BV1 - binocular and spatial vision

What is utrocular vision and what are the characteristics?

eyes function separately:

-independent eye movements

-complete crossing of ON

-lower vertebraes

-does not following Herings law

What is ambiocular vision and what are the characteristics?

eyes work together:

-coordinated eye movements

-partial decussation of ON

-mammals

-often frontal eyes

what is binocular vision?

the coordinated behavior of 2 eyes in the perception of space

where is the placement of eyes in the head for prey animals?

lateral eyes → provide safety through panoramic view

where is the placement of eyes in the head for predator animals?

frontal eyes → provide better depth perception and visual acuity for offensive behavior

what is angle omega?

angle between optic axis (with eye centered in orbit) and the body midline

What is angle gamma?

angle between the line of fixation and optic axis → nasal-temporal division in ambiocular vision

Who has a large vs small angle gamma?

small: mammals

large: prey animals

what are the advantages of ambiocular vision?

stereopsis → possible by coordinated eye movements and retinal correspondence

better VA → frontal eyes have better angle gamma ∴ better optics

What does oculocentric direction look like in ambiocular vision and how does that affect what we see?

the foveas of each eye are assigned a common oculocentric direction → we must bifoveally fixate to avoid visual confusion

What is confusion?

two dissimilar objects in the same visual direction

two eyes have the same oculocentric (β) direction i.e. they're aligned on the two different objects

diplopia is created because the two objects don't fall on corresponding points

Characteristics of binocular vs monocular vision?

1. BV has much more sensitive/better depth perception

2. BV and MV have same brightness

3. eyes dark adapt independently of each other

4. BV sees better → probability seeing for BV is 75%, monocular 50%

Why does binocular vision not have better brightness than monocular?

the luminance of two eyes are averaged NOT summed

How does wearing plus spectacles affect ocular direction?

prismatic effects of plus lenses require the eye to rotate more → image appears farther to the side

this causes patient to past point

What is past pointing?

patient reaches farther to one side because they think the object is farther than it actually is

How does wearing minus spectacles affect ocular direction?

the prismatic effects of minus lenses require the eye to rotate less → image appears less to the side

this causes the patient to not grab far enough for the object

How do the prismatic effects of lenses vs CL affect TBI patients?

they have poor adaptation → switching from glasses to CL or wearing bifocals is disorienting

What are the two theories surrounding binocular ocular direction?

dominant eye theory

cyclopean theory

What is the dominant eye theory?

binocular visual directions are just the visual directions of the dominant eye

What is the cyclopean theory?

binocular visual directions are the average of the two eyes

Where is the ego center located?

between the eyes but 10cm behind the plane of the eyes

location of dens (atlas/axis) - center of rotation of head

What is the ego center?

the body's reference point for egocentric direction

Where does the dominant eye theory say the ego center is?

egocenter is at the dominate eye

(αL + βL) or (αR + βR)

equation is basically → angle eye is pointed from center + disparity of object from direction of eye

or χ L/R (i.e. egocentric location of individual eye)

What does the cyclopean theory say about the ego center?

egocenter is at the midpoint between the eyes

[(αL + βL) + (αR + βR)]/2

What is retinal correspondence?

each retinal point in one eye has the same oculocentric direction in the other eye

When do corresponding points occur?

When βL=βR

What is Hering's window?

fixation is spot on window → tree on right and house on left

tree and house will appear in the same location (confusion) → 2 foveas have same oculocentric direction

diplopia bc tree does not fall on corresponding points for the 2 eyes

what is the appearance of the tree and house when bifoveal fixating on tree?

images of house fall on another pair of corresponding points → tree and house appear in proper locations

What is anomalous retinal correspondence (ARC)?

rewiring of corresponding points → prevents confusion and diplopia (with strab)

How would ARC look in a right esotrope?

all corresponding points on OD shifted nasally

What is harmonious ARC?

if the rewired corresponding points superimpose the image exactly

What type of vision is it if there is no retinal correspondence?

utrocular → lack of correspondence is confused with harmonious ARC

what would Hering's window look like in utrocular eyes?

tree and house would be correctly localized by each eye → NO retinal correspondance

What causes retinal (absolute) disparity?

stimulation of non-corresponding retinal points (anytime βL ≠ βR)

What is the retinal disparity formula?

βL-βR → gives the angular separation of images

When is retinal disparity zero?

when βL=βR

What type of diplopia do esotropes have and why?

uncrossed

esotrope eye perceives object more temporal

EX: R esotropia → OD perceives image as more right (image hits nasal retina) → uncrossed

What type of diplopia do exotropes have and why?

crossed

exotrope eye perceives object more nasally

EX: R exotropia → OD perceives image as more left (hits temporal retina)→ crossed diplopia