1b Visual System Flashcards
1
Q
What is the palpebral fissue?
A
The line of the eye where the eyelashes sit
2
Q
What is the limbus?
A
The border between the cornea and the slcera?
3
Q
What is the caruncle?
A
The inner most fleshy corner part of the eye
4
Q
What is the medial canthus?
A
Where the caruncle meets the sclera
5
Q
What neurotransmiter controls the release of tears?
A
Acetylcholine
6
Q
Where are tears produced?
A
Lacrimal gland
7
Q
Where are tears drained from?
A
Puncta - opens on the medial lid margin
8
Q
What do the tears flow through in order to gather in the tear sac?
A
Gather in the tear sac
9
Q
How to the tears exit the tear sac?
A
Through the tear duct - into the nasal cavity
10
Q
What is the function of the tear film?
A
Maintains smooth cornea-air surface and regulates the oxygen supply to the cornea - as the normal cornea has no blood supply
11
Q
What are the secondary functions of the tear film?
A
Bactericidal properties
Removal of Debris - through tear film and blinking
12
Q
What are the three layers of the tear film called?
A
Most superficial = Lipid Layer
Water layer
Mucinous Layer
13
Q
What is the function of the superficial lipid layer?
A
Reduce tear film evapouration
14
Q
What is the lipid layer of the tear film produced by?
A
Meibomian glands
15
Q
what is the water layer of the tear film do?
A
Thickest layer so acts as a lubricant
16
Q
What is the role of the mucinous layer of the tear film?
A
Maintains surface wetting and keeps the tear on the eye
17
Q
What is the conjunctiva?
A
Thin, transparent tissue which covers the outer surface of the eye
18
Q
What are the three layers of the eye?
A
Sclera - hard and opaque
Choroid - pigmented and vascular
Retina - Neurosensory tissue
19
Q
What is the sclera?
A
The white of the eye - tough and opaque tissue which serves as the eyes protective outer coat
20
Q
What is the water content of the sclera?
A
High
21
Q
What is the cornea?
A
The transparent, dome-shaped window covering the front of the eye.
22
Q
What is the water content of the cornea like?
A
Low water content
23
Q
What is the function of the cornea?
A
Powerful refracting surface, providing 2/3 of the eye’s focusing power. Like the crystal on a watch, it gives us a clear window to look through
24
Q
What are the five layers of the cornea?
A
1 – Epithelium
2 – Bowman’s membrane
3 – Stroma – its regularity contributes towards transparency
4- Descemet’s membrane
5- Endothelium – pumps fluid out of corneal and prevents corneal oedema
25
What happens if the cornea becomes hydrated?
becomes cloudy
26
What is the uvea?
Vascular coat of eyeball and lies between the sclera and retina.
27
What are the three parts of the uvea called?
Composed of three parts – iris, ciliary body and choroid.
28
What is the choroid?
Choroid - lies between the retina and sclera. It is composed of layers of blood vessels that nourish the back of the eye.
29
What is the function of the iris?
Controls the amount of light which is entering into the eye - has tiny muscles which dilate and constrict the eye
30
What is the structure of the lens?
It is composed of an outer acellular thin capsule,
encasing a core of regular elongated cell fibres.
31
What percentage of the eyes refractory power comes from the lens?
1/3 of the eye focusing power - higher refractive index than aqueous fluid and vitreous
32
What is a cataract?
The lens may loose its transparency with age,
resulting in an opaque lens, known as Cataract.
33
What is the retina?
Thin layer of tissue which lines the inner part of the eye
Responsible for capturing the light rays which enter into the eye - light impulses are then sent to the brain for processing via the optic nerve
34
What is the function of the optic nerve?
Transmits electrical impulses from the retina to the brain
35
What is the visible portion of the optic nerve called?
The optic disc
36
Where does the optic nerve connect to the back of the eye?
Near the macula
37
What is the blind spot?
Where the optic nerve meets the retina, there are no light sensitive cells
38
What is the macula?
A small and highly sensitive part of the retina responsible for detailed central vision - located roughly in the centre of the retina
39
what is the structure found at the center of the macula?
Fovea
40
Which part of the eye allows us to perform tasks which require central vision like reading?
