Term
| What is the cornea part of? What is it embryologically related to? |
|
Definition
| Cornea part of outer coat (1/6th) of the eye, it is embryologically related to the skin (surface ectodermal cells) |
|
|
Term
| What does the cornea lack? |
|
Definition
| Smooth muscles and blood vessels. |
|
|
Term
| Functions of the cornea? (2) |
|
Definition
Optical function
1) transparency (must be maintained)
2) refraction (responsible for 2/3 of refraction taking place in the eye)
- Protection - somewhat rigid fibrous structure. |
|
|
Term
|
Definition
| 11.7 X 10.6 mm (horizontal x vertical) |
|
|
Term
| Central thickness of cornea |
|
Definition
| 535 um (Doughty), or .0535mm |
|
|
Term
|
Definition
1) Anterior: 7.8mm
2) Posterior 6.42 mm |
|
|
Term
| Front surface refractive power |
|
Definition
|
|
Term
| Refractive index of cornea |
|
Definition
|
|
Term
| Percent collagen in cornea? Other proteins? |
|
Definition
| Collagen: 15%, other proteins 5% |
|
|
Term
|
Definition
1) Epithelium (outermost)
2) Anterior Limiting Lamina (Bowman's Membrane"
3) Stroma
4) Posterior Limiting Lamina (Descement's Membrane)
5) Endothelium (innermost layer) |
|
|
Term
| Ocular surface formed by what distinct epithelia? How many? |
|
Definition
| 3 continuous but distinct epithelia: corneal, limbal & conjunctival epithelium. |
|
|
Term
| The corneal epithelium makes up about what % of corneal thickness? |
|
Definition
|
|
Term
| Corneal epithelium: what type of layer/how many layers |
|
Definition
| Stratified layer, 5-7 layers of tightly packed cells |
|
|
Term
| Embryologically, epithelium derived from where? |
|
Definition
|
|
Term
| Why in a normal eye epithelium not keratinized? |
|
Definition
| Does not express the cornified cytoskeleton in typical epidermal cells (can have keratinization in severely dry eyes/vitA deficiency) |
|
|
Term
| What are the 3 types and shapes of cells in the epithelium? |
|
Definition
Basal cells (tall columnar),
Wing cells (umbrella/intermediate),
Squamous cells (flattened) |
|
|
Term
| Where are basal cells attached & underlying ALL |
|
Definition
Basal cells attached to the basement membrane
Underlying ALL - hemidesmosomes |
|
|
Term
| Thickness of BM? Does it increase in thickness? |
|
Definition
| 120 -200 nm, increases 3nm per year for the young |
|
|
Term
| When are signs of duplication of BM epithelium common? |
|
Definition
| Older persons 60 yrs or higher, signs of duplicate BM are common. |
|
|
Term
| Where do basal cells form numerous desmosomal contacts with neighbors? |
|
Definition
|
|
Term
| Why are there desmosomes and interdigitations for the epithelium? |
|
Definition
| Makes the epithelium mechanically strong and capable of resisting mechanical shearing forces (rubbing eye, contact lens wear) |
|
|
Term
| What is the weakest part of the epithelium? |
|
Definition
| Columnar basal cell layer |
|
|
Term
| Why is the columnar basal cell layer so weak? |
|
Definition
| Cells will rupture just internal to the nuclei, leaving the basal plasma lemma and some cytoplasm still attached to the basement membrane |
|
|
Term
| Where do mature basal cells migrate? |
|
Definition
| Anteriorly towards the tear film |
|
|
Term
| What happens once a basal epithelial cell has lost its contact with the basement membrane? |
|
Definition
| Becomes post-mitotic, loses its capacity to divide. |
|
|
Term
| How does the squamous epithelial cells leave the corneal epithelium? |
|
Definition
| Sloughed off into the tear film |
|
|
Term
| What mechanism drives this process of cell exfoliation? |
|
Definition
|
|
Term
| How long does it take for some basal cells to reach the surface once they leave the basement membrane? |
|
Definition
|
|
Term
| Total epithelial renewal takes how many days? |
|
Definition
|
|
Term
| What 3 factors is the corneal epithelial renewal rate dependent upon? X+Y=Z |
|
Definition
X = overall basal cell mitosis
Y = slow centripetal movement from the periphery to the center of the cornea
Z - loss of surface cells |
|
