Ocular Physiology Flashcards
What type of blinking is most common?
Spontaneous.
How many blinks is normal per minute?
12-15
What part of lid does spontaneous blinking?
palpebral
Reflex blinking nerves
CN II dazzle and menis. CN V-irritation CN VIII-loud noises.
What part of eye does reflex blinks?
palpebral
Which is the only reflex that does not involve the cortex?
Dazzle. All other begin in the frontal lobe.
What causes voluntary blinking
palpebral and orbital.
Benign essential belpharospasms
Contractions of orbiculares oculi, procures, and corrugated.
Bell’s phenomenon
Upward and out eye with forced closure
Which glands can increase secretion with blinking?
Meiobomian
What do accessory lacrimal glands do?
Basal or maintenance tears
What does the main lacrimal gland do?
Reflex or emotional tearing
Which glands help with lipid layers?
Meiobomian, Zeiss, Moll.
Horners
Contractions on closure and shortens the cannaliculi
How does blinking help tear film
Goes from lateral to medial
How many eyelashes do we have
150 on top and 75 on bottom
What is lipid layer made of
fatty acids, cholesterol, waxy esters.
How do tears change with age?
Decrease in lysozyme and lactoferrin and decreased aqueous protection
What does contact lens wear do?
Increases electrolyte and protein concentration due to tear evaportion
How do tears change under closed eye conditions
Increases IA and serum albumin
How are mucin layer unique
Capable of mixing with lipid and water.
Where are goblet cells found?
Inferonasal fornix and bulbar conj (most temporal)
What do goblet cells need for development
Vitamin A
Bitot’s spots
foamy build up of keratin on the cornea. Caused by vitamin A deficiency.
Lipid soluble vitmins
DEAK
Antioxidants
ACE
Water soluble vitamins
B and C
What is TBUT evaluating
The tear film evaporation due to an inefficient lipid layer
What does the mucin layer interact with
glycocalyx of the epithelium.
Normal tear production per minuts
1 ul/min.
Normal tear film osmolarity
308
Main ions to osmolarity
Na and K
How does DES affect tear osmolarity
Increase is osmolarity
What kind of drops would you use with DES
hypotonic. More water.
Potassium concentration in tears
Very high! helps to maintain health of corneal epithelium.
Average pH of tears
7.45
pH of tears when sleeping
decreases
pH of tears with DES
increases due to increased osmolarity
What are most ophthalmic drugs
weak bases.
Stapedius muscles
Dampen sound. Innervated by CN VII
Vestibule
Linear VOR. Movements of head or body from side to side.
Semi-circular canals
Angular VOR. Rotation movements of the body or head.
Saccades
contralateral and FEF and SC. EX: Right FEF controls saccades to the left
Pursuits
ipsilateral parietal lobe. Right pursuit driven by right parental lobe.
VOR
Your body is moving!
How are the layers of the cornea in response to water
Epithelium: lipophilic, stroma: hydrophobic, endo: lipophilic.
UV c
200-290
UV B
290-320
UV A
320-400
What absorbs from 200-300
Cornea (epi and bowman).
What absorbs from 300-400
Lens
What absorbs from 300-350
vitreous
What absorbs above 400
retina
What vitamin helps the lens
Vitamin C
What does the precise spacing in the lens do?
Destructive interferance
Corneal desturgence
The relative dehydration of the cornea
Epithelium Pump mechanism
Na in and Cl, H20 and K+. Out. Has an Na/K ATPase pumps that puts NA in stroma and NA/K/CL cotransporter Will then pump K in aqueous and CL in epithelium which then leaves with H20.
Endothelium Pump Mechanism
Pumps NA in and Cl, water, and bicarbonate out. Use an NA/K ATPase pump.
Major factors in corneal desurgence
Na in and Cl, and H20 out. (bicarbonate in endo).
K+ factor in corneal dusurgence
The sensor.
Partial pressure of O2 in the eyes with open conditions
144 mm HG
How does eye get oxygen during closed eye conditions
Palpebral conj, aqueous humor
Critical PPO2 for the cornea
10-20 mm HG.
Transmisibility
DK/t. How much oxygen will diffuse over a given thickness.
Nutrition for cornea
glucose is low in tears but high in aqueous humor. Corneal epithelial cells can also store glycogen for mitosis.
How many days for cornea to regenerate
7-14 days.
Steps when trauma to cornea happens
Mitosis in basal stops, squamous cells migrate, mitosis increases rapidly.
How long for healing if BM is damaged
8 weeks
Why can corticosteroids and tetracyclines be used for RCE
MMPs degrade hemidesmosome formation and these drugs stop that from occurring and help formation
Which layers cannot regenerate
Bowman’s and endo.
