Visual system Flashcards

Question

where is teh lacrimal gland found and what does it do ?

Answer 1

lacrimal gland resides within the orbit, latero-superiorly to the globe: secretes tears at a constant rate even in the absence of irritation or stimulation (basal tears)

Answer 2

Tears can be formed by : Basal Reflex Emotion

Answer 3

Tear film Tear film drains through the two puncta, tiny openings on the upper and lower medial lid margin. Puncta form opening of the superior and inferior canaliculi which converge and drain into the tear sac then tear duct and nasal cavity. Structure: see below

Answer 4

Mot superficial part of eye Maintains smooth cornea-air surface, provides oxygen supply to cornea (avascular normally), removal of debris, bacteriacide

Answer 5

Superficial lipid layer: reduces tear film evaporation – produced by a row of Meibomian glands along the lid margin. Aqueous (water) tear film (tear gland): delivers O2 and nutrients to surrounding tissues and factors to protect from bacteria Mucinous layer corneal surface: maintains surface wetting. The mucin molecules act by binding water molecules to the hydrophobic corneal epithelial cell surface.

Answer 6

Cornea is innervated by sensory fibres of cranial nerve V1 (Ophthalmic trigeminal) which relays signal to CNS

Answer 7

Mediated by the parasympathetic nervous system (acetylcholine neurotransmitter), innervating the lacrimal gland

Answer 8

Clear window: powerful refracting surface, ⅔ of eye focussing power Transparent, low water content, covers front of eye, avascular

Answer 9

``` 5 layers Epithelium Bowman’s membrane Stroma: regularity → transparency Descement’s membrane Endothelium: pumps fluid out of corneal, preventing oedema ```

Answer 10

it turns white

Answer 11

transparent biconvex structure suspended posterior to the iris Funcion focuses light rays onto the retina, ⅓ of eye focussing power (higher refractive index than aqueous fluid and vitreous Accommodation Elasticity ( it needs to be transparent and have a high refractive power for function

Answer 12

Outer acellular capsule | Regular inner elongated cell fibres - transparency (can be lost with age: CATARACTS)

Answer 13

Thin layer of tissue responsible for capturing light rays which are sent to brain for processing via the optic nerve

Answer 14

Transmits electrical impulses from retina to brain, connecting near macula Visible portion: optic disc Creates a Blind spot : Where the optic nerve meets the retina there are no light sensitive cells . The corresponding landmark for the blind spot is the optic disk

Answer 15

Creates a Blind spot : Where the optic nerve meets the retina there are no light sensitive cells . The corresponding landmark for the blind spot is the optic disk

Answer 16

small and highly sensitive retinal region (roughly in centre pf retina , temporal to optic nerve) responsible for detailed central vision. Macula allows us to: appreciate detail perform tasks that require central vision (reading) contains the highest concentration of photosensitive cone cells (+ low concentration of rods).

Answer 17

Fovea is the centre of the macula Most sensitive part of retina Highest concentration of cones - to perceive in detail low rod concentration - aka less sensitive to light which is why stars brighter out of corner of eye

Answer 18

detailed day and colour vision the region of highest visual acuity that is concerned with the centre field of vision is the fovea (most cones) Reading, facial recognition

Answer 19

Assessed by visual acuity assessment

Answer 20

Loss of foveal vision, leads to poor visual acuity

Answer 21

Shape, movement, navigation vision, ‘Night vision’ Assessed by visual field assessment Extensive loss of visual field leads to inability to navigate in environment (white stick despite perfect visual acuity)

Answer 22

Assessed by visual field assessment

Answer 23

Extensive loss of visual field leads to inability to navigate in environment (white stick despite perfect visual acuity).

Answer 24

outer middle inner

Answer 25

Photoreceptors (1st order neuron), detection of light

Answer 26

Bipolar cells (2nd order neuron), local signal processing to improve contrast sensitivity, regulate sensitivity

Answer 27

Retinal ganglion cells (3rd order neuron), transmission of signal from eye to brain

Answer 28

rod | cone

Answer 29

more rod cells than cone cells Longer outer segment with photo-sensitive pigment 100x more sensitive to light than cones Slow response to light Scotopic/night vision Peripheral and night vision, more photoreceptors, more pigment, higher spatial and temporal (time) summation, recognises motion Highest conc in periphery 20-40 degrees away from the fovia

Answer 30

Less sensitive to light, but faster response Photopic vision: day light fine vision, colour vision Central and day vision, recognises colour and detail High conc in fovia

Answer 31

The eye captures different coloured lights though different receptors S cones: blue (<400 to 530, peak at 420nm) M cones: green (400 to >600, peak at 540) L cones: red (400 to >600, peak at 570) Rods: not colour sensitive (night vision, spatial recognition, 400 to 600 peak at 500) Cones used to see colour

Answer 32

deuteranomaly/ daltonism achromatopsia / full colour blindness

Answer 33

Deuteranomaly/Daltonism: don’t perceive red but are not completely colour blind caused by the shift of M-cone sensitivity towards that of the L-cone causing red-green confusion (Green appears red) Most frequent

Answer 34

full colour blindness ( only effect small pat of population )

Answer 35

ishihara test

Answer 36

Transmits signal from eye to the visual cortex Visual pathway landmarks eye optic nerve (ganglion nerve fibres), optic chiasm (half of the nerve fibres cross here), optic tract (ganglion nerve fibres exit as optic tract), lateral geniculate nucleus (ganglion nerve fibres synapse at lateral geniculate nucleus), optic radiation (4th order neuron) primary visual cortex or striate cortes (within the occipital lobe)

Answer 37

Optic ganglion nerve fibres → Lateral geniculate nerve fibres → Optic radiations → Primary visual cortex

Answer 38

First order neurons - road and cone retinal photoreceptors Second order neurons - retinal bipolar cells Third order neurons - retinal ganglion cells

Answer 39

Optic Nerve (CN II) Partial Decussation at Optic Chiasma – 53% of ganglion fibres cross the midline Optic Tract Destinations Lateral Geniculate Nucleus (LGN) in Thalamus – to relay visual information to Visual Cortex

Answer 40

Optic chiasma : important landmark in visual pathway 53% of ribres cross at OC Contralateral fibres originate from nasal retina and carry modalities of peripheral vision (temporal visual field) Uncrossed ipsilateral fibres are responsible for nasal visual field (originate from temporal retina)

Answer 41

Lesions anterior to optic chiasma affect visual field in one eye only

Answer 42

Damages crossed ganglion fibres from nasal retina in both eyes Temporal Field Deficit in Both Eyes – Bitemporal Hemianopia

Answer 43

Right sided lesion – Left Homonymous Hemianopia in Both Eyes | Left sided lesion – Right Homonymous Hemianopia in Both Eyes

Answer 44