|
Term
| About how many cells at any given time undergo mitosis? |
|
Definition
|
|
Term
| When traumatized, initial epithelial response is to INHIBIT or PROMOTE mitosis? |
|
Definition
| Inhibit mitosis, promote cell migration to surface layer. |
|
|
Term
| After trauma, when later mitotic activities return, how many cells undergo mitosis on day 3? day 6? day 10? |
|
Definition
day 3 = 53%
day 6 = 14%
day 10 = 4% |
|
|
Term
| What cell layer does mitosis predominantly occur? |
|
Definition
|
|
Term
| Which cell layer has high level of metabolic & synthetic activity (i.e., extra mitochondria & more prominent Golgi apparatus) |
|
Definition
|
|
Term
| Basal cells have large reserves of what component to be used in case of epithelial stress? |
|
Definition
|
|
Term
| What is the heigh of basal cell's columnar shape? |
|
Definition
|
|
Term
|
Definition
| Convex external surface & concave internal surface |
|
|
Term
| Wing cells contain what type of filaments? What are they made up of? |
|
Definition
| Tonofilaments, made up of cytokeratins |
|
|
Term
| What is the shape of squamous cells? |
|
Definition
| Flattened polygonally shaped, large cytoplasm/nucleus ratio |
|
|
Term
| What type of junction do squamous cells exhibit? |
|
Definition
| Zonula occludens/tight junctions - prevents fluid from leaking into the cornea. |
|
|
Term
| What do squamous cells have to absorb nutrients from the tear film and to harbor a thin glycocalyx layer? |
|
Definition
| Microvilli and microplicae |
|
|
Term
|
Definition
| A glycoprotein secreted b the epithelial cells, important for the adherence of mucus component of tear film. |
|
|
Term
| Where are the corneal epithelium stem cells believed to be located in the basal cell layer? |
|
Definition
|
|
Term
| Mechanical removal of central epithelium results in what type of recovery? |
|
Definition
|
|
Term
| Removal of the limbal epithelium leads to what damage? |
|
Definition
| Permanent damage to both l limbal and corneal epithelium with loss of central transparency and vascularization . |
|
|
Term
| Limbal stem cells are slow or fast-cycling? |
|
Definition
Slow cycling (don't divide frequently)
Can keep on dividing forever - slow but steady |
|
|
Term
| Stem cells give rise to daughter cells which do what? |
|
Definition
| Move centripetaly to form the basal epithelial cells of the cornea. |
|
|
Term
| Renewal rate of corneal epithelium is altered for what type of person? |
|
Definition
Contact lens wearer
1) basal cells divide at a lower rate due to oxygen transmissibility rate of contact lens material
2) epithelial cells migrate at a slower speed
3) normal apoptotic epithelial surface cell death significantly reduced |
|
|
Term
| Controlled regeneration of epithelial cells & continuous departure of cells from corneal surface? |
|
Definition
| Programmed cell death aka desquamation |
|
|
Term
| In the XYZ theory, what do they stand for? |
|
Definition
X = overal basal cell mitosis to the surface
Y = slow centripetal movement of cells (epithelial cells migrate from periphery --> center of cornea)
Z = loss of surface cells |
|
|
Term
| In a normal corneal epithelium, what percentage of cells undergoing mitosis? apoptosis? |
|
Definition
| 4% undergoing mitosis, 1% undergoing apoptosis |
|
|
Term
| Programmed cell death is a genetically controlled event. How? |
|
Definition
| A signal transduction cascade, reduces mitochondria permeability which downstream, effects the death effectors |
|
|
Term
| Apoptotic characteristics for the corneal epithelium? (5) |
|
Definition
Cell shrinkage
Chromosomal condensation
Cytoplasmic blebbing
Nuclear degeneration
Final step: PHAGOCYTOSIS (receptors in the cell membrane) |
|
|
Term
| Desquamation is a what type of process? without what? |
|
Definition
Apoptotic, orderly process
WITHOUT inflammatory response, necrotic death or injury |
|
|
Term
| what are the 3 theories on how cells are dying? |
|
Definition
1) classic apoptosis: cytoplasmic blebbing, nuclear degeneration
