Ocular Physiology (Done) Flashcards
1
Q
Which muscles control spontaneous blinking?
A
Palpebral portion of orbicularis oculi
2
Q
Reflex blinking caused by touch is mediated by which CN?
A
CN V
3
Q
Reflex blinking caused by loud noises is mediated by which CN?
A
CN VIII
4
Q
How many blinks/minute on average?
A
12-15
5
Q
Which muscle is associated with reflex blinking?
A
Palpebral portion of orbicularis oculi
6
Q
When winking, which muscles are controlling this?
A
palpebral and orbital portions of orbicularis oculi
7
Q
Which muscles are involved with Blepharospasm?
A
Procerus, corrugator, and orbicularis
8
Q
How many meibomian glands located on upper and lower lids, respectively?
A
30-40 and 20-30
9
Q
Blinking stimulates lipid release from meibomian glands via which type of secretion?
A
Holocrine secretion
10
Q
Where are glands of Krause located?
A
Fornices
11
Q
Where are glands of Wolfring located?
A
Tarsal conjunctiva
12
Q
What happens to the canaliculi during a blink?
A
Muscle of Horner contracts, causing canaliculi to SHORTEN as they move medially towards the lacrimal sac
13
Q
Where is the muscle of Horner located?
A
It is part of the palpebral portion of the orbicularis and surrounds the canaliculi
14
Q
What happens to the lacrimal sac during a blink?
A
as orbicularis contracts, lacrimal sac is pulled away from the nose, which creates a negative pressure that helps draw tears into the lacrimal sac
15
Q
How many eyelashes on upper and lower lid, respectively?
A
150 and 75
16
Q
Which components of the aqueous layer of the tears help in anti-bacterial measures?
A
IgA, lactoferrin, and lysozyme
17
Q
What is the anterior lipid layer composed of?
A
fatty acids, cholesterol, and waxy esters
18
Q
List as many things as you can think about what is found in the aqueous layer of the tear film…GO!
A
Na, K+, Cl-, IgA, lactoferrin, lysozymes, Vitamin A (all-trans retinol), enzyme co-factors, HCO3-, glucose, urea, lactate, citrate, Vitamin C, albumin, growth factors, and VEGF
19
Q
Under closed eye conditions, is IgA higher or lower in concentrations?
A
HIGHER
20
Q
As age increases, what happens to lactoferrin and levels of lysozyme within the tears?
A
THEY DECREASE!
21
Q
What innervates the main lacrimal gland?
A
Parasympathetic fibers from CN VII, sympathetic fibers, and sensory nerves of V1
22
Q
What makes the mucin layer of the tear film unique?
A
It is capable of mixing with lipid AND water»therefore, able to spread tears evenly over hydrophobic corneal surface
23
Q
What produces the mucous layer of the tear film?
A
goblet cells, as well as squamous cells of the cornea & conjunctiva
24
Q
Where are the greatest concentrations of goblet cells found?
A
Inferonasal fornix & bulbar conjunctiva (mostly temporally)
25
What do goblet cells require in order to develop properly?
Vitamin A>>no Vit. A means keratinization of conjunctiva and cornea>>BITOT SPOTS
26
Which type of stimulation can cause an increase in goblet cell mucous secretions?
Parasympathetic nerve stimulation
27
Which part of the corneal epithelium does the mucin layer interact with in order to provide an evenly spread tear film?
Mucin layer interacts w/ the GLYCOCALYX of the corneal epithelium
28
What is the total tear volume on the ocular surface?
7-9 uL
29
What is the maximum amount of fluid that the eye can hold?
20-30 uL
30
What are the main contributors to tear osmolarity?
Na+ and Cl->>Ca2+ and K+ also importantn in aqueous portion of tears
31
Which mineral is essential for hemidesmosome formation in the BM of the corneal epithelium?
Calcium>>jelly bumps on contact lenses
32
How much more potassium is found in the tears compared to the blood?
4 X as much
33
Would Hypotonic or Hypertonic eye drops be used for Dry Eye?
Hypotonic because dry eye causes increased tear osmolarity (hypotonic solution is about 150 mOsm/L)
34
What happens to the pH of tears during sleep?
tears become more ACIDIC>>b/c of the byproducts of anaerobic respiration
35
What happens to the pH of tears in dry eye syndrome?
tears become more BASIC
36
The auditory ossicles (i.e. malleus, incus, then stapes) are located between which 2 structures?
located between the tympanic membrane and oval window
37
What is the function of the tympanic membrane (i.e. eardrum)
amplifies the sound waves by 10-20X
38
What does the stapedius muscle do?
dampens the amount of vibrations placed on the auditory ossicles>>stapedius innervated by CN VII, just before exiting the skull via stylomastoid foramen
39
Which nerve innervates the tensor tympani muscle?
branch from V3 of CN V
40
Which section of the ear do mechanical vibrations get converted into neural signals?
