Senses 1- The Eye

Question 1

What is the sclera?

Answer 1

• white of the eye
• tough white skin that protects
• covers all of the eye except cornea
• supports eyeball

Question 2

What is the cornea?

Answer 2

• clear portion of the sclera
• Allows light into the eye
• Acts as fixed lens
• Two thirds of light refraction takes place in the cornea

Question 3

What is the pupil?

Answer 3

allows light into the eye
Size determines amount of light entering eye
Bright light - pupil constricts-small
Dim light - pupil dilates-larger

Question 4

What is the iris?

Answer 4

muscle
Coloured part of eye
-Circular muscle
Controls opening of pupil

Question 5

What is parasympathetic stimulation?

Answer 5

causes circular muscles in the iris to contract which causes constriction

Question 6

What is sympathetic stimulation?

Answer 6

causes radial muscles to contract

Question 7

What is a lens?

Answer 7

1) Made of transparent fibres in clear
     membrane
2) Allows precise focussing of light 
     onto retina at the back of eye
3.  Suspended by ligament attached to ciliary muscle which contracts to change the shape of the lens
4.  Fine focusing mechanism
5.  Non uniform index of refraction

Question 8

What arethe aqueous humor and vitreous humor?

Answer 8

Transparent gel like liquid filling the eye
Provides nutrient to cornea and eye lens
Helps maintain eye ball shape with its pressure

Question 9

What is the retina?

Answer 9

1) Internal membrane
2) Contains light receptive cells (rods and cones)
3) Converts light to electrical
signals
4) Signals leave eye via optic nerve

Question 10

What is the optic nerve?

Answer 10

1. transmits electrical impulses from retina to brain

2. blind spot- no photoreceptors

Question 11

Where is light focused?

Answer 11

• Cornea
• Entering lens
• Exiting lens

Question 12

What is accommodation?

Answer 12

the process by which the eye changes optical power to maintain a clear image or focus on an object as it’s distance varies
DISTANCE
-light rays almost parallel- do not need much refraction, cillary muscles relaxed, fibres taut, flat lens (relaxed)
NEAR
-light rays diverge- need more refraction
-cillary muscles contract, fibres slack, rounded lens= greater strength for near vision

Question 13

What is myopic eye?

Answer 13

eye is elongated- nearsighted

• concave lens used
• when light comes in its refractive and converges together too soon

Question 14

What is hyperopic eye?

Answer 14

eye is squished together -farsighted

• convex lens used
• light rays converge together at the back of the eye too far back from the focal point

Question 15

What is presbyopia?

Answer 15

lens harden with age
cannot accommodate for near
bifocal lens

Question 16

What is the Retina?

Answer 16

• Recieves light focused by lens
• Converts light via network of nerve cells
• chemical reaction occur here to produce images

Question 17

Structure if the Retina- Choroid

Answer 17

• Vascular layer providing oxygen and nutrients to outer retina especially fovea
• Absorbs any light not absorbed by photoreceptors

Question 18

Structure of the Retina- Retinal Pigment Epithelium

Answer 18

• Pigmented layer for light absorption and reducing oxidative stress
• Tight junctions forms blood brain (retina) barrier
• supports photoreceptors

Question 19

Structure of the Retina- Photoreceptors

Answer 19

2 types: concentrated in fovea, high acuity day photopic (sharp vision) and colour vision
3 types (blue, red, green)
Rods: dark (scotopic) vision. Not present in central retina

Question 20

Structure of the Retina- Horizontal cells

Answer 20

interneurons connecting photoreceptors laterally

help to integrate and regulate input from multiple photoreceptor cells

Question 21

Structure of the Retina- Bipolar cells

Answer 21

Connect photoreceptors to retinal ganglion cells

Facilitate sensory processing through horizontal and amacrine cells

Question 22

Structure of the Retina- Amacrine cells

Answer 22

• interneurons connecting bipolars laterally
• inhibitory
• interact with retinal ganglion cells

