Special senses - eyes Flashcards
What is the retina also known as?
Nervous tunic
What are the two layers of the retina called?
Pars ceca retina
Pars optica retina
What is the pars ceca retina?
Outer pigmented layer
Not photosensitive
Where do the pars ceca retina and pars optica retina arise from?
Optic nerve and fundus
What is the fundus?
Rounded portion at the back of the eye
Where does the pars ceca retina line and terminate at?
Lines the posterior iris and ciliary body
terminates at the pupillary margin
What is the pars optica retina?
Inner non pigmented area
Contains the photosensitive rods and cones
Where does the pars optica retina terminate?
Ora serrata - ridge further back than the cornea
What is the area of maximum optic resolution called?
Macula
What is the area where the optic nerve forms called?
Optic nerve
What are the cells found in the pars optica retina?
Ganglion cells Amacrine cells Horizontal cells Bipolar cells Muller cells
What are muller cells?
Glial cells
What is the outer capsule of the lens made up of?
Elastic fibres
How does the lens change shape?
Zonular fibres and suspensory ligaments attach the outer capsule of the lens to the ciliary body which constricts and relaxes
What is the inner substance of the lens made up of?
Hard nucleus of concentric sheets of fibres joining at Y shaped sutures
What are the different chambers of the eye?
Anterior chamber
Posterior chamber
Vitreous chamber/body
What fluid is found in the anterior and posterior chambers?
Aqueous humour
What fluid is found in the vitreous chamber/body and what does it do?
Vitreous humour - pads out eye
What embryological structure is found in the vitreous chamber and why?
Hyaloid canal - hyaloid artery travels through it and supplies the developing lens in embryo
Where is the anterior chamber located?
Between the cornea and the iris
Where is the posterior chamber located?
Between the iris and the lens
Where is aqueous humour produced?
Posterior chamber
Where is the vitreous chamber located?
Between the lens and the retina
What is the vascular layer of the eye called?
The choroid
Where is the tapetum lucidum located?
Part of the choroid layer
In the fundus
What animal doesnt have a tapetum lucidum?
Pig
What does the tapedum lucidum do?
Reflects light back onto retina a second time so better sight in night
What is a deviated eye called?
Strabismus
What is a collie eye defect?
Colour diluted eye
No tapetum lucidum
What does a fundus of a small ruminant look like?
Twisted vessels
What feature is specific to a calf retina?
Ring of myelinated fibres around perifery of optic disc
How does diabetes cause cataracts?
High blood glucose increases sorbitol inside lens which causes osmosis, cell swelling and death
Where does the eye arise from?
Neuroectoderm
What area of the neural plate form the optic vesicles?
Optic sulci
What form from the optic sulci?
Optic vesicles which form the eyes
What does contact of the optic vesicles with the ectoderm form?
Lens placode
What is formed from invagination to form the lens and vitreous structures?
Optic cup
What is collie eye anomaly?
Congenital inherited disease, causes blindness, hypoplasia of the retina
What is a defect of the closing of the cup structures forming the iris called?
Coloboma
What is it called when the embryonic vascular network of the eye doesnt break down?
Persistent pupillary membranes
Where are the anterior and posterior poles of the eye?
Highest point on cornea and posterior surface
Where is the optic axis?
Between the two poles
What are the 3 main layers/tunics of the eye?
External fibrous tunic
Middle vascular tunic
Internal nervous tunic
What are the 3 features of the external fibrous tunic?
Cornea
Sclera
Limbus
What is the cornea?
Front of eye, avascular and transparent
What is the sclera?
Dense collagen with blood vessels
What is the area of the sclera where the optic nerve passes called?
Cribiform region
What is the limbus?
Junction between the sclera and the cornea
What is a deep corneal ulcer called?
Descemetocele
What are the scleral blood vessels called?
Long and short posterior ciliary arteries
Anterior ciliary arteries
Where do the scleral blood vessels arise from?
External opthalmic artery
What is another name for the vascular tunic?
Uvea
What are the 3 features of the vascular tunic?
Choroid
Ciliary body
Iris
What causes constriction of the iris?
Oculomotor nerve - parasympathetic
What feature of the iris is found in ungulates?
Iridic granules - reduces glare/brightness
Where is the ciliary body located?
Opposite limbus
How does aqueous humour leave the anterior and posterior chambers?
Pectinate ligament
Where does aqueous humour drain into?
Scleral venous sinus
What divides the anterior and posterior chambers?
Iris
What affects drainage of the aqueous humour?
Iridocorneal angle
What supplies sympathetic innervation to the vascular tunic?
Cranial cervical ganglion
What does the sympathetic fibres innervate?
Orbital muscle and dilator of pupil
What do the sympathetic fibres follow to the orbit?
Opthalmic branch of trigeminal nerve
What do the parasympathetic fibres innervate in the eye?
Constrictor of pupil and ciliary muscle
