Visual system Flashcards
1
Q
What are the different parts of the eye?
A
- upper and lower eyelid
- lateral and medial canthus
- palpebral fissure
- pupil
- iris
- sclera
- caruncle
- limbus (border between cornea and sclera)
2
Q
What is the role of tear film?
A
- maintains smooth cornea-air surface
- oxygen supply to cornea (cornea is avascular)
- removal of debris (with blinking)
3
Q
What is the structure of the tear film?
A
- lipid layer
- water layer
- mucin layer
4
Q
Describe the superficial lipid layer of the tear film?
A
- reduce tear film evaporation
- produced by a row of Meibomian Glands along the lid margins
5
Q
Describe the mucus layer corneal surface of the tear film?
A
- maintains surface wetting
- has microvillus and epithelial cells
- mucin molecules act by binding water molecules,
to the hydrophobic corneal epithelial cell surface.
6
Q
What is the role of the aqueous tear film layer?
A
- delivers oxygen and nutrient to the surrounding tissue
- contains bactericide
7
Q
Which layer in the tear film protects the tear film from rapid evaporation?
A
lipid layer
8
Q
What is the conjunctiva?
A
thin, transparent tissue that covers the outer surface of the eye
9
Q
Where is the conjuctiva?
A
It begins at the outer edge of the cornea, covers the visible part of the eye, and lines the inside of the eyelids
10
Q
What is the blood supply of the conjunctiva?
A
by tiny blood vessels
11
Q
What is the sclera?
A
- tough, opaque tissue that acts as the protective outer coat
- high water content
12
Q
What are the 5 layers of the cornea?
A
- epithelium
- Bowman’s membrane
- Stroma
- Descemet’s membrane
- Endothelium
13
Q
What is the role of stroma in the eye?
A
regularity contributes towards transparency
14
Q
What is the role of the endothelium in the eye?
A
pumps fluid out of the cornea and prevents corneal oedema
15
Q
What is the cornea?
A
- transparent, dome shaped window covering the front of the eye
- low water content
16
Q
What is the role of the cornea?
A
- refracting surface
- provides 2/3 of the eye’s focusing power
17
Q
What are the 3 layers of the coat of the eye?
A
- sclera
- choroid
- retina
18
Q
What is the role of the sclera?
A
- protects the eye
- maintains the shape of the eye
19
Q
What is the choroid?
A
the middle, pigmented vascular layer of the coat
20
Q
What is the role of the choroid?
A
- provides circulation to the eye
- shields out the unwanted scattered light
21
Q
What is the retina?
A
the innermost neurosensory layer
22
Q
What is the role of the retina?
A
responsible for converting light into neurological impulses, transmitted to the brain by the optic nerve
23
Q
What is the uvea?
A
vascular coat of eyeball
24
Q
Where is the uvea?
A
between the sclera and retina
25
What are the 3 parts that make up the uvea?
- iris
- ciliary body
- choroid
26
What is the role of the iris?
controls light levels inside the eye
27
What is the iris?
- coloured part of the eye
| - embedded with tiny muscles that dilate and constrict the pupil size
28
What is the role of the human lens?
responsible for 1/3 of the refractive power of the eye
29
What is the structure of the lens?
- outer acellular capsule
| - regular inner elongated cell fibres
30
What can happen to lens with age?
- opacification
| - cataract
31
What is the retina?
thin layer of tissue that lines the inner part of the eye
32
What is the role of the retina?
responsible for capturing the light that enters the eye, sent to brain, via the optic nerve
33
What is the role of the optic nerve?
transmits electrical impulses from the retina to the brain
34
Where is the optic nerve?
- connects to the back of the eye near the macula
| - the visible portion of the optic nerve, is the optic disc
35
Where is the blind spot?
on the optic disc
36
What is the macula?
a small and highly sensitive part of the retina
37
What is the role of the macula?
- responsible for detailed central vision
| - central vision (like reading)
38
Where is the macula?
in the centre of the retina, temporal to the optic nerve
39
What is the fovea?
the centre of the macula
40
What is the structure of the fovea?
