1.03 Ocular surface - cornea, sclera and conjunctiva

Label

1. Orbital portion of lid

2. Tarsal portion of lid

3. Lateral/temporal canthus

4. Tarsal portion of lid

5. Inferior palpebral furrow

6. Orbital portion of lid

7. Superior palpebral furrow caruncle

8. Medial/nasal canthus

Label the medial canthus

1. Lacrimal lake

2. Semilunar fold

3. Lacrimal papillae

4. Lacrimal caruncle

5. Lacrimal punctum

6. Front edge of lid Superior

7. Rear edge of lid

8. Gray line

9. Orifices of tarsal glands

What dees lid margin contain

Cilia (lashes)

What is the ocular surface

The ares between the open eyelids thats exposed to the environment

Label

1. Iris

2. Ciliary body

3. Choroid

4. Vascular tunic

5. Neural part

6. Pigmented part

7. Neural tunic (retina)

8. Cornea

9. Sclera (fibrous tunic)

Label

1. Fornix

2. Eyelid

3. Eyelash

4. Limbus

5. Pupil

6. Ocular conjunctiva

7. Palpebral conjunctiva

8. Ora serrata

9. Focea

10. Optic nerve

Functions of the sclera

Label the posterior view of the sclera

1. Superior rectus muscle

2. Superior oblique muscle

3. Vortex vein

4. Medial rectus muscle

5. Long posterier ciliary artery

6. Long ciliary nerve

7. Vortex vein Medial rectus

8. Inferior rectus muscle

9. Short ciliary nerves

10. Inferior oblique muscle

11. Optic nerve

12. Lateral rectus muscle

13. Short posterior ciliary arteries

Where in the eye is the sclera the thickest

At the back

Where is the conjunctiva located

Overlies the sclera and the underside of the eyelid

Not part of the same tunic of sclera

Functions of the conjunctiva

What is the conjunctiva composed of

Loose areolar connective tissue (lamina propria containing a rich blood supply with a covering of epithelial cells

Special features of the conjunctiva

Can renew itself if damaged (sclera cant)

Many blood vessels - provides metabolic needs for other structures of the eye

Why is the fornix region of the conjunctiva uneven

So fornix can stretch

Where are most goblet cells located

In the fornix region of the conjunctiva (bular and palpebral)

What happens to the number of functional goblet cells as you age

Decrease

What does the bulbar conjunctiva cover

Starts at the limbus and covers all the visible area of sclera

Ends at fornicies (superior and inferior)

What does the palpebral conjucntiva cover

Starts are fornicies and covers the entire internal surfaces of the eyelids

Ends at the eyelid margins

What is the fornix conjunctiva

The transition region between bulbar and palpebral conjunctiva

There are 2 fornix regions superior and inferior

Bulbar conjunctiva dimentions in order

Temporal > medial, superior = inferior

Palpebral conjunctiva dimentions in order

Lateral > medial, superior > inferior

Does the bulbar conjunctiva have blood vessels

No

You can see the underlying scleral/episcleral blood vessels

Why is there no conjunctiva over the cornea

Too loose and would reduce vision

What are the palisades of vogt

Finger like processesRadial ridges/folds at the limbus

Contain stem cells to regenerate corneal epithelium

Loops of capillaries run through the palisades and terminate at the margin of the cornea

What does anterior ciliary artery supply

The anterior region of the eye (conjunctiva, sclera, iris and ciliary body)

and forms the episcleral arteries

What does the episcleral venous plexus do

Drains blood from the limbal region

What is present at the scleral limbus

Loops of capillary blood vessels which terminate at the limbus and dont enter the transparent cornea

Label the limbus

1. Corneal limbus

2. Scleral limbus

3. Palisades of vogt

4. Finger like processes

What is the ‘normal’ appearance of the palpebral conjunctiva

When the eyelid is inverted if its light it is healthy

Functions of the cornea

1. Image formation

   • allows light to enter the eye

   • Acts as a positive (convex) refracting surface

2. Maintains image quality by providing a smooth, renewable ocular surface

Dimensions of the cornea

1. 12mm

2. 8mm

3. 11mm

4. 12mm

5. .53mm

Label the zones of the cornea

1. Optical zone

2. Corneal scleral junction

3. Diameter chord

4. Capdiameter

5. Pripheral zone width

Approximate diameter of the corneal zones

• central optical

• Paracentral (mid)

• Peripheral

• Limbal

Central optical 3-4mm

Paracentral (mid) 4-7mm

Peripheral 7-11mm

Limbal 11-12mm

Characteristics of the corneal zones

• central optical

• Paracentral (mid)

• Peripheral

• Limbal

• central optical - most spherical, symmetic - overlies pupil

• Paracentral (mid) - gnerally spherical but flatter than central zone

• Peripheral - cornea flattens the most here

• Limbal - next to the scleral sulcus and the sclera

The optical powerr if the cornea is determined by… Therefore…

Its curvature

Therfore power varies acoss the corneal surface

Lowest radius of curvature is _ and gives the _ power

At the centre

Greatest power (43D)

Highest radius of curvature is _ and gives the _ power

At the periphery

Lowest powerr (37D)