``` monocular blindness bitemporal hemianopia right nasal hemianopia homonymous hemianopia quadrantanopia macular sparing ```

Answer 45

Bitemporal hemianopia: caused by pit gland tumour COMMON

Answer 46

Homonymous hemianopia: caused by stroke (cerebrovascular accident)

Answer 47

(contralateral) homonymous hemianopia with macular sparing: caused often by stroke, damage to primary visual cortex (area representing macula receives dual blood supply from PCA from both sides)

Answer 48

Pupillary function: regulates light input to the eye like a camera aperture

Answer 49

In light: pupil constriction Decreases spherical aberrations and glare Increases depth of field - sew near response triad from previous lecture Reduces bleaching of photo-pigments Pupillary constriction mediated by parasympathetic nerve (within CNIII)

Answer 50

In dark: pupil dilation Increases light sensitivity in the dark by allowing more light into the eye Pupillary dilation mediated by sympathetic nerve

Answer 51

afferent | efferent

Answer 52

Rod and cone photoreceptors synapse with bipolar cells which then synapse on retinal ganglion cells. Pupil-specific ganglion cells exist at posterior third of the optic tract before entering the lateral geniculate nucleus synapsing upon the dorsal brainstem. These pupillary retinal ganglion cells form the pupillary reflex afferent pathway. Afferent pathway from each eye synapse on Edinger-Westphal Nuclei on both sides of the dorsal brainstem

Answer 53

Edinger-Westphal nucleus → Oculomotor nerve (Parasympathetic nerve) Synapses at the ciliary ganglion upon the short posterior ciliary nerve pupillary sphincter.

Answer 54

Direct light reflex - constriction of pupil of light stimulated eye

Answer 55

Consensual light reflex - constriction of pupil of other (fellow) eye

Answer 56

Afferent ( right and unilateral ) | Efferent ( right and unilateral )

Answer 57

Damage to the optic nerve No pupil constriction in both eyes when the right eye is stimulated with light (No consensual or direct reflect) Normal pupil constriction in both eyes when the left eye is stimulated with light. There is a consensual reflex in the right eye.

