Ocular Physiology Flashcards
Most common type of blinking
Spontaneous
-Contraction of palpebral portion
Reflex blinking and what parts of the brain controls each
CN 8- auditory. Frontal lobe/cortical input
CN 5- touch and irritation. Frontal lobe/cortical input
CN II- menace and dazzle. CN 7 efferent response.
3 types of blinking
Spontaneous, reflex, and voluntary.
What contributes to the lipid, aqueous, and mucin portions of the tear film
**but remember the new model suggests 2 layers total: lipid + mucoaqueous
Lipid:
Meibomian glands (holocene, sebaceous)
Zeiss (holocene, sebaceous)
Moll (procaine)
Aqueous
Main lacrimal gland (merocrine)
Krause (in the fornicil conj, merocrine)
Wolfring (in the tarsal conj, merocrine)
Mucin
Epithelial cells of conj and K that produce the glycocalyx
Goblet cells- high concentration caruncle, bulbar conj IN and temporal, ABSENT at the limbus.
Aqueous layer of the tears
- What is the main component?
- What nutritional components
- what protective components
Water is the main component
Na+, Cl-, and K+
-Same amounts of NaCl as the blood, MORE K+ (4x than the blood)
Protective: Lysozyme- anti peptidoglycan Lactoferrin- FE chelating IgA Beta Lysin works with lysozyme.
Normal pH of the cornea
-how does it change with sleep?
7.45
Sleep –> Less O2 –> Anaerobic respiration –> acidic byproducts –> decrease pH
Lipid layer composition
Fatty acids, cholesterol, waxy esters.
released by blinking and the paraymp NS
What portion of the tear film is capable of mixing with lipids and water
The mucous layer. This allows the mucous layer to mix with aqueous layer of the tears and spread evenly over the hydrophobic corneal epithelium.
Goblet cells require ___
Without, what occurs?
Require vitamin A.
Without = bitot spots/keratinization of the conj
___ is the most common cause of mucous fishing syndrome
dry eye
tear film thickness Tear film volume Max tear film volume Average tear production per minute Average eye drop volume
3 micrometers 7-9 microliters Max is 20-30 microliters Avg tear production/min: 1 microliter Eye drop: 50 microliter
normal tear film osmolarity
308 mOsm/L and is isotonic to the healthy cornea surface
Na+ and Cl- in the tear film are the main contributors to osmolarity
Dry eye syndrome causes a ___ in tear film osmolarity
Increase, meaning that the tears are pulling fluid from the K.
Use HYPOtonic eye drops with osmolarity around 150, which is way less than 308, the normal isotonic value of tears and K
Most topical eye drops are
- weak ____ (acid or base)
- Ionized or non ionized?
Weak bases
Non-ionized form to promote drug absorption across the hydrophobic K epidemic and endothelial.
How is the external ear separated from the middle ear?
What about the middle ear from the inner ear?
Tympanic separates external from middle
Oval window separates middle from inner
Roll of tympanic membrane
Separates external from middle ear
Amplifies sound waves by 10-20x
Auditory ossicles
-What are they and where are they located
Middle ear
Don’t MIS these
Malleus, incus, and stapes from anterior to posterior.
They amplify and transmit vibrations from the tympanic membrane.
Which two muscles dampen the amount of vibrations placed on the auditory ossicles?
Stapedius: innervated by CN7.
The stapedius stops the stapes
This means that it dampens the amount of vibrations
Tensor Tympani- Innervated by a branch of V3
Role of the inner ear and components
Converts mechanical vibrations into neural signals.
Contains the bony labryinth which has 3 parts- cochlea, vestibule, and semi-circular canals. All innervated by CN 8
Cochlea: Contains organ of cortical and contains hair cells.
Vestibule: Contains utricle and saccule that help maintain balance. They detect linear acceleration and cause linear VOR (reflex eye movements that are equal and opposite to the motion of the head) Utricle is horizontal, saccule is vertical.