Which layer can regenreate
epithelium and descents.
Does the anterior or posterior lens change more in curvature with accommodation?
The anterior
What structure has the most protein in the body?
The lens.
How does the lens maintain it’s water balance
Na/K ATPase pump. Na leaves and water follows.
Resurgence in Epithelium vs. lens
Epithelium pumps NA in and Cl and H20 out. Lens pumps Na out.
How does lens get energy?
Anerobic metabolism. Has lots of hexokinase.
What happens with diabetic cataract?
Excess sorbitol in the lens.
Glutathione
Good for the lens.
Absobic Acid
Vitamin C. Also protects from damage.
What layer of lens can do aerobic respiration
epithelium.
Why is there a large amount of lactate in the lens?
Large amount of anerobic metabolism
Which part of the lens has the sutures?
Fetal
Which part of the lens needs the greatest energy and nutrients?
Anterior epithelium (why it is good that it can do aerobic respiration)
What type of collagen is in the lens
Type IV.
Where is the lens capsule thickest
Front
What contributes to cataract formation
Decreases glutathione, decrease in crystallin factors, and an increase in Ca.
Which part of lens has the highest refractive index
The embryonic.
Aqueous humor secretion and age?
Decreases
Choroid has a high concentration of protein. Why?
To create a gradient that will absorb excess H20 from the retina and into the choroid
What type of collagen is the viterous
Type 2
Gag in the viterous
Hyaluronic acid.
Vitamin C in the viterous
Very high.
Metabolic function of the viterous
No metabolic function so instead acts as a metabolic buffer and storage area
Where in the vitreous is collagen highest
Near the base.
How does hyaluronic acid change with age
increases (liquidifaction)
Perfusion pressure
Parteries-Pveins
What are two factors causing resistance
Autonomic and autoregulation
what are two things that can autoregulate
ON axo flow and retina. Pericytes control this.
What does sympathetic cause
vasoconstriction
what does para cause
vasodilation
Ocular perfusion pressure
Diastolic pressure-IOP.
Critical closing pressure
The pressure where the blood vessel collapse and blood flow stops.
Transmural pressure
Pressure across the vessel wall. Pressure outside vs. inside vessel.
Does the sympathetic system affect retinal blood flow?
NO! DO not innervate the CRA past the lamina cribosa. Do innervate uvea though. If there is a sudden increase in BP then the sympathetic will constrict the uveal blood vessels to decrease flow
Parasympathetic system and retinal blood flow?
Parasmpathic is most prevalent in uveal tract. Minimal influence on choroidal and retinal blood flow. Causes vasodilation with drop in blood pressure
IOP must be ______ that the episcleral venous pressure
Greater. Allows outflow
IOP must be _____ than the ICP
Greater. Allows axoplasmic flow.
IOP must be _____ than the retinal and uveal arteries
Lower. Allow nutrients to be delivered
Which vessels in the uvea are fenestrated
MACI and choroidal capillaires
Blood supply in the fovea
Avascular so supplied by choriocapillaris
Blood retinal barrier
Blood vessels of retina and RPE
How does light absorption change the photopgigment
goest from 11-cis-retinal to all-trans-retinal.
Recycling of the photopigments
11-cis-retinal->all trans retinal–>all trans retinol–>RPE–>11 cis retinol–>11-cis retinal.–>photopigments
Dark Current
Na coming in and out. Depolarizes the photoreceptor
What happens with light
CGMP closes the Na channel and hyper polarization occurs and does not produce glutamate.
Gaba and Glycine
Inhibitory. Amacrine and horizontal.
Which cells are off cells
photoreceptors, off center bipolar, horizontal. All hyper polarize in response to light. Less glutamate
On center bipolar
Depolarizes in response to light. Normally inhibited by glutamate.
Off center bipolar
hyper polarize in response to light. Excited by glutamate so less=hyper polarize
Rod bipolar
Always ON. Depolarize to light.
Horizontal cells
Off cells. Hyper polarize to light. No center surround.
Amacrine cells
On center. Depolarize to light. Have center surround.
On center ganglions
synapse with on center bipolar and depolarize to light.
Off center ganglions
synapse with off center bipolar and hyper polarize to light.
Action potentials
All or nothing response-Amacrine and ganglion are AP. All others are not
Graded potentials
Determined by amount of photons absorbed. All but ganglion and amacrine.
Pyramidal motor pathway
complicated voluntary movements.
Medulla
Where most pathways cross. Above is contralateral. Below is ipsilateral.
Reticulospinal
Complex voluntary movement
Tectospinal
Uses the SC
Spinalthalamic
Hot pain.