Fovea
41
What is the concentration of cones and rods like in the fovea?
Cones are high, rods and low
42
Why is the fovea particularly important?
Only the fovea has the highest concentration of cones in order for us to perceive high detail
43
What is the anatomical land mark for the physiological blind spot?
Optic disc
44
What is central vision?
Detailed, day vision - only the fovea
45
what is peripheral vision for?
Shape, movement and night vision, as well as navigation
46
What is the result of extensive loss of visual field?
Unable to navigate in an unfamiliar environment,
47
What is found in the outer layer of the retina?
Photoreceptor cells - involved in the detection of light
48
What is found in the middle layer of the retina?
Bipolar cells (2nd order neurones)
49
What is the function of the bipolar cells?
Local signal processing to improve contrast sensitivity
50
What does the inner layer of the retina contain?
Retinal ganglion cells (3rd order neurones)
51
What is the function of the retinal ganglion cels
Transmission of signal from the eye to the brain
52
What is the structural differences between the cones and the rods?
Rods = Longer outer segment
Cones = Shorter outer segment
53
What is the difference between rods and cones?
Rods = More sensitive to light, but slower response
Cones = Less sensitive to light, but faster response
54
Which photoreceptor cell is responsible for day light fine vision and colour?
Cones
55
Which photoreceptor cells is responsible for night vision?
Rods
56
What is scotopic vision?
Peripheral and night vision
57
Where can one find the highest concentration of Rod photoreceptors in the retina?
20-40 degrees away from fovea
58
Which cones are used for blue?
S-Cones
59
Which cones are used for Green?
M-Cones
60
Which cones are used for Red?
L-Cones
61
What colour are rods sensitive to?
Rods are used for night vision and spatial recognition and are not really sensitive to any particular colour
62
What is dueteranomaly, or Daltonsim?
most common type of colour blindness - red colourness
63
What is achromatopsia?
Full colour blindness
64
What is the name of the colour blindness test?
Ishihara test
65
what is refraction?
Then light goes from one’s medium to another, it changes velocity
66
What is the index of refraction and how is it calculated?
Ratio of speed of light in a vacuum to speed of light in a medium
67
What can the index of refraction be used for?
Help identify a material
68
What happens to the path of light when it changes from one medium to another?
Path changes
69
What is the angle of incidence?
Equal to the angle of reflection, is the angle at which light is reflected off the new medium
70
What are the two types of lenses?
Concave and convex
71
What does a convex lens do to light?
Takes the light rays and brings to a single focal point
72
What does a concave lease do?takes light rays and spreads them out
73
What is an example of an application of a converging lens?
A camera
74
What is emmetropia?
Perfect eye - adequate correlation between the axial length and refractive power
Parallel light rays fall on the retina without the need for accomodation
75
What is ametropia?
Mismatch between axial length and refractive power so parallel light rays do not fall onto the retina
76
What is myopia?
Near sightedness
77
What is hyperopia?
Far sightedness
78
Where do the light rays converge in myopia?
Parallel rays converge at a focal point which is anterior to the retina - in front of it
79
What are the causes of myopia?
Excessive long globe and excessive refractive power
80
What are the symptoms of myopia?
Blurred distant vision
Squinting to attempt to improve visual activity
Headaches
81
What are the treatments for myopia?
Diverting lens in glasses
Contact lenses
Refractive lens surgery
82
What is hyperopia?
Parallel rays converge at a focal point posterior to the retina
Etiology : not clear, inherited Causes
83
What are the causes of hyperopia?
•excessive short globe (axial hyperopia) : more common
•insufficient refractive power (refractive hyperopia)
84
What are the symptoms of hyperopia?
visual acuity at near tends to blur relatively early
• nature of blur is vary from inability to read fine print to near vision is clear but suddenly and intermittently
blur
• blurred vision is more noticeable if person is tired , printing is weak or light inadequate
• asthenopic symptoms : eyepain, headache in frontal region, burning sensation in the eyes, blepharoconjunctivitis
• Amblyopia – uncorrected hyperopia > 5D
85
What are the asthenopic symptoms of hyperopia?
Eye pain
Headache
Burning sensation in eyes
Blepharoconjuctivitis
86
What is amblyopia?
