Ocular Exam 1 - Study Guide

fibrous tunic

sclera, cornea 

vascular tunic/uvea

iris, ciliary body, choroid

retina layer

Retinal pigmented epithelium, neural layer

Cornea make up x/6 of the fibrous tunic

1/6

Cornea structural function

maintains globe shape 

cornea’s protection function

against external penetration and UV light

cornea’s refractive function

principle refracting surface

sclera makes up x/6 fibrous tunic

5/6

structural purpose of the sclera

mantains the globe shape

sclera protection purpose 

against external penetration

sclera function

attachment site for EOM’s

horizontally the cornea is how wide in diameter?

12mm

vertically the cornea is

11 mm

the cornea shape is

aspherical and prolate

aspherical

curvature is flattened from center to periphery

prolate shape

looks like a grape, vertical axis is longer 

Power of the cornea

+42.00 D

factors that directly affect the amount of corneal refraction

change of index (air to cornea or from cornea to aqueous humor, curvature of the anterior corneal surface and posterior surface 

eccentricity

rate of flattening of the cornea from center to the periphery

example of corneal abberations

flattned cornea (lasik), irregular corneal shape, uneven curvature

corneal thickness centrally to peripherally

540 to 670 mm

Layers of the cornea

epithelium

bowman’s layer

stroma

descemet membrane 

endothelium 

how many microns thick is the epithelium?

50 mm

how many microns thick is bowman’s layer?

10 mm

How many microns thick is the stroma

500 mm

how many microns thick decemet’s layer

4-16mm 

How many microns thick is the endothelium

5 mm

What are the layers of the corneal epithelium

1 layer columnar basal cells, 2-3 layers wing cells, 2-3 layers of surface cells

what happens to the corneal epithelium thickness throughout the lifetime?

stays the same

What happens to the paracentral and peripheral epithelium, especially near the limbus

thins with age

Basal cells

only mitotically active cells in the corneal epithelium

basal cells produce what?

basal lamina/ basement membrane

hemidesmosomes

attach basal cells to the basement membrane via integrins and other protein complexes

Achoring plaques

EMC structures, link hemidesmosomes to collagen fibrils in the stroma 

T or F Desmosomes and gap junctions are less numerous in basal cells

true

wing cells

polygonal shape with cytoplasmic wing like extensions

how are wing cells joined to each other

desmosomes (to the surface and basal cells) and gap junctions

Surface cells

flattened, non-keratinized squamous cells

What are microplicae and microvilli for?

increase surface area for tear film interaction

microvilli

finger like

microplicae

ridges

apical surface cells (microvili and microplicae) do what?

stabilize the tear film by binding to mucin via glycocalyx

tight junctions encircle what structures to create barriers that block tear fluid and pathogens from entering the cornea

surface cells

how long does it take for the cornea epithelium to renew/turnover

7-10 days

what is the source of renewal for corneal epithelium renewal?

stems cells located in the limbus (palisades of vogt)

stem cells divide symmetrically or asymmetrically?

asymmetrically - produce one stem cell and one transient amplifying cell

what does a transient amplifying cell do?

migrate towards the basal layer and populate it

corneal wound healing phases

latent phase, migration, proliferation, epithelium reattachment 

What happens in latent phase of corneal epithelium wound healing?

hemidesmosomes and desmosomes disassemble, surrounding epithelial cells change shape (flatten)

Migration phase of healing

basal cells slide over exposed basement membrane

actin filaments and integrins guid migration

proliferation of epithelial wound healing

basal cells undergo mitosis to restore cell numbers

cells stratify and differentiate into normal layers

epithelial reattachment

new hemidesmosomes, desmosomes, tight junctions, and anchoring fibrils form

basement membrane reattaches 

corneal epithelium- langerhan cells

type of dendritic cell (APC)

Where are langerhan cells?

normally in the peripheral cornea, rarely central when healthy

what do the langerhan cells do?

capture and process antigens, migrate to regional lymph nodes, activate t cells, increase in number and migrate centrally

what are some inflammatory conditions that can cause langerhan cells to be activated?

infection, dry eye, contact lens wear, keratitis

Bowman’s Layer

randomly dispersed collagen fibrils

no cells present here 

can the bowman’s layer regenerate?

no- replaced by epithelial cells or stromal scar tissue if injured

is the bowman’s layer impacted during PRK

yes, but it has no detrimental effect

what is the function of the bowman’s layer?

physical barrier, resisting injury or infection from penetrating deeper into cornea

Stroma

90% of total thickness of cornea, 78% water

What is the composition of the stroma?

collagen fibrils, keratocytes, extracellular ground substance (matrix)

What is largely determined by the stroma?

strength, shape, clarity of cornea

The stromal collagen fibrils are organized how?

lamelle

How many lamelle are on the cornea

200-300

fibrils of collagen in the stroma are what

regular spaced (latticework) and parallel to the cornea

near the limbus, what happens to collagen fibrils of the cornea

the diameter increases 

how far do stromal collagen fibrils extend?

limbus to limbus

adjacent lamelle are at angles, but are what to the corneal surface

parallel

keratocytes

synthesizes collagen and extracellular matrix

dendritic cells

phagocytic immune cells

what is the ground subtance or extracellular matrix function

fill in the area between lamelle and cells

what is the composition of ECM/ ground substance 

proteoglycans = core protein + GAGs 

What do GAG's do?

hydrophilic, negatively charged, attract water

Why are GAGs important

maintain precise spatial relationship between fibrils

Descemet’s Membrane

basement membrane of corneal endothelium

What are the two layers of descemet’s layer

anterior banded layer

posterior non-banded layer 

Corneal endothelium barrier function

cells act as a leaky barrier that allows nutrients to diffuse from the aqueous humor into the stroma

Corneal endothelium pump function

ionic pumps actively transport fluid out of the stroma and into the anterior chamber

What is the corneal endothelium make up

monolayer of hexagonal cells

corneal endothelium cell density

4000

how much corneal endothelium cell loss do we have per year

1%

What does loss of endothelium cells cause 

cell migration and morphology 

can endothelial cells regenerate

no

polymegathism

variability in cell size

polymorphism

variation in shape

guttata

small, droplet like deposits or thickening 

what causes guttatta 

loss or dysfunction of endothelial cells 

Basement membrane growths in the periphery, not a problem are called what?

Hassall-Henle Bodies

What drives water out of the stroma into aqueous humor

active ion transport system

corneal sensory nerve

CN5, branch V1

density of corneal nerve endings is greater or less centrally than peripherally

greater

sensory nerve networks 

supepithelial, subbasal, intraepithelial

supepithelial location

anterior stroma

subbasal

between bowman’s and basal epithelium

Intraepithelial

naked nerve endings between cells

most of the nerves serving the cornea enter form where

nasal and temporal limbus

What happens to nerves as they move radial

they lose their myelin sheath

corneal nerve function

sensory detection, reflex tear production, blink reflex, neuropeptide secretion

Where does the cornea receive nutrients from?

diffusion from air, aqueous humor, limbal conjunctiva and episceral capillaries