Semi circular canals: Communicate with the vestibule and contain ampullae that detect angular acceleration/rotational movement and cause angular VOR
Saccades
- What are they
- Controlled by what portions of the brain
- Contra or ipsi
Rapid eye movements that maintain fixation on the object
Controlled by contra FEF in the frontal lobe and superior colliculus
Ex: Right Frontal lobe controls saccades to the left.
Pursuits
- What are they
- Controlled by what portions of the brain
- Contra or ipsi
Smooth tracking movements that maintain foveation on slow moving objects
Controlled by ipsi parietal lobe.
Right pursuit controlled by right parietal lobe..
Control of vergence is where in the brain and driven by what
Brainstem driven by retinal disparity
is the K epi hydrophobic or Phillic?
what molecules are allowed thru?
What about the stroma and endothelium?
K epi and endothelium are highly hydrophobic
Limit the absorption of hydrophilic and ionized
Absorb hydrophobic and non-ionized.
Epi is hydrophobic
Stroma is hydrophilic
Endo is hydrophobic
Which layer of the K contains macula occludens
Endothelium
occluder- kids and water will peak thru
UV A, B, and C ranges
What parts of the eye absorb each
C is 100-280
B is 280 to 315
A is 315 to 400
cornea and bowmans absorbs UVC and most of UVB (under 300)
Lens absorbs
UVA is absorbed by the lens
Wavelengths greater than 400 are transmitted to the retina
Less than 300- K and bowmans
300-400 lens
300-350 vitreous
400+ retina
Factors that contribute to minimal light scattering in the cornea
Corneal crystallins- located in the cytoplasm of the epithelial and endothelial cells. Maintain K transparency by limiting light scattering. Similar to lens
Ascorbate (vitamin C) and glutathione- Protect from UV and free radicals
Collagen fibers lay in a network of GAGs. The collagen have a unofmr size and precisely spaced less than half the wavelength of visible light from one another. Proteoglycans and high water content help maintain appropriate collagen spacing.
Avascular
What is a proteoglycan
-What is the main one in the K
Core protein with one or more covalently linked GAG. Sulfonation of the GAG side chain helps the proteoglycan bind to water. Creates hydrophilic environment and keeps spacing.
Keratin sulfate.
Deturgescence relies on what two layers of the K
Endo and epi
What types of pumps are on the K epi that help with deturgenence and how does it work?
Na/K ATPase pump and Na/K/Cl co transporter.
Na+ passively enters the K epi
Na+/K+ ATPase actively moves Na+ into the stroma to create gradient
Na/K/Cl transporter uses the gradient to move all 3 ions into the epi.
Cl- and K+ diffuse back into the tears and water will follow, contributing to the dehydration of the K. **K+ is important bc Cl- follows it, and water follows that
K+ is very sensitive to pH. A hypoxic K will result in less K+ movement into the tears. Therefore, less Cl- and water are moving into the tears. Results in K swelling and increased K thickness.
Macula occludens and adherins
Occludens are located on the ednothelium
Adherins are like desmosomes, spot weld
How does the pump system on the endo work to contribute to K deturgesence
Na+ is moved into the endothelium by the Na+/K+ ATPase pumps. K+, Cl-, and bicarb are pumped into the aqueous. Water follows.
Overall picture of deturgesence
Na+ is transported into the stroma.
K+, Cl- and bicarb are pumped out into the tears and aqueous. Water follows.
K+ is very important and highly responsive to pH. Any change in pH results in K edema.
3 factors that influence K deturgesence
Epi pumps
Endo pumps
Aquaporins located in the epi and endo and regulate bi-directional water transport.
Mild K edema in the morning is due to what
Build up of lactate from anaerobic respiration
Critical PPO2 for the K
10-20mmHg
CL worn while sleeping just have PPO2 above this level.
Dk/t
Dk- Oxygen permeability, depending on the material. x 10^ -11. Higher Dk means the faster O2 will travel thru the material.
t- thickness of the material. Measured in cm.
