1.04 ocular surfaces - cornea, sclera, and conjunctiva

Question 1

what are the functions of the sclera

Answer 1

1. provides robust connective tissue shell to contain and protect internal structures of the eye
2. opaque to prevent entry of light and minimize internal scatter
3. rigid enough to enable rotation of the eye over a large range without physical distortion
4. rigid enough that normal variations in intraocular pressure do no affect vision

Question 2

conjunctiva (anterior to sclera) functions?

Answer 2

1. joins eyeball to the eyelids
2. provides smooth renewable surface covering anterior eye and posterior eyelids
3. carries blood vessels for nourishment of the limbus, cornea, and posterior eyelids
4. secretes mucus for the tear film.

Question 3

what are the 3 regions of the conjunctiva

Answer 3

• Bulbar conjunctiva - starts at the limbus covers all visible area of the sclera. ends at fornices (superior and inferior)
• Fornix conjunctiva - transition region between bulbar and palpebral conjunctiva . there are 2 fornix regions - superior and inferior
• Palpebral conjunctiva - starts at the fornices. covers the entire internal structures of the eyelids. ends at eyelid margins

Question 4

the 3 different types of conjunctivia and further divided into what groups

Answer 4

Superior bulbar conjunctiva - superior fornix, scleral conjunctiva and limbal conjunctiva

Inferior bulbar conjunctiva - Inferior fornix, scleral conjunctiva and limbal conjunctiva

Superior and inferior palpebral conjunctiva - marginal conjunctiva, orbital conjunctiva and tarsal conjunctiva

Question 5

what are the functions of the cornea

Answer 5

1. image formation (allows light to enter as it is transparent)
2. acts as a positive refracting surface
3. maintains image quality by providing a smooth, renewable ocular surface
4. It is about 12mm in diameter
5. The cornea and lens together are responsible for bringing light to a focus on or near the retina

Question 6

what are the layers of the sclera

Answer 6

1. Tenons capsule or fascia bulbi (outermost) - connective tissue layer covering the eye from limbus to optic nerve: collagen bundles radial from limbus. lies between the conjunctiva and episclera at the limbus and contains no blood vessels
2. Episclera - loose vascularised surface layers of scleral connective. collagen bundles circumferential.
3. scleral stroma - layers of collagen fibres as in the cornea but much less regular
4. Lamina Fusca(innermost) - loose collagen interface to choroid, rich in pigment

Question 7

which part of the conjunctivia has the most goblet cells and what do these do

Answer 7

• Fornix region has the most goblet cells
• They secrete mucus and is distributed throughout the conjunctival epithelium
• number of goblet cells decrease with age hence older people tend to have drier eyes

Question 8

what are the layers of the cornea

Answer 8

1) corneal epithelium - multi layered renewable barrier and is 6 cells thick.

2) Bowmans layer - it is continuous with underlying stroma

3) Stroma (substantia propria) - forms 90% of cornea

4&5) Descemet’s membrane and endothelium - endothelium removes water from cornea to keep it down to a certain level of hydration otherwise it becomes swollen. helps to keep transparency of the cornea

Question 9

the ocular surface is comprised of what structures

Answer 9

cornea
sclera
conjunctiva

Question 10

the ocular surface is protected and maintained by the

Answer 10

eyelids
tear film