- highest concentration of cones
| - low concentration of rods
41
What is central vision?
- responsible for central fine vision and daytime colour vision
- also known as macular vision
42
How does loss of central vision present?
problems with:
- reading
- recognising facfes
43
What is used to assess central vision?
visual acuity assessment
44
What is the role of peripheral vision?
detecting:
- shape
- movement in the environment
- night vision
45
How does loss of peripheral vision present?
problems navigating the world
46
What is used to assess peripheral vision?
visual field assessment
47
What are the 3 layers of the retina?
```
Retinal pigment epithelium
Neuroretina:
- outer layer of photo-receptor
- middle layer of intermediate neurons
- inner layer of ganglion nerve cells
```
48
What is the role of the outer layer of the neuroretina?
- photoreceptors (1st order neuron)
| - detection of light
49
What is the role of the middle layer of the neuroretina?
- bipolar cells (2nd order neuron)
| - local signal processing to improve contrast sensitivity, and regulate sensitivity
50
What is the role of the inner layer of the neuroretina?
- retinal ganglion cells (3rd order neurons)
| - transmission of the signal from the eye to the vbrain
51
What is the outermost layer of the retina?
retinal pigment epithelium
52
What is the role of the retinal pigment epithelium?
- nutrient transport from the choroid to the photo receptor cells
- removes metabolic waste from the retina
53
What are the 2 main types of photoreceptors?
- rods
| - cones
54
What is the structure of rods?
- Longer outer segment with photo-sensitive pigment
- 100 times more sensitive to light than cones
- Slow response to light
- 120 million rods
55
What are rods responsible from?
Responsible for night vision (Scotopic Vision)
56
What are cones responsible for?
- Less sensitive to light, but faster response
- Responsible for day light fine vision and colour vision (Photopic Vision)
- 6 million cones
57
Where are photopigments synthesized?
inner photo-receptor segment, and then transported to the outer segment
58
What is the structure of the outer segment of photoreceptors?
- stacks of discs
- distal discs with deactivated photo-pigments (shedded from the tips)
- phago-cytosed by the retinal epithelial cells
- deactivated photopigments are regenerated inside the retinal epithelial cells,
and then transported back to the photo-receptors.
59
Where are rods found?
- widely distributed all over the retina
- highest density outside the macula
- density decreases towards the periphery
60
Where are cones found?
distributed only in the macula
61
Where can one find the highest concentration of Rod photoreceptors in the retina?
20-40 degrees away from the fovea
62
What are the three sub-types of cones?
- S-Cones (short wavelength) - colour blue,
- M-Cones (medium wavelength) - colour green,
- L-Cones (long wavelength) - colour red.
63
What does yellow light stimulate?
- M-cones and L-cones equally
64
What is the most common form of colour vision deficiency?
Deuteranomaly
65
What causes Deuteranomaly?
the shifting of the M-cone sensitivity peak towards that of the L-cone curve,
causing red-green confusion
66
What is the term given to full colour blindness?
Achromatopsia
67
What is Anomalous trichromatism?
colour vision deficits can be caused by a shift in the photo-pigment peak sensitivity
68
What is Dichromatism?
when only 2 cone photo-pigment sub-types are present
69
What is Monochromatism?
complete absence of colour vision
70
What is Blue cone monochromatism?
the presence of only blue L-cones
71
What do patients with Blue Cone Monochromatism experience?
normal day light visual acuity
72
What is Rod Monochromatism?
a total absence of all cone photo-receptors
73
What do patients with Rod Monochromatism experience?
no functional day vision
74
Where is the lacrimal gland?
- in the orbit
| - latero-superior to the globe
75
What does the lacrimal gland do?
It produces tear at a constant level,
| even in the absence of irritation or stimulation.
76
What is a Basal tear?
It produces tear at a constant level,
| even in the absence of irritation or stimulation.
