S&P Exam 2

where is vision best

the fovea

define fixation

the alignment of the eyes

• to see properly your eyes have to be aligned properly

what muscles of the eyes does fixation use

extra-ocular muscles

what happens when both of your eyes are aligned properly

the image is brought back to the brain and helps with depth perception

what happens with fixation when you have a lazy eye

your brain will suppress the image or information that is coming in from it

define focus

focusing of light onto the retina

• onto the fovea specifically

what muscles are used with focus

intra-ocular muscles (inside of the eyes)

• AKA ciliary muscles

how do fixation and focus work together

you need fixation to have focus

• you can be fixated on something but not focused on something

what are the characteristics extra-ocular muscles

• 3 pairs of the eye muscles

• most precise muscles in the body and are very good at what they do

• fatigue, drugs, and alcohol impact these muscles first

define superior

on top

define inferior

below

give a rundown of the superior and inferior rectus muscles

• if the superior contracts, the inferior relaxes and vise versa

• they are used for up and down movement mostly

how many eye movements are there in an average day

3000

true or false; all eye muscles move when the eyes do

true

where are the superior and inferior rectus muscles connected

they attach straight back

what are the medial and lateral rectus muscles

• contracting the medial muscles brings the eyes inward

• helps to see distance

  • closer = eyes crossed

  • further = eyes parallel

• helps to look side to side

define medial

median

• by the nose

• toward the middle of the head

define lateral

side

• near the ear

where are the medial and lateral rectus muscles connected

they attach straight back

what are the superior and inferior oblique muscles

• help control the roll of the eyes (like turning a door knob)

• fine tuning movements

• helps with control and gaze stability

where are the superior and inferior oblique muscles connected

to the nose

• they run perpendicular to the other ciliary muscles

what are the different kinds of eye movements

• voluntary

• involuntary

what are the voluntary eye movements

• saccade

• smooth pursuit

• vergence

define saccade

quick, jerky, ballistic eye movements

• made voluntarily and involuntarily

• change from one object to another

what does ballistic mean

once you start the movement you cant stop it

what is the function of a saccade, give an example

quickly scans the environment

• ex: looking for a friend in the football stands, reading

how long does it take to complete a saccade

it depends on what you are looking at

define smooth pursuit

smooth pursuing an environment

what is the function of smooth pursuit and an example

for tracking moving objects

• ex: finger moving in front of your face without moving your head, watching a bird fly

  • you need the object to follow or you’re completing a saccade

are saccades and smooth pursuit mutually exclusive

yes!

define vergence

the rotation of the eyes to converge/diverge

• eyes move in opposite directions

• converge = in

• diverge = out

what does vergence allow us to do

see different distances

how does your vision change when your eyes converge

you go from seeing far to seeing near

• close up looking

how does your vision change when your eyes diverge

you go from seeing near to seeing far

• far away looking

are vergence and saccades and smooth pursuits mutually exclusive

no, vergence can go with either of the other 2

define microsaccades

the eye shivering or tremmoring

• small

• normal

• not visible

what are microsaccades for

to prevent photoreceptor fatigue

• fine spatial judgements

• compensating for the very paid fall off of acuity

• changing the spatiotemporal pattern of information that arrives at the retina

• directed to objects that we are attending

define nystagmus

pattern of eye movement

• there is a smooth pursuit and saccadic aspect

define optokinetic nystagmus

relative eye movement where the eyes will involuntarily track a continually moving object

• a type of nystagmus

• aka OKN

• measure of visual acuity in infants

give an example of OKN

watching a train pass by

define end point nystagmus

type of nystagmus

give an example of end point nystagmus

moving your eyes to the right while holding your head steady

• your eyes start to drift upwards but then snap back down

define vestibular-ocular reflex (VOR)

reflective eye movement

• equal in magnitude but opposite direction of the head movement

what is the function of VOR

to maintain fixation during head movements

• helps with gaze stability

• help compensate for angular rotations of the head

• robust reflex

• compensatory eye rotation by the semicircular canals when they sense head rotation

why is gaze stability important

you want alignment set to be able to focus properly

define accommodation

focusing of light (bending or refracting) to get it on the retina (fovea specifically)

how much of the work does the cornea do in accommodation and what

• 2/3 of the work

• bending of the light

how much of the work is done by the lens during accommodation and what

• 1/3 of the work is done

• focuses the light onto the retina

what does lasik surgery do

reshapes the cornea

when you are looking at something close up, what are the characteristics of the lens

