Flashcards in Exam 1 Remington- Cornea Deck (123):
What are the two functions of the cornea?
Transmission and Refraction
What is refraction of the cornea dependent on?
Curvatures, length, different indices
Anterior diameter of the cornea
12 mm horizontal, 11 mm vertical
Posterior diameter of the cornea
Horizontal and vertical diameters of 11.7 mm, sclera impinges inferiorly into cornea
Central thickness of the cornea
Peripheral thickness of the cornea
Anterior radius of curvature of the cornea
Posterior radius of curvature of the cornea
_____ radius of curvature means a steeper curve
What is regular astigmatism?
Principle meridians 90 degrees apart
What are 3 types of regular astigmatism?
WTR, ATR, and oblique
What is WTR astigmatism?
Vertical meridian is steepest (shortest radius of curvature) think football
What is ATR astigmatism?
Horizontal meridian is steepest
What is oblique astigmatism?
Steepest meridian at 45 or 135 degrees
What is irregular astigmatism?
Principle meridians are not 90 degrees apart
How is irregular astigmatism corrected?
What is the function of the plasma membrane lipid bilayer?
Controls molecular entrance and exit
What is the function of the cytoskeleton?
Structure and intercellular transport
What is the function of ribosomes?
What is the function of the endoplasmic reticulum?
What is the function of the Golgi apparatus?
3 types of cellular transport
Diffusion, facilitated diffusion, active transport
What do aquaporins do?
What type of channels are aquaporins?
Bidirectional in the cornea and lens
3 types of cell surfaces
Apical, lateral, and basal
What is a basal cell surface?
Sits on basement membrane, connective tissue
The basement membrane consists of what 2 types of lamina?
Basal and reticular
Basal lamina is secreted by what cell?
Reticular lamina secreted by what cell?
What are the 2 shapes of intercellular junctions?
Zonular and macular
Belt-like goes all the way around cell
What are the 2 types of intercellular junctions?
Adhering and occluding
Adhering intercellular junction
Narrow intercellular space, transmembrane adhesion molecules, and contributes to cell stability
Occluding intercellular junction
Focal fusion of outer leaflet of plasma membranes, seals off intercellular space (NOTHING gets through)
What is a terminal bar?
Adjacent ZO + ZA
Circular attachment plaque, filaments extend into cellular cytoplasm, adhesive mucoprotein fills intercellular space
Attachment of basal surface to underlying CT, filaments join intercellular plaque to plaque in CT
Kind of tube, sends from one cell to the next rapidly
Transmembrane channel or pore
What does a connexon do?
Joins cytoplasm of adjoining cells
A connex___ is composed of 6 protein connex___
What do gap junctions do?
Permits passage of small molecules, nutrients, and ions
Gycoprotein covering surface of the cell
The corneal epithelium consists of what kind of cells?
What does the surface layer of the corneal epithelium consist of?
Non-keratinized, microvilli, glycocalyx, intercellular junctions (desmosomes and zonular occludens)
What is the function of zonular occludens in the intercellular junctions?
What is the purpose of fluorescein straining in evaluating the corneal epithelial surface?
Evaluates the barrier function of the surface layer
What happens when fluorescein is instilled in the tear film?
Flurescein will not penetrate the epithelial tissue as long as ZO are intact. If disrupted, dye can pass through Bowman's layer into the anterior stroma.
What is in the wing cell layer of the corneal epithelium?
Intercellular junctions ( desmosomes and gap junctions), DOES NOT contain ZO
What is known as the transition layer of the corneal epithelium?
Wing cell layer
What is known as the germinative layer of the corneal epithelium?
What intercellular junctions are in the basal layer of the corneal epithelium?
Desmosomes, gap junctions, hemidesmosomes
What secretes the basal lamina portion of the BM?
In hemidesmosomes, fibrils attach to _____ in stroma
What do plaques contain?
What are two causes of recurrent corneal erosion?
EBMD ( epithelial basement membrane dystrophy) and incomplete healing of abrasion
Condition caused by defective nutrition or metabolism, also malformed hemidesmosomes
What are signs and symptoms of recurrent corneal erosion?
Areas of sloughed epi, pain
What is the treatment of recurrent corneal erosion?
Bandage contact lens and corneal puncture
What does corneal puncture do?
Stimulates BM adhesion
Epithelial replacement is _______
Where does cell division occur in the corneal epithelium?