77
What is a Reflex tear?
the increased tear production,
| in response to ocular irritation.
78
What is the tear reflex pathway composed of?
- the afferent pathway
- the central nervous system
- the efferent pathway
- the lacrimal gland.
79
What innervates the cornea?
by the sensory nerve fibres via the Ophthalmic Branch of the Trigeminal Nerve
80
What is the afferent pathway involved in the tear reflex?
the trigeminal nerve relays signal to the CNS
81
What is the efferent pathway involved in the tear reflex?
the parasympathetic nerve
82
What innervates the lacrimal gland?
The lacrimal nerve, from the ophthalmic branch of the trigeminal nerve
83
How does the tear film drain to eye from the lacrimal gland?
- drains through the 2 puncta, openings on the upper and lower medial lid margins
- flow through superior and inferior canalculi
- both canalculi converge as a common canaliculus, drain tear into the tear sac
- exits sac thrrough tear duct into nasal cavity
84
What happens if you hydrate the cornea?
it whitens
85
How do you test for colour blindness?
Ishihara test
86
What are the 2 types of lenses?
- converging (convex)
| - diverging (concave)
87
What is a converging lens?
- convex
| - takes light rays and bring them to a point
88
What is a diverging lens?
- concave
| - takes light rays and spreads them outward
89
What is Ametropia?
mismatch between axial length and refractive power
| light doesn't fall on the retina
90
What are the different types of Ametropia?
- near sightedness (myopia)
- far sightedness (hyperopia)
- astigmatism
- presbyopia
91
What is the mechanism of myopia?
parallel rays converge at a focal point anterior to the retina
92
What are the causes of myopia?
- excessive long globe (axial myopia)
| - excessive refractive
93
What are the symptoms of myopia?
- Blurred distance vision
- Squint in an attempt to improve uncorrected visual acuity when gazing into the distance
- Headache
94
How do you treat myopia?
- Correction with diverging lenses (negative lenses)
- Correction with contact lens
- Correction by removing the lens to reduce refractive power of the eye
95
What is hyperopia?
Parallel rays converge at a focal point posterior to the retina
96
What are the causes of hyperopia?
- excessive short globe (axial hyperopia)
| - insufficient refractive power (refractive hyperopia)
97
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
- eyepain
- headache in frontal region
- burning sensation in the eyes
- blepharoconjunctivitis
98
What is Amblyopia?
reduced vision in one eye caused by abnormal visual development early in lif
99
What is the treatment for Hyperopia?
- Correction with converging (positive lenses)
- Correction with positive lens + cataract extraction
- Correction with contact lens
- Correction with intraocular lens
100
What is the mechanism of Astigmatism?
Parallel rays come to focus in 2 focal lines rather than a single focal point
101
What is the cause of Astigmatism?
- hereditary
- 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)
102
What are the symptoms of an Astigmatism?
- headache
- eye pain
- blurred vision
- distortion of vision
- head tilting and turning
103
What is the treatment for an Astigmatism?
regular:
- cylinder lenses with or without spherical lenses (convex or concave), Sx
irregular:
- rigid cylinder lenses, surgery
104
What is Presbyopia?
- Naturally occurring loss of accommodation (focus for near objects)
- distant vision intact
105
When does Presbyopia start to develop?
onset from 40 years old
106
How do you treat Presbyopia?
- reading glasses (convex lenses) to increase refractive power of the eye
- spectacle lens (Monofocal lenses : spherical lenses, cylindrical lenses, Multifocal lenses)
- contact lenses
107
What are the benefits of using contact lenses?
higher quality of optical image and less influence on the size of retinal image than spectacle lenses
108
What are the indications to use contact lenses?
- cosmetic
- athletic activities
- occupational
- irregular corneal astigmatism
- high anisometropia
- corneal disease
109
What are the disadvantages of using contact lenses?
- careful daily cleaning and disinfection
| - expensive
110
What are the possible complications associated with contact lenses?
