Eye 1

Question 1

what % of sensory receptors in the human body are located in the eyes

Answer 1

over 50%

Question 2

Name the 3 main components of the eye

Answer 2

bony orbit
accessory structures
eyeball itself

Question 3

Describe the bony orbit

Answer 3

the eyeball is a sphere - 2.5cm in diameter, suspended within a cavity in the skull = bony orbit - by muscles controlling its movements, consists of a roof, floor and medial & lateral walls (superior orbital wall, medial orbital wall, inferior orbital wall, lateral orbital wall, apex region)

Question 4

Describe the role of periorbital fat

Answer 4

partially cushions eyeball, thick layer, protects it during movement

Question 5

Name 5 accessory structures of the eye

Answer 5

eyelid
eyelashes
eyebrows
lacrimal apparactus
extrinsic eye muscles

Question 6

Describe the roles of the Eyelids

Answer 6

upper and lower eyelids (Palpebrae), shade the eyes during sleep, protect the eyes from excessive light and foreign objects, spread lubricating secretions over the eyeballs

Question 7

Describe the tarsal plate within the eyelids

Answer 7

a thick fold of connective tissue within the eyelid that gives its form and support, embedded n each tarsal plate are rows of sebaceous glands known as tarsal or Meibomian glands - secrete a fluid that helps keep the eyelids from adhering to each other

Question 8

Describe the conjunctiva of the eyelids

Answer 8

a thin, protective mucous membrane, lines the inner aspect of the eyelids and the surface of the eyeball, it covers the sclera but not the cornea

over the sclera the conjunctiva is vascular

Question 9

Describe the role of eyelashes

Answer 9

protect the eye from debris

sebaceous ciliary glands at the base of the hair follicles release a lubricating fluid onto the lashes

Question 10

Describe the role of the eyebrows

Answer 10

help protect the eyeballs from 
foreign objects
perspiration
direct rays of the sun
provide facial expression

Question 11

Describe the lacrimal apparatus

Answer 11

the lacrimal glands produce and secrete about 1ml of lacrimal fluid (tears) per day, the tears drain into the lacrimal ducts and out onto the surface of the conjunctiva of the upper lid, the tears then pass medially over the anterior surface of the eyeball, the tears then enter 2 small openings called lacrimal puncta, from the puncta the tears pass into the lacrimal canals which lead into the lacrimal sac and then into the nasolacrimal duct

Question 12

Describe which lacrimal fluid contains

Answer 12

salts, some mucus and lysozyme - a protective bactericidal enzyme

Question 13

What is the function of tears

Answer 13

to protect, clean, lubricate and moisten the conjunctiva and corneal epithelium

Question 14

Describe the extrinsic eye muscles

Answer 14

extend from the walls of the bony orbit to the sclera of the eye, surrounded in the orbit by a significant quantity of orbital fat, capable of moving the eye in almost any direction

Question 15

Name the 6 extrinsic eye muscles that move each eye

Answer 15

superior rectus muscle
inferior rectus muscle
lateral rectus muscle
medial rectus muscle
superior oblique rectus muscle
inferior oblique rectus muscle

Question 16

Which cranial nerves are the extrinsic eye muscles supplied by

Answer 16

Oculomotor (III) - supplies the superior, medial, inferior and inferior oblique rectus muscles
Trochlear (IV) - supplies the superior oblique rectus muscle
Abudcens (VI) - supplies the lateral rectus muscle

Question 17

Name the 3 layers of the eyeball

Answer 17

Fibrous tunic - superficial layer
Vascular tunic - middle layer
Retina - inner layer

Question 18

Describe the cornea of the eyeball

Answer 18

a transparent coat that covers the coloured iris, its curved and so helps focus light onto the retina

Question 19

Describe the sclera of the eyeball

Answer 19

‘white of the eye’, covers entire eyeball except the cornea, gives shape to the eyeball, makes it more rigid, protect its inner parts, serves as a site of attachment for the extrinsic eye muscles