Answer 58

Difference response pending on which eye is stimulated

Answer 59

Pupil constriction Damage to right 3rd nerve No right pupil constriction whether right or left eye is stimulated with light Left pupil constricts whether right or left eye is stimulated with light

Answer 60

Same unequal response between left and right eye irrespective which eye is stimulated

Answer 61

Swinging torch test: relative afferent pupillary defect

Answer 62

partial pupillary response is still present when the damaged eye is stimulated. Elicited by the swinging torch test – alternating stimulation of right and left eye with light. Both pupils constrict when light swings to left undamaged eye. Both pupils paradoxically dilate when light swings to the right damaged eye, as a result of reduced drive for pupillary constriction in both eyes.

Answer 63

Voluntary or involuntary of movement of eyes Necessary for acquiring and tracking visual stimuli Facilitated by the six extraocular muscles innervated by the three cranial nerves (III, IV and VI)

Answer 64

Facilitated by the six extraocular muscles innervated by the three cranial nerves (III, IV and VI)

Answer 65

Duction – Eye Movement in One Eye Version – Simultaneous movement of both eyes in the same direction Vergence – Simultaneous movement of both eyes in the opposite direction Convergence – Simultaneous adduction (inward) movement in both eyes when viewing a near object

Answer 66

``` Saccade – short fast burst, up to 900°/sec Reflexive saccade to external stimuli Scanning saccade Predictive saccade to track objects Memory-guided saccade ``` Smooth Pursuit – sustain slow movement Slow movement – up to 60°/s Driven by motion of a moving target across the retina.

Answer 67

``` Six muscles Attach eyeball to orbit Straight and rotary movement Four straight muscles Superior rectus Inferior rectus Lateral rectus Medial rectus ```

Answer 68

Moves the eye up.

Answer 69

Moves the eye down.

Answer 70

Also called the external rectus Attaches on the temporal side of the eye Moves the eye toward the outside of the head (toward the temple)

Answer 71

Also called the internal rectus Attached on the nasal side of the eye Moves the eye toward the middle of the head (toward the nose)

Answer 72

Attached high on the temporal side of the eye. Passes under the Superior Rectus. Moves the eye in a diagonal pattern down and out Travels through the trochlea

Answer 73

Attached low on the nasal side of the eye. Passes over the Inferior Rectus. Moves the eye in a diagonal pattern - up and out.

Answer 74

``` Third Cranial Nerve (oculomotor) Superior Branch Superior Rectus – elevates eye levator palpebrae superioris - raises eyelid (not shown) Inferior Branch Inferior Rectus – depresses eye Medial Rectus – adducts eye Inferior Oblique – elevates eye Parasympathetic Nerve – constricts pupil ```

Answer 75

Fourth Cranial Nerve (trochlear) | Superior Oblique – depresses eye

Answer 76

Sixth Cranial Nerve (abducens) | Lateral Rectus – abducts eye

Answer 77

Extraocular Muscle Testing – Isolate muscle to be tested by maximizing its action and minimizing the action of other muscles Abduction – Lateral Rectus Adduction – Medial Rectus Elevated and Abducted – Superior Rectus Depressed and Abducted – Inferior Rectus Elevated and Adducted – Inferior Oblique Depressed and Adducted – Superior Oblique

Answer 78

``` Up (Elevation) Supraduction – one eye Supraversion – both eyes Down (Depression) Infraduction – one eye Infraversion – both eyes Right – Dextroversion Right Abduction Left Adduction Left – Levoversion Right Adduction Left Abduction Torsion – rotation of eye around the anterior-posterior axis of the eye ```

Answer 79

``` Affected eye down and out Droopy eyelid (loss of elevator palpebrae superioris) Unopposed superior oblique innervated by fourth nerve (down) Unopposed lateral rectus action innervated by sixth nerve (out) ```

Answer 80

Affected eye unable to abduct and deviates inwards | Double vision worsen on gazing to the side of the affected eye

Answer 81

Nystagmus – Oscillatory eye movement Optokinetic Nystagmus = Smooth Pursuit + Fast Phase Reset Saccade Optokinetic Nystagmus Reflex is useful in testing visual acuity in pre-verbal children by observing the presence of nystagmus movement in response to moving grating patterns of various spatial frequencies Presence of Optokinetic Nystagmus in response to moving grating signifies that the subject has sufficient visual acuity to perceive the grating pattern