- infectious keratitis
- giant papillary conjunctivitis
- corneal vascularization
- severe chronic conjunctivitis
111
What are intraocular lenses?
replacement of cataract crystalline lens
112
What are the benefits of using intraocular lenses?
- best optical correction for aphakia
| - avoid significant magnification and distortion caused by spectacle lenses
113
What happens in accomodation?
- Relaxation of Zonules
- Thickening of Lens
- Increase of Lens Refractive Power
114
What is the Staar intra-collamer lens (ICL) used to treat?
correction of the myopia and astigmatism
115
Where is a Staar intra-collamer lens (ICL) placed?
in between the iris and natural lens of the eye
116
What is Emmetropia?
- normal eye
| - adequate correlation between axial length and refractive power
117
What is the purpose of Near Response Triad?
adaptation for near vision
118
What is the Near Response Triad?
- Pupillary Miosis
- Convergence
- Accomodation
119
What happens in Pupillary Miosis?
sphincter pupillae cause the pupil to constrict, increasing the depth of field
120
What happens in Convergence?
medial recti contract, adducting the eyes to align both eyes towards a near object
121
What happens in Accomodation?
circular ciliary muscle acts, allowing the lens to accommodate (increase refractive power of lens for near vision)
122
What are the possible surgeries to correct refractive errors?
- Keratoreactive surgery, eg: LASIK
| - Intraocular surgery: clear lens extraction, IOL
123
What happens in LASIK?
- cutting of the corneal flap
- Flipping of corneal flap
- Photorefractive treatment (laser)
- Corneal stroma reshaped post laser
- Corneal flap back in position
124
What happens in clear lens extraction + IOL?
- same as cateract extraction
| - implantation of artificial lens
125
What is the disadvantage of a clear lens extraction +IOL?
lose accommodation, patient will need reading glasses
126
What is a Phaco tip?
US tip that breaks down the lens and removes it
127
What is the role of the visual pathway?
transmits signal from eye to the visual cortex
128
What are the landmarks of the visual pathway?
- 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
129
What relays information to the visual cortex?
Lateral Geniculate Nucleus in Thalamus
130
What is the impact of a lesion anterior to the optic chiasma?
affects the visual field in only one eye
131
What is the impact of a lesion posterior to the optic chiasma?
affects the visual field in both eyes
- Right sided lesion: Left Homonymous Hemianopia in Both Eyes
- Left sided lesion: Right Homonymous Hemianopia in Both Eyes
132
What are the nerves that cross at the optic chiasma responsible for?
temporal visual field
133
What are the nerves that do not cross at the optic chiasma responsible for?
the nasal visual field
134
What is the impact of a lesion at the optic chiasma?
temporal field deficit in both eyes - bitemporal hemianopia
135
What can cause a bitemporal hemianopia?
enlargement of a pituitary gland tumour
136
What can cause a homonymous hemianopia?
stroke (cerebrovascular accident)
137
What can damage to the primary visual cortex due to stroke cause?
Homonymous Hemianopia of the contralateral side, with sparing of macula central vision
138
Why is damage to the primary visual cortex unlikely?
receives dual blood supply from both right and left posterior cerebral arteries
139
What happens to the pupil in light?
pupil constrict
140
Why does the pupil constrict under light?
- decreases spherical aberrations and glare
- increases depth of field
- reduces bleaching of photo-pigments
141
What mediates pupillary constriction?
parasympathetic nerve (within CNIII), causing circular muscles to contract
142
What happens to the pupil in dark?
pupil dilation
143
Why does the pupil dilate in the dark?
increases light sensitivity in the dark by allowing more light in
144
What mediates pupillary dilation?
the sympathetic nerve, causing radial muscles to contract
145
What happens in the afferent pathway of the pupillary reflex?
- Rod and Cone Photoreceptors synapsing on Bipolar Cells synapsing on Retinal Ganglion Cells
- Pupil-specific ganglion cells exits at posterior third of optic tract before entering the Lateral Geniculate Nucleus
- Afferent (incoming) pathway from each eye synapses on Edinger-Westphal Nuclei on both sides in the dorsal brainstem
146
What happens in the efferent pathway of the pupillary reflex?
