Cornea 2 Flashcards
What is the function of tight junctions?
barrier( but not as good as epithelial)
T/F Tight junctions do completly encircle the cells like zonula occludena
F Do not completely encircle the cells like zonula occludens
T/F Tight junctions are also called macula occludens
T
T/F Tight juncitons are a leaky barrier between aqueous and stroma in the endothelial cell-cell adhesion
T
What is the function of gap juncitons?
For intercellular communication
Where are gap junctions found?
lateral membranes
T/F Gap junctions do contribute to the endothelial barrier
F. Gap juncitons do not contribute to the endothelial barrier
What type of junctions interconnected endothelial cells?
tight junctions and gap junctions
What is the difference between macula occludens and zonula occludens?
Macula occludens do not completely encircle the cells
T/F gap junctions can also be found in the apicolateral membranes not just the lateral membranes
T
Two factors contribute to the prevention of stromal swelling what are they?
- barrier funciton of the endothelium
2. pump funciton of the endothelium
water is maintined at \_\_% A)88% B)68% C)78% D)80%
78
T/F The barrier of the endothelium is incomplete compared with the epithelial barrier
T/F If the corneal endothelium is disrupted the stroma will swell up less, compared to if the metabolic pump was disrupted
T
F MORE
With the endothelium disrupted the corne's stroma swells at \_\_\_\_\_ um/hr A)50 B)127 C)107 D)100
127
With just the metabolic pump disrupted, the cornea’s stroma swells at __ um/hr
A)13
B)20
C)33
D)40
33
T/F normal leakage of Fluid is vital in the stroma of the cornea
T
Why is normal leakage of fluid vital in the stroma of the cornea?
because this fluid is the source of nutrients (glucose and amino acids) for the cornea (avascular)
Early studies showed that maintainence of corneal thickness/water content is ________dependent(a metabolic energy-dependent process)
temperature (corneal hydration)
if the cornea is cooled the cornea ____
swells
if the conrea has a normal temperature the cornea has __normal/abnormal__thickness
normal thickness
what happens in the cornea if there is a continual movement of water, if there is nota a mechanisms present to remove fluid from the stroma ?
leads to stromal swelling and loss of transparency
T/F temperature reversal is a phenomenon of the cornea swelling when cooled and returns to normal when at a normal tempature?
Temperature reversal clearly shows that the maintenance of corneal hydration is a metabolic ____-_____ process
T
energy-dependent
___ to ___ ml/hr of water is moved by the endothelium from stroma to aqueous humor
A.7-8
B. 6-8
C. 7-10
D 6-10
6 to 8
Temperature reversal is clearly demonstrated by eye ____ corneas that swell during refrigeration and return to normal thickness and transparency after grafting.
bank
in which membrane is the NA+K+pase pump located in the cornea,?
basolateral membrane
NA+K+pase pump has a _____ pump sites/cell
A.1.510^8
B. 310^6
C. 1.510^6
D 310^8
1.5 X10^6
What inhibits the NA+K+pase pump?
Ouabain
Explain how Ouabian inhibits the NA+K+pase pump
stops sodium transport, causes corneal swelling, prevents temperature reversal, and eliminates the transendothelial potential difference
____ pump disruption represents movement of fluid and solutes from the aqueous humor into the __stroma/epithelium/endothelium_____
metabolic; stroma
_______ is a lipophyllic cardiac , glycoside is a structurally related compound to ouabain
Digoxin
Why can you do corneal grafting?
Due to temperature reversal
T/F the sodium pump respond to increases in the endothelial permeability
T
Corneal ______ are droplet like accumulation of non banded collagen on the posterior surface of ______ membrane
corneal guttata; Descemet’s
Human corneas with guttata have pump site densities of _______ sites per cell.
A. 610^8
B. 710^5
C. 610^6
D 710^6
C. 6*10^6
Inflamed edematous cornea has ______ endothelial pump site despite increase permeability
A. increase
B. decrease
B. decrease
Human corneas with guttata has large pump sites densities what does this suggest?
