Cornea (Dr. Scott)

Question 1

Describe the surface anatomy of the cornea

Answer 1

• Part of fibrous tunic
• Transparent and tough
• Avascular
• Highly innervated

Question 2

What is the thickness of the corneal tear film?

What is it made up of?

Answer 2

• 7 microns thick

- Made up of electrolytes, metabolites, proteins, enzymes and lipids

Question 3

Describe the limbal region.

Answer 3

• Bulbar Limbus: Tenon’s capsule strongly adheres to episclera and conjunctiva; outermost limbus
• Corneoscleral Limbus: Juncture of cornea and sclera; middle limbus
• Conjunctival Limbus: Conjunctiva extends 1 mm bdyond corneoscleral limbus

Question 4

Describe the dimensions of the cornea

Answer 4

• Anterior 1/6 of eye
• Area is 1.3 cm^2
• Steeper curvature than sclera

Question 5

The cornea is a major _____ component of the eye

Answer 5

Refractive

Question 6

Which has a steeper curvature, the sclera or the cornea?

Answer 6

Cornea

Question 7

What are the horizontal and vertical dimensions of the anterior view of cornea?
Radius of Curvature?

Answer 7

• Slightly Elliptical
• Horzontal: 11.7 - 12.6 mm
• Vertical: 10.6 - 11.7 mm
• Radius of Curvature: 7.8 mm

Question 8

What are the horizontal and vertical dimensions of the posterior view of cornea?
Radius of Curvature?

Answer 8

• Circular
• Horizontal and Vertical: 11.7 mm
• Radius of Curvature: 6.5 mm

Question 9

What is the overall dioptric power of the cornea?

Answer 9

3/4 refractive power of the eye

Ranges from 43.1 - 48.8 D

Question 10

What is the index of refraction of the cornea?

Answer 10

1.376

Question 11

Define astigmatism and differentiate between regular and irregular astigmatism.

Answer 11

• Unequal curvature of cornea
• Regular: flat and steep meridians are 90 degrees apart (With the rule - steeper in vertical meridian; Against the rule - steeper in horizontal meridian; Oblique - steeper in oblique axis)
• Irregular: steepest and flattest meridians are not 90 degrees apart

Question 12

What is lenticular asigmatism?

Answer 12

Unequal curvature of the lens

Question 13

What is the average corneal thickness?

Answer 13

• Central: 0.52 mm

- Peripheral: 0.70 mm

Question 14

What is the optical zone of the cornea?

Answer 14

Central 4 mm

Question 15

What is the rate of production of tear film?

Answer 15

1.2 microliters/minute

Question 16

What are the 3 layers of the corneal tear film and what secretes each layer?

Answer 16

1. Lipid/Oily: Secreted by meibomian glands in the palpebrae and caruncle
2. Aqueous layer: Secreted by lacrimal gland
3. Mucous layer: Secreted by the goblet cells in the conjunctiva

Question 17

Describe the function of the oily and mucous layers of the tear film

Answer 17

Oily: Helps prevent the aqueous layer from evaporating
Mucous: decreases the surface tension and provides a smooth, wetable surface for the aqueous layer

Question 18

What is the glycocalyx?

Answer 18

Very thin layer between the tear film (mucous layer) and the cornea surface

Question 19

What disease could result due to a poorly functioning or absent lipid layer of the tear film?

Answer 19

Dry Eye Disease - because the lipid layer would not be preventing tears from evaporating

Question 20

What are some symptoms of dry eye?

Answer 20

• Itching, burning, dry
• Sensitivity to light/blurry vision
• Problems wearing contact lenses
• Watering eyes

Question 21

What is a corneal abrasion?
What are symptoms?
First reaction?
What to do?
Treatment?

Answer 21

• Scratch on cornea, usually painful but not severe
• Pain, feeling that something is in eye, tearing, discomfort when blinking
• First reaction is to rub eye
• Rinse with lean water, do not rub
• Treatment: eye care professional, aggressive lubrication, antibiotic ointment or drops

Question 22

What is fluorescein dye commonly used for?

Answer 22

A green dye used to asses size/depth/damage of corneal epithelium due to corneal abrasion

Question 23

What are the Palisades of Vogt?

Answer 23

Stem cell depot for cornea and bulbar conjunctiva