- Edinger-Westphal Nucleus
- Oculomotor Nerve Efferent
- Synapses at Ciliary ganglion upon the Short Posterior Ciliary Nerve
- Pupillary Sphincter
147
What stimulates the efferent pathway on both eyes?
the afferent pathway for either eye
148
What is the direct light reflex?
constriction of the pupil of the light-stimulated eye
149
What is the consensual light reflex?
constriction of the pupil of the other eye (light shone in opposite eye to this one)
150
What happens if the right afferent pupillary pathway is damaged?
- stimulation of the right eye will elicit weak,
or no pupillary constriction in both eyes.
- BUT, Normal pupil constriction in both eyes when left eye is stimulated with light
151
What happens if the right efferent pupillary pathway is damaged?
no pupillary constriction in the right eye, and normal pupillary constriction in the left eye, whether right eye or left eye is stimulated.
152
How do you detect a relative afferent pupillary defect?
swinging torch test
153
What happens in a swinging torch test?
- 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.
154
What is duction?
eye movement in one eye
155
What is version?
simultaneous movement of both eyes in the same direction
156
What is vergence?
simultaneous movement of both eyes in the opposite direction
157
What is convergence?
```
simultaneous adduction (inward) movement in both eyes when viewing a near object
(angle greater at a near target)
```
158
What are the 2 different types of eye movement?
- saccade (short, fast burst)
| - smooth pursuit (sustain, slow movement)
159
What is saccade?
- Reflexive saccade to external stimuli
- Scanning saccade
- Predictive saccade to track objects
- Memory-guided saccade
160
What is smooth pursuit eye movement?
- Slow movement – up to 60°/s
| - Driven by motion of a moving target across the retina.
161
What are the 6 muscles of the eye?
- medial rectus
- lateral rectus
- superior rectus
- inferior rectus
- superior oblique
- inferior oblique
162
What are the 4 straight muscles of the eye?
- medial rectus
- lateral rectus
- superior rectus
- inferior rectus
163
What is the role of the superior rectus?
moves the eye up
| maximally in abducted position
164
What is the role of the inferior rectus?
moves the eye down
| maximally in abducted position
165
What motion do the superior and inferior rectus cause when the eye is adducted?
torsion motion
166
Where is the lateral rectus attached?
temporal side of the eye
167
What is the role of the lateral rectus?
moves the eye towards the outside of the head (towards the temple)
168
Where is the medial rectus attached?
on the nasal side of the eye
169
What is the role of the medial rectus?
moves the eye toward the middle of the head (towards the nose)
170
Where is the superior oblique attached?
- high on the temporal side of the eye
- passes under the superior rectus
- travels through the trochlea
171
What is the role of the superior oblique?
moves the eye in a diagonal pattern, down and out
172
Where is the inferior oblique attached?
- attached low on the nasal side of the eye
| - passes over the inferior rectus
173
What is the role of the inferior oblique?
moves the eye in a diagonal pattern, up and out
174
What innervates the lateral rectus?
CN 6 - abducens nerve
175
What innervates the superior oblique?
CN 4 - trochlear nerve
176
What innervates the superior rectus?
CN 3 - superior branch of the oculomotor nerve
177
What is innervated by CN3 (oculomotor nerve)?
- levator palpebrae superioris (raises eyelid)
| - superior rectus
178
What innervates the inferior rectus?
CN 3 - inferior branch of the oculomotor nerve
179
What innervates the medial rectus?
CN 3 - inferior branch of the oculomotor nerve
180
What innervates the inferior oblique?
CN 3 - inferior branch of the oculomotor nerve
181
What innervates pupil constriction?
