Physiology of Vision

Question 1

What are the three layers of the eyeball?

Answer 1

Outer fibrous layer (sclera)
Middle vascular layer (choroid)
Inner neural layer (retina)

Question 2

In which layer does the biochemical activity and hyperpolarisation take place?

Answer 2

Inner neural layer

Question 3

Answer 3

Question 4

What happens at bright light enters the eye?

Answer 4

Pupil constricts

Question 5

What happens when the light is dim?

Answer 5

Pupil dilates

Question 6

What allows the pupil to change size?

Answer 6

Muscles of the iris

Question 7

What produces a focused image on the retina?

Answer 7

Cornea & lens

Question 8

How is focus changed in the eye?

Answer 8

By varying the shape of the lens

Question 9

What do cataracts do?

Answer 9

Make the lens opaque - stops light entering the eye making it difficult to see

Question 10

What changes the power of the image in the eye?

Answer 10

Iris (constricting and dilating) can vary diameter x4 - which varies retinal intensity by x16.

Question 11

What absorbs unwanted light in the eye?

Answer 11

A pigmented layer being the retina

Question 12

How many times does light bend in the eye?

Answer 12

Twice - once when passing through the cornea and once when passing through the lens.

Question 13

Which part of the eye bends the light the most?

Answer 13

Cornea - bends 2/3rds

Lens - bends 1/3

Question 14

What shape is the lens?

Answer 14

Biconvex

Question 15

Does a convex lens converge or diverge light rays?

Answer 15

Converging - brings rays together

Question 16

Does a concave lens converge or diverge light rays?

Answer 16

Diverges light rays - spreads them apart

Question 17

What is the refractive power of a lens measured in?

Answer 17

Diopters

Question 18

What is the focal length of a lens?

Answer 18

Distance between a convex lens and its focal point (where the rays converge)

Question 19

What can affect the focal length of a lens?

Answer 19

Genetics
Pathology

Length of eyeball
Curvature of lens

Question 20

What is long sightedness called? What is it caused by?

Where is the focal point of the lens?

Answer 20

Hypermetropia (Hypermetropic)

Eyeball too short or Lens too weak

Focal point - behind the retina

Question 21

What is short sightedness called? What is caused by?

Where is the focal point of the lens?

Answer 21

Myopia

Eyeball is too long to lens is too strong.

Focal point - in front of the retina

Question 22

What is the most common refractive disorder of the eyeball? What is it caused by? What does it do to vision?

Answer 22

Astigmatism

Caused by curved eyeball (more rugby than football)

Means that light is focussed in more than one place.

Question 23

Which refractive disorder is more common in the elderly? What does it do?

Answer 23

Presbyopia

Caused by laxity of the lens - doesn’t return to its normal shape

Question 24

What type of lens do you need as a corrective lens for myopic patients?

Answer 24

Concave (diverging)

Question 25

What type of lens do you need as a corrective lens for hypermetropic patients?

Answer 25

Convex (converging)

Question 26

Where does the optic nerve leave the eye?

Answer 26

In the optic disc

Question 27

Which is most sensitive part of the retina? How does it appear under an ophthalmoscope?

Answer 27

Fovea Small yellow spot - far eyeball

Question 28

What does the fovea have?

Answer 28

Lots of special cones for detailed vision

Question 29

Answer 29

Question 30

Which cells are found in the neural layer?

Answer 30

Ganglion cells Bipolar cells Photoreceptor cells (rods & cones) Amacrine & horizontal cells (supportive)

Question 31

What do rods detect?

Answer 31

Black & white vision Night vision Dim light

Question 32

What do cones detect?

Answer 32

Colour vision & bright light

Question 33

What happens once photoreceptors are excited?

Answer 33

Signals are transmitted through the retina (photoreceptors to bipolar cells to ganglion cells) to the optic nerve fibres and then to the occipital cerebral cortex

Question 34

What is the process by which photons of light are converted to electrical signals?