Dk/T is the transmissibility x10^-9
Decreased O2 leads to
Accumulation of H+ ions resulting in increased acidity of the corneal cells. This means the pH decreases. This causes a change in K+ channels– causing massive efflux of K+ from keratocytes with subsequent collagen damage and scar formation.
(K+ exiting the K is necessary, but not in huge amounts due to change in pH)
3 ways glucose is produced in the K
Anaerobic glycolysis (85%)
Aerobic glycolysis
Hexose monophosphate shunt
What supplies O2 to the cornea during open and closed eye conditions
Open- oxygen supplied to ALL LAYERS by the atmosphere
Closed- anterior K supplied by the lids, posterior K supplied by the aqueous
What supplies nutrients to the K
Aqueous supplies nutrients to ALL LAYERS
AA, glucose, and vitamin C
Remember that the lens rarely has any nutrients (high water and K+ content)
What corneal layer can store glycogen
Epi
__ cells are the only mitotic cells in the epi
Basal
derived from differentiating limbal stem cells in the palisades of Vogt
Trauma to the K what happens
- Basal mitosis stops
- Fibronectin serves as scaffolding for epithelial cells to migrate over the wound. Hemidesmosomes help attach epi to BM
- Basal cell mitosis resumes at rapid rate.
*healing will occur more slowly if BM is damaged. Usually due to sharp cut or fingernail.
healing time of K epi
Healing time of K BM
7-14 days
8 weeks
What prolongs the resolution of an abrasion involving the K BM?
What causes it to take so long- 8 weeks?
MMP degrade hemidesmosome formation, which attaches the basal epi to the BM.
Steroids and tetracycline decrease MMP activity, spending up recovery time.
Which 2 k layers CAN regenerate? which two CANNOT
CAN- Epi and descemets
CANNOT- bowmans and endothelium (Bowmans was made during gestation by the anterior stroma)
Neurotrophic Keratitis
What is it and what causes it
CN V damage, decreased K sensitivity, dx with cotton swab test
HSV, HZO, stroke, DM
What contributes to the dioptric powers of the eye
K- 2/3
lens- 1/3
Which part of the eye contains the largest concentration of proteins in the body
Lens
To make the protein, the lens requires a lot of glucose and oxygen from the aqueous.
What pump does the lens have? How does it regulate water
Na+/K+ ATPase pump moves Na+ into the aqueous and K+ into the lens. Water follows Na+ into the aqueous = more transparency of the lens.
Aging changes of the choroid
Bruchs membrane increases with age and drusen accumulates in the inner collagenous membrane
Choriocap decreases in thickness
Overall thickness of the choroid decreases with age
Does the concentration of hyaluronic acid in the vitreous increase or decrease with age
Increase
Flow of hemodynamics equation
Flow = pressure of arteries entering - pressure of veins exiting / resistance
Perfusion pressure
How easily blood can pass through a given tissue.
Difference between the pressure of blood flow entering and leaving the eye.
Approx 50mmHg
Directly related to diastolic BP, indirectly related to IOP
Ocular perfusion pressure formula
Diastolic pressure - IOP
If OPP is below 50, the patient could be at risk for glaucomatous changes or ischemia to the ONH.
Which 2 areas of the eye have autoregulation? What cells allow this to happen?
Retina and ONH due to pericytes.
Autoregulation allows blood flow to be maintained at a constant rate despite moderate variations in the mean arterial pressure and the IOP.
Transmural pressure
Pressure across the blood vessel wall. Subtract pressure outside the vessel from the pressure inside the vessel
Critical closing pressure
Pressure at which blood vessel collapses and blood flow stops.
Elevated IOP in acute angle closure causes a reduction in blood flow through the CRA –> decrease in perfusion pressure. Retinal vessels respond by dilating through autoregulation. If IOP remains high long enough, the CRA will reach its critical closing pressure = CRAO.
