The Eye & Orbit Flashcards
(40 cards)
what are the 3 layers of the eye?
the fibrous coat, vascular coat and sensory coat
what is the role of and what makes up the fibrous coat?
it is a complete coat that envelops the entire globe, it is the outermost coat and contains collagen, it is made up of the sclera= the whites of the eyes and forms the posterior 5/6s of the eyeball and most anteriorly is the transparent 1/6th of the eyeball called the cornea
what is the role of and what makes up the vascular coat?
it is the 2nd layer of the eye and goes all the way around apart from where there is the opening of the pupil anteriorly, it is made up of the iris= front of the eye just behind the cornea which gives you the colour of your eye, behind the iris is the ciliary body and then behind this is the a vascular structure called the choroid
what is the role of and what makes up the sensory coat?
it is the 3rd layer and only extends to just anterior of the equator of the eyeball in a serrated margin called the ora serrata and is made up of the retina
what nerve leaves the posterior aspect of the eyeball?
the optic nerve= cranial nerve II
what is the composition of the sclera?
collagen fibres of different diameters arranged quite irregularly giving it the white opaque appearance and gives attachment to the muscles moving the eyeball
what is the composition of the cornea?
very fine uniform collagen fibres which allow light to pass through and are therefore transparent
what is the role and composition of the iris?
it controls the diameter of the pupil and so contains a series of circular and radial muscles that control the diameter and so control the amount of light rays entering the eyeball
what is the role and composition of the ciliary body?
it suspends the lens by little web-like zonules/suspensory ligaments that help suspend the crystalline lens and produces a fluid called aqueous hummer which fills the space in front of the lens
what is the role and composition of the choroid?
richly vascular and supplies blood to the outer layers of the retina
what is the role and composition of the retina?
has lots of neurones including modified neurones called rods and cones which react to light falling on the retina and enable us to see
where and what is the role of the aqueous humor?
found in the anterior segment of the eye and is secreted by the ciliary body- the constant production, circulation and reabsorption helps to maintain the intra-ocular pressure
where and what is the role of the vitreous humor?
found in the posterior segment of the eye and helps push the retina back against the choroid to prevent it from getting detached- there is almost no circulation but the water in vitreous humor keeps getting replenished
what is the pathway of aqueous humor?
produced in the ciliary body and passes through the canal of Schlemm and the angle of the anterior chamber which is the angle between the edge of the iris and the end of the sclera and start of the cornea- the trabecular meshwork helps fluid drain into the canal
what is the crystalline lens?
a transparent biconvex structure which can become more or less convex and is suspended from zonules by the circular body (which are present 360*)
what bones make up the the orbital cavity?
frontal bone, zygoma, maxilla, lacrimal bone, ethmoid bone and sphenoid bone (which is divided into the lesser and greater wings by the fissure)
what are the 3 foramina in the orbital cavity?
the optic foramen, superior orbital fissure and the inferior orbital fissure
why are the walls of the the orbit especially the medial and inferior walls weak?
because adjacent to them are air filled spaces called the paranasal sinuses which makes them susceptible to damage
what surrounds the orbit since it is much smaller in length than the orbital cavity?
orbital fat cushions globe which is very important for support
what are the eyelids?
skin on the outside with specialised hair follicles with sebaceous glands and mucous membrane on the inside (conjunctiva) and within the eyelids are 2 sets of muscles- 1 goes all the way around the orbit which helps close the eyelids and the other which comes from the back of the orbit and attaches to the eyelids to helps you to open eyelids or raise the eyelids
what diseases can affect the fat surrounding the eyes and what does this cause?
hypertrophies such as thyroid disease which pushes the eyeball outwards giving the eye a staring appearance and it is also one go the last reserves of fat that disappear in starvation so a sunken eyeball suggests the patient is quite late in the process of starvation
what are the glands found in the eyelids?
meibomian glands which secrete an oily substance that lines the outside of the tear film and prevents from evaporation
what is the conjunctiva?
thin vascular membrane that covers the inner surface of the eyelids and loops back over the sclera but does not cover the cornea (as would impede light)- it is pink due to high number of capillaries
what is the function of the lacrimal apparatus?
tear forming system