• fat

• thick

• stronger

when you look at something far away, what are the characteristics of the lens

• thin

• weaker

does the eye have more or less work to do when viewing something near

more

• the light needs to come in and then go parallel and converge to hit the retina

define diopter and the formula

the measure of the lens strength

• 1/focal length (meters) = D

how does lens strength work

the higher the number means the higher the lens and a shorter focal distance

accommodation vs vengence

• seeing near: eyes converge and accommodation strengthens

• seeing far: eyes diverge and accommodation weakens

• they help control one another

what is accommodative convergence

the lens gets fatter and the eyes converge

what is convergent accommodation

the eyes converge and the lens gets fatter

define emmetrope

individuals that do not need an optical correction

• the light is focused on the retina by the cornea and the lens

define myopia

nearsightedness - you can see close up but not far away

characteristics of myopia

• common among people

• accommodative system is too strong

• the light is focused in front of the retina - too close to the lens

• could mean that the eyeball is too short

how do you correct for myopia

with a concave lens to diverge light slightly before it hits the lens

• diverges the light slightly to move the focal point back

what are late onset myops

someone who is fine throughout elementary school and develops myopia later in life

define hyperopia

farsightedness - you can see far but not close up

what are the characteristics of hyperopia

• the cornea and the lens are too weak

• the light is focused behind the cornea and light is too far from the lens

how do you correct for hyperopia

use a convex lens to converge light to the lens and hit the retina

• moves the focal point closer

• you need more converging of the light

define astigmatism

someone has multiple focal points

• mainly the cornea or lens

characteristics of astigmatism

• no matter the orientation the curvature is still the same (if the lens is basketball shaped)

• the orientation will change the curvature (if the lens is football shaped)

how do you correct for astigmatism

the individual will be given an axis

• the lens given to the individual will be stronger on one axis than the others

define presbyopia

• elder vision/old eyes

• lens can yellow

• lens could cloud

when does presbyopia occur and who gets it

• usually late 30s/early 40s but could start in late 20s

• everyone

what does it mean if the lens yellows

there are a lot of layers of the lens built up

what does it mean if the lens clouds

you have developed cataracts

how to treat for cataracts

surgery

• emulsify the cataract and replace the lens with a haptic

• the new lens will ever focus the exact same

define senile miosis

as we age, the maximum dilation of the pupil decreases

• most likely related to a muscular thing (iris)

• we wont see as well at night with age without artificial light (sunglasses at night)

define sclerosis and its characteristics

the lens hardens

• tougher to move the lens

• eventually the lens gets locked in place

• makes it harder to see up close

what does it mean if you have an increased number of floaters

buildup of proteins that flake off in the vitreous in the eye

• aka biojunk

how do floaters act

• they move with you

• sometimes they are noticeable and sometimes they arent

what can reflect light (floaters)

anything floating around in the eye

is there is fix for floaters

no - they are there for life

who was Lord Maskelyne

• royal astronomer

• said that he was myopic only at night

• main scientist who was studying longitude

what are the parts of “night myopia”

• myopia - blur aspect

• night - light aspect

how was night myopia classified

anomalus myopia because there is no known cause

• only some people had this

what is the resting state concept

every muscular system has a resting state

• the preferred state it wants to be in

what are the characteristics of the resting state

• takes no effort to be here (its a preferred location)

• its the starting point for effort or activity

give an example of resting state

raising your hand

what is fatigue

extended effort

what is classic theory

states that accommodation rests at the far point (infinity)

who were the scientists behind classic theory and what was the issue

Donder and Helmholtz

• they studied people that were dead

what is modern theory

accommodation rests at an intermediate distance

who was the scientist behind modern theory

schoberg

what is a laser optometer

measuring accommodation without stimulating it

what are the characteristics of a laser optometer

the speckle pattern of a laser doesn’t accommodate stimulation

• some people have speckles that move with it while others say it moves opposite

  • this depends on the distance you are viewing the laser from

• you can see the speckles but not focus on them

• there is a distance that the speckles dont move at all

what is dark focus

its the study of speckle movement from a laser

what are the characteristics of dark focus

• it changes with age

• there is variability

• it uses modern theory

what does dark focus state

if there isnt a strong stimulus, we will go towards our resting state

• none of us know our resting state of accommodation

what is the average dark focus

23 - 24 inches

who were the scientists behind dark focus

Leibowits and Owens

what is the resting state of vergence

the inward turning of the eyes

• dark focus where your eyes are focused to a distance in the dark

what is dark vengence

aka nonius alignment technique

• you flash 2 lights in the dark and the subject continues to move them until they align with one another

• is variable

• said to be an intermediate distance

what was the average distance of dark vengence

around 27 inches