyes

What is meridional amblyopia?

Caused by uncorrected astigmatism where vision is blurry in one meridian but clear in the perpendicular direction

What is ametropic amblyopia ?

Reduced vision in one eye due to uncorrected refractive error

What is occlusion amblyopia?

Lazy eye that is caused by something blocking clear vision in one eye

What is the treatment of amblyopia?

Must be done immediately during critical period:

• First is refractive correction done via ret

• Second is occluding good eye so brain can respond to weak eye

• Computerised treatment can train the usual system

What would we observe if px was looking left?

We’d observe right medial rectus and left lateral rectus (RMR - LLR)