Immediate threat to vision in acute angle closure
CRAO
Sudden spike in blood pressure causes an increase/decrease in sympathetic system and vasoconstriction/dilation of the uveal blood vessels
high BP –> increase in sympathetic system –> vasoconstriction
Sudden decrease in blood pressure causes an increase/decrease in parasympathetic system and vasoconstriction/dilation of the uveal blood vessels
Decrease in BP —> Increase parasympathetic –> vasodilation of the uveal blood vessels
If IOP is 15, should the pressure be higher or lower in the following:
Episcleral veins
Intracranial pressure
Retinal/uveal arteries
Episcleral veins - must be lower pressure. Higher pressure would cause back flow of aqueous –> increase IOP.
Intracranial pressure - must be lower than IOP for axoplasmic flow to occur. Higher pressure would cause papilledema.
Retinal/uveal arteries- Must be higher than the IOP. If IOP was higher, then it would compress the retinal arteries and cause ischemia.
Axoplasmic flow
Flows from the eye to the brain. This requires a higher eye pressure than brain pressure.
If brain pressure is higher than eye pressure, papilledema will occur. Cerebrospinal fluid will spill from the subarachnoid space onto the optic disc margins and surrounding RNFL.
Protein content must be highest in the choroid vasculature. Why?
So excess water is pulled from the retina, across the RPE, and into the choroid. This promotes the adherence between the RPE and neurosensory retina.
the majority of blood flow in the ocular vessels occurs where
Choriocapillaris
Primary responsibility of the choroid
Provide outer retina with nutrients such as oxygen, glucose, and vitamin A
Fan
Where does blood flow after the major arterial circle of the iris
MACI (fenestrated) in the CB–> Minor arterial circle (non fenestrated) of the iris in the iris stroma –> pupillary margin
and then back again
watershed layer of the K
OPL gets blood supply from CRA and choroid
Capillary systems of the CRA are in which layers
RNFL and INL (larger)
Capillary free zones
Center of the fovea (cannot have CWS or hemes)
Surrounding arteries
Ora
In rods, where is rhodopsin located
In cones, where is iodopsins located
Rods- within disc
Cones- stored in invaginations of the plasma membrane, not within the discs.
Cone and rod visual pigments contain what basic structure
Both contain an opsin- membrane apoprotein that allows for a varied absorption spectrum. Cones have cyanolabe, erythrolabe and chlorolabe. Rods have rhodopsin.
Both contain a chromophore- 11 cis retinal (Vitamin A derivative)
Vitamin A diffuses through large pores of the choriocapillaris to the RPE. Then what happens
RPE converts vitamin A (11 cis retinol) into 11 cis retinal.
When sun hits the RPE, 11 cis retinal is converted to all trans retinal.
all trans retinal moves from the disc lumen into the cytoplasm and is reduced to all trans retinol. Then shuttled back into the RPE where it is coverted to 11 cis retinol.
Cycle starts all over again.
Stargardt’s
Mutation in the ABCA4 transmembrane protein that moves all trans retinal from the photoreceptor disc lumen to the cytoplasm.
Leads to degeneration of the photoreceptors and RPE.
Membrane potential of photoreceptor in the dark and light
Dark -50mv
light: -70mv
Dark current
Na/K+ ATPase pumps on the inner segment pumps Na+ out and K+ into the PR cell.
Na+ re-enters the cell through a channel opened by cGMP. The positive flow of ions into the cell during darkness keeps the membrane at -50mv. AKA depolarized, causing glutamate to be released.
What happens to the dark current when there is light
The absorption of light by rhodopsin triggers phototransduction. Transducin, a G protein, decreases the concentration of cGMP –> less Na+ enters the cell –> membrane potential decreases from -50mv to -70mv. Cell is hyper-polarized and stops releasing glutamate.
Which cells produce graded responses
Which cells produce action potentials
Graded- Photoreceptors, bipolar cells, horizontal cells
Action potential- Amacrine and ganglion cell
There are two types of cone bipolar cells- on center and off center. How do they respond to glutamate and light
Bipolar cels have center-surround receptive fields (spatial antagonism)
On center depolarizing cone bipolar cells
Inhibited by glutamate, hyper-polarized in the dark.
