Cornea 1

What are the major concepts regarding the Cornea?

1. Part of fibrous tunic

2. Transparent

3. Tough

4. Highly innervated

5. Avascular

6. Major REFRACTIVE component of the Eye

What are the dimensions of the cornea?

Anterior 1/6th of the eye

Area: 1.3 cm²

Steeper curvature vs Sclera

What is the External Scleral Sulcus?

Where the cornea and sclera meet

What is the anterior dimensions of the corneal?

Horizontal: 11.7-12.6 mm

Vertical: 10.6-11.7 mm

What are the dimensions for Posterior Cornea?

Horizontal/Vertical: 11.7 mm

What is the overall dioptric power of the WHOLE cornea?

+43.00 D

What are the Radius of curvature for the Cornea?

Anterior: 7.8 mm

Posterior: 6.5 mm

What is the refractive index of the Cornea?

1.376

What type of refractive error is most common?

Axial

What is Astigmatism?

Unequal curvature of refractive structures

Multiple focal points, can’t be focused as one on the retina

What is WTR, ATR, and Oblique Astigmatism?

WTR— Steeper in Vertical meridian (power is in the horizontal)

ATR— Steeper in the Horizontal meridian (power is in the vertical)

Oblique— Steeper curvature in oblique axis (neither 90 or 180 and outside the range)

What is Irregular and Lenticular Astigmatism?

Irregular— Steepest and flattest meridians are NOT 90 degrees apart

Lenticular— Unequal curvature of the lens.

What is the Average Central Corneal Thickness?

520-550 um

What is the average Peripheral Corneal thickness?

670 um

What happens if there are thick or thin corneas to IOP?

Thick— Artificially high IOP

Thin— Artificially low IOP

****Thin central corneas are a risk for Glaucoma

African Americans generally have thinner corneas

What is a Pachymeter?

Measures central corneal thickness with ULTRASOUND

What is the Bulbar Limbus?

Fascia Bulbi (Tenon’s capsule)— Green

Strongly adheres to episclera and conjunctiva

What is the Corneoscleral Limbus?

Juncture of cornea and sclera, 1-2 mm wide —Blue

***You shouldn’t see blood vessels grow past the Corneoscleral Limbus

What is the Conjunctival Limbus?

Conjunctiva extends 1 mm beyond corneoscleral limbus —Red

What is the optical zone?

Central 4mm of cornea —yellow

What are some characteristics of the Corneal Tear Film?

3 microns thick

3 layers

Volume of 6.2 microliters

Rate of production 1.2 microliters/sec

What makes up the lipid layer?

Secreted by Meibomian glands

What makes the aqueous layer?

Lacrimal gland

What makes the mucous layer?

Goble cells in Conjunctiva.

Is the tear film distinct layers?

No, form a colloidal matrix

What is glycocalyx?

Secreted by epithelial cells

Includes trans membranous mucins

What are the characteristics of Corneal Histology?

Predominantly Extracellular material

Sheet of cells

Anterior epithelium has 5-7 layers

Endothelium is MONOlayer

Attach via basement membranes

What are the layers of the Cornea?

1. Epithelium

2. Bowman’s layer

3. Stroma

4. Descemet’s membrane

5. Endothelium

What are the characteristics of Corneal Epithelium?

Non-keratinized Stratified squamous epithelium

50-60 um in thickness

Continuous with bulbar conj. epithelium

Melanocytes and Langerhann’s cells

ANCHORS TO basement membrane

How many layers make up the Epithelium?

5-7

What cell types make up the Epithelium?

Apical (superficial layer), 1-2 layers

Wing cells, 2-3 layers, Desmosomes/gap junctions

Columnar basal cells, held to Bowman’s layer by hemidesmosomes.

Why is Microplicae important?

Helps maintain mucoid layer

Loss of these “ridges” can lead to dry eye symptoms.

What is found between Apical cells?

TIGHT JUNCTIONS

Zona Occludens take 1 hr to reform

What are the characteristics of Wing Cells?

Attached to adjacent cells via desmosomes

Gap junctions

Become flatter the higher they move to surface

What are some characteristics of Basal Cells?

Attached via desmosomes

Gap Junction

Mitotic division

What is the Lamina Lucida?

Translucent layer of Basement Membrane

What is Lamina Densa?

Dark layer composed of collagen

Below Lamina Lucida

What are the two layers of the Basement Membrane?

Lamina Lucida, Densa

How long does it take to replace corneal epithelim?

7-10 days

If the basement membrane gets damaged, how long does it take to repair?

Months

Why is Adhesion Complexes important?

It keeps epithelium from sloughing off

Be able to know where gap junctions and Hemidesmosomes are at

Draw

Where are Langerhan’s Cells found?

Peripheral cornea

Antigen recognition and processing

Where are Melanocytes found?

Peripheral cornea

What are Palisades of Vogt?

Limbal stem cell population

What are these structures?

A. microplicae

B. Corneal nerve

C. Bowman’s layer

D. Naked nerve

E. Lymphocyte

F. Basement membrane

G. Anterior Stromal lamellae

What is a corneal abrasion?

Scratch on the cornea

Painful, but not usually severe

Symptoms of Corneal Abrasion

Pain

Foreign body sensation

Tearing

Discomfort when blinking

What do you do with a Corneal Abrasion?

Rinse with clean water/saline

DO NOT RUB

Aggressive lubrication, antibiotic ointment or drops.

What are some Epithelial Dystrophies?

Meesman’s Dystrophy

Subepithelial Mucinous Dystrophy

Gelatinous Drop-like Dystrophy

What are some characteristics of Bowman’s Layer?

Structural support

Oriented collagen fibers

NO KERATOCYTES

8-12 um thick

Pores for passage of corneal nerve fibers

DOS NOT REGENERATE

If damaged, replaced by thickened epithelium

Is Bowman’s membrane a true basement membrane?

NOPE

Characteristics of the Stroma?

90% of Corneal thickness

450-500 um

Collagen, Keratocytes, ground substance

Collagen organized in layers (lamellae)

GAGS pull aqueous humor into cornea

Keratocytes interspersed between lamella (maintains collagen/ground substance)

What is Munson’s sign?

You can see Keratoconus corneal protrusion when pt. looks at down gaze

What are some Stromal Dystrophies?

Lattice Dystrophy Type 1

Granular Dystrophy Type 2

Schnyder’s Dystrophy Type 1

Congenital Stromal Dystrophy