When there is an uncorrected hyperopia of more than 5D in one eye
87
If a person has good reading vision, which condition do they have?
Hyperopia
88
What type of lens is used in glasses to treat hyperopia?
Converging lens
89
What is an astigmatism?
When the parallel rays come to focus in two focal lines,
90
What is the cause of an astigmatism?
Refractive media is not spherical - refract differently along one meridian than along meridian perpendicular to it-- >2 focal points (punctiform object is represent as 2 sharply defined lines)
91
What are the symptoms of an astigmatism?
Headache
Eye pain
Distortion of vision
Head tilting and turning
92
What is the treatment of a regular astigmatism?
Cylinder lenses with or without spherical lenses
93
What is the treatment of an irregular astigmatism?
Rigid cylinder lenses, surgery
94
What is the near response triad?
Three actions of the eye in order for adapt for near vision
Increase depth of field
Align both eyes towards a near object
Increase refractive power of lens for near vision
95
What is pupillary miosis ?
Pupil constricts which increases the depth of field of the eye
96
Which muscle is responsible for the contraction of the pupil?
Sphincter pupillae
97
What is the benefit of a larger depth of optic field?
Eye is able to maintain clear forms over a certain range of viewing distances which relying on accomodation
98
What is convergence?
When the eyes adduct medial,y at the same time to align the eyes towards a near object
99
How does convergence occur?
Simultaneous contraction of the medial rectus extra ocular muscles from both eyes
100
Which muscles allow for accomodation of the eye?
Circular ciliary muscles
101
What does accomodation do?
Increases the refractive power of lens for near vision
102
What is presbyopia?
Naturally occuring loss of accommodation onset from age 40
Distant vision is intact
103
How is presbyopia corrected?
Corrected by reading glasses - increases refractive power of the eye
104
Why does the lens lose its ability to accommodate?
Natural lens loses elasticity
105
What is the treatment of presbyopia?
Convex lenses in near vision - reading glasses or bifocal
106
What are the two types of optical correction?
Contact lenses
Intraocular lenses
107
What is an intraocular lense?
Replacement of a cataract crystalline lens
108
Why are intraocular lenses the best treatment for aphakia?
Avoid significant magnification and distortion caused by spectacle lenses
109
What is aphakia?
Absense of crystallin lens
110
What is the problem with intraocular len?
They are monofocal, so provides help for distance but patient will need some reading glasses for near by activity
111
What are the surgical options for treatment of eye problems?
Keratorefractive surgery :RK, AK, PRK, LASIK, ICR, thermokeratoplasty
Intraocular surgery : clear lens extraction (with or without IOL), phakic IOL
112
Describe the steps of surgical correction?
. . . . .
.
. .
Surgical correction
Pre operative eye
Initial cutting of corneal flap
Cutting of corneal flap
Flipping of corneal flap
Photorefractive treatment (laser)
Corneal stroma reshaped post laser
Corneal flap back in position Treatment completed
113
What is clear lens extraction and an intraocular lens?
Remove the lens and then add an artificial ones - patient will still need reading glasses as they lose the ability to accommodate
114
What is the visual pathway?
The visual pathway is the neurological pathway,
where by vision is converted to neurological impulses, to be transmitted from the eye to the visual cortex, the posterior part of the brain.
115
Where do the cell bodies of the optic nerve originate?
The retina
116
Where do the optic nerve from each eye, converge?
Optic chiasm
117
What happens to the ganglion nerve fibres at the optic chiasm?
About half of the ganglion nerve fibres cross at the optic chiasma, and exit along the contra-lateral Optic Tract, while the remaining ganglion nerve fibres exit along the Optic Tract on the same side.
118
Where do the ganglion nerve fibres synapse?
Lateral Geniculate nucleus
119
What is the fourth order neurone in the visual pathway?
Optic radiation - takes information from the lateral geniculate ganglion to the primary visual cortex in the occipital lobe
120
What cortex is involved in higher visual processing?
Extra-striate Cortex
121
What are the first second and third order neurones of the retinal visual pathway?
