M6S3 Special Sense - The Eye

Question 1

Vision

Answer 1

Requires special visual receptors called photoreceptors located at back of eye (but first anterior and accessory structures which play role in vision as light passes through them before reaching photoreceptors)

Question 2

Accessory Structures of the eyeball

Answer 2

-important structures outside eyeball that protect and move eyeball

1. Lacrimal gland
   -produces tears, which keep cornea or outside surface of eyeball, moist and clean
   -tear drainage system important and part of lacrimal apparatus (as shown in anterior view)
2. Eyelid
   -upper eyelid contains elevator palpebrae superioris muscle and Orbicularis oculi muscle, which control opening and closing of eye (respectively)
3. Extrinsic eye muscle
   -6 extrinsic eye muscles that you to move your eye to increase range of motion

*refer to goodnotes

Question 3

Extraocular eye muscles

Answer 3

• located outside of eyeball itself
  -name based on location
  Superior oblique
  Medial rectus
  Inferior rectus
  Superior rectus
  Lateral rectus
  Inferior oblique
  *refer to goodnotes image

Question 4

General features of the eye

Answer 4

-globe structure
-majority of eye situated within skull
-complex organ
-has different layers

Question 5

Cavities of eye

Answer 5

-eye seperated into 2 fluid-filled cavities
-cavities delineated by lens

Posterior chamber
Anterior chamber
Anterior cavity: composed of anterior and posterior chambers, both which filled with aqueous humour (watery type fluid)
Lens: seperates anterior cavity of the eye from posterior cavity
Posterior cavity: posterior compartment filled with vitreous humour (gelatinous fluid)
*refer to goodnotes

Question 6

Layers of the eye

Answer 6

-internal portion of eye composed of three layers, or tunics

Outer layer - Fibrous
-fibrous tunic outermost layer of eye and has 2 portions located internally and externally to lens
-2 portions are continuous with one another
Sclera: internal aspect of fibrous tunic, located posterior to lens. Sclera forms white portion of eye and a layer of dense connective tissue that acts as point of attachment for extrinsic eye muscles
Cornea: external aspect of fibrous tunic, located anterior to lens. Cornea is transparent enabling light transmitting
Lens:

Middle layer - Vascular
-vascular layer (the uveal tract) is middle layer of eye and made up of 3 parts
Choroid: contains blood vessels that supply eye with oxygen and nourishment
Ciliary body: produces aqueous humour and contains the ciliary muscles (intrinsic eye muscles), which control shape of lens
Iris: contains sphincter and dilator muscles (intrinsic eye muscles) which control the narrowing and widening of pupil. Iris also contains pigments, which give eye its colour

Deep layer - Sensory (Retina)
-sensory tunic innermost layer of eye which consists of 4 main parts:
Neural layer: outer most region of neural layer made of photoreceptors rods and cones), which light sensitive. These receptors send signals through smaller nerves to axons of ganglion cells (inner most layer of retina) exit the posterior aspect of the globe to brain to form CN II
Optic disc: area where smaller nerves cell axons converge. Location were we can see when we look into eye
Macula: central area of retina, lateral to optic disc. The central depression of macula, the fovea, area where fine detailed vision occurs
Optic nerve (CN II):
*refer to goodnotes

Question 7

Flow of aqueous humour

Answer 7

-produced by ciliary processes in posterior chamber
-flows through the pupil into anterior chamber and exits at anterior chamber angle (junction of iris, ciliary body and cornea) through the trabecular meshwork into Schlemm’s canal
-ultimately into episcleral venous channels
-which drains into systemic circulation
*refer to goodnotes for image

Question 8

Glaucoma

Answer 8

-normally aqueous humour able to flow naturally from eye through trabecular network in drainage angle
-in glaucoma, flow is blocked and doesn’t flow out of drainage angle properly, causing excess fluid to accumulate in chambers of eye
-this puts increased pressure on structures in eye, leading to damage of neural tunic (or retina) and nerves in this layer

Question 9

What symptoms would likely occur in a patient with glaucoma if their lens became distrusted and blood flow to neural tunic or retina stopped?

Answer 9

-damage to retina or neural tunic
-inability to see
-distortion of optic nerve
-reduced vision