INNER EAR
41
What are the 3 parts of the bony labyrinth?
Cochlea, Vestibule, and Semi-circular canals
42
Which structure separates the external ear and middle ear?
Tympanic membrane
43
Which brain structure controls horizontal saccades?
CONTRALATERAL frontal eye fields in the frontal lobe and superior colliculus
44
Which structure controls Pursuit movements?
IPSILATERAL parietal lobe
45
If a pt. is having problem with saccades to the RIGHT side, which side is affected?
deficient saccades to right side would indicated right frontal eye field damage
46
What types of junctions are found in corneal epithelium that limit the absorption of hydrophilic, ionized molecules through?
Zonula occludens
47
Which junctions are found in the corneal endothelium?
Macula occludens
48
What are the ranges of UV-A, UV-B, and UV-C light?
200-290, 290-320, and 320-400nm
49
Which layers block UVC and UVB light?
epithelium and Bowman's
50
More than 99% of light above ______ wavelength is transmitted through the cornea.
99% of light over 400nm is transmitted
51
What are some factors contributing to DECREASED light scattering in cornea?
Corneal crystallins (similar to crystallins in the lens), Vitamin C & Glutathione (protect cornea from UV rays and free radical scavengers), avascular nature of the cornea, proteoglycans (which fill space b/w corneal cells and collagen fibrils), high water content of cornea helps maintain regular spacing between collagen too
52
What is the major proteoglycan found in the corneal stroma?
Keratin Sulfate>>proteoglycans help maintain spacing between collagen fibrils
53
What are the 2 main transport mechanisms in the corneal epithelium?
Na+/K+ ATP ase pump & Na+/K+/Cl- co transporter
54
Explain the mechanism of movement of ions between the epithelium and the stroma..
1. Na+ enters epithelial cells from tear film
2. Na+/K+ pump moves Na+ into stroma>>aka Na+ higher [ ] in stroma compared to epithelium
3. Na+/K+/Cl- utilizes higher [ ] to move these ions from stroma into epithelial cells
4. Cl- and K+ have own channels that allow for passive diffusion back into tears and towards aqueous humour
5. Movement of K+ into aq. humour
6. Cl- moves into tears; water follows>>dehydration of cornea
55
A hypoxic cornea will produce what change in pH?
Higher acidity
56
Explain mechanism of movement of ions between stroma and endothelium...
1. Na+ enters endothelial cell from stroma
2. Na+/K+ pump pumps Na+ out of endothelium into aqueous humour>>therefore, higher Na+ [ ] in aq. compared to endothelium
3. Na+/H+ pump move H+ ions out of endothelium into aqueous in exchange for transfer of Na+ back into the endothelium
4. Movement of H+ into aq.>>decrease in extracellular pH causing CO2 to diffuse into endothelium
5. CO2>>H2CO3>>H+ and HCO3- ions
6. Bicarbonate and Cl- move from endo to aq. Water follows contributing to water dehydration
57
What are the major factors for water transport across epithelium and endothelium?
Na+ absorption and Cl-excretion
58
Which structures supply oxygen to the cornea under closed eye conditions?
1. superior palpebral conj & limbal vasculature supply epithelium and anterior stroma
2. aq. humor supplies post. stroma and endothelium
59
Why is the cornea slightly edematous upon awakening in the morning?
Build-up of lactate from anaerobic respiration and limited supply of O2 when eye is closed
60
Why are minus CL's more capable of transporting O2 compared to plus CL's?
minus lenses are THINNER in the center compared to plus lenses
61
What does Dk/t mean?
how much oxygen will diffuse through a contact lens of a given thickness
62
Why does the cornea become acidic when is edematous?
decreased levels of O2 can lead to an accumulation of H+ ions produced by glycolysis, resulting in increased acidity of corneal cells
63
What is the primary glucose contributor for the cornea?
Aqueous humor
64
What is the main mechanism of production of glucose for the cornea?
Anaerobic glycolysis (85%)>>minor contribution from aerobic glycolysis and hexose monophosphate shunt
65
The entire corneal epithelium replaces itself every _______ days.
7-14 days
66
What are the steps in epithelial regeneration?
1. Basal cell mitosis is INHIBITED
2. Fibronectin released--serves as scaffolding for epithelial cells to migrate over the wound
3. Hemidesmosomes are then created
4. Basal cell mitosis resumes at rapid rate (but only once wound is closed w/ a single layer of cells and cell to cell junctions are created)
67
Complete healing of the BM takes _______ time.