A greater capacity for the endothelial pump to counteract the leak across the barrier
T/F Sodium potassium ATPase is located in the plasma membrane of cells
T
The Sodium potassium ATPase has two ocular functions it controls what and produces what?
control of corneal hydration and production of aqueous humor
Corneal stroma readily takes up ______ and excess of it need to be pumped out the maintain corneal _______>
water; deturgescence (decrease in swelling)
Sodium ions is transported by Sodium Potassium ATPase is pumped ____ channels between endothelial cells
into
Na ions being pushed generates ______ pressure
to which water follows
osmotic
The directionality is helped by density of sodium ions in ______ membrane
Descemets
Energy source-glucose, Adequate buffer- bicarbonate, and Substrate- calcium, glutathione etc., are ideal for what
intraocular irrigating solution
Cornea __pH/bloodpressure__ extremes causes corneal edema
pH
T/F Normal saline lacks components of the aqueous humor
T
T/F Glutathione bicarbonate ringers solution GBR has the least affect on the corneal thickness compared to NaCl and Lactated ringers solutions
T
Which type of intraocular irrigation solution has the most affect on corneal thickness? and has a percentage of ___?
A) 0.8%
B)0.7%
c)0.5%
D) 0.9%
0.9 % , NaCl
T/F Lacted Ringer’s and saline solutions of 0.9% overcome the buffering capacity of the vitreous humor
F. Aqueous humor
What does it mean if the intraocular irrigating solutions in the cornea are overcoming the buffering capacity?
means cornea is unable to resist the pH change
T/F endothelial cells always regenerate
F. NEVER regenerate
When endothelial cells are lost (due to trauma , aging, disease) endotheiall wounds are covered by the spreading of cells from ____ areas
adjacent
T/F In larger defects of the corneal endothelium (like keratoconus problems) a very small amount of cell migration occurs in order to heal the wound
F. In larger defects of the corneal endothelium (like keratoconus problems) a MORE EXTENSIVE cell migration occurs in order to heal the wound
T/F Keratoplasty is surgery on the cornea , refers to a corneal graft procedure
T
After Keratoplasty(corneal graft) , migration of endothelial cells over the wound edge go to the \_\_center/periphery\_\_ and establish \_\_gap/tight\_\_ junctions to establish \_\_epithelial/endothelial \_\_ barrier
periphery, tight, endothelial
For proper corneal function there must be adequate endothelial cell __volume/density___ and __large/small/uniform___ size and shape
density, uniform
polymegathism is a change in cell __shape/size__
size
Pleomorphism is a change in cell __size/shape__
shape
T/F polymeagthism and pleomorphism stay the same throughout your life
F. change with age
The degree of uniformity of cell size is deteremined by measuring the areas of the ____apical/base__ membranes of a populations of cells and calculting the coefficitne of variation of cell size
apical
The Coefficient of Variation (CV) is the standard deviation of __median/mean__ of cell area over the __median/mean__ of cell area
mean , mean
the normal CV(coefficinet of variation) of the endothelium in the cornea is ? A) 0.35 B)0.40 C)0.25 D)0.30
0.25
What does it mean if the CV(coefficinet of variation)> 0.25 , is it polymegathism or pleomorphism ?
the cell size is variable = polymegathism
T/F As polymegathism increases with an increased CV cells start to look more uniform.
F. look more variable
Healthy cornea has ____to___% ___hexaganoal/octogonal__ cells
A) 80-90
B)70-100
C)70-80
D)80-100
70-80, hexagonal
A increase/decrease in hexagonal shape with an increase/decrease in cells with <6 sides shows endothelial stress (cornea) which means it is pleomorphism
decrease, increase
Lasik has no significant effect on endothelial cells _____shape/density__ or __percent/shape__ of hexagonal cells with myopia of ___ to ___ diopters
A) 2.25-14.5
B)2.25-10.45
C)3.25 -14.5
D)3.25-15.5
density , percent
A)2.25-14.5
Why must there be a residual 200 microns of stroma above the corneal endothelium after LASIK?
to adequately maintain and protect the corneal endothelial structure and barrier function
T/F Laser in situ keratomileusis is a current technology in which corneal stroma is ablated by an excimer laser underneath a lamellar flap
T known as LASIK
CV (coefficinet of variation) of cell \_\_\_size/shape\_\_ imporves \_\_\_years after lasik A)1 B)5 C)4 D)3
size
D)3years
If there is a change in CV after lasik what was the likely affect? and in what percentage of patients had a history of it?
A)30%
B)50%
C)91%
D)81%
the likely effect in change of CV is from contact lens removal , because they had a histroy of contact lens wear
91%
T/F penetration keratoplasty is the removal of full-thickness “button” of cornea and replacement with donor corneal tissue–also known as PK
T
In recent studies of corneal grafts(PK) a long term follow-up of clear graft 15-33 years after the procedure was done. The endothelial cell count range was from ___ to ___ cells/mm^2
A)600-1243
B)675-1200
C)575-1200
D)575-1243
D)575-1243
In recent studies of corneal grafts(PK) a long term follow-up of clear graft 15-33 years after the procedure was done.
