Flashcards in Eye Deck (63)
In the horse, a portion of the orbit is contributed to by the zygomatic process of which bone?
In the dog, which vessels pass through foramina to gain access to the orbit?
Ophthalmic artery and vein
Cranial nerves 2, 3, 4, 6 (optic, oculomotor, trochlear, abducens)
Ophthalmic branch of cranial nerve 5
What are the three layers of the orbital fascia?
Fascial sheaths of the extra-ocular muscles
Which species do not possess a retractor bulbi muscle?
Birds and snakes
What are the functions of the eyelids?
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
At what age do cats and dogs open their eyes?
What is the eyelid opening called?
The cilia on the upper eyelid (eyelashes) are associated with which glands?
Modified sweat glands (glands of Moll)
Sebaceous glands (glands of Zeis)
What causes a stye to form?
Infection of sebaceous or sweat glands in the upper eye lid
In the dog, the lateral palpebral ligament is absent, but what is its function replaced by?
Retractor anguli oculi muscle
Closure of the eyelids is due to what?
Contraction of the orbicularis oculi muscle, which is innervated by the facial nerve (CN VII)
Sensory innervation to the eyelids is via which nerve?
This branches into what?
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)
What is the nictitating membrane?
Where does it sit?
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
What are the three portions of the tear film?
The lacrimal nerve is a branch of which nerve?
Ophthalmic branch of CNV
Provides parasympathetic and sympathetic innervation
What are the three layers of the globe and what do they do?
Fibrous layer- supports the eyeball shape
Uvea- provides nutrition to the structures of the eye and acts to alter light transmission
Neural layer- retina
What is the cornea?
How thick is it in dogs and cats?
The clear, curved rostral surface of the eyeball which transmits and refracts light.
Which 2 factors give the cornea its clarity?
Lack of corneal blood vessels
Arrangement of lamellae
What makes up the anterior and posterior uvea?
Anterior uvea= iris and ciliary body
Posterior uvea= choroid
Describe the pathway of aqueous humour
It is produced in the posterior chamber, flows through the pupil into the anterior chamber and drains at the iridocorneal angle
What are the 4 layers of the choroid?
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
What is aqueous humour produced by?
Ciliary processes of the ciliary body
What is the normal range for intra-ocular pressure in a dog?
How is a glaucoma formed?
When production of aqueous humour exceeds drainage and intra-ocular pressure rises
What are 'floaters'?
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.
How does a cataract form?
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.
What are the 3 inner layers of the retina?
Nerve fibre layer
Ganglion cell layer
Inner plexiform layer
Where are cones most numerous?
Area centralis of the retina
Which area of the retina has the most ganglion cells?
Give 3 functions of the retinal pigment epithelium
Phagocytoses spent photoreceptor segments
Vitamin A metabolism
Moves metabolites into and out of the retina