CN 3 - the parasympathetic branch of the inferior oculomotor nerve
182
How do you test the action of the inferior rectus muscle?
depressed and abducted position
183
How do you test the action of the superior rectus muscle?
elevated and abducted position
184
How do you test the action of the medial rectus muscle?
adducted position
185
How do you test the action of the lateral rectus muscle?
abducted position
186
How do you test the action of the inferior oblique muscle?
elevated and adducted position
187
How do you test the action of the superior oblique muscle?
depressed and adducted position
188
What is supraduction?
elevation of one eye
189
What is supraversion?
elevation of both eyes, simultaneously
190
What is infraversion?
depression of both eyes, simultaneously
191
What is infraduction?
depression of one eye
192
What is abduction?
refers to duction movement of one eye, moving away from the nose.
193
What is adduction?
to duction movement of one eye, moving towards the nose.
194
What is dextroversion?
involves simultaneous right eye abduction, and left eye adduction.
195
What is levoversion?
involves simultaneous left eye abduction, and right eye adduction.
196
What is torsion?
rotation of eye around the anterior-posterior axis of the eye
197
How does third nerve palsy present?
- 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)
198
What muscles are affected in third nerve palsy?
everything but:
- lateral rectus (abduction)
- superior oblique (depression)
199
How does sixth nerve palsy present?
- Affected eye unable to abduct and deviates inwards
| - Double vision worsen on gazing to the side of the affected eye
200
What is Nystagmus?
oscillatory movement of the eye
201
What is Opto-kinetic Nystagmus?
physiological nystagmus,
| triggered by the presentation of a constantly moving grating pattern.
202
How does Opto-kinetic Nystagmus look?
The eyes track along the grating motion, with smooth pursuit up to a limit, and resets the eye position to the centre, with a burst of fast saccade motion.
203
What does the presence of Opto-kinetic Nystagmus suggest?
the subject has sufficient visual acuity to perceive the grating
204
What can cause a constant dilated pupil?
- overaction of the sympathetic nervous system (causes mydriasis via dilator pupillae)
- underaction of parasympathetic nervous system (causes miosis via sphincter pupillae).
205
What are the 2 different forms of lesions?
- medical
| - surgical
206
What are medical CN3 lesions?
- the vasculature to the nerve (the central portion of the nerve)
- tend to not affect the pupil (‘pupil sparing’) as the parasympathetic fibres running to the eye are in the outer portion of the nerve.
207
What are surgical CN3 lesions?
compresses the outer portion of the nerve fibres, which is where the parasympathetic nerves run (affecting the pupil)
208
What can cause a medical CN3 lesion?
microvascular disease due to hypertension, T2DM
209
What can cause a surgical CN3 lesion?
- posterior communicating artery aneurysm
| - In relation to the Circle of Willis: CN3 runs in between the posterior cerebral and the superior cerebellar artery.
210
How do you treat a medical CN3 lesion?
better metabolic control of their condition
211
How do you treat a surgical CN3 lesion?
assessment of aneurysm
| may involve clipping
212
What could cause tonically dilated pupil in the right eye. Upon shining light into the right eye, the pupil is slow to react compared to the left. The left eye reacts when light is shone into the right eye. ?
- Damage to parasympathetic ciliary ganglion which is involved in the pupillary-light reflex.
- Parasympathetic fibres travel with CNIII (oculomotor) to synapse at the ciliary ganglion before innervating the iris and ciliary body.
213
What site of damage can cause absent reflexes and impaired sweating?
dorsal root ganglia of the spinal cord
214
How does pilocarpine work?
a muscarinic receptor agonist that acts on M3 receptors in the iris sphincter muscle. This results in contraction of the muscle (miosis) and constriction of the pupil. These are independent of the parasympathetic tract.
215
What is an Adie's pupil?
- light-near dissociation
| - reinnervation that takes place as a result of damage to the ciliary ganglion
216
what causes there innervation that takes place as a result of damage to the ciliary ganglion?
- involves up regulation of postsynaptic receptors but the reinnervation is aberrant, causing fibres directed for the ciliary body to end up targeting the iris.
- As a result, the patient develops more meiosis with near accommodation than they do to light.
