Lecture 1 Flashcards
what are 3 advantages of having 2 eyes?
having a spare eye, larger FOV, and better visual function due to binocular summation
how large is our monocular field?
145 degrees
how large is our total visual field?
180+ degrees
how large is our binocular visual field?
130+ degrees
what is stereopsis?
it arises from the subtle difference between images in each eye
what is the real advantage of binocularity?
highly accurate depth perception
what happens if you fail to align the two eyes?
strabismus, amblyopia, diplopia, suppression, etc.
what can occur if the two eyes are aligned but the system is stressed?
incorrect refractive balance, dissimilar images between eyes due to anisometropia or retinal disease, over/under convergence, and conflicts between accommodation and convergence
what are 3 misconceptions about binocular vision?
some assume that the only advantage to binocular vision is stereopsis, without binocular vision you have no depth perception, and some think that stereoscopic depth perception helps them judge depth for distant objects
what is physical space?
the “real world” or 3D space around us and all the objects located in it (also known as object space)
what is visual space?
your perception of the physical space in relation to you - it is a construct of the brain
what is the goal of vision?
to construct a visual space that looks like a physical space
what happens when the visual space doesn’t match the physical space?
normal = optical illusion abnormal = metamorphopsia
what is visual direction under monocular conditions called?
oculocentric = eye centered
what is the Principal Visual Direction (PVD)?
the direction signaled by the fovea, the oculocentric sense of “straight ahead” and has zero direction
under monocular conditions how is the oculocentric (visual direction) measured?
the angle between PVD (principal visual direction) and the secondary visual direction
what is the oculocentric direction if the angle < 0?
negative angle (to the left side)
what is the oculocentric direction if the angle > 0?
positive angle (to the right side)
what happens to the oculocentric direction as the eye moves to fixate on a new target?
as you shift the direction of the fovea - the PVD also shifts with it
what is a local sign?
a unique oculocentric direction associated with a specific retinal point and is determined by retinotopic mapping of the retinal locus in LGN and cortex
what shows the neural basis of local signs?
mechanical visual phosphenes
what determines the local sign size?
the brain (not retina)
what relates to local sign size and what is it the basis for?
relates to retinal eccentricity and is the basis for directional discrimination
how large are foveal local signs?
1/7 the size of foveal cones
what is the basis for hyperacuity (Vernier acuity)?
local sign size
are peripheral local signs larger or smaller than peripheral cones?
much larger
what is a local sign disorder?
metamorphopsia - a perception of object shape that differs from its true shape
what are 2 causes of metamorphopsia?
neuroanatomical (retinal diseases or strabismus, amblyopia) and optical (keratoconus)
what is eccentric fixation (EF)?
PVD becomes associated with the local sign of peripheral retina other than the fovea, the patient perceives straight ahead and is not aware they are off center
what two conditions can eccentric fixation be found in?
strabismic amblyopia and long term (years) macular disease
what is eccentric viewing (EV)?
PVD is still associated with the fovea and the patient is aware of using peripheral vision to see
what conditions can eccentric viewing be found in?
short term macular disease and in low vision rehab
what is the visual direction under binocular conditions called?
egocentric = head centered
what is the cyclopean eye?
represents a single hypothetical eye located approximately midway between the two eyes
if you are gazing at an object located directly in front of the head, what is the oculocentric and egocentric directions?
oculocentric direction of each eye = 0
egocentric direction = 0
if you are gazing at an object located directly in front of the right eye, what is the oculocentric and egocentric directions?
oculocentric direction of each eye = 0
egocentric = positive angle (to the right of the head direction)
the brain receives input from both eyes and computes the egocentric direction based on what 2 sets of data?
the retinal location of the objects image in each eye (oculocentric) and each eye’s orientation or direction of gaze
if you are looking at a target to the left side of the head without turning the head, what are the oculocentric and egocentric directions?
oculocentric OD = 0
oculocentric OS = 0
Egocentric = negative
if you are looking at a target to the right side of the head with turning the head at the object, what are the oculocentric and egocentric directions?
oculocentric OD = 0
oculocentric OS = 0
egocentric = 0
while fixating on a target located straight ahead and you notice a second target at your right side, what is the oculocentric direction for the second target?
oculocentric OD = positive
oculocentric OS = positive
egocentric = positive