Question 23

Structure if Retina- Retinal Ganglion cells

Answer 23

• output cells from retina

- relay info from retina to brain via optic nerve

Question 24

Fovea

Answer 24

• special pit-like area at the back of the eye

- only cones present no rods

Question 25

Rods

Answer 25

• 120 million throughout retina
• Absent from fovea
• rod shaped
• sensitive to dim light
• not sensitive to colour (monochromatic)
• many rods feed into one retinal ganglion cells
• poorly resolved images
• light sensitive pigments- rhodopsin

Question 26

Cones

Answer 26

• 6-7 million
• condensed at the fovea
• cone shaped
• require bright light
• 3 types for colour vision (red, green and blue)
• 1 cone feeds into one ganglion cell at fovea
• well resolved images
• light sensitive pigment- iodopsin

Question 27

Phototransduction

Answer 27

• Process through which light is converted into electrical signals
• occurs in the retina through photoreceptors
• photoreceptor to encodes a light stimulus as a chemical output
• detection of light carried out on membrane disks
• contain 1000’s of molecules of rhodopsin (photoreceptor molecule)

-Rhodopsin contains Opsin (protein) and retinal (sensitive)
-Dark = cis form
-light= trans form
-changes shape of opsin protein- bleaching
Reverse action trans to cis requires enzyme reaction and is very slow

Question 28

How does phototransduction work?

Answer 28

• light changes rhodopsin structure
• Alters permeability to Na+ in photoreceptor (graded potential)
• Sensory neurone in optic nerve (action potential)
• Brain

Question 29

What is the visual pathway- optic chiasm?

Answer 29

when information reaches the optic chiasm it crosses over to each side of the brain to ensure a full image is obtained 55% crosses over

Question 30

What is the lateral Geniculate Nucleus?

Answer 30

• structure in the thalamus part of midbrain
• Receives input from retinal ganglion cells
• input and output from ganglion cells
• input and output connections to visual cortex
• one in each hemisphere
• leave LGN and goes to visual cortex

Question 31

What is the Primary Visual cortex?

Answer 31

• Located in the occipital lobe
• input from LGN via optic radiation
• sends information to 2 pathways
  1) ventral steam- form recognition and object presentation
  2) Dorsal stream- motion, object location, eye and arm control

Question 32

Sclera- Scleritis

Answer 32

• Inflammation of sclera
• usually associated with underlying disease
• can progress to other parts of the eye
• immediate treatment to reduce long term vision loss

Question 33

Cornea- corneal ulcer

Answer 33

• open sore of the cornea
• many causes- infection, physical/chemical trauma, corneal drying, over use of contact lenses
• Very serious- may result in blindness

Question 34

Pupil/iris- Coloboma

Answer 34

• Hole in iris
• underdeveloped tissue during pregnancy
• can be syndromic or caused by foetal alcohol syndrome
• one or both eyes affected
• variable impact on vision
• treatment- coloured contact lens

Question 35

Lens- Cataract

Answer 35

• age related, congenital or trauma
• clouding of the lens (clumps of protein)
• decrease vision
• Surgery- removal of old lens via suction and insertion of plastic lens

Question 36

Visual Disease- Retina

Answer 36

Age related Macular Degenaration

• Affects central retina
• build up of waste material/ blood vessels
• occurs 50-60’s
• Progressive without treatment
• injections
• mild vision loss- blindness

Retinal Detachment
-Tear allows fluid under retina
-Risk factors- high myopia, trauma, family history
Requires prompt action - surgery

Question 37

Strabismus

Answer 37

• misalignment of the eyes
• common in children
• amblyopia- suppression
• loss of depth perception
• treat amblyopia with patching
• surgical correction

Question 38

What is vision acuity?

Answer 38

a measure of foveal vision (fine spatial)

Question 39

What is retinal disparity?

Answer 39

allows judgement of distance
the closer an object the greater the disparity
requires binocular vision (image from either eye)