Trigemothalamic
pain and hot from face.
Medial lemniscus
Touch, pressure, vibration.
SNS roles
vasodilation in skeleton muscle, dilates the bronchioles, increases blood glucose levels.
Preganglionic SNS
Release acetycholine
Post ganglionic SNS
Releases Norepinephrine
Which is the only gland innervated by preganlionic SNS
Adrenal gland
What does PSN release
acetylcholine for both
When do you use CT
bone, calcium, or emergency. Look at ca density.
When do you use PET
cancers. Looks at glucose uptake
When do you use MRI
soft tissue, look at mobile protons-more water-diseased tissue.
Where is the LGN located?
Thalamus.
Is LGN simply a rely station?
NO! Is is also a center for processing input from multiple sources and deciding what is sent to V1
Who does LGN receive input from?
Optic tract, SC, V1 (last two are feedback)
Which layers of LGN receive mango? Parvo? Konio?
Magno=1,2 Parvo=3-6 Konio=inbetween
Which layer are ispliateral in LGN
2,3,5
Which layers are contralateral in LGN
1,4,6
Where is the first area that binocular processing occurs?
V1
Medial to lateral in lgn
fovea->peripheral vision
Anterior to poster in LGN
inferior to superioer
Dorsal to vental LGN
Same spot in the VF
Optic radiations of inferior
Temporal lobe in meyer’s loop
Optic radiation of supeior
Parietal lobe.
Parvo cells
Sensitive to red green, fine details, and slow motion but have a slower transmission speed
Magno cells
monochromatic and are most sensitive to fast movements and large details.
Visual Cortex
Striate cortex, boardman 17 or V1.
layer 4 of visual cortex
receives input from optic radiations. Have ocular dominance columns.
Layer 3 of visual cortex
Axons to other cortical layers
Layer 6 of V1
Sends feedback back to LGN
Function of V1
examine basically features before relaying information to more complex processing centers (v2-v5)
Layer 5 and 6 of V1
subcortical areas (SC, Thalamus, midbrain, pons)
V2-V5
Responsible for complex processing. Includes IT (what) and MT (where)
SC
Receives input from V1 and fibers that exit the optic tract. Controls saccades, visual orientation, and foveation.
FEF
Only receives information from V1. Does near response and saccades.
Simple Cells of the Visual Cortex
respond to orientation of stimuli. Have elongated center surround
Complex cells of the visual cortex
Respond to motion and orientation. NO center surround.
Hypercomplex cells
Process combined input from multiple cells
How does V1 process information
heriarchialy.
EOG
Measures the health of the RPE
Arden ratio
EOG. The ratio of light peak to dark trough
What arden ratio do we want
Above 1.80
ERG
Looks at activity of outer retinal layers. No ganglion cell layers.
A wave
negative and photorceptors
B-wave
positive and bipolar and muller
C-wave
positive and RPE
How to isolate rod function on EOG
Blue flash with a slow flicker in a dim background
How to isolate cone function on EGO
Red flash with a fast flicker in a bright background.
Pattern ERGs
Target the ganglion cels
VEP
Latency of brain activity to visual stimulus
Normal VEP
100 sec
What always causes anisocoria
efferent pathway problem
Near response
FEF gets input from V1 and synapse with EW (no pretectacl)
SNS and EW
Sympathetic fibers inhibit the EW from constant parasympathetic features.
Goldman measurement
Based on elasticity of the cornea. Based on cornea thickness of 520.
Thick corneas on goldman
Overestimate
NCT
Time
Pascal
Contour. Do not take corneal thickness into account
Average IOP
15
How to decrease IOP w/o topical
Exercise, drink beer, marijuana.
When is IOP highest
330-530 AM
How often is the total volume of the aqueous replaced
every 100 minutes
Uveoscleral is Presure _____ while corneal scleral is Pressue _______
independent dependent
What are two conditions that can increase episcleral venous pressure
Spurge-Weber and arteriovenous fistulas.
Osmolarity of the aqueous
Slightly hyper osmotic to plasma due to bicarbonate.
How can aqueous be made? What is the main one?
Diffusion, ultrafilteraion, active secretion. Active secretion.
Pumps that make aqeuous
NA/K atpase pump pumps NA into the posterior chamber. Bicarbonate is also made and causes water and Cl to follow.
What can cause covering of the TM
Diabetes, CRVOs, Uveitis, hyphema
What can cause injury to the TM
Fuchs heterochromatic iritis, glaucomatocyclic crisis (trabeculitis that can cause damage), angle recession glaucoma.
Occlusion of the TM
Pseduoedcofiliative glaucoma or Pigment dispersion glaucoma.