It was found that an endothelial cell loss rate of ___% from 3-5 years after PK, 13x rate decrease in normal corneas which is ___%
A)7.8% , 0.6%
B)8.7%. 0.6%
C)8.7%, 0.5%
D)7.8%, 0.5%
A)7.8% , 0.6%
Intraocular lens implantation can lead to __epithelial/endothelial__ cell loss
endothelial
The mean overal endothelial cell loss in IOL (intraoclular ens implantation) surgery is \_\_\_\_ after \_\_\_ months after A)8.5% ,12 B)9.0%. 10 C)10%, 10 D)11%, 12
8.5% , 12 months
what type of anesthesia was used in the study of endothelial cells after phacomulsification with IOL implantatoin? retrobulbar/introbulbar
retrobulbar anesthesia
T/F phacomulsification is use of ultrasonic vibration to break up a cataract into small fragments and emulsify them , making them easier to suction out of the eye
T
With KCN (keratoconus) and Type 2 Diabetes:
Endothelial morphology (stays the same/changes)
(Does/Doesn’t) have decrease in cell density
(increase/decrease) CV of cell size and (increase/decrease)% of hexagonal cells
changes
doesn’t
increase, decrease
With KCN (keratoconus) and Type 2 Diabetes, how much decrease is there in hexagonal cells?
A)30%
B)50%
C)40%
D)80%
50%
T/F In Keratoconus (KCN) stress on cornea causes epithelial remodeling
F. endothelial
What other type of disease after a long duration, was found to also decrease cell density besides type 2 diabetes?
(edema/type 1 diabetes/high cholesterol)
type 1 diabetes
T/F Patients with diseases of long duration also demonstrate a decrease in cell density
T
Type 1 diabetes (increases/decreases) cell density
decreases
After ____ years of age there is a (increase/Decrease) in endothelial cell density
A)30
B)40
C)50
D)60
40 , decrease
Why is special care needed when doing cataract surgery on those with glaucoma or diabetes? and which layer of the cornea is of interest (endothelium/epithelium/bowmans layer)
to minimize the surgical stress to the endothelium
T/F long-term contact lens wearers have no effect on the corneal endothelium morphology
F. there are morphologic abnormatilies of the corneal endothelium
What specific type of change is there in long term contact wearers corneal endothelium ? polymegathism/phacomulsification/pleomorphism
polymegathism
T/F ONLY long term use of polymethylmethacrylate lenses and daily wear soft contact lenses have been reported to effect the corneal endothelium
F
polymethylmethacrylate lenses
daily wear soft contact lenses
AND –extended-ear soft contact
T/F There is an absence of morphological abnormalities of the endothelium in eyes wearing highly (deoxygen/oxygenated) permeable silicone elastomer lenses
oxygenated
T/f hypoxia (oxygen deficiency) is responsible for the observed effects on the corneal endothelium of long term use CL wears
T
What does the coined term CLUE stand for when talking about long-term use contact lens wearers and its effects?
contact lens-use endotheliopathy syndrome
Cornea is richly supplied with (motor/sensory) nerves
sensory
T/F the iris is one of the most sensitive tissues in the body
F. cornea
Cornea is innervated by the (abducens nerve/trigeminal nerve/cranial nerve) via (anterior/posterior) ciliary nerves
trigeminal , anterior
Which two are not innervated in humans?
bowman’s layer/epithelium/endothelium/ descemt’s membrane/stroma
endothelium, descemet’s membrane
Most of the receptors in the cornea are what type of receptor?
nociceptors (pain)
T/F nociceptors when stimulated give perception of pain
T
Nociceptors usually have the (highest/lowest) threshold for mechanical stimulation
lowest
T/F because nociceptors have a low threshold abrasion, ulcers , bullous keratophathy have low pain conditions
F. extremely painful conditions
Stroke, diabetic neuropathy, and herpes simpelx lead to (motor/sensory) denervation
sensory
What type of denervations causes these two sypmtoms? (sensory/motor) and choose the correct effect.
(Loss/increase) in foreign body sensations cause mechanical cornea damage
(Low/High) incidence of epithelial erosions and neurotrohic ulcers
Sensory
loss
high
Lasik cause (increase/decrease) corneal and conjunctival sensitiviey up to ____ months of follow up
A)12
B)16
C)20
D)10
decrease
B)16
Cl wear causes (increase/decrease ) corneal sensitivity
decrease
T/F Both soft and rigid gaspermeable lens wearers produce a increase in corneal sensitivitly
F. DECREASE
Atmosphere , aqueous humor, and limbal vasculature is where (oxygen/sodium/water) comes from for corneal metabolism
oxygen
What three places does oxygen come from for corneal metabolism?
atmosphere, aqueous humor, limbal vasculature
Compared to tears which one of the three has a low amount of oxygen?
