Lecture 9-1 Functional Entrance Tests part 1

what are the three types of ocular procedures

refractive (vision correction to see clearly), functional (binocular vision), health (pathology)

why do we need two eyes

due to binocular summation and to see stereopsis

why do we need stereopsis

to gain depth perception and more precise eye-hand coordination

drawbacks of having two eyes

binocular vision disorders, misalignment of two eyes, and advanced neural circuitry

define strabismus

misalignment of two eyes

define asthenopia

eye fatigue or eye strain, or discomfort from eyes trying to work together

define strabismus

an eye turn, or misalignment of the eyes in any direction

define diplopia

double vision or seeing two of something

define suppression

image from one eye is suppressed or “shut off” by the brain and only seeing an image from one eye (the one not shut off) when both eyes are open

define amblyopia

reduced vision (BCVA) in one or both eyes due to improper visual development

define accommodation

change in thickness of the lens (inside of the eye) to focus at different distances

what is biocular vision

use of the two eyes independently with both eyes open, but seeing a different image/target with each eye

what is binocular vision

simultaneous contribution of both eyes to perceive a single image of the object

what caused amblyopia?

development problems as we are not born with it

define fusion

ability to process image from each eye and see one single image

define fixation

the eye(s) viewing or looking directly at the target presented

what are the two things required to obtain binocular fusion

motor alignment (muscles or movement) and sensory fusion (visual processing)

how does the motor system work to create motor fusuion

Motor system (muscles) moves the eyes to bring the object of attention onto the fovea and align both eyes to enable binocular single vision

what is required to obtain motor fusion

adequate vergence eye movements

define vergence

simultaneous movement of the eyes in “opposite directions” to maintain the image on the fovea (disconjugate eye movement)

what does it mean when the eyes move in opposite directions for vergence

the work looks in different directions when observing convergence and divergence

define convergence

movement of eyes inward to a near stimulus

define divergence

movement of eyes outward to a near stimulus

define versions

simultaneous movement of the eyes in the same direction to maintain the image on the fovea

of each eye (conjugate eye movement)

how do we obtain sensory fusion

The visual cortex (brain) combines superimposed views obtained independently by the two eyes (how we see “3D” or depth)

what kind of process is sensory fusion?

neuro-physical

is sensory fusion objective or subjective

subjective

is motor fusion objective or subjective

objective

define sensory fusion

The ability to combine sensory information (form, color, size, illuminance, location in space) from the right eye and the left eye into a single percept

define oculocentric direction

monocular, eye-centered visual direction

define egocentric direction

binocular, self-centered visual direction

which direction is relative to the eye? oculocentric or egocentric

oculocentric

which direction is relative to the person? oculocentric or egocentric

egocentric

what is the principal visual direction in the oculocentric direction?

the primary reference line of sight that connects the fovea to the object (visual axis), and the reference against which all other directions are judged

define local sign

Direction perceived based on retinal (receptor) image location (2-dimensional, “2D”) and mapping where objects are located relative to the eye

local sign occurs due to neurons processing direction but how is that made possible

by retinotopic mapping in the lateral geniculate nucleus (LGN) & striate cortex

direction and images formed by individual eyes (oculocentric) are averaged to form what

binocular (egocentric) direction that is located midway between eyes

what is the cyclopean eye or egocenter

the direction relative to a single point within our head when binocular

what is the term called when one eye is favored

eye dominance

in the motor ocular dominance test, how do we tell which eye is the dominant eye

it is the eye in which the target is the most centered

in the sensory ocular dominance test, how do we tell which eye is the dominant eye

it is the eye that sees blurrier

for the sensory ocular dominance test, why is the dominant eye the eye that sees blurrier?

because we rely on that eye more to see clearer and that eye becomes blurry when we put a lens over it

define corresponding points

pair of points, one in each eye (on the retina), that when stimulated simultaneously or rapidly in succession are perceived to lie in a single common visual direction

what is the map of corresponding points called

Vieth-Müller Circle or theoretical horopter

define horopter

imaginary line joining the spatial loci of all corresponding points in space

how should the images look if they land on our horopter

clear and single because this is our plane of view

how does the horopter change in our eyes?

based on fixation point (unique and centered to that point)

define Panum’s Fusion Area

Slightly non-corresponding points seen as single in front of and behind the horopter

if an image lands on the Panum’s Fusion Area, how should they apear

they are not as clear as the images on the horopter

when does diplopia happen

when binocular disparity is too large

how does pinhole affect the Panum’s fusional area

it makes the area larger

examples of biocular testing

cover test and W4D

define non-corresponding (or disparate) points

retinal points of each eye (in reference to the fovea) that do not correspond to the same point/place in space

what does non-corresponding (or disparate) points produce, lead to, or allow us to see?

