Cornea (Dr. Scott) Flashcards
Describe the surface anatomy of the cornea
- Part of fibrous tunic
- Transparent and tough
- Avascular
- Highly innervated
What is the thickness of the corneal tear film?
What is it made up of?
- 7 microns thick
- Made up of electrolytes, metabolites, proteins, enzymes and lipids
Describe the limbal region.
- 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
Describe the dimensions of the cornea
- Anterior 1/6 of eye
- Area is 1.3 cm^2
- Steeper curvature than sclera
The cornea is a major _____ component of the eye
Refractive
Which has a steeper curvature, the sclera or the cornea?
Cornea
What are the horizontal and vertical dimensions of the anterior view of cornea?
Radius of Curvature?
- Slightly Elliptical
- Horzontal: 11.7 - 12.6 mm
- Vertical: 10.6 - 11.7 mm
- Radius of Curvature: 7.8 mm
What are the horizontal and vertical dimensions of the posterior view of cornea?
Radius of Curvature?
- Circular
- Horizontal and Vertical: 11.7 mm
- Radius of Curvature: 6.5 mm
What is the overall dioptric power of the cornea?
3/4 refractive power of the eye
Ranges from 43.1 - 48.8 D
What is the index of refraction of the cornea?
1.376
Define astigmatism and differentiate between regular and irregular astigmatism.
- 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
What is lenticular asigmatism?
Unequal curvature of the lens
What is the average corneal thickness?
- Central: 0.52 mm
- Peripheral: 0.70 mm
What is the optical zone of the cornea?
Central 4 mm
What is the rate of production of tear film?
1.2 microliters/minute
What are the 3 layers of the corneal tear film and what secretes each layer?
- Lipid/Oily: Secreted by meibomian glands in the palpebrae and caruncle
- Aqueous layer: Secreted by lacrimal gland
- Mucous layer: Secreted by the goblet cells in the conjunctiva
Describe the function of the oily and mucous layers of the tear film
Oily: Helps prevent the aqueous layer from evaporating
Mucous: decreases the surface tension and provides a smooth, wetable surface for the aqueous layer
What is the glycocalyx?
Very thin layer between the tear film (mucous layer) and the cornea surface
What disease could result due to a poorly functioning or absent lipid layer of the tear film?
Dry Eye Disease - because the lipid layer would not be preventing tears from evaporating
What are some symptoms of dry eye?
- Itching, burning, dry
- Sensitivity to light/blurry vision
- Problems wearing contact lenses
- Watering eyes
What is a corneal abrasion? What are symptoms? First reaction? What to do? Treatment?
- 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
What is fluorescein dye commonly used for?
A green dye used to asses size/depth/damage of corneal epithelium due to corneal abrasion
What are the Palisades of Vogt?
Stem cell depot for cornea and bulbar conjunctiva
