The Eye

1

anterior pole

2

limbus

3

equator

4

meridian

5

posterior pole

6

optic axis

7

optic nerve

Why is the limbus clinically relevant

incision made here to access lens for cataracts surgery

What is the optic axis?

light axis

What 2 parts does the eye consist of?

• eyeball

• adnexa

Where is the eyeball housed?

orbit of skull

What does the adnexa consist of?

• orbit

• para-orbital areas

• eyelids

• lacrimal apparatus

• ocular muscles

1

zygomatic arch

2

orbit

3

coronoid process

4

sagittal crest

5

nuchal crest

6

occipital condyle

7

auditory bulla

8

mandibular fossa

9

angular process

10

mandibular condyle

11

mandible

1

dorsal oblique muscle

2

dorsal rectus muscle

3

retractor bulbi

4

medial rectus muscle

5

optic nerve

6

ventral rectus muscle

7

ventral oblique muscle

What shape is the eyeball?

pretty much spherical

In what species does anteroposterior compression occur?

horses and cattle

What is the cornea?

transparent part of the anterior eye

1

fibrous coat (sclera and cornea)

2

vascular coat (uvea)

3

nervous coat (retina)

How many tunics in the eye are there?

3

What are the 3 tunics in the eye?

• fibrous (sclera & cornea)

• vascular (uvea)

• nervous (retina)

4

filled with vitreous humor (posterior chamber)

5

optic disc

6

ciliary body

7

iris

8

filled with aqueous humor (anterior chamber)

9

cornea

10

lens

What does the outermost layer/fibrous tunic consist of?

• sclera

• limbus

• cornea

What does the middle layer/vascular tunic consist of?

• choroid

• ciliary body

• iris

What does the innermost layer/nervous tunic consist of?

retina

What tissue is the fibrous tunic composed of?

dense collagenous tissue

What does the fibrous tunic provide?

form, shape and protection to the eye

What is the point where the sclera and cornea meet called?

limbus

What is the limbus?

where sclera and cornea meet

What colour is the sclera?

white

What fibres is the sclera composed of?

collagenous and elastic fibres

What is the sclera anteriorly covered in?

bulbar conjunctiva

How many extrinsic ocular muscles are there?

7

Where do the 7 extrinsic ocular muscles of the eye insert?

posteriorly to sclera

What happens posteriorly on the sclera?

• extrinsic ocular muscles insert

• penetrated by blood vessels and nerves 

What is the pink arrow pointing to?

sclera

What is the yellow arrow pointing to?

cornea

Does the cornea contain blood vessels?

NO

Does the sclera contain blood vessels?

YES

What is the cornea composed of?

special kind of connective tissue arranged in a lamellar form

How do nutrients permeate through the cornea?

• from vessels in the limbus

• via lacrimal fluids and aqueous humor

What does the surface of the cornea have?

free nerve endings so very sensitive

What reflex is the nerve endings in the cornea involved in?

corneal reflex

What state is the cornea maintained in?

dehydrated state

What are the main functions of the cornea?

• support of intraocular contents

• refraction of light because of its curvature

• transmission of light because of its transparency 

1

tear film

2

corneal epithelium

3

corneal stroma

4

Descemet’s membrane

5

endothelium

What is the uvea?

middle vascular layer around the eyeball

What is the choroid?

lines sclera from optic nerve to near the limbus

What is the ciliary body?

thickened zone opposite limbus

What is the role of the iris?

projects into the anterior chamber of the eye

Is the choroid, ciliary body or iris most posterior?

choroid

Is the choroid, ciliary body or iris most anterior?

iris

What are the main roles of the uvea (middle layer)?

• supply blood

• elevates lens

• regulates lens curvature

• adjusts size of pupil

fundus

posterior part of internal eye visualised with an ophthalmoscope

What is the choroid firmly attached to?

sclera

What is the choroid?

dense network of blood vessels embedded into heavily pigmented connective tissue

Dorsally in the fundus, what does the choroid form?

light-coloured reflective area called the Tapedum lucidum

What structure in the eye are ‘cats eyes’ on roads based on?

tapetum lucidum

Why are canines adapted to have a tapetum lucidum?

nocturnal adaptation

Which species do not have a tapetum lucidum?

humans and pigs

Which species has the least blood vessels?

horse

In what part of the eye are the blood vessels?

choroid

In what part of the eye is the optic disc?

retina

What is the ciliary body?

at level of limbus, vascular coat forms thick circular rounded mass, contains numerous muscle bundles

What is the main role of the ciliary body?

regulates shape of lens

1

lens

2

ciliary body

3

choroid covered by pigmented outer layer of retina

3’

remnants of inner nervous layer of retina (which has been removed)

4

dorsal rectus muscle

5

ventral rectus muscle

6

medial rectus muscle

7

lateral rectus muscle