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THE VISUAL SYSTEM Flashcards

1
Q

what is bitemporal hemianopia?

A

ocular defect that leads to impaired peripheral vision in the outer temporal halves of the visual field of each eye caused by damage to the optic chiasm

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2
Q

what is homonymous hemianopia?

A

a visual field defect involving either the two right or the two left halves of the visual fields of both eyes
usually caused by a brain injury

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3
Q

what is quadrantanopia?

A

A loss of vision in a quarter of the visual field. The defect is usually bilateral as it is typically caused by a lesion past the optic chiasma.

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4
Q

what is the conjunctiva?

A

a continuous, clear, thin membrane that covers the front surface of the eye and inner surface of eyelids

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5
Q

what are the 2 segments of the conjunctiva?

A

bulbar conjunctiva and palpebral conjunctiva

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6
Q

what does the bulbar conjunctiva cover?

A

sclera

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7
Q

what does the palpebral conjunctiva cover?

A

inner surface of eyelids

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8
Q

whats the function of the conjunctiva?

A

keeping eye surface moist and protected from dust, debris, infections

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9
Q

what is found within the fibrous layer of the eye?

A

cornea and sclear

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10
Q

what is the cornea and what is its function?

A

a transparent layer covering the iris and pupil, which allows light to enter the eye and refract it

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11
Q

where does the cornea get oxygen from?

A

directly from the air

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12
Q

what innervates the cornea?

A

opthamic division of trigeminal nerve

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13
Q

at what point does the cornea meet the sclera?

A

the corneal limbus

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14
Q

whats within the vascular layer of the eye?

A

iris
lens
ciliary body
choroid

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15
Q

what determines the colour of a person’s iris?

A

melanin amount

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16
Q

what are the muscles in the iris?

A

sphincter and dilator pupillae muscles - control size of pupil and therefore how much light enters the eye

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17
Q

what alters the shaoe of the lens?

A

ciliary bodies

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18
Q

what are ciliary bodies?

A

ciliary muscles and processes that connect to suspensory ligaments which are attached to the lens

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19
Q

what is the choroid?

A

the middle layer of tissue in the wall of the eye that is brown in colour so can absorb light and contains many blood vessles (between sclera and retina)

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20
Q

whats the function of the choroid?

A

supplies the outer retina with nutrients, and maintains the temperature, light regulation and volume of the eye

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21
Q

whats found in the neural layer of the eye

A

the retina

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22
Q

outline the structure of the retina?

A

has a macula which has a dense amount of photoreceptors and the fovea is in the centre of this and is where visual acuity is highest due to the most cones

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23
Q

whats within the retina?

A

ganglion cells, bipolar cells, photoreceptors

horizontal cells and amacrine cells

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24
Q

what are the 2 types of photoreceptors?