8 weeks
68
What do matrix metalloproteinases do?
degrade hemidesmosome function>>prescribe tetracyclines to decrease MMP activity
69
Does the stroma regenerate?
Kind of. It replaces itself when damaged, but with a very different textured tissue>>new collagen is larger and less organized, resulting in a scar.
70
What is neurotrophic keratitis?
CN V damage and decreased corneal sensitivity
71
What are some changes that occur in the cornea with age?
more ATR astigmatism, BM thickens, DM thickens, corneal arcus increases, endothelial cell density decreases
72
List all of the changes that occur in the lens w/ accommodation?
1. decrease in tension in lens zonules
2. ant. pole of lens moves forward & ant. curvature increases
3. post. pole moves back slightly; post. curvature increases
4. lens thickness increases
5. ant. chamber depth decreases
6. lens diameter decreases
7. lens power increases
73
Over 70% of glucose required by the lens is produced by _______________.
Anaerobic Glycolysis
74
What happens in the lens if hexokinase enzyme is not present? (enzyme used to convert glucose to glucose-6-phosphate)
glucose will be converted to sorbital via the enzyme aldose reductase>>excess sorbital creates osmotic gradient favoring H2O, ultimately leading to lens swelling, lens fiber damage, and cataract formation
75
What is the primary protector against oxidative damage in the lens? and what is its purpose?
Glutathione>>acts as a REDUCING AGENT
76
How is glutathione associated with cataract formation?
Glutathione DECREASES with age--a factor in cataract formation
77
Is Vitamin C. concentration higher in the aqueous humor or the lens?
LENS
78
Where are ions pumped by Na+K+ pump between the lens epithelium and aq. humor?
Na+ pumped into the aqueous humor and K+ into the lens
79
What produces the secondary lens fibers of the lens during adult growth?
Anterior lens epithelium
80
What produces the embryonic nucleus of the lens during embryological development?
formed from primary lens fibers of the posterior lens epithelium
81
Where does mitosis of fiber cells occur?
Germinative zone of the Anterior lens epithelium
82
In the lens, where does aerobic respiration occur?
Limited to the anterior lens epithelium
83
Where in the lens is the greatest metabolic demand?
Anterior lens epithelium
84
Where is a majority of the mitochondria in the lens located?
Anterior lens epithelium
85
What is the purpose of alpha crystallins?
Act as molecular chaperones by preventing degradation of other crystallins
86
What happens to the lens when there is a decrease in crystallins?
increase in insoluble proteins, causing change in collagen cross-linking, which promotes increased H20 in the lens>>cataract formation
87
Does the ant. lens capsule or posterior lens capsule increase in thickness during life?
Anterior lens capsule
88
What type of collagen comprises the lens capsule?
Type IV>>it is the thickest BM in the entire body too!
89
What happens to the anterior and posterior radius of curvature throughout life?
Ant. & Post. both decrease>>lens becomes more convex throughout life
90
In respect to glutathione, Ca2+, Na+, and H20--do these increase or decrease in value throughout life?
Glutathione DECREASES, everything else INCREASES
91
Where in the lens does nuclear sclerosis begin?
Begins in the embryonic nucleus
92
Where is the greatest concentration of crystallins in the lens found?
Embryonic nucleus>>also the highest refractive index of 1.41
93
Does ciliary muscle contraction decrease with age?
NO>>loss of accommodation with age is secondary to changes in the lens
94
Bruch's membrane ________ in thickness with age.
increases
95
Choriocapillaris _________ in thickness with age.
decreases
96
Overall choroidal thickness _________ with age.
decreases
97
What effect does the gel-like consistency of the vitreous have on drug absorption?
It decreases the bioavailability of topical drugs
98
What makes up the vitreous substance? What type of collagen?
H20, Type II collagen, and hyaluronic acid (GAG)
99
What is the purpose of Hyaluronic acid?
proves support to collagen fibers, maintains proper collagen fibril spacing, and maintains viscosity of the vitreous
100
Vitamin C is how many times higher in concentration in the vitreous than in the blood plasma?
40X greater!
101
What is the most common cause of a PVD?
Vitreous syneresis
102
Where is collagen concentration the highest and lowest in the vitreous, respectively?
Vitreous Base and vitreous center
103
What happens to the concentration of hyaluronic acid throughout life?
20-50 yr old stable; after 50 years, INCREASES
104
What is the mean arterial pressure of the arteries entering the eye
65 mmHg
105
What is the mean arterial pressure in the episcleral veins leaving the eye?
