Contents of Orbit Flashcards
What bone forms the supraorbital margin?
the frontal bone
What bones form the infraorbital margin?
zygomatic and maxilla
What bones form the roof of the orbit?
frontal bone and the lesser wing of sphenoid
What bones form the floor of the orbit?
maxilla, zygomatic and palatine
What bones form the lateral wall of the orbit?
zygomatic, greater wing of sphenoid
What bones form the medial wall of the orbit?
maxilla, lacrimal bone, ethmoid, body of sphenoid
Which bones are at risk in a blow out fracture?
lacrimal bone and ethmoid bone
What is the sclera?
the white of the eye
What is the cornea?
the anterior 1/6th of the outer layer of the eye that is transparent and bends light
Why is the sclera white and the cornea transparent when they are both made of collagen?
in the sclera the collagen is laid down in whirls for strength but in the cornea the collagen is laid down in bundles (lamellae) and within each lamellae all the fibrils are the same length and diameter and are evenly spaced and run in parallel
What are the 5 histological layers of the cornea?
epithelium, bowman’s layer, stroma, descemet’s membrane, endothelium
Why would you get a scar of the cornea?
if the stroma of the cornea was damaged and the order of the collagen was disrupted
What is the anterior chamber angle?
the junction between the cornea and iris where aqueous humour drains out of the eye via the canal of schlemm
What is the uvea?
the middle coat of the eye - contains the ciliary bodies, choroid and the iris
What are the functions of the ciliary bodies?
formation of aqueous humour, tethers lens, accommodation
Where is the aqueous humour formed?
by the two layers of ciliary epithelium on the ciliary processes that come off the ciliary bodies
What are zonules?
ligaments that attach the ciliary body and the lens
What happens when the ciliary muscle contracts?
the zonules which connect the ciliary body to the lens loose their tension which allows the lens to bulge and the eye can focus close up
What innervates the ciliary muscle?
parasympathetic via CNIII
What is presbyopia?
the loss of accommodation with age caused by reduction in flexibility of the lens
What 2 muscles control the iris and what are they innervated by?
sphincter pupillae constricts the pupil and is controlled by parasympathetic innervation from CNIII, dilator pupillage dilates the pupil and is controlled by the sympathetic nervous system
What is the choroid?
the layer underneath the retina which contains the blood vessels which supply the retina
What is the fovea?
the area of the retina with the highest visual acuity - avascular, thin and with the highest density of cones
What is the lamina cribosa?
the sclera that crosses the optic nerve and forms a sieve like structure through which the axons have to pass
What artery supplies the blood to the orbit and what is it a branch of?
the opthalmic artery - the first branch of internal carotid
What is the first branch of the opthalmic artery and what does it supply?
the central retinal artery - supplies the inner retina
What blood vessels supply the photoreceptors in the outer retina via the choroid?
the long and short posterior ciliary arteries
What blood vessels supply the anterior structures of the eye?
the anterior ciliary arteries
What 2 muscles control the eyelids, what do they do and what are they innervated by?
orbicularis occuli closes the eyelid and is innervated by CNVII, legator palpebrae superioris opens the eyelids and is innervated by CNIII
What are the 3 layers of the globe of the eye?
the outer layer is the sclera and cornea, the middle layer is the uvea and the inner layer is the retina and optic nerve