When light is present, less glutamate is released –> Depolarization.
Off center depolarizing cone bipolar cells
Excited by glutamate, depolarized in the dark
When light is present, less glutamate is released –> hyperolarization
Cells with center-surround receptive fields
Bipolar
Amacrine
ganglion
Horizontal cells do not !!
How do horizontal cells respond to light
They do not have center-surround receptive fields
They hyper polarize in response to light
Graded potential
Which cells hyperpolarize in response to light
PR, horizontal cells and Off center cone bipolar cells.
How do amacrine cells respond to light
have center/surround receptive fields
Depolarize in response to light
Action potential
2 types of ganglion cells based on their response to light
On center/off surround: Synapse with on center bipolar cells and depolarize in response to light.
Off center/on surround: Synapse with off center bipolar cells and hyper polarize in response to light.
Midget ganglion cells
Small ganglion cells that have a single dendrite that synapses with a midget bipolar cell which synapses with a single cone in the fovea.
High resolution
Aging changes of the retina
RNFL decreases –> vertical cup size increases
ILM thickens (decreases foveal reflex)
Rod density decreases with age (scotopic function does not decline)
RPE cells decrease
Lipofuscin and drusen increases
Atrophy increases around the ONH (peripapillary atrophy), in PP (decrease in RPE pigment) and periphery (paving stone degeneration)
Pyramidal motor pathway plays a role in
Pathway
Where does it decussate
Complicated motor movements.
Begins in motor cortex, axons join to form the International capsule.
Decussation at the medulla.
-90% cross and form the lateral corticospinal tract– controls distal muscles
-10% stay ipsi and make up the anterior corticospinal tract- controls proximal muscles
Lesion above medulla leads to contra motor problems
Recticulospinal pathway
-Controls what?
Involved in the control of complex voluntary movements, along with the pyramidal pathway.
They originate at the reticular formation within the pons and the medulla. they descend ipsi and synapse at the spinal cord.
Tectospinal pathway
- Role
- Origin
- Decussation point
Reflexive head movements and response to visual stimuli.
Fibers originate in the superior colliculus and then immediately cross
Spinothalamic pathway/anterolateral pathway
HOT SPINE! Think someone just put a hot dagger in your spine.
-Pain and temperature
Trigeminothalamic pathway
Carries pain and temp from the face
Pathway originates in the trigmeninal ganglion cells
Decussate in the medulla
Medial Lemniscus pathway
Carries information about touch, pressure, and vibration.
Cross over at the medulla
Mechanical information from the upper body travels along the cuneate (lateral) path.
Information from the lower half of the body travels along the gracilis tract (more medially).
How does the autonomic system affect the bronchioles
Sympathetic- brochodilate, vasoconstrict, mydriasis.
Parasympathetic- Bronchoconstrict, vasodilate, miosis
Sympathetic system pre and post ganglion locations/names
Pre ganglionic neurons are located in the throacic/lumbar regions of the of the spinal cord in the lateral horn of the grey matter.
Their axons travel to the sympathetic chain located in the vertebral column.
Fibers that carry info to the head and thorax will synapse within the sympathetic chain. Post ganglionic neurons will continue to the target organ.
Fibers that carry info to the pelvis and abdomen will pass through the sympathetic chain and synapse at the autonomic ganglia (celiac, superior mesenteric, and inferior mesenteric ganglia) Post ganglionic fibers will then go to the target tissue
SANNA
Sympathetic - Ach - Nicotinic - NE - adrenergic
Only gland that is innervated directly by pre-gangloionic sympathetic fibers
Adrenal gland.
All other pre ganglionic fibers synapse at the sympathetic chain or abdomen autonomic ganglia.
Pre ganglionic parasympathetic location
Craniosacral
Post ganglionic neurons are located within ganglia that are very close to their target tissue.
Why would you get a CT
What does it do
analyzes bone and calcification
EMERGENT situations
Uses ionizing radiation to compare calcium density
Denser tissue appears white
PET
Analyzes metabolic activity of tissues. compares glucose uptake of neighboring tissues.
