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Year 2 Semester 2 > Eye > Flashcards

Eye Flashcards

0
Q

In the dog, which vessels pass through foramina to gain access to the orbit?

A

Ophthalmic artery and vein
Orbital vein
Cranial nerves 2, 3, 4, 6 (optic, oculomotor, trochlear, abducens)
Ophthalmic branch of cranial nerve 5

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1
Q

In the horse, a portion of the orbit is contributed to by the zygomatic process of which bone?

A

Temporal

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2
Q

What are the three layers of the orbital fascia?

A

Outer=periorbita
Fascia bulbi
Fascial sheaths of the extra-ocular muscles

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3
Q

Which species do not possess a retractor bulbi muscle?

A

Birds and snakes

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4
Q

What are the functions of the eyelids?

A

Close to exclude light
Protect the eyeball
Spread the tear film across the eye and into the lacrimal punctae
Help to remove foreign material from the eye

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5
Q

At what age do cats and dogs open their eyes?

What is the eyelid opening called?

A

10-14 days

Palpebral fissure

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6
Q

The cilia on the upper eyelid (eyelashes) are associated with which glands?

A 
Modified sweat glands (glands of Moll)
Sebaceous glands (glands of Zeis)
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7
Q

What causes a stye to form?

A

Infection of sebaceous or sweat glands in the upper eye lid

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8
Q

In the dog, the lateral palpebral ligament is absent, but what is its function replaced by?

A

Retractor anguli oculi muscle

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9
Q

Closure of the eyelids is due to what?

A

Contraction of the orbicularis oculi muscle, which is innervated by the facial nerve (CN VII)

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10
Q

Sensory innervation to the eyelids is via which nerve?

This branches into what?

A

Trigeminal (CN V)
Branches into ophthalmic branch (innervates most of upper lid and medial part of lower lid) and maxillary branch (innervates lower lid and joins with ophthalmic branch to supply lateral portion of upper lid)

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11
Q

What is the nictitating membrane?

Where does it sit?

A

Third eyelid
A reflection of conjunctiva containing a T-shaped cartilage support.
Sits ventromedially in the conjunctival sac, and the free edge is snug against the eyeball

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12
Q

What are the three portions of the tear film?

A

Lipid layer
Mucin layer
Aqueous layer

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13
Q

The lacrimal nerve is a branch of which nerve?

A

Ophthalmic branch of CNV

Provides parasympathetic and sympathetic innervation

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14
Q

What are the three layers of the globe and what do they do?

A

Fibrous layer- supports the eyeball shape
Uvea- provides nutrition to the structures of the eye and acts to alter light transmission
Neural layer- retina

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15
Q

What is the cornea?

How thick is it in dogs and cats?

A

The clear, curved rostral surface of the eyeball which transmits and refracts light.
0.7mm thick

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16
Q

Which 2 factors give the cornea its clarity?

A

Lack of corneal blood vessels

Arrangement of lamellae

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17
Q

What makes up the anterior and posterior uvea?

A

Anterior uvea= iris and ciliary body

Posterior uvea= choroid

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18
Q

Describe the pathway of aqueous humour

A

It is produced in the posterior chamber, flows through the pupil into the anterior chamber and drains at the iridocorneal angle

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19
Q

What are the 4 layers of the choroid?

A

Suprachoroidea-transition between sclera and choroid
Large vessel layer-cools the eye
Medium vessel layer-contains tapetum lucidum
Choriocapillaris-consists of fenestrated capillaries which supply the retina

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20
Q

What is aqueous humour produced by?

A

Ciliary processes of the ciliary body

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21
Q

What is the normal range for intra-ocular pressure in a dog?

A

15-25mmHg

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22
Q

How is a glaucoma formed?

A

When production of aqueous humour exceeds drainage and intra-ocular pressure rises

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23
Q

What are ‘floaters’?

A

Clumps of hyaluronic acid, occurs in old age when the lamellar arrangement of fibrils in the vitreous humour breaks down and the vitreous becomes more liquid.

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24
Q

How does a cataract form?

A

Changes inside the lens disrupt normal metabolism and lead to deposition of lens protein or accumulation of vacuoles and disruption of lens fibres.
This affects transparency and size of lens.

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25
Q

What are the 3 inner layers of the retina?

A

Nerve fibre layer
Ganglion cell layer
Inner plexiform layer

26
Q

Where are cones most numerous?

A

Area centralis of the retina

27
Q

Which area of the retina has the most ganglion cells?

A

Visual streak

28
Q

Give 3 functions of the retinal pigment epithelium

A

Phagocytoses spent photoreceptor segments
Vitamin A metabolism
Moves metabolites into and out of the retina

29
Q

How are cats able to actively protrude their third eyelids?

A

They possess some striated muscle in their third eyelids

30
Q

What does each layer of the tear film do?

Lipid layer, mucin layer, aqueous layer

A

Lipid layer: produced from meibomian glands; reduces evaporation and creates a barrier at the lid margin
Mucin layer: produced by conjunctival goblet cells; stabilises the tear film
Aqueous layer: produced by lacrimal glands and 3rd eyelid gland; provides lubrication, protection and nutrition to the epithelium it covers

31
Q

What suspends the lens?