2) terminal differentiation: cells randomly/spontaneously shed away from corneal surface. NO SIGN of apoptosis
3) ghost cells - anucleate, prior to being sloughed off into the tear film |
|
|
Term
| during wound healing, increase/decrease of epithelial cell apoptosis at site of injury? |
|
Definition
|
|
Term
| As cells at surface prepare to die, underlying cells secrete what MUCINS? |
|
Definition
| MUC1,4,16 ( at corneal epithelium and tight junction proteins) |
|
|
Term
| Why are tight junction proteins important? |
|
Definition
| To maintain tight barrier and resist invasion. |
|
|
Term
| Surface of epithelium exposed to myriad of forces which induce cell-shedding. What are these forces? (3) |
|
Definition
Hypoxia - eyes closed when sleeping and wearing contact lenses
Shearing force from blinking |
|
|
Term
| The highest number of apoptotic cells are where on the cornea? |
|
Definition
|
|
Term
| Apoptosis is a direct result of what? |
|
Definition
Blinking of eyelid or,
overall movement of cells themselves from peripheral to central (basal to surface) |
|
|
Term
| Hypoxia causes increase/decrease of epithelial shedding? |
|
Definition
| DECREASE in cell shedding (CL wearers have tons of corneal ulcers) |
|
|
Term
| Dry eyes (increase/decrease) cell shedding? |
|
Definition
|
|
Term
| Non-epithelial cells in the epithelium consist of: |
|
Definition
langerhan cells
neurons,
WBC (should not be present unless active pathological condition) |
|
|
Term
| Langerhan cells are located where? |
|
Definition
| Peripheral, always in basal cell layer. Afferent and efferent limb of immune response. |
|
|
Term
| What causes LOSS of langerhan cells? |
|
Definition
|
|
Term
| What causes INCREASE of langerhan cells in the cornea? |
|
Definition
| Overnight contact lens wear |
|
|
Term
| Langerhands (more/less) numerous in cornea to skin? |
|
Definition
| LESS. But they are in the peripheral and basal cell layer of the corneal epithelium. |
|
|
Term
| If the epithelial injury is DEEPER than the epithelium... |
|
Definition
|
|
Term
| if the epithelial injury is within the epithelium... |
|
Definition
|
|
Term
| blunt injury to the eye, what happens to the columnar basal cells? |
|
Definition
| will rupture below the nucleus leaving the BM still attached to the ALL |
|
|
Term
| Hemidesmosomes are attached to what in the epithelium? |
|
Definition
|
|
Term
| ALL shows what types of collagen fibers? |
|
Definition
Type I
Type 7 - fibrils anchor BM to stromal tissue |
|
|
Term
|
Definition
| Mostly in basal cell layer, also in some wing-cell layers |
|
|
Term
|
Definition
| loss of superficial layers with Zonular occuldens to allow fluid to enter the epithelium, fluid accumulation separates the cells making them even more fragile. |
|
|
Term
| What is the function of the numerous tiny microvilla/microplicae that form the surface of the apical epithelium? |
|
Definition
1) stabilize tear layers
2) increase SA of the cornea |
|
|
Term
| 6 functions of the epithelium |
|
Definition
1) physical protection - renewable protective layer of the ocular surface
2) refraction
3) UV radiation filter - overall contribution to corneal blocking of UVR
4) tear stabilizing - microvilli along epithelial surface for stabilizing tears
5) fluid barrier - epithelial surface has zonular occludens
6) microorganism sheild - tight barrier against invasion |
|
|
Term
| The Anterior Limiting Lamina aka Bowman's Membrane is how deep |
|
Definition
|
|
Term
| What is acellular with modified stromal tissue? |
|
Definition
|
|
Term
| ALL has what type of collagenous fibers? |
|
Definition
Type 1
Type 7 - fibrils fused with BM anteriorly/posteriorly and ground substance at ALL to contribute to epithelial adherence |
|
|
Term
|
Definition
|
|
Term
| Light scatter with the ALL? |
|
Definition
| Little to no light scatter |
|
|
Term
| The ALL + stromal interface has tissue overlapping of what in both directions? |
|
Definition
|
|
Term
| the shallow overlapping of 2 tissues is for what purpose? |
|
Definition
