Cornea Flashcards
what is included in the outermost fibrous tunic of the eye
the transparent cornea and the opaque sclera
how much of the eyeball does the cornea contribute
1/6th
what is the corneoscleral limbus
the area of the merging of the cornea and the sclera
how much refractive power does the cornea contribute
(43.1 to 48.8D) 3/4
how thick is the central and peripheral part of the cornea
the center is about 0.52mm and increases to 0.70mm
how big is the optical zone
the central 1/3 of the cornea or 4mm
what are the 5 layers of the cornea
epithelium, bowman’s layer, stroma, descemets membrane, endothelium
what cells make up the corneal epithelium
stratified nonkeratinized, nonsecretory, squamous epithelium
is the corneal epithelium regularly or irregularly arranged
regular to permit light to enter
what cells are absent in the center of the corneal epithelium that are present in the periphery
melanocytes and immunocompetent dendritic cells
what is the most superficial layer of the corneal epithelium
the apical layer
what does the apical layer of the epithelium secrete
glycocalyx- also has microvilli and ridges to increase the surface area to stabilize the tear film
how are the apical cells joined together
tight junctions along the lateral walls to prevent passage of fluid between the cells and excessive uptake of fluid from the tear film
what layer is directly below the apical layer
wing cell layer
how do the wing layer connected
via desmosomes and communicate gap junctions
what shape are wing cells
polyhedral , anterior surface is convex/posterior concave to fit over the basal cells
what is the basal cell layer (basement membrane) made of
columnar cells, stand in perfect alignment
how do the basal cells attach to the basement membrane (basal lamina)
hemidesomosomes, communicate with gap junctions
how is the basement membrane formed for the basal cell layer of the epithelim
secreted by the basal cells, anchored by fibrils pass through the basement membrane and bowmans layer
how are the basal cells and the wing cells connected
via desmosomes
when the basal cells are migrating toward the center of the cornea, where do they originate from peripherally
the Palisades of Vogt
what are the Palisades of Vogt
located in the radial folds of the epithelium of the limbus, may harbor stem cells
which layer of the corneal epithelium undergoes mitotic division
the basal cells
what is the second layer of the cornea
bowman’s layer
why is bowman’s layer not a membrane
It is PAS -
can bowman’s layer regenerate?
No, it is produced pre-natally, lacks keratocytes (fibroblast) cells
what replaces bowman’s layer if it is damaged
the epithelium thickens in its place
which layer of the cornea is the thickest, about 90%
the stroma (substantia propria)
what is the stroma made of
an extracellular matrix of arranged collagen fibers
how far apart must the collagen fibrils be to keep the cornea transparent
must be less than one half the wavelength of visible light (400-700nm)
where is descemet’s membrane
lies on the posterior surface of the stroma (substantia propria) serving as a basement membrane for the corneal endothelium
which layer of the cornea thickens from birth to adult
Descemet’s membrane
can descemet’s membrane be reformed if damaged
yes
what is Schwalbe’s line
the anterior border ring of the trabecular meshwork- where Descemet’s membrane abruptly stops at the corneal margin
what are Hassall-Henle Bodies
small transparent growths, that increase with age, on the posterior surface of Descemet’s membrane at the periphery of the cornea, they protrude the anterior chamber
what is corneal guttata
when Hassall-Henle Bodies occur in the central cornea instead of the periphery
what is the corneal endothelium comprised of
single layer of flat, hexagonal arranged cells, uniform size, with the apical end facing the anterior chamber and basal ends apposed to Descemet’s membrane
what type of barrier does the corneal endothelium provide
a leaky barrier allowing nutrients from the aqueous humor to enter the avascular stroma
what junctions are connecting the corneal endothelium cells
macula occludens, dont completely encircle the cells to allow a leaky barrier
what is the corneoscleral limbus
junction of the cornea and the sclera, encircles the peripheral cornea, external scleral sulcus is here
where are the trabecular meshwork and canal of schlemm located
in the internal scleral sulcus
at the corneal periphery, which structures are continuous with others
corneal epithelium- conjunctival epithelium, corneal stroma- scleral stroma, corneal endothelium- endothelial cells of trabecular meshwork
which layers terminate at the corneal periphery
Bowmans layer and Descemet’s membrane
what is the sensory innervation to the cornea
long ciliary nerves from the ophthalmic division of the trigeminal nerve
where do the long ciliary nerves travel to reach the cornea
through the perichoroidal space between the sclera and the choroid
which layers of the cornea do not have innervation
Descemet’s layer and corneal endothelium