A

Zonular fibres

32
Q

Where is the main site of drainage of aqueous humour?

A

Iridocorneal angle

33
Q

What are the 4 major layers of the choroid?

A

Suprachoroidea-transition between sclera and choroid, elastic, pigmented
Large vessel layer-contains vascular plexus, cools the eye
Medium vessel layer-contains vessels and tapetum lucidum
Choriocapillaris-consists of fenestrated capillaries which supply the retina

34
Q

Aqueous humour is produced by which 3 processes?

A 
Diffusion (of solutes down conc. gradient into the aqueous)
Ultrafiltration (due to differences in hydrostatic pressure in ciliary body capillaries, and intra-ocular pressure)
Active secretion (of Na, which brings water across too)
35
Q

What is the function of the lens?

A

To focus light on the retina

36
Q

Which structures are visible in the fundus?

A

Optic disc, retina, retinal pigment epithelium (RPE), choroid and sometimes the sclera

37
Q

Where is the tapetum lucidum located?

A

Medium vessel layer of the choroid

38
Q

In which ways can drugs be administered to penetrate the globe?

A

Topically
Crossing the cornea, conjunctiva or sclera
Systemically by crossing the blood:ocular barrier

39
Q

After topical administration of an ocular drug, what are the 3 ways it can be distributed?

A

Drained by lacrimal drainage system
Penetrates into the eye via cornea/sclera
Enters systemic circulation through conjunctival and nasal vessels

40
Q

How much of a topically-applied drug actually reaches the anterior chamber?

A

Between 1 and 10%

41
Q

How can intra ocular bioavailability of a drug be improved?

A

Increasing retention of the drug in the Palpebral fissure

By increasing its ability to penetrate the cornea

42
Q

What are the layers of the cornea that a drug has to penetrate?

A

Epithelium (tight junctions) (can get through epithelium by moving between cells (paracellular, water-soluble) or moving through cells (transcellular, lipid-soluble))
Bowman’s layer
Stroma (facilities diffusion of water-soluble drugs but not lipid-soluble)
Descemet’s membrane
Endothelium (gap junctions, both lipid and water-soluble drugs can pass through)

43
Q

After a drug has penetrated the cornea, where does it go?

A

Aqueous humour -> iris -> ciliary body

44
Q

Is the ionised form of a drug water or lipid soluble?

A

Ionised form= water-soluble

Nonionised form= lipid-soluble

45
Q

What does the blood:ocular barrier consist of?

A

BAB (blood:aqueous barrier) and BRB (blood:retinal barrier)

46
Q

Why would we want to dilate the pupil?

A

To facilitate better fundic examination

47
Q

How do we dilate the pupil?

A

Use either:
Sympathomimetic to contract the dilator muscle
Parasympatholytic to relax the Iris sphincter muscle eg Atropine

48
Q

What kind of stimulation causes pupils to constrict and dilate?

A

Sympathetic -> pupils dilate

Parasympathetic -> pupils constrict

49
Q

How can you investigate Horner’s syndrome?

A

Dogs with Horner’s syndrome present with constricted pupils.

Give a sympathomimetic dug (α1-selective adrenergic drug eg phenylephrine) to dilate the pupils.

50
Q

Which drug can you use as a tear substitute?

A

Pilocarpine, increases tear production, parasympathomimetic

51
Q

How do we treat glaucoma?

A

By increasing outflow of aqueous humour, reducing production or both

52
Q

What types of drugs can we use to treat glaucoma?

A 
Osmotic diuretics (draws water out of aqueous)
Carbonic anhydrase inhibitors (produce bicarbonate ions which draw water out of the aqueous, eg Brinzolamide)
Beta blockers (reduce aqueous formation, b1 antagonists eg betaxolol)
Parasympathomimetics (constrict the pupil which widens the drainage angle and so increases aqueous outflow eg pilocarpine)
53
Q

What is the function of:
Atropine
Pilocarpine

A

Atropine: dilates pupil
Pilocarpine: constricts pupil

54
Q

What are the functions of rods and cones?

A

Rods-sensitive to low light levels but not colour. Black and white night vision.
Cones-sensitive to bright light/day vision. Provide colour vision.

55
Q

Where does the optic nerve leave the eyeball?

A

Slightly ventral to the posterior pole

56
Q

The axons of which cells form the optic nerve?

A

Ganglion cells

57
Q

Which layer of the retina is supported by the choroid?

A

Nervous layer (receptor cells, rods and cones)

58
Q

What is the retinal pigment epithelium attached to?

A

Choroid

59
Q

Which layers of the eye contribute to the iris?

A

Choroid, retina, cornea

60
Q

What fills the anterior and posterior chambers?

A

Aqueous humour

61
Q

What prevents backflow of aqueous humour from the anterior to posterior chamber?

A

The valve-like action of the iris

62
Q

Why does a corneal ulcer take a long time to heal?

A

Superficial ulcers heal rapidly because the outermost layer of the cornea is an epithelium (epithelial cells have a huge capacity for regeneration).
However, a deep ulcer heals slowly because the collagen fibres in the main body of the cornea don’t have their own blood supply (important for delivering WBCs to produce scar tissue).
Sometimes a conjunctival flap is required to provide a blood supply

Year 2 Semester 2 (16 decks)

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