Ophthalmology General

Question 1

Chalazion

Answer 1

impacted material in the meibomian gland, bursting leading to granuloma formation

Question 2

Internal Hordeolum

Answer 2

Infected meibomian gland (stye)

Question 3

Glands of Zeiss and Moll

Answer 3

less important glandsassociateo with skin hairs and cilia

if infected -> external stye (external hordeolum)

Question 4

Tarsal plate

Answer 4

poorly developed fibrous structure running along upper and lower eyelids, meibomian glands in it. surgical landmark and holding layer for sutures.

Question 5

Musculature of the eye

Answer 5

Orbicularis oculi - eyelid closure
Levator palpebral superioris - lifting upper eyelid
Mullers muscle -maintains upper eyelid

Question 6

Nasolacrimal system

Answer 6

Tears -> medial canthus, collected in the puncta.

Question 7

Caniliculi

Answer 7

Lacrimal ducts

Question 8

Lacrimal sac

Answer 8

Upper portion of nasolacrimal duct into which 2

Question 9

Nasal punctum

Answer 9

• opening of the nasolacrimal duct in to the nasal cavity

Question 10

Lacrimal gland

Answer 10

• below dorsolateral orbital rim, produces 70% tears

Question 11

tear film

Answer 11

• mucous layer secreted by corneal epithelial cells and goblet cells of conjunctiva
• aqueous layer, water and solutes, defense mechanism (Igs and lactoferrin)
• lipid layer secreted by meibomian glands, prevents evaporation

Question 12

Layers of the cornea

Answer 12

> epithelium 
- shed as squamous cells in 1 week cycle
- basal cells at limbus = stem cells
> stroma 
- collagen
- lamella layers
> uDescement's membrane
- during progressive ulceration of the cornea, before perforation develops, forms a descemetocele (surgical emergency)
> endothelium
- v thin
- keeps cornea dehydrated via NaK pumps
- no regenerative capacities

Question 13

Limbus

Answer 13

transition between cornea and limbus (may be pigmented)

Question 14

Sclera

Answer 14

white of the eye, continuous with limbus and cornea

• covered by subconjunctival connective tissue (episclera/Tennon’s capsule)
• v thin at equator and near optic disk
• lamina cribs where axons of ganglion cells exit the eye to form the optic nerve

Question 15

Extraocular muslces

Answer 15

• recti (dorsal, ventral, lateral, medial rectus)
• obliques (dorsal with trochlear pulley mechanism, ventral oblique)
• retractor bulbi

Question 16

Iris

Answer 16

Constricrot and dilator muscles

• dilator stronger, and in disease may contract -> miosis
• pupillary zone, iris collateral and ciliary zone

Question 17

What are PPMs?

Answer 17

Persistant pupillary membranes

• fetal vasculature remnants arise from the iris collateral
• may stay in iris or cornea/lens -> opacity

Question 18

What are synechiae?

Answer 18

• adhesions of the iris to other structures d/t uveitis
• anterior = cornea
• posterior = lens

Question 19

Ciliary body

Answer 19

• has own musculature
• focusing
• can cause pain if contracted d/t disease
• produces aqueous humour via carbonic anhydrase enzyme

Question 20

Anterior uvea consists of..

Answer 20

Iris and ciliary body

Question 21

Posterior uvea consists of ..

Answer 21

Choroid and tapetum lucidum

• feeds the retina
• carnivores much more reflective tapetum
• horses have “stars of Winslow” all over tappet fund (end on choroidal capillaries that give tappet fundus a subtle, pin prick spotted appearance

Question 22

Where is aqueous humour resorbed/outflow?

Answer 22

• iridocorneal angle “conventional”

- “unconventional” = uveoscleral outflow as absorbed. Esp important in the horse.

Question 23

Zonules

Answer 23

Arise in ciliary body, attach to lens and lens equator

Question 24

Layers of the lens

Answer 24

• front and back bellies
• lens capsule
• epithelial cells that produce lens fibres
• suture lines: at the confluence of the lens fibres, Y shaped in anterior lens and upside down Y shape in posterior part of the lens
• cortex: youngest part of the lens, produced by lens epithelial cells - cells will lose nuclei and become part of the nucleus, becoming more compacted with age (nuclear sclerosis)
• lens nucleus (ambreyonic, fetal, juvenile and adult layers)

Question 25

components of the retina

Answer 25

• 1 epithelial layer (outermost, RPE retinal pigment epithelium) nurses the photoreceptors
• 9 neural layers: outermost contain photoreceptors (rods and cones) innermost contain ganglion cells and neural fibre layer -> optic nerve
• retinal vasculature: containes paired arterioles and venules (venues larger) dorsal, lateral and medial ones. Branching.
  > Horses have more subtle retinal vasculature (few short BVs emanating from optic disk few mms into periphery)

Question 26

Optic nerve head/disk/papilla

Answer 26

• dog contains fluffy myelin -> square/diamond shaped not round. Plus anastomosing vasculature on top (cats none.)
• very round in the cat d/t lack of myelin
• horses optic disk is oval in the horizontal axis, salmon coloured, larger.

Question 27

Optic nerve

Answer 27

• arises from optic disk
• fibres from nasal (medial) and lateral retina
• right and left fibres decussate at the optic chiasm and post chasmal nerves = the optic tract

Question 28

What is the anterior segment comprised of?

Answer 28

Anterior and posterior chamber, divided by IRIS

Question 29

What does the posterior segment contain?

Answer 29

• Vitreous body
• Fundus (retina/choroid/sclera)
  > depedning on level of pigmentation of the choroid, may be able to see choroidal BVs and sclera behind.
  > some animals may be atapetal (have no tappetum lucidum) so tappet reflex will be red like humans

Question 30

What is the fund reflex?

Answer 30

• tapetal/fundic reflex = reflection of light coming through the pupil in response to an external light
• usually yellow/green/orange, may be red in atepetal animals

Question 31

what nerve innervates orbicularis oculi?

Answer 31

CN7 (facial)

Question 32

what nerve innervation Mullers muscle?

Answer 32

Sympathetic Innervation (-> ptosis in horners)

Question 33

Outline the basic visual signal once light has reached the photoreceptor layer

Answer 33

• rods and cones
• inner retina
• ganglion cells
• nerve fibre layer
• optic disk (axons go through lamina cribrosa of the sclera and are bunched together into a nerve)
• optic nerve
• optic chiasm
• optic tract
• lateral geniculate nucleus (before this, branches for PLR)
• Optic radiaton
• VIsual cortex

Question 34

Outline the pathway of the PLR response

Answer 34

…optic tract

• pretectal nucleus
• E-W and amteriomedian nucleus
• PS fibres of oculamotor nerve (CN3) with ciliary ganglion to pupillary musculature

Question 35

Which cranial nerves are of importance in ophthalmology?

Answer 35

2: optic (vision)
3: oculomotor (dorsal, medial and ventral recti, ventral oblique, PS innervation of the pupil)
4: trochlear (dorsal oblique)
5: trigem, ophthalmic branch (sensation)
6: abducens (lateral rectus -> abduction of the globe and lateral movement. In animals can also pull globe into orbit though abductor muscles -> retrobulbar fat displacement -> protrusion of the TE)
7: facial (blink)
8: vestibulocochlear (conjugated eye movement, ocular movement in response to sound)

Question 36

What controls the secretion of the lacrimal glands?

Answer 36

• PS innervation mostle
• first PS fibres travel with CN7 facial and then int he pterygopalatine fossa they travel with and are distributed by CN5 trigem.

Question 37

See booklet 5/5/15 for list of terms and definitions

Answer 37

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