First Order Neurons – Rod and Cone Retinal Photoreceptors
Second order Neurons – Retinal Bipolar Cells
Third Order Neurons –Retinal Ganglion Cells
122
what happens to the retinal ganglion fibres after entering into the optic nerve?
become myelinated to improve signal transmission
123
What type of visual defect do you get when you have a lesion which is anterior to the optic chiasm?
Lesions anterior to Optic Chiasma affect visual field in one eye only
124
What type of visual defect do you get when you have a lesion which is posterior to the optic chiasm?
Lesion occurring posterior to the Optic Chiasma will affect visual field simultaneously in both eyes,
because of the fibre crossing at the chiasma.
125
Where do the crossed fibres predominantly originate from?
predominantly originate from the nasal retina,
responsible for the temporal half of the visual field in each eye.
126
Where do the uncrossed fibres predominantly originate from?
The uncrossed fibres predominantly originate from the temporal retina,
responsible for the nasal half of the visual field in each eye.
127
Lesion at optic chiasm?
Bitemporal hemanopia - temporal field deficit in both eyes
128
Lesions posterior to optic chiasm?
Right sided lesion – Left Homonymous Hemianopia in Both Eyes
Left sided lesion – Right Homonymous Hemianopia in Both Eyes
129
What is the most common cause of bitemporal hemaniopia?
Typically caused by enlargement of Pituitary Gland Tumour
130
What is the most common cause of homonymous hemianopia?
On the other hand, homonymous hemianopia is typically caused by stroke,
or cerebrovascular accidents in the brain.
131
What does damage of the primary visual cortex lead to?
Homonymous Hemianopia with Macular Sparing
132
Why is the macula spared in damage t the primary visual cortex?
Area representing the Macula receives dual blood supply from Posterior Cerebral Arteries from both sides
133
What happens to the pupil in the light?
Constriction
134
What nerve mediates pupillary constriction?
Parasympathetic nerve - within CNIII
135
What causes the circular muscles to contract and what does this lead to?
parasympathetic stimulation - pupil constriction
136
What causes the radial muscles to contract and what does this lead to?
Sympathetic stimulation - pupil dilation
137
When does the pupil dilate?
In dark environments
138
Why does the pupil constrict in light?
decreases spherical aberrations and glare
increases depth of field
reduces bleaching of photo-pigments
139
Describe the efferent pathway of the pupillary reflex?
Edinger-Westphal Nucleus -> Oculomotor Nerve Efferent ->
Synapses at Ciliary ganglion ->
Short Posterior Ciliary Nerve -> Pupillary Sphincter
140
Where do the afferent fibres of the pupillary reflex become the efferent?
Edinger-Westphal Nuclei
141
What is the direct and consensual reflex?
Direct Light Reflex –Constriction of Pupil of the light-stimulated eye
Consensual Light Reflex – Constriction of Pupil of the other (fellow) eye
142
What is the neurological basis of the direct and consensual reflex?
Afferent pathway on either side alone will stimulate efferent (outgoing) pathway on both sides
143
What is the observed difference in afferent and efferent defects
In short, afferent defect produces different responses between eyes, depending on which eye is stimulated.
Efferent defect produces the same unequal responses between left and right eye, no matter whether left or right eye is stimulated.
144
What is the swinging torch test?
Shining light between right and left rapidly
145
What is a relative afferent pupillary defect?
When the damage to the afferent pathway is incomplete
146
What is the best way to test the relatife afferent pupillary defect?
Swinging torch test
147
Describe a positive swinging torch test for a relative afferent pupillary defect?
Both pupils constrict,
when light swings to the left eye with intact afferent pathway.
Both pupils will paradoxically dilate,
when the light swings to the right eye with damaged afferent pathway, as a result of relatively reduced drive for pupillary constriction in both eyes.
148
What facilitates the movement of the eye?
It is facilitated by the six extraocular muscles in the orbit,
innervated by the three cranial nerves.
149
What is duction?
Eye movement in one eye, without making any reference to the movement in the other eye
150
What is version?
Simultaneous movement of both eyes in the same direction?
151
What is vergence?
Simultaneous movement of both eyes in the opposite direction
152
What is convergence?
Simultaneous adduction (inward) movement in both eyes when viewing a near object
153
What is a saccade?
Short fast burst
154
When might you use a saccade eye movement?