| an optical function (rather than structural requirement) |
|
|
Term
|
Definition
|
|
Term
|
Definition
|
|
Term
| The stroma is derived from what? |
|
Definition
|
|
Term
| The stroma is derived from what? |
|
Definition
|
|
Term
| Peripherally, the stroma is continuous with what? |
|
Definition
|
|
Term
| Name the fiber collagen types in the stroma |
|
Definition
Type 1 collage - bulk of stroma
Type II - cultured embryonic cornea
Type III - stromal repair
Type IV - BM at anterior/posterior extremes of the stroma
Type V & VI - also present |
|
|
Term
| What is collagen in bundles called in the stroma? |
|
Definition
|
|
Term
|
Definition
| fixed cells between the lamellae, parallel to the corneal surface. |
|
|
Term
| What gives the transparency of the cornea? |
|
Definition
| Uniform arrangement of lamellae and collagen fibers |
|
|
Term
| How many lamellae give or take are in the stroma? |
|
Definition
|
|
Term
| Keratoconus is due to loss of what? What % of population have it? |
|
Definition
Loss of lamellae
Thinning of lamellae
Loss of keratocytes
Happens (1/2000) pple |
|
|
Term
| Keratoconus is the condition of what? |
|
Definition
| weakening of anterior ectasia |
|
|
Term
|
Definition
thinner, more intertwined
more keratocytes
terminate centrally in the cornea |
|
|
Term
|
Definition
thicker
placed flat over each over
bridge the entire cornea |
|
|
Term
| 1st sign of stromal edema (vertical striae) |
|
Definition
| POSTERIOR aspect, because posterior separates 1st before anterior lamellae (intertwined) |
|
|
Term
| the ALL is parallel with what? |
|
Definition
|
|
Term
| The anterior lamellae approaches the ALL to level off and run parallel. Where do they terminate? |
|
Definition
| In the sub-ALL, in electron-dense formations (EDF) |
|
|
Term
|
Definition
Electron-dense formations
Provide anchorage for terminating lamellae ending with the central corneal zone. |
|
|
Term
| What provides evidence that lamellae do not cross the cornea from limbus to limbus? |
|
Definition
|
|
Term
| What is the diameter of collagen fibers forming lamellae? |
|
Definition
|
|
Term
| What is sensitive to the envt? |
|
Definition
|
|
Term
| Low/acidic pH (5.75) causes what to stromal collagen |
|
Definition
| Disorganization of fibrils |
|
|
Term
| Transparency is maintained in the stroma as long as... |
|
Definition
| the distance between fibrils do not exceed 1/2 of the wavelength |
|
|
Term
| What is the number 1 cell in the corneal stroma? What else is located in the stroma? |
|
Definition
Keratocytes = #1
also have PMN, lymphocytes, plasma cells, and histiocytes in the stroma |
|
|
Term
| How many keratocytes in the adult cornea? |
|
Definition
|
|
Term
| Are there keratocytes in the ALL? Where are kertocytes densest? |
|
Definition
No keratocytes in the ALL
Greatest density right below the ALL in the stroma
Progress deeper in the stroma, keratocyptes drop by 30% |
|
|
Term
| Pattern of keratocytes in the stroma? |
|
Definition
| Clockwise spiral throughout |
|
|
Term
|
Definition
Flattened to paper-thin proportions
Extend laterally & vertically
give rise to "translamellar keratocytes" or TLK |
|
|
Term
| How are adjacent keratocytes linked? |
|
Definition
|
|
Term
| Keratocytes are derived from what? |
|
Definition
| Embryonic mesoderm (fibroblastic) |
|
|
Term
|
Definition
| Mitochrondria, RER, Golgi, and more |
|
|
Term
| In corneal development, keratocytes are responsible for production of what? |
|
Definition
Mucopolysaccharides
Collagen fibers (ground substance) |
|
|
Term
| Keratocytes process of synthesizing new collagen lasts how long? |
|
Definition
|
|
Term
| Which type of cells are responsible for their own structural integrity? |
|
Definition
|
|
Term
| Non-pathological stroma has a (fast/slow) turnover of mucopolysaccharides? |
|
Definition
|
|
Term
| How do keratocytes help insure corneal transparency? |
|
Definition
| Tethering of collagen lamellae, insures regular arrangement |
|
|
Term
How do keratinocytes communicate laterally?