Where is the sclera the thinnest

Anterior to the equator of the eye

List the Layers of the sclera

1. Tenons capsule/Fascia Bulbi

2. Episclera

3. Scleral stroma

4. Lamina fusca

Decribe the tenons capsule

Its a connective tissue layer covering the eye from limbus to optic nerve - collagen bundles radial from limbus

Lies between conjunctiva and episclera at the limbus (connecting external and interal)

Contains no blood vessels

Describe the episclera

Most external layer of the sclera

Loose vascularied surface layers of sclral connective tissue

Collagen bundles circumferential

Describe the scleral stroma

Thickest part of the sclera

Layers of collagen fibres as in the cornea but much less regular and unevenly spaced so opaque

What is the limbus

Region of transition from cornea to sclera/conjunctiva

Opaque to transparent

Its external part involves bulbar conjunctiva and its interal part involves the anterior angle

What is limbal conjunctiva formed by

An epithelium and a loose connective tissue stroma

What is limbal stroma composed of

Scleral and corneal tissues that merge

Conjunctival stromal vessels form what

Peripheral corneal arcades which extend anteriorly to termination of bowmans layer

label Anterior angle

A. Limbal conjunctiva

a. Conjunctivaal stromal vessels

B. Tenon capsule

b. Peripheral cornealarcades

C. Episclera

c. Episcleral vessels

D. Limbal stroma

d. Vessels forming intrascleral plexus

e. Vessels forming deepscleral plexus

f. Collagen fibres (scleral spur)

g. Ciliary muscle

h. Schlemms canal

i. Trabecular meshwork

j. Uveal meshwork

k. Iris process

1.epithlium

2.loose connective tissue stroma

Arrow. Bowmans layer

Double arrow. Decements membrane

Label layers of cornea

1. Corneal epithelium

2. Bowmans layer

3. Corneal stroma/substantia propia

4. Decemets membrane

5. Corneal endothelium

6. Anterior chamber

Which layers of the corneal are made of collagen

Bowmans kayer

Corneal stroma

Decemets membrane

What is the most external layer of the cornea

Epithelium

What types of cells make up the corneal epithelium

Structure of corneal epithelium

Stratifed squamous

6 cells thick columnar basal cells Rest on a thin basement membrane

Squamous surface cells are removed by blinking and replaced by cells underneath

Cells migrate from basal to to surface layer, changing shape as they do

Renewal of cells in the corneal epithlium

Cells at the edge of the cornea (limbus) divide and migrate into the cornea to form basal cells.

Basal cells migrate from basal layer to surface layer and transform/change shape into wing cells and then squamous cells

Squamous surface cells are removed by blinking and replaced by cells underneath

Basal cells → wing cells → squamous cells

Label the cells in the corneal epithlium

1. Squamous cells

2. Wing cells

3. Basal cells

4. Basement membrane

5. bowmans layer

Why is it easier for the limbus to regenerate cells compared to the cornea

Better blood supply

Function of the corneal epithlium

Renewable barriers to water movement into the cornea

What is bowmans layer made of

A dense meshwork of interwoven collagen fibrils (connective tissue)

What makes corneal stroma transparent

Regular arrangement of collagen fibrils

75-80% water to ensure a fibre arrangement that supports transparency

what type of cells is the corneal endothelium made of

Simple cuboidal epithelium

It is a single layer of metabolically active cells

Regular arrnagement of hexagonal cells

Functin of the corneal endothelium

- Active pumping (active transport) of water out the corneal stroma in order to maintain the required level of water for corneal transparency to keep the regular arrangement

- allows enterence of nutrients from aqueous

- ionic pumps - high metabolic activity

How does the corneal endothelium maintain a high metabolic acitivity

Gets its supply of energy by diffusion as theres no blood vessels running through the endothelium

How can we view the corneal endothelium

Specular reflection using a slit lamp biomiscroscope

Function of decemets membrane

Sitck endothelium to stroma

How does decemets membrance change as you age

Becomes thicker

How does endothelial cell layer of the cornea change with age

Endothelial cell density decreases as theyre not regenerated so remaining cells increase in size to fill space

Become more irregular

Pump/barrier becomes less effective - more water enters corneal stroma which causes the cornea to swell

What are the 2 types of nerves and what are they associated with

Sensory - mediates sensation

Motor nerves - controls muscles and glands

Structures can have a sensory supply, motor supply or both

What type of nerves does the cornea have

Sensory nerves

(It has no muscle or glands so no motor nerves)

In which directions do nerves enter the cornea

Medial and lateral directions

Where are nerves located in the cornea

Mostly in the anterior cornea (external layers)

Nerves in the cornea

Long ciliary nerve to limbal region

Brnaches towards the anterior angle

Nerves absent in posterior stroma and decemets membrane

Nerves terminate in epithelium

Nerves from basal layer run between epithelia to end in squamous cells

What is a blue sclera

Thin sclera - allows light through

Less opaque - see pigmented choroid

Subconjunctival hemmorage cause

Blood vessels pops and bleeds between episclera and conjunctiva (blood has nowhere to go)