Monitor metastasis in cancer.
MRI
- How does it work
- Best for imaging what
- Contra
Analyzes soft tissue.
Excites free protons located in water to a higher energy state. As the protons relax back down, they give off energy detected by the machine.
Diseased tissue has more water content –> more free protons.
Contra: claustrophobia, any magnets in the body (pace maker, defibrillator, cochlear implant)
Where is the LGN located
Dorsolateral aspect of the thalamus.
2 LGNs located on the left and right side of the thalamus.
Where does the LGN receive info from
The retina
Feedback from V1
Superior colliculus
Axons that leave the LGN are called
Optic radiations
Layers of the LGN. Which are ipsi/contra and magno/parvo/konio
2,3,5 ipsi
1, 2 magno on the ventral/bottom of the LGN.
Konio are located between each of the 6 layers
Macular fibers project to a large central dorsal wedge that makes up 2/3 of the LGN.
Parvocellular
Red/green
Fine details/high spatial frequencies
slow motion/low temporal frequencies
slower speed of transmission of visual signal
Layers 3-6 of the LGN
Magnocellular
More in the periphery- affected by glaucoma.
Monochromatic
Fast motion/high temporal frequencies
large details/low spatial frequencies
High speed of transmission bc they have larger axons compared to parvo.
layers 1 and 2 of the LGN.
Konio cells respond to what colors
Blue/yellow
Parvo does red/green
V1 gives basic info such as
size orientation direction Shape Texture
How is layer 4 of V1 organized
Layer 4 receives information from LGN. The cells are organized into ocular dominance columns that respond to input from one eye only. The ocular dom columns are further divided into hypercolumns that differentiate orientation.
Contains:
- Non oriented cells that have center surround receptive fields
- Simple cells/P cells: Respond to orientation, edges, color, and depth. P cells of the parvo system are simple cells that are organized within blobs of V1. Blobs respond to color.
- Complex cells/M cells: Responds to objects moving in a certain direction with a certain orientation. M cells of the magno system are complex cells.
- End stopped cells respond to lines with a specific length.
Layers of V1 and what they respond to
2 & 3 process and send to other cortical layers
4 receives input from the LGN. Organized into OD columns– hyper columns.
5 & 6 send axons to subcortical areas (superior colliculus, thalamus, midbrain, pons)
6 sends direct feedback to the LGN, allowing V1 to regulate its own input.
What are the roles of V2-V5
Complex visual processing
Travels to the IT cortex for “What”
and travels to MT cortex for “where”
Voluntary saccades are initiated by input from what 2 areas
FEF and superior colliculus
Cortical magnification of the fovea
Visual input from the fovea makes up a large percentage of the visual cortex
EOG
measures the difference in charge between the front and back of the eye
Analyzes health of the RPE
The electrical potential is lowest after 8 minutes of dark adaptation and highest after 10 minutes of light adaptation
Light peak/dark trough = arden ratio.
Want it to be > 1.8
Helpful to dx bests disease
ERG
Records graded potentials produced within the retina in response to light.
Prior to ERG, pt is maximumly dilated and dark adapted.
Rod function isolated by using a blue flash with slow flicker, dim background.
Cone function isolated by using red flash with fast flicker, bright background.
A wave- photoreceptor cells
B wave- bipolar, muller cells
C wave- RPE
A and B wave are abnormal in RP and stargartz
Proportion of rods to cones
13:1
What can you use these ERGs for?
Pattern
Multifocal
Serial
Pattern- targets ganglion cells y using a complex stimulus.
Multifocal- Record responses at multiple locations within the retina
Serial- Used to track intraocular foreign bodies.
2 Triads of RP
Artery attenuation Pallor disc Bony spicules CME PSC ONH drusen
VEP
Analyzes electrical response (latency) of brain activity to a visual stimulus.
Patient sits in front of a screen that displays an alternating checkerboard pattern.
