Anatomy and Review of the Eye

Question 1

What kind of animals have a closed orbit?

Answer 1

Herbivores

Question 2

What kind of animals have an open orbit?

Answer 2

Carnivores

Question 3

What should a healthy eyelid look like?

Answer 3

Smooth edges with a continuous line from medial to lateral canthus. Should sit flat against the eye (small gap is normal in some breeds). Lower eyelid has no hairs

Question 4

What are the white dots along the eyelid edge?

Answer 4

Meibomian gland openings

Question 5

What is the function of the meibomian glands?

Answer 5

Secrete oil onto the eye forming the oil layer of the tear film to prevent the eye from drying out.

Question 6

What is a sty?

Answer 6

An infection of the meibomian glands

Question 7

What does the third eyelid look like?

Answer 7

Positioned at the medial canthus. Can be pigmented or not or a variation of pigmentation

Question 8

What is the third eyelid made up of?

Answer 8

Fold of conjunctiva with a cartilaginous core to hold its shape and a tear gland buried deep in the medial edge

Question 9

What differences are there between cat and dog eyes?

Answer 9

Cats don’t have proper eyelashes. Can often see third eyelid. Eyelids cover edges of cornea and common for proteins/dirt to sink below lower eyelid

Question 10

What does the conjunctiva cover?

Answer 10

Lines the eyelid, folds back at conjunctival fornix, covers the globe, stops at the limbus

Question 11

What is the limbus?

Answer 11

Junction between cornea and sclera where the conjunctiva fully attaches to the sclera

Question 12

Why is the limbus clinically important?

Answer 12

If there is a lot of pigment a chronic irritation can cause proliferation of pigment which migrates across the cornea and obscures vision

Question 13

What is the Perkinjee reflexes? How are they used clinically?

Answer 13

Reflection of light off the cornea. can use it to judge the surface

Question 14

What are the outer layers of the eye?

Answer 14

Sclera, cornea and limbus

Question 15

What makes up the uvea?

Answer 15

Iris, ciliary body, choroid

Question 16

Which way does the equator of the eye run?

Answer 16

Runs the edge of the lens and splits the eye into anterior and posterior chamber

Question 17

What makes up the posterior segment?

Answer 17

Vitreous cavity filled with vitreous humour

Question 18

What makes up the anterior segment?

Answer 18

Anterior chamber (between cornea and iris) and the posterior chamber (between iris and lens)

Question 19

What are the three zones of the iris?

Answer 19

Pupillary zone (closest to pupil), cilliary zone (outside of iris covering cilliary body) and iris colourette (inbetween two zones)

Question 20

What are persistent pupillary membranes (PPMs)?

Answer 20

Remnants of blood vessels of foetal vasculature that should have disappeared at 2 weeks and arise at iris colourette

Question 21

What are synechiae?

Answer 21

Adhesions to cornea/lens from iris colourette. Classed as either anterior/posterior depending on where they attach

Question 22

What is the function of the iris?

Answer 22

Opens and closes in response to light

Question 23

What are the different shapes of the iris/pupil in animals?

Answer 23

Dogs = round
Cats = slit
Horses and ruminants = letterbox

Question 24

What is the granular iridica?

Answer 24

Granular dark black epithelial material in horses eye

Question 25

What is the function of the ciliary body?

Answer 25

Produces aqueous humour and has powerful muscles which help with focusing of the lens

Question 26

What is the position of the choroid?

Answer 26

Sandwiched between the retina and sclera

Question 27

What is the function of the choroid?

Answer 27

Provides extra blood supply to the retina

Question 28

What is the tapetum?

Answer 28

Orange colour under the retinal vessels

Question 29

What can you see if the choroid has no pigment?

Answer 29

Can see red stripes (blood vessels) and white of the eye behind it

Question 30

What holds the lens in place?

Answer 30

Zonials

Question 31

What are the different parts of the lens?

Answer 31

``` Capsule = external part Cortex = thin layer below the capsule Nucleus = centre of the lens ```

Question 32

What is the function of the cortex?

Answer 32

Has active cells making fibres which are added to the nucleus and as more fibres are made the nucleus condenses

Question 33

What is nuclear sclerosis?

Answer 33

As the nucleus condenses less light can pass through so it appears opaque

Question 34

What is nuclear sclerosis often confused with?

Answer 34

Cataracts

Question 35

What is the retina?

Answer 35

Innermost layer of the eye made up of numerous layers and cells

Question 36

What are the two types of photosensitive cells and what are their function?

Answer 36

``` Rods = night vision, no good contrast, no good colour, no good definition Cones = day vision, good contrast colour and definition ```

Question 37

What is the fundus?

Answer 37

Brown colour with retinal vasculature, optic disc and tapetum lucidum

Question 38

What indicates retinal changes?

Answer 38

Changes in yellow-green tapetum/brown area

Question 39

How is the equine fundus different?

Answer 39

Very large salmon optic disc with several very small blood vessels coming out about 0.5mm with not very many ventrally. Not very shiny/colourful tapetum

Question 40

How many layers of the retina are there?

Answer 40

10 9 neurological 1 epithelial

Question 41

What is the clinical significance of the retinal pigmental epithelium?

Answer 41

Can become diseased and is left behind in retinal detachment

Question 42

Where does the aqueous humour exit and what is its clinical significance?

Answer 42

Iritocorneal junction. If disease affects angle drainage is affected can change intraocular pressure = glaucoma