Answer 34

Phototransduction

Question 35

What is the visual pathway in the brain?

Answer 35

From optic nerve to optic chaism to optic radiations and to the occipital cortex.

Question 36

Do we have more rods or cones?

Answer 36

More rods (120m to 5m)

Question 37

How many layers is the retina made of?

Answer 37

3 direct (receptors, bipolar cells and ganglion cells) and 2 transverse layers (horizontal and amacrine cells)

Question 38

What are the function of the transverse layers of the retina?

Answer 38

Signal processing including lateral inhibition

Question 39

What are the photosensitive pigments found in rods and cones?

Answer 39

Rods = Rhodopsin Cones = Photopsin - each one has either red-sensitive, green-sensitive or blue-sensitive pigment

Question 40

What type of channels are used in phototranduction?

Answer 40

cyclic Guanosine Monophosphate (cGMP)

Question 41

What is the difference between different colours?

Answer 41

Their wavelength (Red 570, Green 535 and Blue 445)

Question 42

What causes colour blindness?

Answer 42

Loss or modification of one of the three cone pigments.

Question 43

Which gene carries the red and green pigments? What does this explain?

Answer 43

X Why colour blindness is more common in males than females

Question 44

Which gene carries the blue pigment? Why is this rarer?

Answer 44

Found on chromosome 7 (not sex-linked) = which means it is much rarer to find as usually are 2 copies of chromosome 7.

Question 45

What does the visual system in the brain comprise of?

Answer 45

Eye Optic nerve Optic chiasm Optic tract Lateral geniculate nucleus Optic radiation Visual Cortex Visual Association Cortex

Question 46

Which nucleus is found after the optic chiasm?

Answer 46

Lateral geniculate nucleus

Question 47

Answer 47

Question 48

What are the two fields of vision?

Answer 48

Temporal Nasal

Question 49

What does the optic nerve from each retina do after leaving the eye?

Answer 49

Divides into L & R halves

Question 50

What happens to the two halves of the optic nerves in the chiasm?

Answer 50

L halves and R halves from each eye combine to form optic tracts

Question 51

Where do optic tracts relay? Where in the brain is this found?

Answer 51

Lateral geniculate nucleus Found in the thalamus

Question 52

Where does part of each optic tract travel to?

Answer 52

Superior colliculus in the mid-brain

Question 53

Where does the output from the lateral geniculate nucleus go?

Answer 53

To the striate cortex in the occipital lobe.

Question 54

Which Brodmann area is the primary visual cortex?

Answer 54

17

Question 55

What do the following lesions cause?

Answer 55

Question 55

What do the following lesions cause?

Answer 55

Question 56

What is the term of loss of vision in the same half of both eyes?

Answer 56

Homonymous hemianopia

Question 57

What is the term for loss of vision in opposite halves of both eyes?

Answer 57

Bitemporal hemianopia

Question 58

What is the term of loss of vision centrally?

Answer 58

Scotoma

Question 59

What can cause scotomas?

Answer 59

Retinal damage Lesions in visual cortex Tumours in optic nerve, chiasm, tract or radiation.

Question 60

What is a common cause of bitemporal hemianopia?

Answer 60

Pituitary adenomas

Question 61

Which stream of the cortex is concerned with locomotion, motion & action?

Answer 61

The dorsal stream

Question 62

Where is the dorsal stream found in the cortex?

Answer 62

From the occipital to parietal cortex

Question 63

Which stream of the cortex is concerned with object & face identity and conscious perception?

Answer 63

Ventral stream

Question 64

Where is the ventral stream found in the cortex?

Answer 64

From the occipital to the temporal cortex

Question 65

Which disorder means that a patient is unable to recognise and identify visually presented objects or persons despite having normally functioning senses?

Answer 65

Visual agnosia

Question 66

What causes visual agnosia?

Answer 66

Problems between the occipital lobe and the temporal lobe - is a ventral stream problem.

Question 67

What is the inability to recognise familiar faces called?

Answer 67

Prosopagnosia