Vertically? (for anterior/posterior communication) |
|
Definition
Laterally - gap junctions
Vertically - anterior/posterior communication - TLK |
|
|
Term
| Individual keratinocytes are how far apart? |
|
Definition
|
|
Term
| How do keratinocytes have a functional role in healing the corneal stroma? |
|
Definition
|
|
Term
| 5 functions of keratinocytes? |
|
Definition
1) matrix turnover (healing process)
2) intracorneal communications
3) reservoir for glycogen (energy source)
4) intralamellar tethering (corneal transparency)
5) wound healing - secrete new matrix |
|
|
Term
| What is the thickness of the PLL also known as Descemet's Membrane? |
|
Definition
|
|
Term
| at birth, what is the thickness of the PLL? |
|
Definition
| 3um (grows +1um per 10 years) |
|
|
Term
| which layer synthesizes and secretes constructive material for the PLL? |
|
Definition
|
|
Term
| peripheral PLL thickening is known as |
|
Definition
|
|
Term
| central cornea thickening in the PLL is known as... |
|
Definition
| guttata (or latin: guttae) |
|
|
Term
| abnormal endothelial BM synthesis due to thickening in the central cornea is called? |
|
Definition
|
|
Term
| What is Fuch's dystrophy? |
|
Definition
| thickening of PLL in the central cornea, disrupts the endothelial pump. |
|
|
Term
| Fuch's dystrophy may lead to the loss of what? |
|
Definition
| corneal transparency (keratoplasty) |
|
|
Term
| How is edema avoided in the endothelium? |
|
Definition
| Keep coverage of posterior cornea |
|
|
Term
| anterior protruding of PLL which follows erosion of overlying stroma |
|
Definition
|
|
Term
| single layer of flat squamous and hexagonal cells that cannot reproduce |
|
Definition
|
|
Term
| what is the thickness of the endothelium? |
|
Definition
|
|
Term
| where is the endothelium formed from? |
|
Definition
|
|
Term
| where does the endothelium terminate as a monolayer? |
|
Definition
| at the periphery, the limbus (but continues in a modified form to become the trabecular meshwork) |
|
|
Term
| the endothelium continues in a modified form after the limbus to become... |
|
Definition
|
|
Term
| How many endothelial cells does one have at birth? |
|
Definition
|
|
Term
| How many endothelial cells does one have at 20-30 yrs? |
|
Definition
|
|
Term
| How many endothelial cells does one have at 40-50 yrs? |
|
Definition
|
|
Term
| How many endothelial cells does one have at 80 yrs? |
|
Definition
|
|
Term
| What is the functional limit of endothelial cells? |
|
Definition
|
|
Term
| what causes the loss of endothelial cells? |
|
Definition
age
may be accelerated by trauma, surgery, disease, UVR |
|
|
Term
| What percentage does central endothelial cell density decrease at? |
|
Definition
|
|
Term
| the ability of the endothelial cells to completely cover the posterior corneal surface is more important for what? |
|
Definition
| contribution to corneal transparency than fluid pump function |
|
|
Term
| what happens without complete coverage of the endothelium? |
|
Definition
|
|
Term
| endothelial cells are densely packed with what? |
|
Definition
|
|
Term
| the endothelium controls the movement of fluid between what? |
|
Definition
|
|
Term
| when fluid imbalance in the endothelium is disturbed, what happens? |
|
Definition
edema
lose transparency of the cornea |
|
|
Term
what substance travels into the cornea from aqueous?