15 mmHg
106
What is the approximate perfusion pressure in the eye?
50 mmHg
107
How do you calculate ocular perfusion pressure?
OPP= diastolic blood pressure-IOP
108
Are glaucoma patients more likely to have a increased or decreased OPP?
LOW OPP'S; Remember, if IOP increases (like in glaucoma), OPP decreases!
109
What are most likely responsible for autoregulation within the blood supply of the retina and the optic nerve?
Pericytes
110
What is the immediate threat to vision in acute angle closure? and why?
CRAO>>increased IOP, leads to decreased OPP>>retinal vessels increased vessel diameter through autoregulation>>if IOP remains high long enough, CRA reaches critical closing pressure
111
What effect does the sympathetic system have on blood vessels?
Causes vasoconstriction--especially when BP increases>>resulting in compensatory reduction in blood flow
112
The IOP must be _________ than the episcleral venous pressure so aq. humor can drain
GREATER
113
The IOP must be _________ than the intracranial pressure in order to maintain an axoplasmic gradient that flows from the ON towards the brain.
GREATER
114
Why does Papilledema occur?
Results from a reversal in axoplasmic gradient between the eye and the brain due to an increase in intracranial pressure.
Therefore, CSF spills from subarachnoid space onto optic disc margins and surrounding RNFL.
115
What % of blood flow in the ocular vessels occurs in the choriocapillaris?
60%
116
What makes up the Major Arterial Circle of the Iris?
anterior ciliary arteries + long posterior ciliary arteries
117
What forms the Minor arterial circle of the iris?
formed by anastomoses of the iris radial vessels
118
Where does the central fovea receive its blood supply from?
The underlying choriocapillaris
119
The CRA forms 2 networks of capillaries>>where are they located?
RNFL (superficial) and INL (deep capillary network)
120
The blood-retinal barrier is formed by tight junctions in 2 locations:
1. Between endothelial cells lining retinal vessels.
2. Between RPE cells
* Remember, blood is toxic to the retina
121
What are some of the histological changes that occur in Diabetic Retinopathy?
1. increase blood glucose damages pericytes
2. Basement membranes of retinal capillaries also damaged, allowing blood and plasma to leak into surrounding retinal tissue
122
Vitamin A is an alcohol retinol that is oxidized in the RPE to form __________.
11-cis retinal
123
What is the first transformation when light is absorbed by a photorecptor?
11-cis-retinal to all-trans-retinal
124
What is the membrane potential of a photoreceptor in the dark?
(-50mV)
125
What type of potentials do photoreceptors produce?
Graded potentials
126
Which types of cells release GABA and Glycine?
Horizontal and Amacrine cells
127
Which retinal cells release Glutamate?
rods, cones, bipolar cells, and most ganglion cells
128
In the dark, photoreceptors are ____________ and constantly release __________ to bipolar cells and cGMP keeps ______ channels open to promote depolarization.
DEPOLARIZED, GLUTAMATE, Na+
129
When rhodopsin is dissociated, the activation of which enzyme leads to decrease in cGMP [ ]?
Transducin
130
What happens to sodium channels when cGMP decreases?
Na+ channels CLOSE, resulting in increased cell membrane charge (-65mV)>>This hyperpolarization results in a decrease in release of glutamate to bipolar cells
131
What controls whether or not the photoreceptors decrease their release of glutamate?
Closure of Na+ channels
132
Which type of potentials do Bipolar cells produce?
Graded potentials
133
What happens to a on-center bipolar cell when light is present?
less glutamate is released, resulting in DEPOLARIZATION; on-center BP cells are inhibited by glutamate and are thus HYPERPOLARIZED in the dark
134
What happens to off-center bipolar cell when light is present?
less glutamate is released, resulting in HYPERPOLARIZATION; off-BP cells are excited by glutamate and are thus depolarized in the dark
135
Horizontal cells respond with __________ potentials and _____________ in response to light
Graded potentials, Hyperpolarized
136
What is the purpose of horizontal cells?
Impact the surround response of BP cells by providing inhibitory feedback to PR cells
>>they also provide lateral inhibition, which fine-tunes the neural signal
137
PR's, horizontal cells, and Off-center BP cells are unique because they ___________ in response to light.
HYPERPOLARIZE
138
Amacrine cells have ______ potentials and always _______ in response to light.
Action potential, depolarize
139
What do amacrine cells do?
Fine-tune the signal between BP and ganglion cells.
140
Ganglion cells respond to BP cells with _______ potentials.