Normal latency is 100ms
Tectotegmental tract
Pretectal nucleus projecting to ipsi and contra EW nuclei
Damage here –> Neurosyphilis/ARP and parinauds/dorsal midbrain syndrome.
(Pupils accommodate at near, but don’t react to light)
CN 3 pre and post ganglionic fibers
Pre ganglionic parasympathetic fibers leave each EW nucleus in the midbrain and travel to the ciliary ganglion within the orbit.
Post ganglionic parasympathetic fibers project from the ciliary ganglion to the iris sphincter and ciliary muscles.
Anisocoria is always a result of an afferent/efferent pathology
efferent
Near response pathway
Pupillary constriction mediated by supra nuclear input from FEF
FEF activates EW
EW projects to ciliary ganglion
Ciliary ganglion projects to the sphincter muscle and ciliary muscle.
*Somewhat similar to the light response pathway, but this does NOT involve the pretectal nucleus. This is why the light response can be damaged, but the near response can remain intact.
The sympathetic NS actively inhibits the EW nuclei in order to stop miosis?
through supra nuclear control.
Sympathetic stimulation during waking hours results in supra nuclear inhibition, causing a decrease in EW activity –> normal pupil size.
During sleep, less symp input –> miotic pupils
GAT
- size of probe
- how does it work
- based on what law
- assumes CCT of what
3.06mm
gently flattens (applinates)
Imbert fick law- pressure inside an infinitely thin, dry sphere covered by a thin membrane is = to the force necessary to flatten that sphere.
-520micrometers
How does NCT work
Airstream flattens a circular area of the cornea.
The amount of TIME between the initiation of airstream and peak response is converted to mmHg
Variable and less predictable
How does pascal tonometry work
It contours to the cornea- CCT does not affect results.
Peak IOP hours
Nocturnal, midnight to 6am. Specifically 3:30-5:30 AM
IOP can vary how much in the normal person
2-5mmHg per day
A person with glaucoma may have 10mmHg variations
The total amount of aqueous outflow is ___ microliters/min
The total volume of aqueous is ___ micoroliters
Total volume is replaced every ___ minutes or __ hours
2.5 microliters/min outflow
250 microliters total
Replaced every 100 mins/2 hours
2 syndromes that increase episcleral venous pressure resulting in increased IOP
Sturge weber
Arteriovenous fistula
The aqueous is hyper or hypotonic to the plasma
Hypertonic by 5mOsm
Aqueous is produced and secreted by the NPCE of the ciliary processes. The production involves which processes
- Diffusion- plays minimal role
- Ultrafiltration- Passive flow of blood plasma from the capillaries into the ciliary stroma. Caused by increased in hydrostatic (heart) pressure.
- Active secretion- requires ATP. Accounts for 80-90% production. Na+, Cl- and bicarb are pumped into the posterior chamber. Water follows
Covering of the TM can lead to glaucoma
- neo of the angle due to DM, CRVO, and OIS may cause PAS
- Uveitis. Inflammatory cells clog angle.
- Hyphema.
Injury to the TM can cause glaucoma
- Fuchs- chronic inflammation can damage TM
- Glaucomatocyclitic crisis/posner schlossman syndrome- Acute inflammation of the TM (trabeculitis)
- angle recession glaucoma. Separation of the iris from the iris root `
Occlusions of the TM can lead to glaucoma
Pseudoexfoliative glaucoma- Pupillary TIDs, bullseye appearance on lens, systemic disease.
PDS- Mid peripheral TIDs, schiae line, kruckenberg spindle
Long standing inflammation can do what 3 things
Cells get in TM –> Glaucoma
Strips melanin from ant boarder layer –> Heterochromia
Cataracts
Aqueous humor vs plasma
- AA
- Protein
- Vit C
- Lactate
- Bicarb
- pH
Aqueous has: More AA Less protein Vitamin C x 20 More lactate less bicarb more acidic (drop in pH to 7.2)
Uveitis occurs secondary to a breakdown in the
blood aqueous barrier
- NPCE
- Iris vessels (minor arterial circle)
- Schlemms
