The Eye and How It Works pt 2 Flashcards
OD
Right Eye.
Oculus dexter: OD
OS
Left Eye.
Oculus sinister: OS.
OU
Both Eyes.
Oculus uterque: OU.
PRN
When necessary/as needed.
Pro re nata: PRN.
STAT
Immediately.
Statim: STAT.
Gtts
Gtts.
Guttae: eyedrops.
SX
Sx.
Surgery. (can also mean symptoms)
Dx
Dx.
Diagnosis
Fusion
two eyes that work together to give one image. Delicate balance!
Binocular vision
Ability of the eyes to fuse two images into a single image.
Balance of motor and sensory function.
-Equal impulses to each eye.
-Contraction of muscle equivalent to relaxation of opposing.
Suppression
Ignoring of the blurred image. Clear image and blurred image cannot be fused.
Overlap
Seeing more with two eyes than one.
Apprrox 35° of vision is overlap
Locking device - Merges peripheral vision to ensure central fusion.
Fixation
Looking straight ahead.
Requires stability and good monocular function (each eye has to work independently).
Fixation can be impacted by (3)
Nystagmus.
Macular Disease.
Strabismus.
What is strabismus?
misalignment of 2 eyes not pointing in the same direction
diplopia
seeing double
What happens in strabismus? (4)
1- diplopia
2 - Amblyopia develops b/c stronger eye takes control
3 - one eye points in a different direction from other
4 - brain is forced to choose an eye to focus with
Fusion
both eyes focusing together
Fixation
One eye focusing
How is fusion disrupted?
by covering an eye
heterophoria
the direction the eyes point at rest
esophoria
eyes turned inward
exophoria
eyes turned outward
hyperphoria
one eye is pointed a little higher than the other
convergence
eyes come together to look at near objects (reading, etc)
Positions of Gaze.
Primary Positions - Straight-ahead position.
Secondary Positions - Horizontal or vertical movement (looking up, down, L or R)
Tertiary Positions - Oblique movement (eyeroll)
Duction
Movement of ONE eye from one position to another.
Version
Movement of two eyes in the same direction.
Lateral Rectus
Moves eye horizontally away from nose.
Abduction.
Medial Rectus
Moves eye towards nose.
Adduction.
Intorsion
Right Eye moves from 12:00 to 1:00.
Primary Action: right superior oblique.
Secondary Action: right inferior rectus.
Extorsion
Right Eye moves from 12:00 to 11:00.
Primary Action: right inferior oblique.
Secondary Action: right superior rectus.
Superior Rectus
Elevates eye.
Intorsion,
Adduction.
Inferior Rectus
Depresses eye.
Extorsion,
Adduction.
Superior Oblique
Intorts eye.
Depression,
Abduction.
Inferior Oblique
Extorts eye.
Elevation,
abduction.
Volition
Frontal lobe of brain.
rapid, high speed movement of the eye that ends quickly (like a quick eye turn)
Don’t get visual info from this
pursuit
watching something move (like watching a plane move across the sky)
occipital lobe
slow, smooth, gliding motion of eye - DO get visual information while moving
Vergence
Simultaneous ocular movements in which the eyes are directed to an object in the midline in front of the face.
Convergence.
Rotate inward.
Constriction of pupils.
Accommodation.
Divergence.
Rotate outward.
Accomomdative triad
convergence
pupillary constriction
accommodation
What happens in convergence in the accommodation triad?
alleviates diplopia (double vision) and moves the eye to an object
What happens in pupillary constriction in the accommodation triad?
formation of pinhole
What happens in accommodation of accommodative triad?
brings object on retina
monocular depth perception cues
Magnification (comparing size of 2 objects)
Confluence of parallel lines (railroad tracks)
Interposition of shadows (big vs small shadows)
Blue-gray mistiness of objects at greater distances.
Parallax (looking at movement of 1 object)
stereopsis
Higher quality of binocular vision.
Each eye views at object at slightly different angle.
Therefore: Fusion of images occurs by combining slightly dissimilar images.
Range of focus
Range an object can be seen without accommodation (20 feet or 6 meters).
aka - the distance where the eye doesn’t have to work to focus
Range of Accommodation.
Distance an object can be carried to eye and kept in focus.
Continual readjustment.
Power of accommodation.
Dioptric equivalent of that distance (range of accommodation)
What stimulates accommodation
blurred image on retina
measurement for accommodation
Range and power of accommodation.
Closest point of an accommodative target.
Range = cm.
Power = diopters.
Steps of accommodation (4)
Object moves closer to the eye.
Light must be converged.