what travels out of the cornea to mix with the aqueous? |
|
Definition
|
|
Term
| zonular occludens, desmosomes, hemidesmosomes, gap junction: make up what type of corneal cell? |
|
Definition
|
|
Term
| zonular occludens/tight junction, zonular adherens/intermediate, gap junctions and significant BM secretion: what type of corneal cell? |
|
Definition
|
|
Term
| in the endothelium, what junctions are on the apical side? what is their function? |
|
Definition
tight junctions (zonular occludens)
function: to limit the movement of fluid between the cells |
|
|
Term
| what pattern do tight junctions surround the cell? |
|
Definition
| discontinuous, to limit but not exclude fluid movement |
|
|
Term
| endothelial lateral walls have what type of junctions? function? |
|
Definition
gap junctions, apical side
facilitate cellular exchange and communication. NOT a barrier to fluid movement |
|
|
Term
| This junction in the endothelium, weaker than desmosomes, is structural in function by supporting cell to cell adherence |
|
Definition
| Intermediate junction (zonular adherens) |
|
|
Term
| These cells react to chronic anterior hypoxia (usually from CL) |
|
Definition
|
|
Term
| variability in cell area: |
|
Definition
|
|
Term
| originally, in the endothelium, cells are what size/shape? |
|
Definition
uniform in size & shape
always hexagonal |
|
|
Term
| Cells become 5 or 7-sided as a result of |
|
Definition
| chronic hypoxia (usually from CL wear) |
|
|
Term
| What happens in contact lens-induced polymegethism? |
|
Definition
| forces associate with extracellular fluid movement and accumulation affect the 3-d shape |
|
|
Term
| imbalance of fluid movement in the endothelium leads to what? |
|
Definition
| lateral sides to re-orientate themselves, but then being unable to refold, adapt an oblique angle compared to the normal vertical orientation |
|
|
Term
| the stretch lateral sides unable to refold in the endothelium leads to what? |
|
Definition
| lots of overlapping, which leads to a cell having a large anterior but small posterior surface or vice versa. |
|
|
Term
| endothelial cells alter their shape, what stays the same? |
|
Definition
|
|
Term
some endothelial cells are larger than others due to what?
why? |
|
Definition
trauma, UVR, aging
due to losing cell density and neighboring cells spreading out to fill the gap |
|
|
Term
| neighboring cells spreading to fill the gap due to loss of cell density explains: |
|
Definition
| polymegethism & polygonality |
|
|
Term
| why is CL-induced polymegethism different in etiology? |
|
Definition
| no associated cell lose, no space to fill |
|
|
Term
| a variation in cellular size |
|
Definition
|
|
Term
|
Definition
|
|
Term
| cells with a varying number of sides |
|
Definition
|
|
Term
| EDF have a projection size of what? |
|
Definition
|
|
Term
| nerves lose their myelination how far into the cornea? |
|
Definition
|
|
Term
| which direction do nerves enter the eye as short ciliary nerves close to the ONH? |
|
Definition
|
|
Term
| long ciliary nerves enter the eye in what direction? |
|
Definition
| horizontally, more anteriorly |
|
|
Term
| nerves enter posteriorly as... |
|
Definition
| short ciliary nerves (close to the ONH) |
|
|
Term
| nerves enter horizontally and more anteriorly as |
|
Definition
|
|
Term
| corneal nerves utilize what type of neurotransmitters? |
|
Definition
|
|
Term
| corneal nerves traverse approx how much of the cornea? |
|
Definition
|
|
Term
| nerve fibers enter the cornea and move in which direction? branch in which direction? |
|
Definition
| radially, branching towards the apex |
|
|
Term
| what continues into the suprachoroid layer and superior aspect of the ciliary body after entry into the cornea? |
|
Definition
|
|
Term
| the cornea's normal touch threshold is |
|
Definition
|
|
Term
| contact lens wearers have a (higher/lower) touch threshold? |
|
Definition
|
|
Term
| reduced corneal sensitivity in CL wearers is related to what? |
|
Definition
|
|
Term
| greater Oxygen permeability means |
|
Definition
| the less loss of sensitivity |
|
|
Term
| 2 corneal nerve functions |
|
Definition
1) defense
2) trophic (loss of corneal nerves leads to neuroparalytic keratitis) |
|
|
Term
| loss of corneal nerves leads to what? |
|
Definition
|
|
Term
| origin of corneal nerves (2) |
|
Definition
- ophthalmic division of CNV1 (bulk of corneal sensory fibers)
- maxillary division |
|
|
Term
|
Definition
1) epithelium - most dense
2) stroma - 2nd line of defense |
|
|
Term
| where is there little communication between 2 plexi? |
|
Definition
|
|
Term
| stromal nerve fibers terminate very close to where? |
|
Definition
|
|
Term
| stromal nerve fibers respond to what type of stimuli? |
|
Definition
|
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Term
| epithelial nerve fibers found close/deep to epithelium? |
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Definition
| deep (in the basal cells) |
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Term
| why is it important that epithelial nerve fibers found deep? |
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Definition
| allows for trauma without sensation |
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Term
| are epithelial nerve fibers limited to the basal cell layer? |
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Definition
