Visual systems Flashcards
(131 cards)
1
Q
What are the different optical and functional anatomical components of the eye?
A
- Upper eyelid
- Lower eyelid
- Palpebral fissure
- Lateral canthus
- Medial canthus
- Caruncle
- Sclera
- Limbus (border between cornea and sclera)
- Iris
- Pupil
2
Q
What different types of tears do we have?
A
Basal, reflex and emotional (crying)
3
Q
What is the neurotransmitter of the lacrimal system?
A
Acetylcholine
4
Q
Describe the process by which tears are produced in the lacrimal system
A
- Tears prodcued by the lacrimal gland
- Drain through the 2 puncta, openings on medial lid margin
- Flow through superior and inferior canaliculi
- Gather in tear sac
- Exit tear sac through tear duct into nasal cavity
5
Q
What is the most superficial structure of the eye?
A
the “tear film”
6
Q
What is the role of the tear film?
A
- Maintains smooth cornea-air surface
- Oxygen supply to cornea- normal cornea has no blood vessels
- Removal of debris (tear film and blinking)
- Bactericide
7
Q
Describe the structure of the tear film
A
Composed of 3 layers:
- Superficial lipid layer: to reduce tear film evaporation - produced by a row of Meibomian Glands along the lid margins, v.thin- keeps the tear on the eye
- Aqueous (water) layer: tear film (tear gland) It delivers oxygen and nutrient to the surrounding tissue and it contains factors against potentially harmful bacteria- forms the main bulk of the tear film & thickest layer- acts as a lubricant
- Mucinous Layer corneal surface - maintains surface wetting- keeps film closely attached to eye
The mucin molecules act by binding water molecules,
to the hydrophobic corneal epithelial cell surface.
8
Q
Which layer in the tear film protects the tear film from rapid evaporation?
A
Lipid Layer
9
Q
What is the conjunctiva?
A
- Thin, transparent tissue that covers the outer surface of the eye
- It begins at the outer edge of the cornea, covers the visible part of the eye, and lines the inside of the eyelids
- It is nourished by tiny blood vessels that are nearly invisible to the naked eye
10
Q
Where does the eye sit?
A
within the anatomical space known as the orbit.
11
Q
What are the 3 layers that form the “coat” of the eye?
A
- The outer fibrous opaque layer called the Sclera (hard and opaque)
responsible for protecting the eye,
and maintaining the shape of the eye. - The middle pigmented vascular layer called the Choroid,
responsible for providing circulation to the eye,
and shielding out unwanted scattered light. - The innermost Neurosensory Layer called the Retina,
responsible for converting light into neurological impulses,
to be transmitted to the brain via the Optic Nerve.
12
Q
What is the role of the sclera/ it’s features?
A
“the tough, opaque tissue that serves as the eye’s protective outer coat. “
- High water content
13
Q
What is the cornea?
A
The transparent, dome-shaped window covering the front of the eye
- Attached to sclera
14
Q
What are the features/ what is the role of the Cornea?
A
role= 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 (look inside the eye for disease)
- 5 layered
- Has no blood supply; endothelium absorbs O2 directly
- Low water content
15
Q
What are the 5 layers of the cornea?
A
1 – Epithelium (most superficial)
2 – Bowman’s membrane
3 – Stroma – its regularity contributes towards transparency (made of collagen)
4- Descemet’s membrane
5- Endothelium – pumps fluid out of corneal and prevents corneal oedema- low water content: allows passage of glucose to nourish cornea
16
Q
What is the uvea?
A
Vascular coat of eyeball and lies between the sclera and retina.
17
Q
Describe the structure of the uvea & why is this clinically significant ?
A
Composed of three parts – iris, ciliary body and choroid.
Intimately connected and a disease of one part also affects the other portions though not necessarily to the same degree.
18
Q
What is the choroid? Where is it located?
A
Choroid - lies between the retina and sclera.
It is composed of layers of blood vessels that nourish the back of the eye.
19
Q
What is the Iris & what is it’s role?
A
“Round opening in the centre is the pupil.”
- Embedded with tiny muscles that dilate (widen) and constrict (narrow) the pupil size
- Controls light levels inside the eye similar to the aperture on a camera.
20
Q
Describe the structure of the lens?
A
(lies behind the iris)
Outer acellular capsule
Regular inner elongated cell fibres – transparency
May loose transparency with age – cataract (lens becomes opaque)
21
Q
What is the function of the lens?
A
responsible for one third of the refractive power of the eye.
Transparency
Regular structure
Refractive Power
1/3 of the eye focusing power - higher refractive index than aqueous fluid and vitreous
Accommodation
Elasticity
22
Q
What is the Retina?
A
Very thin layer of tissue that lines the inner part of the eye.
23
Q
What is the function of the Retina?
A
- Responsible for capturing the light rays that enter the eye. Much like the film’s role in photography.
