Vision

Question 1

Eye as a camera

Answer 1

Cornea and lens produce focused image on the retina

Focus is varied by changing shape of lens

Iris acts as diaphragm, varying diameter

Behind retina is pigment which absorbs unwanted light

Question 2

Hypermetropia

Answer 2

Eyeball too short or lens system too weak

Question 3

Myopia

Answer 3

Eyeball too long or lens system too short

Question 4

Structure of the retina

Answer 4

Receptors

• 120 million rods
• 5 million cones

Processing layers

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

Question 5

Rhodopsin and its chromophore

Answer 5

When hit by photon, retinal in rhodopsin flips from 11-cis to all trans

Sets of series of biochemical events which results in electrical change

Question 6

Ganglion cell response

Answer 6

Ganglion cells response weakly to changes in overall light intensity

Respond to local contrast

Ganglion cell responses basic pattern is either on centre or off centre

Question 7

Colour blindness

Answer 7

Results from loss or modification of one or more of the three cone visual pigments

Genes from red and green pigments on X chromosomes

Gene for blue pigment on chromosome 7

Question 8

Central visual pathways

Answer 8

Optic nerve from each retina divides into L and R

In optic the two halves from both eyes combine

Optic tracts relay in lateral geniculate nuclei of thalamus

Part of each optic tract goes to superior colliculus in mid brain

Output of each lateral geniculate goes almost exclusively to striate cortex in occipital lobe

Image of one hald of each combined field represent in one half of V1

Question 9

Visual cortex

Answer 9

Organised into three overlapping patterns

1. Ocular dominance columns
2. Smaller orientational columns where orientation of optimal stimuli varies systemically across the surface
3. Colour blobs; colour information kept separate from orientation and passed to other regions

Question 10

Scotomas

Answer 10

Come in many kinds

May be caused by retinal damage, lesions in visual cortex or pressure from tumours restricting optic nerve, chiasm, optic tract or optic radiation

Question 11

Dorsal stream in cortex

Answer 11

From occipital to parietal cortex

Concerned with location, motion and action

Question 12

Ventral stream in cortex

Answer 12

From occipital to temporal cortex

Concerned with object (and face) identity and with conscious perception

Question 13

Visual agnosia

Answer 13

Condition where a person can see but cannot recognise or interpret visual information

Due to disorder in parietal lobe

Question 14

Prosopagnosia

Answer 14

Special case of agnosia

Inability to recognise familiar faces

Associated with damage to specific parts of the temporal lobe

Question 15

Blindsight

Answer 15

Destruction of striate cortex leads to blindness in part of visual filed that corresponds damaged area

Question 16

Vestibulo-ocular reflex

Answer 16

Stabilises gaze by countering movement of the head

Question 17

Optokinetic reflex

Answer 17

Stabilises the image of a moving object on the retina

Question 18

Pupillary reflex

Answer 18

If one eye is illuminated, both pupils will ontract because both pretectal nuclei and edinger westphal nuclei receive signals from both eyes

Damage to one optic nerve prevents light in that eye from closing the pupil