Action
141
ON-center/OFF-surround Gang. cells synapse w. ON-center BP cells and _______ in response to light.
DEPOLARIZE
142
OFF-center/ON-surround Gang. cells synapse w/ OFF-center BP cells and _______ in response to light.
HYPERPOLARIZE
143
Does rod density decrease with age? If so, how does this affect scotopic function?
Yes, they decrease, but scotopic function DOES NOT decline.
144
RNFL fibers decrease, resulting in an increase in the diameter of the ______ cup.
Vertical
145
A lesion above the medulla, will lead to problems with motor control on the __________ side.
Contralateral side
146
Where do fibers in the tectospoinal pathway originate?
Superior colliculus
147
What type of information does the spinothalamic pathway carry?
Pain and temperature information from the body
148
What does the trigeminothalamic pathway carry?
Pain and temperature info from the face
149
The medial lemniscus pathway carries what type of information?
Info about touch, pressure, and vibration
150
What side will be affected if there is a lesion above the crossover point in the medial lemniscus pathway?
contralateral side>>below crossover would be ipsilateral side
151
Where are pre-ganglionic neurons of the sympethetic system located?
thoracic and lumbar sections of spinal cord
152
Pre-ganglionic sympathetic fibers release ___________.
acetylcholine
153
Post-ganglionic sympathetic fibers release _______________
NE
154
Where are pre-ganglionic neurons located in parasympathetic system?
2nd-4th sacral segments of spinal cord
155
Pre-ganglioniparasympathetic fibers release ________________.
Ach
156
Post-ganglioniparasympathetic fibers release ________________.
Ach
157
Where do the axons of the retinal ganglion cells terminate?
LGN
158
Axons that leave the LGN are called the ____________________.
optic radiations
159
Which location in the brain is where monocular input is combined for binocular processing?
V1!>>LGN neurons are still monocular!
160
Which layer of the visual cortex receives primary visual input from the LGN?
Layer 4
161
What does the inferotemporal cortex role have?
"what" identification of objects
162
What role is middle temporal cortex (MT) for?
identification of spatial relationship of the object>>aka "where" system
163
What are the 2 primary functions of the frontal eye fields?
1. Pupillary response to near objects.
| 2. Activates during initiation of voluntary and reflex eye movements
164
What is considered to be a normal Arden ratio?
1.8
165
What do the A,B, and C waves represent, respectively, in the ERG?
```
A= PR's
B= bipolar and Muller cells
C= RPE cells
```
166
What is the best electrical potential test of choice for analyzing the RPE function?
EOG!
167
In early cases of RP, what does the ERG look like?
scotopic ERG is abnormal>>late stages of RP, ERG is completely extinguished due to poor function of rods and cones
168
What is the pathway for the pupillary response? beginning with the pupillary fibers leaving the optic tract...
Optic tract>>brachium of superior colliculus>>synapse at pre-tectal nucleus in midbrain>>ipsilateral & contralateral Edinger Westphal nucleus
169
During sleep or anesthesia, what happens to the pupils?
they become MIOTIC!
170
When is IOP found to be the highest?
During nocturnal hours (midnight-6AM)
171
What are some of the drugs that DECREASE aqueous production?
B-blockers, alpha-2 agonist, CAI's, hyperosmotic agents, uveitis, decline in blood pressure
172
How many uL/min does the corneoscleral pathway drain?
2.25 uL/min
173
Through which structures does the aq. humor flow through Corneoscleral pathway? is it pressure dependent or independent?
aqueous flows from ant. chamber>>across TM into Schlemm's canal>>episcleral veins drain aq. from Schlemm's canal
>>pressure dependent!
174
What is drainage of the uveoscleral outflow?
| What amount in uL/min?
Aq. drains through ciliary stroma into surrounding vessels of the venous system\
>>0.25uL/min
175
Since total amount of aw. outflow is 2.5uL/min and ant. chamber volume is 250uL, how often is aq. humor fluid replaced?
Every 100 minutes
176
What effect will increased episcleral venous pressure have on IOP?
INCREASED IOP!
177
Active secretion accounts for what % of aqueous humor formation?
80-90%
178
Bicarbonate ions are believed to increase aq. production by increasing __ and ____ flux into the posterior chamber.
Cl- and Na+
>>Na+/K+ pump located within the NPCE pumps Na+ out of cell into post. chamber (water follows)>>Na+ constantly moves from ciliary stroma into PCE
179
How many times more Vit. C is in the aq. humour compared to blood plasma?
20 X more
180
The blood-aqueous barrier consists of tight junctions in what 3 locations?
the iris vessels, enothelium of Schlemm's canal, and the NPCE