Reflexive saccade to external stimuli
Scanning saccade
Predictive saccade to track objects
Memory-guided saccade
155
What is a smooth pursuit?
Smooth Pursuit is a slow sustain movement,
up to 60 degrees per second.
It is an involuntary movement,
driven by a moving target.
156
What are the straight muscles of the eye called?
Superior rectus
Inferior rectus
Lateral rectus
Medial rectus
157
What are the names of the two muscles of the eye which are not straight
Superior oblique
Inferior Oblique
158
what does the superior rectus do to the eye?
Moves the eye up
159
What does the inferior rectus do to the eye?
moves the eye down
160
what does the lateral rectus do?
Moves the eye towards the outside of the head - towards temple
161
What does the medial rectus do?
Moves the eye towards the midline
162
Describe the action of the superior oblique?
Passes under the Superior Rectus.
Moves the eye in a diagonal pattern down and out
163
Describe the action of the inferior oblique?
Moves the eye in a diagonal pattern - up and out.
164
Which eye muscles are innervated by the superior branch of the third cranial nerve - occulomotor?
Superior Rectus – elevates eye
elevator palpebrae superioris - raises eyelid (not shown)
165
Which eye muscles are innervated by the inferior branch of the third cranial nerve - occulomotor?
Inferior Rectus – depresses eye
Medial Rectus – adducts eye
Inferior Oblique – elevates eye
Parasympathetic Nerve – constricts pupil
166
Which eye muscles are innervated by the fourth cranial nerve?
Superior oblique - depresses eyes
167
Which eye muscles are innervated by the 6th cranial nerve?
Lateral Rectus – abducts eye
168
What position of the eye best tests the lateral rectus?
Abduction
169
What position of the eye best tests the medial rectus?
Adduction
170
What position of the eye best tests the superior rectus?
Abducted and Elevated
171
What position of the eye best tests the inferior rectus?
Depressed and abducted
172
What position of the eye best tests the inferior oblique?
Elevated and adducted
173
What position of the eye best tests the superior oblique?
Depressed and adducted
174
what is supraduction and supraversion?
elevation of one eye, and elevation of both eyes
175
What is infraduction and infraversion?
Infraduction – one eye
Infraversion – both eyes
176
What is dextroversion?
Movement of the eyeballs to look at the right
177
What is levoversion?
Movement of the eyes to look at the left
178
What is torsion?
Torsion – rotation of eye around the anterior-posterior axis of the eye
179
What does the eye look like in third nerve palsy?
affected eye is down and out
180
How is the eyelid effected in third nerve palsy?
Droopy eyelid - due to loss of elevator palepbrae superioris
181
Why does third nerve palsy result in a down and out movement of the eye?
Unopposed superior oblique innervated by fourth nerve (down)
Unopposed lateral rectus action innervated by sixth nerve (out)
182
What does 6th nerve palsy result in?
patients are deficit in abduction in the affected eye
Affected eye will deviate inwards
183
What is a nystagmus?
Oscillatory eye movement
184
What is Optokinetic Nystagmus?
Smooth pursuit followed by a reset ot the eye position in the center with a burst of saccade movement
185
What does presence of the opto-kinetic nystagmus show?
The presence of Opto-kinetic Nystagmus signifies that the subject has sufficient visual acuity to perceive the grating.
186
What is the neurotransmitter of the lacrimal system?
Acetylcholine
187
What is the role of the Meibomian glands?
secretes the lipid layer which protects the tear film from rapid evapouration
188
How do mucin molecules affect the tear film?
they bind water molecules to the hydrophobic corneal epithelial cell surface
189
Describe the synthesis of photo pigments
1. discs with deactivated photo pigments are shedded from the tips and phagocytosed by the retinal epithelial cells
2. deactivated photopigments are regenerated inside the retinal epithelial cells and transported by to the photo receptors
190
What is asthenopia?
Eye strain condition which manifests through non-specific symptoms such as fatigue, pain in and around the eyes, blurred vision and occasional double vision
191
What is the most common cause of homonymous hemaianopia?
Stroke of another cerebrovascular accidents of the brain
192
Lesions posterior to what result in homonymous hemianiopia?
Posterior to the chiasma