Contraction of ciliary muscles zonular fibers relax.
Lens changes shape.
6 pieces of the transparent pathway of light
1 -tears
2- cornea
3- aqueous humor
4 - iris
5- lens
6 - vitreous body
three layers of tears
Oil/Lipid.
Aqueous.
mucin
oil/lipid layer of tears
Outtermost layer.
Meibomian Gland.
Evaporation.
Mucin.
Innermost layer.
Goblet cells.
Tiny irregularities.
Mirror-like finish.
How much tears are produced daily?
.5-1 mL of tears produced daily.
Aqueous.
Middle layer.
Lacrimal Gland.
Accessory lacrimal glands in conjunctiva.
Inorganic matter and salts water
Where do tears go?
50% Evaporation.
Other 50%:
Inferior and superior puncta.
Nasal lacrimal duct.
Inferior meatus of nose.
lysozyme
nonpathpgenic bacteria
formation of tears
psychic (caused by emotion)
reflex (cause by uncomfortable retinal stimulation such as when your eyes are dialated)
Cornea - as transparent pathway of light
light must go straight through all 5 layers
no opaque substance
Where does cornea get nourishment since there are no blood vessels?
perilimbal vessels (where conjunctiva meets cornea)
tear film
aqueous humor
edema
swelling
cornea hydrated or not hydrated?
hydrated
sclera - hydrated or not hydrated?
not hydrated
What does the corneal epithelum do?
fast, regeneration of cornea
what does corneal endothelium do?
creates a dam so that there is homeostasis in the eye
What three layers of the cornea can regenerate?
epithelium (no scarring)
Bowman’s layer
Stroma
Aqueous Humor location
between cornea and lens
What is aqueous humor
clear, colorless, watery
Where is aqueous humor formed?
ciliary process behind iris
How does aqueous humor move?
constant circulation
How is aqueous humor formed?
Posterior Chamber -> Pupil -> Anterior Chamber -> Trabecular Meshwork -> Schlemm’s Canal -> Aqueous Veins -> Veins -> Neck -> Heart.
Starts from blood, goes back to blood
How is intraocular pressure measured?
tonometer
What is normal intraocular pressure
13-20 mmHg
Ocular hypertension
intraocular pressure too high
what can change intraocular pressure
respiration (breathing can change pressure by 5 mm Mg)
pulsation
Daily change (2-3 mm Hg)
When is intraocular pressure highest?
6am (generally thought to be due to dehydration)
What does intraocular pressure depend on (2)
amount of aqueous humor
hydration
What is the “shutter” of the eye
iris/pupil
What does the pupil respond to (3)?
arousal (fear, anxiety, erotic stimulation)
direct
consensual (if one eye dilates, so does the other)
What does excessive illumination do to the pupil
activates sphincter muscle to make pupil smaller
What does poor illumination do do pupil?
Activates dilator muscles to make pupil larger and let more light in
Two parts of lens
nucleus (inner part - formed by age 30)
cortex
lens refraction
uniform index refraction - light gets bent 1 way going hrough lens
What nourishes lens
aqueous surrounding it
Vitreous body location
directly behind lens
vitreous body is made of?
transparent gel - makes up about 2/3 of eye
Function of vitreous body
shock absorber
“space between the film”
scotopic
night vision
rods
125.000.000
dim light
photopic
cones (red, green, blue)
straight ahead and color vision
fovea
How do we adapt to dark?
rods - 30 minutes in dark for full activation
rhodopsin
visual purple
destroyed by light
vitamin a
light and the retina
Light.
Photoreceptors.
Bipolar cells.
Ganglion cells.
Retinal synaptic zone.
Axons.
Through optic nerve.
Chiasm.
Optic Tract.
Lateral Geniculate Body.
Occipital Lobe.
positive after images
retinal images
short duration (microscopic movements)
little awareness due to constant eye movements
same color as last color seen
negative afterimages
what you see when you have a flash of light from a picture
retinal photoreceptors are unresponsive after high intensity light
used to test for strabismus
Three pigments of color
red, green, blue
frequency of color blindness
males - 8%
females - less than .1%
How does color blindness develop?
sex linked recessive trait
trichromat
normal color vision
anomalous trichromat
partial deficiency in 1 cone pigment
protanomaly
deficiency in red
poor red-green and blue-green discrimination
dueteranomaly
deficiency in green
poor green-purple and red-purple discrimination
dicromat
complete deficiency in one pigment by preserves the remaining two pigments (protanopia, deuteranopia or tritanopia)
protanopia
no red receptor
deuteranopia
no green receptor
tritanopia
no blue receptor
