Depth perception and Stereopsis Flashcards
What are the monocular cues for depth perception?
Lighting/shading
Texture gradient
Hue attenuation
Overlapping
Motion parallax
Linear gradient
Aerial perspective
Retinal image size
Accommodation
What is the monocular cue lighting/shading?
Light or shade gives clues as to whether an object is pointing/moving towards or away from you
What is the monocular cue texture gradient?
Textures become less detailed as they become further away from you
What is the monocular cue hue attenuation?
The moisture particles in the air make objects appear a lighter hue when far away
What is the monocular cue overlapping?
If one object is in front of another, it appears to overlap the object behind it
What is the monocular cue motion parallax?
Closer objects appear to move faster than objects that are further away
What is the monocular cue linear gradient?
Lines get closer together as they get further away from you
What is the monocular cue aerial perspective?
seeing something from above indicates that it is far away
What is the monocular cue retinal image size?
Known object sizes are used to judge how far away something is
What is the monocular cue accommodation?
If accommodation is being used, you know that the object is closer (subconsciously)
What are the binocular cues to depth perception?
Objective Fronto-parallel plane
Vieth-Muller circle
Horopter
What is the Objective Fronto-parallel plane?
A straight plane in front of you, parallel to the plane which passes through the pupils.
Anything in front or behind the plane gives clues to depth
What is the Vieth-Muller circle?
A circle encompassing the objects in front of you and their corresponding retinal points
Depth able to be perceived from awareness of which corresponding points are being stimulated
What is the horopter?
Curved plane, all points stimulating corresponding retinal points
Able to tell depth from what is on the plane, just in front and behind in Panum’s area, and outside of Panum’s area
What is binocular rivalry?
During physiological diplopia, the brain chooses the ‘better’ image to avoid double vision in the periphery. Often more dominant eye’s image chosen, but if image better in other eye, this will be chosen.
For smaller stimuli, what type of dominance is used in binocular rivalry?
Exclusive - only one image used
For larger stimuli, what type of dominance is used in binocular rivalry?
Mosaic - elements from each image used which are constantly shifting/alternating
What details are prioritised during binocular rivalry?
Detail
Lines/contours
Movement
High contrast
Brighter
Flash
Why does physiological diplopia occur?
Anything outside of Panum’s area is seen on non-corresponding points, so the cyclopean eye sees two of the object.
What level of stereopsis are you able to measure up to in a normal clinic?
60” arc
What is the timeline for stereopsis development?
Starts to develop at 3 months, rapid until 18 months, continues until at least 3 years old
What factors affect/limit stereopsis?
Blur
Motion-in-depth
Temporal characteristics
Contrast sensitivity
Retinal eccentricity
Distance
Why does blur affect/limit stereopsis?
Detail not as clear - unilateral is worse than bilateral bc harder to detect corresponding points
Why does motion-in-depth affect/limit stereopsis?
Harder to locate corresponding points - more retinal disparity
Why do temporal characteristics affect/limit stereopsis?
If something is seen for less time, then it’s harder to gather information about it and coordinate corresponding points/retinal disparity
Why does contrast sensitivity affect/limit stereopsis?
Higher contrast is easier to tell difference between things - unilateral is worse than bilateral
Why does retinal eccentricity affect/limit stereopsis?
Further into periphery is worse due to lack of detail available to find retinal disparity
Why does distance affect/limit stereopsis?
If something is further away, you can see less detail, so it’s harder to distinguish corresponding points and therefore create retinal disparity
What are the methods of assessing stereopsis?
Free fusion
Auto-stereogram
Anaglyphs
Vectographs
Transparent plates
Synoptophore
What kind of disparity is created when objects are behind the horopter?
Uncrossed disparity (image is on nasal retina)
What kind of disparity is created when objects are in front of the horopter?
Crossed disparity (image is on temporal retina)
What level can the Lang test up to?
100/200” arc
What level can the TNO test up to?
60” arc
(15” arc on older versions)
What level can the Titmus test up to?
Fly: 800-3000” arc
Circles: 800-40” arc
Animals: 400-100” arc
What level can the Frisby test up to?
600-5” arc
What is point zero?
The point on the retina where the target’s image falls in a strabismic eye
What is confusion?
Different images are seen on each retina due to strabismus, with diplopia also present
Brain cannot tell which image is ‘correct’
In an esot, where does the image fall and which field is it seen in?
Falls nasal to fovea
Seen temporally
In an exot, where does the image fall and which field is it seen in?
Falls temporal to fovea
Seen nasally
What is a suppression scotomata?
Area between the fovea and point zero where suppression occurs
What are binocular adaptations to a strabismus/diplopia caused?
Suppression
Abnormal retinal correspondence
What are monocular adaptations to a strabismus/diplopia caused?
Amblyopia
Eccentric fixation
What does binocular adaptation mean?
It can only be present when both eyes are open/not covered
During foveal suppression, does diplopia still occur?
Yes, in peripheral locations (anywhere that isn’t within suppression scotomata)
What is ARC?
The corresponding points in the retina of the strabismic eye are ‘readjusted’ so double vision doesn’t occur
Foveal suppression/scotomata are still present
What is harmonious ARC?
Adjustment made = objective deviation size (Prism CT result)
PZ becomes fixation point, lines up with fovea in fixating eye
What is unharmonious ARC?
Adjustment made = subjective deviation size
Fixation point is between fovea and PZ
Why does unharmonious ARC occur?
Due to a change in the angle of the strabismus, normally from surgery or trauma
What is amblyopia?
Reduced VA by at least 2 lines in one eye despite being fully corrected and no pathology present
When can amblyopia be bilateral?
When there is high uncorrected astigmatism (meridional amblyopia)
What are the causes of amblyopia?
Anisometropia
Stimulus deprivation (congenital cataracts)
Refractive error
Strabismus
Early eye disease
Nutritional/toxic
Idiopathic or congenital
What is eccentric fixation?
Fovea doesn’t take up fixation when fixating eye is covered bc the brain has ‘moved’ fovea to a different retinal point - so image is still on fixation point when covered
What is EC with Identity?
The fixation point is on PZ, no movement on CT
What is EC without Identity?
The fixation point is in between the fovea and PZ, some movement on CT
What is intractable diplopia?
Constant, unchangeable diplopia
