Anatomy and Review of the Eye Flashcards
What kind of animals have a closed orbit?
Herbivores
What kind of animals have an open orbit?
Carnivores
What should a healthy eyelid look like?
Smooth edges with a continuous line from medial to lateral canthus. Should sit flat against the eye (small gap is normal in some breeds). Lower eyelid has no hairs
What are the white dots along the eyelid edge?
Meibomian gland openings
What is the function of the meibomian glands?
Secrete oil onto the eye forming the oil layer of the tear film to prevent the eye from drying out.
What is a sty?
An infection of the meibomian glands
What does the third eyelid look like?
Positioned at the medial canthus. Can be pigmented or not or a variation of pigmentation
What is the third eyelid made up of?
Fold of conjunctiva with a cartilaginous core to hold its shape and a tear gland buried deep in the medial edge
What differences are there between cat and dog eyes?
Cats don’t have proper eyelashes. Can often see third eyelid. Eyelids cover edges of cornea and common for proteins/dirt to sink below lower eyelid
What does the conjunctiva cover?
Lines the eyelid, folds back at conjunctival fornix, covers the globe, stops at the limbus
What is the limbus?
Junction between cornea and sclera where the conjunctiva fully attaches to the sclera
Why is the limbus clinically important?
If there is a lot of pigment a chronic irritation can cause proliferation of pigment which migrates across the cornea and obscures vision
What is the Perkinjee reflexes? How are they used clinically?
Reflection of light off the cornea. can use it to judge the surface
What are the outer layers of the eye?
Sclera, cornea and limbus
What makes up the uvea?
Iris, ciliary body, choroid
Which way does the equator of the eye run?
Runs the edge of the lens and splits the eye into anterior and posterior chamber
What makes up the posterior segment?
Vitreous cavity filled with vitreous humour
What makes up the anterior segment?
Anterior chamber (between cornea and iris) and the posterior chamber (between iris and lens)
What are the three zones of the iris?
Pupillary zone (closest to pupil), cilliary zone (outside of iris covering cilliary body) and iris colourette (inbetween two zones)
What are persistent pupillary membranes (PPMs)?
Remnants of blood vessels of foetal vasculature that should have disappeared at 2 weeks and arise at iris colourette
What are synechiae?
Adhesions to cornea/lens from iris colourette. Classed as either anterior/posterior depending on where they attach
What is the function of the iris?
Opens and closes in response to light
What are the different shapes of the iris/pupil in animals?
Dogs = round
Cats = slit
Horses and ruminants = letterbox
What is the granular iridica?
Granular dark black epithelial material in horses eye
What is the function of the ciliary body?
Produces aqueous humour and has powerful muscles which help with focusing of the lens
What is the position of the choroid?
Sandwiched between the retina and sclera
What is the function of the choroid?
Provides extra blood supply to the retina
What is the tapetum?
Orange colour under the retinal vessels
What can you see if the choroid has no pigment?
Can see red stripes (blood vessels) and white of the eye behind it
What holds the lens in place?
Zonials
What are the different parts of the lens?
Capsule = external part Cortex = thin layer below the capsule Nucleus = centre of the lens
What is the function of the cortex?
Has active cells making fibres which are added to the nucleus and as more fibres are made the nucleus condenses
What is nuclear sclerosis?
As the nucleus condenses less light can pass through so it appears opaque
What is nuclear sclerosis often confused with?
Cataracts
What is the retina?
Innermost layer of the eye made up of numerous layers and cells
What are the two types of photosensitive cells and what are their function?
Rods = night vision, no good contrast, no good colour, no good definition Cones = day vision, good contrast colour and definition
What is the fundus?
Brown colour with retinal vasculature, optic disc and tapetum lucidum
What indicates retinal changes?
Changes in yellow-green tapetum/brown area
How is the equine fundus different?
Very large salmon optic disc with several very small blood vessels coming out about 0.5mm with not very many ventrally. Not very shiny/colourful tapetum
How many layers of the retina are there?
10
9 neurological
1 epithelial
What is the clinical significance of the retinal pigmental epithelium?
Can become diseased and is left behind in retinal detachment
Where does the aqueous humour exit and what is its clinical significance?
Iritocorneal junction. If disease affects angle drainage is affected can change intraocular pressure = glaucoma