Question 20

Desciribe the fibrous tunic layer of the eyeball

Answer 20

consists of the anterior cornea and posterior sclera

Question 21

Describe the vascular tunic or uvea layer of the eyeball

Answer 21

composed of 3 parts
Choroid
Ciliary Body
Iris

Question 22

Describe the choroid

Answer 22

lines most of the internal surface of the sclera, produces the pigment melanin - absorbs stray light rays, preventing reflection and scattering of light within the eyeball - ensures image cast on retina remains sharp and clear

Question 23

Describe the anterior portion of the vascular tunic eyeball

Answer 23

the choroid becomes the ciliary body - contains the ciliary muscle, suspensory ligaments (zonules) extends from the ciliary body and attach to the lens
contraction or relaxation of the ciliary muscle changes the tightness of the suspensory ligaments which alters the shape of the lens, adapting it for near or far vision

Question 24

Describe what happens for near vision

Answer 24

ciliary muscles contract and the central lens thickness increases to increase its power

Question 25

Describe the iris within the vascular tunic layer of the eyeball

Answer 25

coloured portion of the eyeball, suspended between the cornea and the lens, attached at its outer margin to the ciliary suspensory ligaments (zonules), iris consists of muscle fibres which function to regulate the amount of light entering the eyeball through the pupil in response to light levels

Question 26

Describe what happens in bright/dim light

Answer 26

bright light causes a decrease in the size of the pupil (constriction) dim light causes an increase in the pupil's size (dilation)

Question 27

What determines eye colour

Answer 27

the amount of melanin in the iris

Question 28

Describe the Retina

Answer 28

lines the posterior 3/4 of the eyeball, and is the beginning of the visual pathway, consists of a pigmented layer and a neural layer the melanin in the pigmented layer helps absorb stray light rays neural (sensory) layer processes visual data before sending it as a nerve impulse to the occipital lobe of the brain via the optic nerve

Question 29

Describe the neural layer of the retina

Answer 29

contains neutrons called photoreceptors - specialised cells that begin the process of converting light rays to nerve impulses 2 types = rods and cones

Question 30

Each retina has how many rods/cones

Answer 30

6 million cones and 120 million rods

Question 31

Explain the difference between rods and cones

Answer 31

rods allow us to see in dim light - don't provide colour vision therefore in dim light we can only see black, white, shades of grey between brighter light stimulates cones which do produce colour vision

Question 32

Describe how the retina can be viewed

Answer 32

with an ophthalmoscope, shines light into the eye through the pupil providing a magnified image of the retina and its blood vessels as well as the optic (II) nerve surface of the retina is the only place in the body where blood vessels can be seen directly and are examine for pathological changes

Question 33

Where does the optic (II) nerve exit the eyeball and what is also visible in an image of a retina

Answer 33

optic (II) nerve exits at the site of the optic disc | also visible are the macula lutea and fovea centralis

Question 34

Describe the optic disc

Answer 34

also called the blind spot, contains no rods or cones so can't see an image striking the blind spot

Question 35

Describe the macula lutea

Answer 35

is in the exact centre of the posterior portion of the retina

Question 36

Describe the fovea centralis

Answer 36

a small depression in the macula lutea, no rods present only cones, area of highest visual acuity or resolution (sharpness of vision)

Question 37

Describe the lens

Answer 37

normally transparent and lacks blood vessels, helps focus images on the retina for clear vision, divides the interior of the eyeball into 2 cavities = anterior cavity and vitreous chamber

Question 38

Describe the anterior cavity formed by the lens

Answer 38

consists of 2 chambers = anterior and posterior chambers, both filled with a transparent watery fluid known as aqueous humor - its function is to nourish the lens and corns and is completely replaced about every 90 minutes

Question 39

Describe the posterior vitreous chamber formed by the lens

Answer 39

contains a transparent jellylike substance called the vitreous body, holds the retina flush against the choroid, giving the retina an even surface for the reception of clear images, doesn't ungergo constant replacement, consists mostly of water, also contains phagocytic cells that remove debris, keeping this part clear for unobstructed vision

Question 40

Describe intraocular pressure within the eyeball

Answer 40

produced mainly by the aqueous humor and partly by the vitreous body, maintains the shape of the eyeball and prevents it from collapsing puncture wounds to the eyeball may cause loss of aqueous humor and the vitreous body causing a decrease in intraocular pressure, a detached retina and in some cases blindess