CorneaSclera 1 Flashcards

Question

which cranial nerve is exposed as a result of ebmd

Answer 1

this occurs in diabetic and older pts. associated with an increased incidence of epithelial erosions. This abnormality of epithelial adhesion may be a result of a reduced depth of penetration of anchoring fibrils through the thickened basement membrane into the stroma. Due to thickness..fibrils can't get through cornea

Answer 2

if easy to dislocate, epi can have erosions you have pain etc Increases chances because epi is exposed and you have no sensation Diabetic have greater chance of infection; blood flow is not good in diabetics Epi is protection of cornea and prevent infection Peripheral nerves will die Loss of innervation in cornea Epithelium is not good/ you’ll experience pain but if nerves arent functioning Don’t feel senses as normal ppl would do…they don’t feel it…increases chance if infection

Answer 3

aka Basal Lamina Basal cells of epithelium rests on basal lamina ≈ 40-60 nm thick Contains: type IV collagen, laminin, the proteoglycan perlecan, fibronectin, and fibrin

Answer 4

Abrasion of the corneal epithelium demands a prompt healing response Must recover the exposed basement membrane with cells After the abrasion, mitosis ceases and the attachment to the basement membrane is lost Cells enlarge, the epithelial sheet migrates by ameboid movement to cover the defect (When you have injury…first step is to close the wound)

Answer 5

to form a barrier to invasion of the eye by pathogens and to uptake of excess fluid by the stroma.

Answer 6

Mitosis resumes An experimental epithelial wound 6mm in diameter is closed with 48 hours and the rate of epithelial cell migration is 60 to 80 µm/hr. An early observation in studies of the cell biology of corneal epithelial wound healing was that protein synthesis by epithelial cells increases during cell migration.

Answer 7

Cell Migration requires ENERGY increase in glycolytic activity during cell migration decrease in glycogen levels in the migrating cells Cells are dependent on anaerobic glycolysis (quick!)

Answer 8

Following wounding of rat corneas, increased expression of glucose transporter GLUT1 mRNA is detectable by 2 hours after wounding, and GLUT1 protein levels increase by 4 hours, peaking at 24 hours after wounding and remaining elevated for at least 2 weeks. By this mechanism, an adequate supply for support of the healing response is maintained.

Answer 9

Synthesis of the growth factors and their receptors increases after corneal wounding, again accounting for the increase in protein synthesis after wounding. Epidermal growth factor (EGF) is present in tear fluid and EGF mRNA is expressed by corneal epithelium, whereas keratocyte growth factor (KGF) and hepatocyte growth factor (HGF) are synthesized by stromal keratocytes.

Answer 10

healing is delayed or normal adhesion is not established

Answer 11

length of cell cycle decreases replication increases When wounding occurs, the length of the cell cycle in the peripheral epithelium and limbus decreases and the number of rounds of replication of transient amplifying cells in the limbus and peripheral corneal increases. After wound healing, the adhesion of the epithelium is reestablished by formation of new hemidesmosomes in the basal cell layer. Periphery of cornea has more nutrition and blood supply through diffusion

Answer 12

the adhesion of the epithelium is reestablished by formation of new hemidesmosomes If the basement membrane is NOT damaged, normal epithelium with adhesion complexes is formed quickly If the basement membrane is damaged, the formation of adhesion complexes is delayed

Answer 13

basement membrane is removed. a new basement membrane must be formed by epitheleial development of normal adhesion delayed for more than 2 months

Answer 14

``` Beneath the Basement Membrane “modified superficial layer of stroma” ≈ 12 µm thick Made of randomly arranged collagen fibrils Type I collagen Acellular ```

Answer 15

An extracellular matrix (ECM) comprised of a lamellar arrangement of collagen fibrils Parallel to corneal surface Individual collagen fibrils separated by a matrix of proteoglycans Keratocytes and fibroblasts – produce and maintain the ECM

Answer 16

``` 200-250 lamellas of collagen fibers Run limbus to limbus Anterior stroma = lie obliquely Posterior stroma = lie orthogonally At the limbus the fibers run circumferentially forming an annulus 1.5 to 2.0 mm wide around the cornea ```

Answer 17

Collagen fibers are made of: Mostly type I collagen Also type V and VI collagen Refractive index n= 1.411 for the collagen fibers n= 1.365 for the extrafibrillar matrix Despite the disparity, minimal light scattering occurs (only 10%): because of the highly uniform size and spacing of the collagen fibers!