depth perception (stereopsis) and how far away an object is

when viewed monocularly, what happens to the non-corresponding points?

they are seen lying in different visual directions

define retinal disparity

images of a single object that do not stimulate corresponding retinal points

define uncrossed disparity and where the image falls

points farther away than fixation and image falls nasal to fovea

define crossed disparity and where the image falls

points closer than fixation point and image falls temporal to fovea

how does uncrossed disparities occur relative to the horopter

occurs when an object is located further away (behind) the horopter

how does crossed disparities occur relative to the horopter

occurs when an object is located closer (in front of) the horopter

define stereopsis

sensory fusion of two dissimilar images resulting in 3-dimensional perception of the object

how does stereopsis happen

due to the small horizontal separation of the eyes causing the images of a single object of regard falling on each foveae to be slightly dissimilar, due to each eye viewing the same object from a slightly different angle

The fixation point of the object is placed where of the eye

corresponding fovea of each eye

define alignment

eyes geometrically aimed at the same location or object in space

define misalignment

eyes not pointed at the same point in space

define phoria

“state or tendency,” often called “resting position of the eyes without a stimulus to fusion

when we do measure and access phoria

when fusion is broken

define tropia

misalignment of the eyes (eye turn)

what visual condition are we able to observe only when eyes are dissociated (such as cover one eye)

phoria

what kind of condition is present even with both eyes open

tropia

define orthophoria

Perfect ocular alignment without any stimulus for fusion, and a balance of ocular muscles of the two eyes in which their lines of vision meet at the object toward which they are directed

define strabismus (tropia)

misalignment of the eyes under normal binocular conditions (stimulus for fusion present)

what might a patient with strabismus experience

diplopia, binocular confusion, anomalous retinal correspondence or suppression

ocular alignment is a balance that requires what (2)

it needs our eye muscles to maintain their posture (motor fusion) and a sensory component (stimulus to fixation)

imbalance of ocular alignment can lead to what

eye turn (tropia) or a phoria other than the ortho position

adaptations to inadequate fusion

suppression, Anomalous Retinal Correspondence (ARC)

consequences of inadequate fusion (2)

diplopia and binocular confusion

define binocular confusion

two different objects seen in one location or direction; one image on one retinal loci (e.g., fovea) and a non-identical image on the corresponding point

define physiological

normal response or occurence

define pathological

occurrence caused by a disease state

define Physiological Diplopia

normal phenomenon in which images fall on non-corresponding points outside of Panum’s Fusional Area

how do we trigger physiological diplopia

when we fixate on an object and attention is paid to an object outside Panum’s fusion area

define suppression as one of the adaptation to inadequate fusion

active inhibition of the image from one eye when both eyes are open (MUCH more common than ARC)

define Anomalous retinal correspondence (ARC)

a “remapping” of the corresponding (retinal) points in which non-foveal point of the deviated eye develops correspondence with the fovea of the fixating eye (cortical event), resulting in the retinal locus point being recalibrated

how does Anomalous retinal correspondence (ARC) occur?

when the visual cortex links non-corresponding retinal points in the eyes to create binocular fusion

corresponding points can be shifted if a patient acquire what adaptation to compensate for inadequate fusion

Anomalous retinal correspondence (ARC)

define Congenital strabismus

condition that is born with (or presents very early in life)

why are patients with cogenital strabismus less likely to experience diplopia

because the brains adapt early in life

define acquired strabismus

condition that is present “later” in life and can be the result of a disease

what do patients with acquired strabismus likely to experience?

diplopia and binocular confusion

define Orthophoria

when the resting position is straight

define Heterophoria

Physiological deviation of the eyes in the absence of stimulus for fusion (resting position not straight)

how do we create heterophoria

through occlusion of the eye or with prism

how does patient compensate for their heterophoria?

using vergence (motor fusion)

between strabismus and heterophoria, which one happens during fusion

strabismus

between strabismus and heterophoria, which one happens during no fusion

heterophoria

everyone must have tropia or phoria. if a patient has tropia, do they have phoria

no phoria

everyone must have tropia or phoria. if a patient does not have tropia, do they have phoria

have phoria and it is one of the types

define motor fusion

ability to align and maintain alignment with a given visual target

what kind of test is Hirschberg Test

motor fusion test