| no, a few small twigs (single axons) - move anteriorly between cells to just beneath surface squamous layer |
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Term
| small nerve branches that move from the stroma into the epithelium traversing the ALL: |
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Definition
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Term
| ramus perforans are most infrequent in the |
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Definition
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Term
| epithelial and stromal plexi function (together/separate) |
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Definition
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Term
| located where: these nerve fibers do not have a schwann cell wrapping/"naked" |
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Definition
| nerve fibers in the epithelium |
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Term
occurs in the PNS.
have schwann cells (myelin insulation) |
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Definition
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Term
| myelinated nerve fibers lose their myelin sheat when? |
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Definition
| 1.5mm into the cornea, after the nerves transverse the limbus |
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Term
what: schwann cell wrapping, no myelin sheath
found: |
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Definition
unmyelinated nerve fibers
found: corneal stroma |
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Term
| nerve fiber without schwann cell or myelin wrapping |
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Definition
NAKED
ALL EPITHELIAL nerve fibers are naked. |
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Term
| what are the naked nerve fibers in the corneal epithelium accompanied by to acts as a schwann cell? |
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Definition
| infolding of epithelial cells |
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Term
| free, unspecialized nerve endings. no special end organ which exists in the skin |
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Definition
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Term
| nerve fibers can often end in a series of swelling, appearing how? |
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Definition
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Term
| corneal nerve fibers convey what types of stimuli |
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Definition
touch, pain = primary
temperature = also sensed (less) |
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Term
very few mitochondria.
small consecutive dilations along fibers
found close to the BM |
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Definition
| simple terminal nerve type |
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Term
| large terminal nerve types: |
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Definition
larger (0.5-2um)
packed with mitochondria |
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Term
Rank in terms of sensitivity, give touch threshold for each
Corneal apex
Corneal conjunctiva
Cornal periphery |
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Definition
| Corneal apex 20> Periphery 40> Conj 70-200 (peaks in the fornix) |
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Term
| lid margin has a cornea touch threshold of |
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Definition
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Term
| caucasian blue eyes have a corneal touch threshold of |
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Definition
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Term
| caucasian hazel eyes have a corneal touch threshold of |
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Definition
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Term
| caucasian green eyes have a corneal touch threshold of |
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Definition
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Term
| caucasian brown/dark brown eyes have a corneal touch threshold of |
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Definition
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Term
African dark brown eyes have a corneal touch threshold of:
Asian? |
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Definition
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Term
Soft contact lens wear: cornea touch threshold
Rigid Gas Perm: CL wear |
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Definition
20-40 mgm/mm2
30-50 mgm/mm2 |
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Term
| after how many hours of CL wear till touch threshold increases? |
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Definition
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Term
| What causes reduction in corneal sensitivity |
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Definition
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Term
| age 31-40 have a touch threshold of |
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Definition
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