Atmosphere/aqueous humor/ limbal vasculature
the one with the low amount of oxygen is ____mm Hg
the oxygen amount in tears is ___mm Hg
A)40 , 100
B)50, 100
C)40, 155
D) 50, 155
aqueous humor
C)40 mmHg 155mm Hg
]which one of the three has a high amount of oxygen for corneal metabolism?
Atmosphere/aqueous humor/ limbal vasculature
atmosphere
Corneal (endothelium/epithelium) consumes 10times more oxygen compared to the (descements membrane/stroma)
epithelium, stroma
How is oxygen delivered to the cornea when you are asleep or closed-eyed?
(bulbar/superior palpebral/ inferior palpebral conjunctiva)
by the vascularized superior palpebral conjunctiva
T/F oxygen is delievered at reduced levels
T
\_\_\_% of oxygen is delivered at reduced levels with eyelid open and \_\_% with eyelid closed A)15, 8 B)21, 10 C)15, 10 D)21, 8
D)21, 8
T/F aphakia is the absence of the eye crystalline lense
T
Post-cataract surgery(aphakia) oxygen tension may (increase/decrease) in the aqueous humor secondary to (increased/decreased) oxygen metabolism by the crystalline lens
increase, decrease
In aphakia , the oxygen in (atmosphere/aqueous humor/limbal vasculature) supplements that in the tears helping to meet oxygen demands and providing (lower/greater) tolerance to hypoxix stress ( oxygen deficiency)
what is a example of this? (using glasses or CL)
aqueous humor
greater
CL
Metabolic requirements for nutrients are supplied to the cornea by the (vitreous humor/aqueous humor/limbal vasculature)
aqueous humor
compared to the aqueous humor (Greater/lesser) amounts of nutrients for the cornea are available in the tears and limbal vessels
lesser
Glucose can be derived from the glycogen stores in the corneal (endothelium/epithelium)
epithelium
Hard contact lens wearers (increase/decrease) available oxygen to corneal epithelium with nearly ___% of reserved used up in __ hours of wear
a) 80% 8 hours
b) 80% 12hours
c) 60% 8 hours
d) 60% 12 hours
This results in conreal _____, in that there is a 20% (increase/decrease) in corneal thickness
decrease
A) 80% 8 hours
edema
increase
With an increase in time, glycogen content in the cornea (decreases/increases) in hard lens wearers compared to soft lens wearers
decreases
Glucose derived from the (aqueous humor/vitreous humor) or glycogen stores is converted to pyruvate by _____-____ pathway and yields
___ number of ATP per glucose molecules
A)3
B)2
C)4
D)8
aqueous humor
embden-meyerhof
2
Under hypoxic (oxygen deficent) conditions , increase in (glucose/lactate) producution which causes cornea ____
lactate, edema
Halo and rainbow formation
increased glare sensitivity
decreases contrast sensitivity
are all symptoms of what?
epithelial edema
Stromal edema manifests in the (anterior/posterior) direciton because the (anterior/posterior) surface is fixed by which two?
descemets memrane/posterior stroma/ bowman’s membrane/anterior stroma
posterior
anterior
bowman’s membrane, anterior stroma
Buckling of which two corneal layers gives rise to vertical striae(wrinkles or folds cause by abnormal pressure)?
endothelial/epithelial/stroma/bowman’s layers/ decement’s membrane
stroma/descemets membrane
Deturgescent (decrease in swelling) can be maintained with a sustaine oxygen level as low as
___mmHg
A)35
B)25
C)20
D)30
25
T/F Small diameter lenses are permeable to oxygen and have no movement needed for tear exchange
F. Small diameter lenses are IMPERMEABLE to oxygen and have GOOD movement needed for tear exchange
T/F Large diameter soft lenses are oxygen impermeable for diffusion through the lens itself
F. large diameter soft lenses oxygen permeability needed for diffusion though the lens itself, tear pump exchange helps to a lesser extent.
Certain byproducts of long term hypoxia and stress that is 12 HETE(12-Hydroxyeicosatetrainoic acid) have the abiity to inhibit what part of the corneal endothelia ?
