The Eye & Orbit

Question 1

what are the 3 layers of the eye?

Answer 1

the fibrous coat, vascular coat and sensory coat

Question 2

what is the role of and what makes up the fibrous coat?

Answer 2

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

Question 3

what is the role of and what makes up the vascular coat?

Answer 3

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

Question 4

what is the role of and what makes up the sensory coat?

Answer 4

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

Question 5

what nerve leaves the posterior aspect of the eyeball?

Answer 5

the optic nerve= cranial nerve II

Question 6

what is the composition of the sclera?

Answer 6

collagen fibres of different diameters arranged quite irregularly giving it the white opaque appearance and gives attachment to the muscles moving the eyeball

Question 7

what is the composition of the cornea?

Answer 7

very fine uniform collagen fibres which allow light to pass through and are therefore transparent

Question 8

what is the role and composition of the iris?

Answer 8

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

Question 9

what is the role and composition of the ciliary body?

Answer 9

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

Question 10

what is the role and composition of the choroid?

Answer 10

richly vascular and supplies blood to the outer layers of the retina

Question 11

what is the role and composition of the retina?

Answer 11

has lots of neurones including modified neurones called rods and cones which react to light falling on the retina and enable us to see

Question 12

where and what is the role of the aqueous humor?

Answer 12

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

Question 13

where and what is the role of the vitreous humor?

Answer 13

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

Question 14

what is the pathway of aqueous humor?

Answer 14

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

Question 15

what is the crystalline lens?

Answer 15

a transparent biconvex structure which can become more or less convex and is suspended from zonules by the circular body (which are present 360*)

Question 16

what bones make up the the orbital cavity?

Answer 16

frontal bone, zygoma, maxilla, lacrimal bone, ethmoid bone and sphenoid bone (which is divided into the lesser and greater wings by the fissure)

Question 17

what are the 3 foramina in the orbital cavity?

Answer 17

the optic foramen, superior orbital fissure and the inferior orbital fissure

Question 18

why are the walls of the the orbit especially the medial and inferior walls weak?

Answer 18

because adjacent to them are air filled spaces called the paranasal sinuses which makes them susceptible to damage

Question 19

what surrounds the orbit since it is much smaller in length than the orbital cavity?

Answer 19

orbital fat cushions globe which is very important for support

Question 20

what are the eyelids?

Answer 20

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

Question 21

what diseases can affect the fat surrounding the eyes and what does this cause?

Answer 21

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

Question 22

what are the glands found in the eyelids?

Answer 22

meibomian glands which secrete an oily substance that lines the outside of the tear film and prevents from evaporation

Question 23

what is the conjunctiva?

Answer 23

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

Question 24

what is the function of the lacrimal apparatus?

Answer 24

tear forming system

Question 25

where is the lacrimal gland found and what does it do?

Answer 25

situated in the orbit laterally and forms tears which coat the surface of the sclera, conjunctiva and cornea

Question 26

what stimulates the lacrimal gland to produce tears?

Answer 26

parasympathetic innervation from the facial nerve

Question 27

how are tears spread over the anterior aspect of the eyeball?

Answer 27

during each blink the eyelids spread the tears evenly on the surface of the cornea

Question 28

where do the tears drain from the eye?

Answer 28

the puncture on the medial side of each eyelid which drains into the lacrimal sac which sits just over the lacrimal bone and drains through the nasolacrimal duct into the inferior meatus of the nasal cavity

Question 29

what is the function of the intrinsic muscles of the eye?

Answer 29

start and end within the eyeball and control pupil diameter and help alter lens curvature

Question 30

what is the function of the extrinsic muscles of the eye?

Answer 30

attach to the orbit and help to move the eye

Question 31

what are the intrinsic eye muscles?

Answer 31

constrictor papillae, dilator pupillae and ciliaris muscle

Question 32

what is the function of the constrictor papillae?

Answer 32

circular muscles found in the iris just outside of the papillary edge and under parasympathetic innervation via the oculomotor nerve constricts the pupil

Question 33

what is the function of the dilator papillae?

Answer 33

radial muscles in the periphery which under sympathetic innervation dilator the pupil through a plexus around the blood vessels

Question 34

what is the function of the ciliaris muscle?

Answer 34

found in the ciliary body and when it contracts it helps make the lens more convex= needed to focus more up close and is innervated by the oculomotor nerve

Question 35

what are the extrinsic eye muscles?

Answer 35

4 straight recti muscles, 2 oblique muscles and the levator palpebral superioris

Question 36

where do the recti muscles arise from and attach to?

Answer 36

they arise from the apex of the orbit from an annular fibrous ring and inset onto the sclera anteriorly

Question 37

where do the superior and inferior obliques attach?

Answer 37

the superior oblique arises from the roof of the orbit posteriorly and the inferior oblique arises from the floor of the orbit anteriorly and the insert posteriorly onto the sclera

Question 38

where does the levator palpebrae superioris attach and what is its function?

Answer 38

attaches to the roof of the orbit to the upper eyelid and doesn’t really move the eye- lies just above the SR and elevates the upper eyelid

Question 39

what nerves innervate which eye muscles?

Answer 39

SO4, LR6 and 3= everything else

Question 40

what controls sensory innervation of the orbit?

Answer 40

branches of the trigeminal nerve= V1 and V2