The basal cells in the corneal epithelium is replenished from what?
Stem cells in the limbus
How do cells move in epithelial replacement?
Basal layer to wing cell layer to surface, barrier function maintained
Where are surface cells sloughed?
Into tear film
What is the cellular composition of Bowman's layer?
Dense irregular CT, acellular
Bowman's layer is considered a ______ layer
How is Bowman's layer compared to the stroma?
Smaller and less regular fibers than stroma
Bowman's layer is produced _____ and cannot be _______
What is a pterygium?
Conj invades corneal tissue, Bowman's layer is lysed
What is another name for stroma?
What is the cellular composition of stroma?
Regular dense CT, collagen fibrils, fibroblasts, ground substance
What is lamellae?
Bundles of collagen
What is the orientation of lamellae?
Fibers are parallel to surface
What is the extent of fibers for the lamellae?
Fibers extend from limbus to limbus
The _____ stroma has a higher incidence of cross liniing among collagen fibers than ______. Why?
Anterior, posterior. Creates more rigidity helping to maintain corneal curvature
What are two names (same cell) for the cells in stroma?
What junctions are fibroblasts joined by in the stroma?
Gap junctions (can get between cells quickly)
What is ground substance composed of?
Proteoglycans and glycosaminoglycans (GAGs)
What do proteoglycans so?
Increase tensile strength
What are GAGs?
Negatively charged side chains
Are GAGs hydrophilic or hydrophobic?
What do GAGs do?
Maintain component spacing
What is the theory of transparency?
Light should pass straight through the cornea, scattered light causes glare
How are fibers arranged in the theory of transparency?
Fibers arranged in a regular lattice pattern
_____ interference occurs in the theory of transparency
What is reduced in the theory of transparency due to destructive interference?
Light scattering is reduced, as long as the distance between different refractive indices is less than 1/2 wavelength of light
What is the relationship between destructive interference and light scatter?
When does the cornea lose transparency?
If the spacing is disrupted
What is keratoconus?
Corneal dystrophy, caused is nutritional or metabolic
What is the initial disruption in keratoconus?
BM and Bowman's
Keratoconus eventually involves what?
Significant stromal thinning
What type of astigmatism does keratoconus produce?
Irregular astigmatism, cannot be corrected with spectacles
What may slow the progression of keratoconus?
What is Munson's sign in keratoconus?
Lower lid conforms to conic shape on down gaze
Currently clinical trials are evaluating collagen cross linking to what?
Slow disease progression
What is collagen cross linking?
Riboflavin saturates the cornea and is then activated by ultraviolet light, this increase cross linking between collagen fibrils thus strengthening the cornea and may arrest the progression of keratoconus
What is the cellular composition of Descemet's membrane?
Dense CT, acellular
What is the BM of corneal endothelium?
Descemet's membrane is highly resistant to ______ ______
Descemet's membrane has ________ properties
What is the termination of Descemet's membrane in the corneal periphery?
How are the cells in the endothelium arranged?
Regular arrangement = endothelial mosaic
What % of cells are hexagonal in the endothelium?
The endothelium does not _______; cells just spread out. Cells appear to be in ______ state.
What are the 4 intercellular junctions in the endothelium?
Lateral interdigitations, gap junctions, occluding junctions, and modified hemidesmosomes
What are occluding junctions?
"Slightly leaky" barrier
What are Hassall-Henle bodies?
Thickenings in Descemet's membrane, they are a normal physiological aging change
Deposits in Descemet's membrane indicative of dysfunction
Recent studies suggest that there is this collagenous layer between stroma and Descemet's membrane
What cells are Dua's layer composed of?
Acellular and composed primarily of collagen type 1
The presence of Dua's layer might be important for what?
Current corneal transplant procedures
Are there corneal BVs?
Why are there no corneal BVs?
There may be an antiangiogenic agent present
What type of sensory innervation is in the cornea?
The cornea has about ____ times as many sensory fibers in the tissue than anywhere else in the body
How many bundles of axons enter the corneal periphery?
Fibers lose the myelin sheath within ___ mm into cornea
What is the innervation pattern of the cornea?
Stomal plexus, subepithelial plexus, intraepithelial plexus
How many axons are in the stromal plexus?
What happens in the intraepithelial plexus?
Schwann cells covering loss as fibers pass through Bowman's