Cornea Scott B6 Flashcards
What gives sensory to the cornea?
V1 ophthalmic
The cornea is part of the _______ tunic.
fibrous
What is unequal curvature of the cornea?
astigmatism
What is flat and steep meridians are 90 degrees apart?
Regular astig
What is steeper in vertical meridian?
With the rule astig
What is steeper curvature in the horizontal meridian?
Against the rule astigmatism
what is steeper curvature in oblique axis?
Oblique astigmatism
What is where the steepest and flattest meridians are not 90 degrees apart?
Irregular astig
What is unequal curvature of the lens?
Lenticular astig
Thicker cornea = ________, false IOP measurement
higher
Thinner corneas = ______, false IOP measurement
lower
__________ measures central corneal thickness using ultrasound.
Pachymeter
When might you want to use a Pachymeter?
Glaucoma, refractive surgery
Fascia bulbi that strongly adheres to episclera and conjunctiva.
Bulbar limbus
This is the juncture of cornea and sclera, 1-2 mm wide.
Corneoscleral junction
conjunctiva extends 1 mm beyond corneoscleral limbus
Conjunctival limbus
Central 4 mm of eye
Optical zone
Anterior cornea has what liquid?
Aqueous humor
Lens has what kind of liquid?
Vitreous humor
Name some defining factors of corneal histology.
Predominantly extracellular material
Covered on each surface by sheet of cells
Anterior epithelium has 4 layers
Posterior epithelium is monolayer
Attached via basement membranes
Stroma is bulk of cornea (ordered collagen layers)
What are the 5 layers of the cornea?
Tear Film Anterior Epithelium Bowman's layer Stroma Descemet's membrane Endothelium Aqueous Humor (anterior chamber)
Lipid or oily layer is secreted by ______________ glands in the palpebrae and caruncle
meibomian
Aqueous layer is secreted by the _______ gland.
lacrimal
Mucous layer is secreted by the ________ cells in the conjunctiva.
goblet
Oily layer prevents the _______ layer from evaporating , while the mucous layer decreases __________ and provides a smooth, wetable surface for the aqueous layer.
aqueous
surface tension
Name the 3 layers of the tear film from anterior to posterior.
Lipid layer
Aqueous layer
Mucous layer
Corneal epithelium has ______________ cells and rests on a ______________.
Stratified squamous (flat) Basement membrane
Corneal epithelium is composed of 5-7 cell layers what are they?
Apical (superficial layer)
-1-2 layers of flat squamous cells near surface
2-3 layers of wing cells
-Attach to each other by desmosomes and gap junctions
A single layer of columnar basal cells
______________ are between lateral surfaces of apical cells.
Tight junctions
Wing cells have ___ layers centrally and ___ layers peripherally.
2-3
4-5
Wing cells posterior surface is ________ and anterior surface is ________.
concave
convex
Basal cells are columnar and attached to the basal lamina by _______________.
hemidesmosomes
Adjacent basal cells communicate via __________and are attached to each other via __________.
gap junctions
desmosomes
Hemidesmosomes attach to what?
Basement membrane
Replacement of the corneal epithelium only takes ____ days, but damage to basement membrane can take months to repair.
7 days
Scratch on the cornea, usually painful but not severe. common in sports from scratch of fingernail
Corneal abrasion
___________ is used to assess damage to corneal epithelium. Will not stain intact cells
Fluorescein dye
This structure harbors stem cells around the corneoscleral limbus.
Palisades of Vogt
Bowmans layer characteristics
Structural support
Randomly oriented collagen fibers
No keratocytes (acellular)
contains channels for passage of nerve fibers
cant be stripped away from stroma as continuous sheet like descemets can.
Does not regenerate
if damaged is replaced by thickened epithelium (aka epithelial facet)
This has 90% of corneal thickness
Collagen, keratocytes, ground substance
GAGs pull aqueous humor into cornea
Keratocytes maintain ground substance and collagen interspersed between lamella
Stroma
___________ are flat cells, that reside between stromal lamellae, and communicate via gap junctions.
Keratocytes
Stromal lamella have what kind of spacing?
Ordered spacing… 1/2 wavelength of visible light
This is a thinning of the stroma leading to bulging of the eye.
Keratoconus
In advanced keratoconus the corneal protrusion may cause angulation of the lower lid on down gaze.
Munson’s sign
If you see a asymmetry of arcus senilis you can suspect a blockage of _________.
Internal carotid
Descemet’s membrane characteristics
Basement membrane of endothelium
Thickens throughout life
Regenerates if damaged
In descemet’s membrane: anterior banded zone is laid down _______ birth. and posterior banded zone is laid _____ birth.
before
after
Kayser-fleisher ring (copper deposits in descemet’s membrane)
Wilson’s disease
Corneal endothelium characteristics:
Monolayer of cells composed of about 400,000 to 500,000 cells
Flat and hexagonal in shape
Apex faces anterior chamber
Cells pump aqueous humor out of cornea to maintain hydration
Joined by maccula occludens (leaky barrier)
Form gap junctions with adjacent cells
No pump action causes stromal edema
As corneal endothelial cells become stressed they dropout. Remaining cells do what?
Remaining cells expand in size and shape to compensate. Less pump available to counterbalance leak of aqueous humor into corneal stroma.
True/False: Cornea is avascular.
True, nutrients are derived from tear film and aqueous humor
How many anterior ciliary arteries are there?
7 every rectus muscle has 2 except lateral rectus has 1
If cornea is inflammed and you have “redness and ciliary flush”, what are the likely vessels that are involved?
Superficial plexus: Anterior conjunctival vessels
If cornea is inflammed and you have “pinkness and ciliary flush”, what are the likely vessels that are involved?
Deep plexus: Iris and ciliary body
The ________ is one of the most highly innervated structures in the body.
cornea
therefore it is 300 to 600 times more sensitive than skin
Cornea receives sensory innervation via the _____________.
Long posterior ciliary nerves
Long posterior ciliary nerves course in the ___________ space. They go and make two plexus, what are they?
suprachoroidal
Intraepithelial plexus
Subepithelial plexus
Know briefly how PRK works.
Numbing drops
Smoothens surface of cornea
Laser reshapes corneal surface
Bandage like soft contact lens is put on the cornea until it heals.
Lasik surgery is done how.
Flap cut around cornea and folded back
Anterior stroma ablated using laser
Flap is replaced
What is the surgery called where incisions are cut around the stroma to flatten the cornea?
Radial Keratotomy
What would be a couple ways of correcting irregular astigmatism?
Penetrating keratoplasty or corneal transplant
Scleral contact lenses
How do scleral contact lenses work?
Liquid reservoir between cornea and contact neutralizes irregular surface of cornea
What are a few pros and cons of Scleral contact lenses?
Pro: Comfort, Lens life 8-10 years, Short adaptation period, many diseases can be treated
Con: High initial cost, more chair time, poor fit can lead to complications (pinching artery), no overnight wear
