Vision

Question 1

what is the role of the macula, optic disc and retina

Answer 1

visual axis, contains fovea (which has highest concentration of cones - best visual acuity)

optic disc blind spot - not rods or cones

detection layer and extension of diencephalon

Question 2

what are the two layers of the retina

Answer 2

neuronal and non neuronal

Question 3

describe the structure of the superficial neuronal layer of the retina and its role

Answer 3

largest - contains photoreceptors, primary bipolar neurones, secondary ganglion neurones whose axons become the optic nerve at the optic disc

transducer light energy into electrical by changing membrane potential

Question 4

describe the structure and role of the non-neuronal layer of the retina

Answer 4

pigmented epithelium which contains melanin which is light absorbing
sits against the choroid which helps maintain metabolic activity of the photoreceptors

Question 5

what types of cells modulate light transmission in the retina

Answer 5

interconnected horizontal and amacrine interneurones

Question 6

what is special about the surrounding of the optic nerve

Answer 6

part of the CNA as extension of the diencephalon so surrounded by meninges

Question 7

what is papillodoema

Answer 7

swelling of the optic disc caused by increased intracranial pressure from CSF

can compress the central retina vein which stops venous drainage

causes headaches, drowsiness, blurred vision and vommiting

Question 8

describe the visual pathway from the retina to the cortex

Answer 8

optic nerve to optic chiasma which go to optic tract (carry second order neurones) to LGN of thalamus. optic radiations of 3rd neurones send fibres from LGN to primary visual (striate nucleus) in the occipital lobe

Question 9

why is vision contralateral

Answer 9

crossing of fibres at the optic chiasma so injury in right eye rooted from upper lesion in left brain

Question 10

describe the organisation of the visual field in the primary visual cortex

Answer 10

upper visual field goes to lower bank of calacrine sulcus
lower visual field goes to the upper bank calacrine sulcus
centre of visual axis goes to the occipital pole

Question 11

why is the visual cortex organised so strangely

Answer 11

because images are flipped upside down and mirror reversed

Question 12

describe the optic routes of upper visual field fibres vs lower visual field fibres

Answer 12

upper - travel to lower bank calacrine sulcus via meyers loop (inferior trajectory)

lower - travel to upper bank of calacrine sulcus via superior trajectory

Question 13

describe the presentation of the macula vs peripheral fields in the visual cortex

Answer 13

macula is represented most posteriorly to tip of occipital pole

peripheral fields more anteriorly

Question 14

what is scotoma and anopia

Answer 14

localised patch of blindness

refers to the loss of one or more quadrants of the visual field

Question 15

what is hemianopia vs quadrantanopia

Answer 15

half of visual field lost

quarter of the visual field last

Question 16

what is homo vs heteronymous

Answer 16

visual loss is similar both eyes vs varied losses of different sides

Question 17

what percentage of optic tract fibres do not go to the LGN

Answer 17

10% go to medial root to the pretectal area of the midbrain to carry out reflexes

Question 18

describe the pupillary light reflex

Answer 18

both pupils constricitng or dilating depending on levels of light
CN2/3 - parasympathetic
acts via edinger-westphal nucleus where interneurones of CN2 synapse with CN3 and travel to cilia ganglion
causing the sphincter papillae to constrict when light enters

Question 19

what is the difference between direct and consensual reflex of the eye

Answer 19

direct - light in one eye same pupil constricts

consensual - light in one eye and the other constricts

Question 20

what would a lesion in CN2 or 3 having upon light being shined in the eye

Answer 20

light in one eye means both pupils constrict

CN2 lesion = loss of direct reflex

CN3 lesion = loss of consensual reflex

Question 21

what is accommodation of the eye

Answer 21

changes that occur when changing gaze from far to near objects

Question 22

what are the three processes involved in eye accommodation

Answer 22

accommodation - colliery muscles contract - lens becomes more rounded - closer things focus

pupil constricts - sphincter pupillae

ocular convergence - medial rectus

Question 23

what is the route of afferent and effect fibres in the visual pathway

Answer 23

afferent carrying visual inout via nerve then tract to LGN but efferent fibres all run within CN3 - parasympathetic to sphincter papillae and ciliary muscles
motor to medial rectus