A

rods and cones

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25
why is the outer layer of pigmented cells so important in the retina?
as it absorbs any light that doesnt hit photoreceptors to prevent scattering of light
26
whats more numerous rods or cones
rods
27
whats the function of rods?
convert visual stimuli in the form of photons (particles of light) into chemical and electrical stimuli - function best in low light
28
whats the function of cones?
They respond differently to light of different wavelengths, and are thus responsible for color vision, and function best in relatively bright light
29
what are the 3 chambers of the eye?
anterior - between cornea and iris posterior - between iris and ciliary processes vitreous 0 between lens and retina
30
outline the fluids in the eye?
anterior and posterior chambers are filled with aqueous humor vitreous chamber is filled with vitreous humor
31
what are conjugate eye movements?
when eyes move in the same direction
32
what is disconjugate eye movement?
when eyes move in opposite direcions
33
whats an example of disconjugate eye movement?
vergence - adjusting the eyes for different viewing distance
34
what are examples of conjugate eye movements?
vestibulo-ocular optokinetic saccade smooth pursuit
35
what is vestibulo-ocular eye movement?
a reflex acting to stabilize gaze during head movement, with eye movement due to activation of the vestibular system
36
what is optokinetic eye movement?
the eye to follow objects in motion when the head remains stationary
37
what is saccade eye movement?
rapid eye movements designed to shift the fovea to objects of visual interest.- shifting focus
38
what is smooth pursuit eye movement?
tracking moving objects
39
what are the 7 extraocular muscles?
``` levator palpebrae superioris superior oblique inferor oblique superior rectus medial rectus lateral rectus inferior rectus ```
40
whats the function of levator palpebrae superioris?
raise the upper eyelid and to maintain the upper eyelid position
41
whats the function of superior oblique muscle?
eye intorsion depression abduction
42
whats the function of inferior oblique muscle?
elevation and abduction of the eyeball
43
whats the function of superior rectus?
elevation adduction medial rotation
44
whats the function of inferior rectus?
depression | adduction and lateral rotation
45
whats the function of medial rectus?
adducts eyeball
46
whats the function of lateral rectus?
abducts eyeball
47
which of the extraocular muscles does the oculomotor nerve innervate?
superior rectus, inferior rectus, medial rectus, inferior oblique and levator palpabrae superioris
48
what innervates the superior oblique muscle?
trochlear nerve (CN4)
49
what innervates the lateral rectus muscle?
abducens nerve (CN6)
50
whats the function of ciliary processes?
produce aqueous humor
51
whats the function of ciliary zonules?
anchors the ciliary body with the lens of the eye to help maintain eye position
52
whats the function of ciliary muscles?
accomodation - changes the shape of the lens when your eyes focus on a near object.
53
what are ciliary bodies?
a circular structure that is an extension of the iris that contains ciliary processes and muscles
54
what is miosis?
excessive pupil constriction
55
what is mydriasis?
pupil dilation
56
what is anisocoria?
when pupils are of unequal size
57
how does pupil constriction occur?
parasympathetic control (oculomotor nerve) of iris sphincter muscles in reponse to increased light
58
how does pupil dilation come about?
sympathetic contol of iris silator muscle in response to dim light
59
where does the parasympathetic control of pupillary constriction originate?
in the Edinger-Westphal nucleus in the midbrain
60
what nerve carries sympathetic control of pupillary dilation to the dilator pupillae muscles?
opthalmic nerve
61
what are the 3 actions of accomodation?
pupil constriction increased convexity of lens to increase refractive power convergence (brings near objects into focus)
62
outline the accomodation reflex pathway?
nerve fibres travel from the occipital cortex to the front eye fields in the frontal lobe. Oculomotor nerve originates from Edinger Westphal nucleus in the midbrain and this goes on to innervate the medial rectus muscle causing convergence it also acts on ciliary and iris sphincter muscles, causing constriction
63
outline the movement of aqeous humor through the eye?
its produced by ciliary processes and circulates within the anterior chamber of the eye. it drains ibto the trabecular meshwork and then into schlemms canal so it can be drained into aqeous veins
64
why is the fovea avascular?
maximizes the optical quality of the fovea pit by reducing light scattering
65
where does the eyeball recieve blood from?
opthalmic artery and its branches
66
whats the most important artery of the eye? why?
central retinal artery - its the onyl artery without collateral circulation occlusion of this artery = blindness
67
whats the venous drainage of the eye?
superior and inferior opthalmic veins which drain into the cavernous sinus
68
what are the capillaries in the choroid called?
choriocapillaris
69
whats the function of the horizontal and amacrine cells in the retina?
they allow information to be shared horizontally across the retina
70
what are the types of cones?
red sensing 60% green sensing 30% blue sensing 10%
71
which area of the eye doesnt have any photoreceptors?
optic dis 'blind spot'
72
what are the 3 cells in the lateral geniculate nucleus?
magnocellular, parvocellular and koniocellular
73
outline how the primary visual cortex is topographic?
the central part of the visual field projects to the back of the brain and the more peripheral part of the visual field projects to a more anterior portion
74
what is V1?
the primary visual cortex
75
whats the fnction of V2?
to recieve information from V1 and pass it on to V3,4,5
76
whats the function of V3?
dorsal V3 = processes motion | ventral V3 = colour sensitivity
77
whats the function of V4?
receptive to colur, brightness and texture
78
whats the function of V5?
receptive to motion
79
what is achromatopsia?
partial or total absence of color vision
80
what is akinetopsia?
motion blidness
81
outline the normal apparaence of the funsu of the eye?
the centre is marked by the macula which will appear yellow the macula contains a depresson called the fovea you will be able to see arteries and veins and at the centre of these is the optic disc
82
what is papilloedema?
swollen optic disc and vessels caused by increased ICP
83
outline the visual pathway?
photoreceptor give impulses to retinal ganglion cells and their acons form the optic nerve nerve enters the cranial cavity from each eye and unite at the optic chiasm. here, fibres from the medial half of each retina cross to the contralateral optic tract but lateral halves remain ipsilateral so the left optic tract contains fibres from left lateral retina and right medial retina and vice versa. each optic tract travels to its corresponding cerebral hemisphere to reach the lateral geniculate nucleus where fibres synapse and travel to the visual cortex
84
what are some leadng causes of blindness?
age-related macular degeneration, cataract, diabetic retinopathy, and glaucoma
85
what are cataracts?
opacification of the lens caused by protein deposition causing a painless decline in vision
86
what is glaucoma?
increased intraocular pressure due to aqueous humor drainage pathway being blocked, causes peripheral vision loss
87
what are the 3 types of glaucoma?
open angle - increased humor production or blocked outflow closed Angel - narrowing of anterior chamber angle so inadequate drainage normal tension
88
what vision is lost in age-related macula degenerative?
loss of central vision but preservation of peripheral vision due to damage of photoreceptors in the macula
89
whats the gentic basis of colour blindness?
recessive and x-linked so affects a lot more males!
90
what is protanopia?
red colour blind
91
what is tritanopia?
blue colour blind
92
what is deuteranopia?
green colour blind
93
what is protanomaly?
red weakness
94
what is deutranomalu?
green weakness - have green cones so can see some shades
95
what is monochromic?
seeing no colour
96
what is tetrachromacy?
super colour vision
97
what are dichromate?
a person who can only distinguish 2 colours
98
what is a trachomat?
a person who can distinguish 3 colours

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