Answer 18

Maurice proposed that corneal transparency is a consequence of a crystalline lattice arrangement of collagen fibrils within stromal lamellas and that light scattered by individual fibrils of uniform diameter is canceled by destructive interference with scattered light from adjacent fibers; therefore light is scattered only in the forward direction. Such an arrangement requires that all collagen fibrils be of equal diameter and that all fibrils be equidistant from each other. Subsequent studies showed that these conditions are not satisfied in the cornea.

Answer 19

Compared to the cornea, in the SCLERA: Fibers are large with greatly varying diameters Not orderly or closely spaced This is why the sclera has a great deal of light scatter and is nontransparent

Answer 20

must be less than1/2 the wavelength of visible light The sizes of collagen fibers do vary, abeit within a relatively small range. Although the collagen fibers vary in diameter, they remain weak scatterers of light because their diameter is a small fraction of the wavelengths of visible light. Edema would increase size between fibrils

Answer 21

With damage to epithelial or endothelial barrier, the cornea swells = loss of corneal transparency This dependence of corneal transparency on the distribution and size of collagen fibrils is supported by observations of swollen corneas and by the structure of the opaque sclera. When the epithelial or endothelial barrier of the cornea is damaged, the stroma imbibes water and swells, leading to a loss of corneal transparency. This uptake of water causes formation of “lakes” devoid of collagen fibers within the stroma. This causes increased divergence of refractive index within the stroma, as well as an increase in distance between collagen fibrils, leading to a wavelength-dependent loss of light transmittance that increases with the amount of corneal swelling.

Answer 22

Fibril diameter: Anterior cornea > Posterior cornea Density of fibrils: Anterior cornea < Posterior cornea It was found that fibril diameter is greater in the anterior cornea than in the posterior cornea, and that the density of fibrils is lower in the anterior cornea than in the posterior cornea in both rabbits and humans. This leads to a twofold (in humans) and threefold (in rabbits) increase in light scatter by the anterior cornea as compared with the posterior cornea.

Answer 23

Water evaporates from the corneal surface at a rate of 2.5 µL/cm2/hr. Evaporation accounts for a 5% thinning of the cornea during the day, compared with the corneal thickness measured when the eyelids open in the morning after nighttime closure. In patients with comprised endothelial metabolic pump function, such as in Fuch’s endothelial dystrophy, epithelial edema is worse in the morning when arising as a result of lack of evaporation at night when the lids are close. Loss of water= 5% leaves cornea in morning Thickness of cornea changes throughout the day ``` Epith not functioning properly Takes in nutrients As water goes out- takes nutrients Water coming in and out of cornea should be same rate….fuchs nothing oushing out= fuchs Edema worse in morning ```

Answer 24

Corneal drying may result in Dellen Dellen Localized area of corneal drying and evaporation Persistance of dellen may reflect: a decrease in stromal fluid flow when stroma hydration is abnormal or minimal lateral flow of water in the cornea

Answer 25

Normal cornea maintains a constant thickness (where IOP is below 50 mm Hg) Because stromal swelling pressure is in a similar range If the IOP is higher than 50 mm Hg or if there is abnormal endothelial function: there is epithelial edema and increased stromal thickness

Answer 26

True Thus mild corneal edema with elevated pressure can lead to high imbibition pressure and subsequent epithelial edema and bullae.