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Vet Phys- The Eye
Eye
Term | Definition |
---|---|
Important Structures of the eye | orbit, globe, conjunctiva, lacrimal system, eyelids |
What's the orbit of the eye? | Bony fossa Separates eye from cranial skull cavity |
What is the function of the orbit? | Provides protection Attachment |
What does the orbit contain? | Eye, extraocular muscles, optic nerve, lacrimal gland |
What are the eyelids? | Dorsal and ventral folds of skin lined with palpebral conjunctiva Rest against ocular surface |
What is the 3rd eyelid? | nictitating membranes aqueous portion of tear film |
Lacrimal gland | aqueous portion of tear film |
meibomian gland | lipid part of tear film |
Cherry eye in dogs | prolapse of 3rd eyelid- Can't function properly |
Clinical signs of cherry eye | Discomfort, conjunctivitis, discharge, dry eye |
conjunctiva | mucous membranes lines eyelid and sclera |
what does the conjunctiva consist of | palpebral- lining the lids bulbar- covering the globe nictitans- covering 3rd eyelid |
Conjunctiva contains..... | Goblet cells, lymphoid tissue, connective tissues, blood vessels and nerves, |
Functions of conjunctiva | prevents corneal desiccation, increases eyelid mobility, protective barrier |
Lacrimal system | tears needed for normal function, ph of 6.8-8.0 |
functions of lacrimal system | Maintain optimal surface, remove foreign material, antibacterial, permit 02 and nutrient passage |
Sclera | thick fibrous outer layer, contains blood vessels, white in colour |
Functions of sclera | joins cornea at the limbus |
cornea | clear, avascular, acts as eyes outermost lens |
Functions of cornea | controls and focuses entry of light into the eye 65-75% of eyes total focusing power |
The globe | outer: cornea/ sclera- supports and maintains shape/ assist passage of light middle: uvea (choroid, cillary body, iris)- provides nutrition/ oddities light entering inner: retina/ optic nerve- conversion of light impulse to electrical signals |
Parts of the globe | Cornea, sclera, uveal tract (iris, cillary body, choroid), lens, retina, vitreous |
Uveal tract: Iris | hole in centre of pupil |
Function of iris | movement of iris controls light quality entering the eye |
antisocoria | unequal size of pupils |
Uveal Tract: Ciliary body | located behind iris, between lens and choroid |
function of cillary body | secretes aqueous humour should flow from posterior chamber to anterior chamber- causes intraocular pressure |
Intraocular pressure | raised pressure- glaucoma lower pressure- hypotomy |
Uveal tract: Choroid | lies between the sclera and retina contains mirror-like layer-shine from dog and cats eyes |
function of choroid | assists in re-stimulating the retina photoreceptors when light reflected back from it Increases visual sensitivity and assists with low light vision |
The lens | biconcave structure no blood vessels or pigment |
Cataract | opacity of the lens |
nuclear sclerosis | hardening of portion seen in older animals |
The retina | inner most layer at back of eye |
retina contains... | photoreceptor cells: rods and cones |
the pupil | allows entrance of light into eye |
inside globe, 3 chambers filled with jelly like substances .... | anterior chamber: aqueous humour posterior chamber: aqueous humour vitreous chamber: vitreous humour |
Functions of the substances | provides nutrients, removes waste products Maintain shape and pressure of the globe to allow persistent light refraction |
amount of light allowed into eye determined by.... | size of pupil (controlled by muscles of iris) |
Creation of an image: | Light enters eye, travels thru transparent corneas moves through aqueous and vitreous humours, through lens lens changes shape by contraction/ relaxation of the muscular cillary body Light stimulates photoreceptors in retinas, impulse sent optic nerve |
2 main types of photoreceptor cell | rods (black and white vision) cones (colour vision) |
retinas of dogs and cats comprise mainly of.... | rods but some cones present |
dichromatic vision | can distinguish some colours- can't distinguish subtle shade colours |
Optic nerve of each eye crosses at... | the optic chasm and enter the cerebral cortex via the mid brain |