This occurs in (short/long) term , volume regulation stress (like Cl wearers, and corneas of diabetic patients)
Na+K+ATPase metabolic pump
long
Contact lens wearers stimulate –> _____ acid this produces–> _____ –>which produces two eicosianoids (12HETE and 8RHDDTrE) —->which diffuses into stroma and inhibits corneal endothelial ____________
arachnoid,
P450
Na+K+ATPase metabolic pump
Decreased rate of mitosis
Reduced oxygen uptake and glucose utilization
smaller numbers of intercellular desmosomes are all associated with what?
Extended wear contact lenses which alter metabolism
Because extended wear lenses alters metabolism it (increases/reduces) metabolic activity and compromises the (endothelial/epithelial) barrier function
decreases
epithelial
Under hypotic conditions there is a increased likelihood of ulcerative microbial keratitis
T
Ulcerative microbial keratitis (loss of luster and transparency)
Xerophthalmia is caused by lack of vitamin __. This occurs (late/early) in the progression of the vitamin deficiency and found in the corneal (endothelium/epithelium)
A
late
epithelium
Vitamin A is required for ____ production
mucin
T/F Xerophthalmia is nonkeratinzaiton of the corneal epithelium
F. KERATINIZATION
T/F Xerophthalmia is found primarily in children of developing countries
T
T/F Xerophtalmia is not a disease that shows there is sociaeconomic, cultural , and political conditions that often account for nutritional deficiency
F IT IS
Volume of adult tear film : __to__microliter
A)8-10
B)8-9
C)7-10
D)7-9
7-9
what is the max amount of cul-de-dac fluid in microliters?
A10-30
B)20-30
C)40-50
D)10-50
20-30 microliter
Average drop of topical meds is ____microliters
A)30
B)20
C)40
D)50
50 microliters
T/F reflex tearing causes slower tear dilution
F. FASTER
Increased protein in tears of inflamed /infected eyes (increases/decreases) bioavailabitliy of the drug
decreases
What limits the absorption of hydrophillic , ionized substances and favors penetration of lipid-soluble hydrophobic compounds
initial barrier: epithelium (tight junctions)
loss of corneal _(endothelium/epithelium)__ greatly enchances penetration of hydrophilic water-soluble pharmacologic agents
epithelium
_____ is a pharmacologic agent that normally traverse the epithelium via transcellular or paracellular routes
gentamicin
Stroma of the cornea has a (hydrophilic/hydrophobic) nature which results in a barrier to (aqueous/lipid) based drugs
hydrophobic, lipid
In the endothelium drug penetration is deteremined mostly by molecular __(shape/size)_
size
Pressing on lacrimal sac
use viscous drops, suspensions, ointments
slow-release delivery systems
contact lenses
porcine collagen corneal shields
–these are all was to (increase/decrease) what through the cornea ?
increase drug penetration
and also increase duratoin of contact of the drug with the ocular surface
Drug ___ are used to prolong shelf life of drugs and protect the eye from infection (prevent bacterial growth
preservatives
Benzalkonium chloride (BAK) , chlorhexidine digluconate, polyquaternium-1 , and thimerosal are all what?
Drug preservatives
What is the most commonly used drug preservative used : Benzalkonium chloride (BAK) , chlorhexidine digluconate, polyquaternium-1 , and thimerosal
BAK
Which drug preservative has been largely discontinued : Benzalkonium chloride (BAK) , chlorhexidine digluconate, polyquaternium-1 , and thimerosal
due to allergic reaction -thimerosal
T/F many topical medication are used to treat ocular disease which include antibiotics , antivirals drugs, antiallergy drugd, and artificial tears for treatment of dry eye
T
T/F the drug BAK can do damage only do damage to epithelium of the cornea
F. Endothelium and epithelium
antibacterial action of BAK breaks down bacterial cell _____ and has a _____ property,
walls, detergent
T/F BAK would not be able to inhibit wound healing
F. it does inhibit epithelial wound healing
One drop of 0.01% BAK causes (increase/decrease) in permeability of the cornea to flourescein
increase
T/F pt with severe dry eye have decreased fluorescein permeabilty therefore compromising their corneal epithelial barrier
F. INCREASED
What drug preservative is used to stabilize BAK ?
EDTA (ethulenediaminetetraacetic acid)
EDTA chelates __(chloride/postassium/calclium) __which is required for maintenance of tight junctions
calcium
T/F when possible ophthalmic products should contain EDTA , especially those for dry eye patients
F. Should NOT
Benzalkonium chloride (BAK) , chlorhexidine digluconate, polyquaternium-1 , and thimerosal
Which two drugs cause endothelial cell degeneration and corneal edema in vitro
BAK, chlorhexidine