- These light impulses are then sent to the brain for processing, via the optic nerve.
24
Q
What is the role of the optic nerve?
A
- connects to the back of the eye near the macula
- transmits electrical impulses from the retina to the brain
- visible portion is called the optic disc
25
What is the "blind spot"
Where the optic nerve meets the retina there are no light sensitive cells. It is a blind spot
26
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, temporal to the optic nerve
- The fovea is the very centre of the macula. The macula allows us to appreciate detail and perform tasks that require central vision such reading.
27
What is the fovea?
The most sensitive part of the retina
- It has the highest concentration of cones (fine vision), but a low concentration of rods (more sensitive to light)
- This is why stars out of the corner of your eye are brighter than when you look at them directly.
- But only your fovea has the concentration of cones to perceive in detail
28
What are the 2 types of vision?
Central and peripheral vision
29
What is "central"/ foveal/ Macular vision?
Responsible for detailed, central vision and daytime colour vision – fovea has the highest concentration of cone photoreceptors
Reading, facial recognition
30
How is central/ foveal vision tested?
Assessed by visual acuity assessment
31
What does a loss of foveal vision cause?
Loss of foveal vision – Poor visual acuity
Patients with loss of central vision will have problems with reading, and recognizing faces.
32
What is peripheral vision?
Peripheral Vision specializes in detecting shape, movement in the environment and night Vision
Navigation vision
33
How is peripheral vision assessed?
Assessed by visual field assessment
34
What does a loss in peripheral vision cause?
Extensive loss of visual field – unable to navigate in environment, patient may need white stick even with perfect visual acuity
Patients with extensive loss in peripheral vision will have problems navigating the world.
35
Describe the structure of the retina
- The retina forms the innermost layer of the coat of eye in the posterior segment.
- The retinal pigment epithelium transports nutrient from the choroid to the photo-receptor cells,
and removes metabolic waste from the retina.
Outer layer:
Photoreceptors (1st order neuron)
Detection of Light
Middle layer:
Bipolar Cells (2nd order neuron)
Local signal processing to improve contrast sensitivity, regulate sensitivity
Inner layer:
Retinal ganglion cells (3rd order neuron)
Transmission of signal from the eye to the brain
36
What are the 2 main classes of photoreceptors?
Rods and Cones
37
Compare rods with cones
RODS:
Longer outer segment with more photo-sensitive pigment
100 times more sensitive to light than cones
Slow response to light
Responsible for night vision (Scotopic Vision)
120 million rods
CONES:
Less sensitive to light, but faster response
Responsible for day light fine vision and colour vision (Photopic Vision)
6 million cones
38
Describe the distribution of the photoreceptors
RODS:
- Rod photo-receptors are responsible for night vision,
known as Scotopic Vision.
- Rod photo-receptors are widely distributed all over the retina, with the highest density just outside the macula.
- The density of rod photo-ceptors gently tails off towards the periphery.
NOTE that rod photo-receptors are completely absent within the macula.
CONES:
- Cone photo-receptors are responsible for day vision,
or Photopic Vision.
- Cone photo-receptors are distributed only within the macula.
39
Where can one find the highest concentration of Rod photoreceptors in the retina?
A) Optic Disc
B) Fovea
C) 10-20 degrees away from fovea
D) 20-40 degrees away from fovea
D) 20-40 degrees away from fovea
40
the eye captures different colours through different photoreceptors, true or false?
TRUE
41
What colours do each photoreceptor capture?
In humans, there are three cone photo-pigment sub-types:
the S-Cones with photo-pigment sensitive to short wavelength – colour blue,
the M-Cones with photo-pigment sensitive to medium wavelength – colour green,
and the L-Cones with photo-pigment sensitive to long wavelength – colour red.
This forms the basis of colour vision.
Rods are used for night vision and spatial recognition and are not really sensitive to any particular colour
42
How do we see other colours than red, blue and green, like yellow? what photoreceptors are stimulated?
Yellow light has a wavelength between the peak sensitivity wavelengths of M-Cones and L-Cones.
Yellow light stimulates both M-cones and L-cones equally.
Biologically, we experience yellow light as a combination of green and red light.
43
What is the commonest form of colour vision deficiency?
- Deuteranomaly also known as Daltonism is the most frequent form of colour blindness.
- People with deuteranomaly are not completely colour blind but they don’t perceive the colour red.
It is caused by the shifting of the M-cone sensitivity peak towards that of the L-cone curve,
causing red-green confusion. This is called Anomalous Trichromatism. Deuteranomaly is the commonest form of Anomalous Trichromatism.
44
What condition causes full colour blindness?
achromatopsia
45
Colour Vision deficits can also be caused by the absence of one or more of the 3 cone photo-pigments.
What are the different types of deficits?
1. In Dichromatism, only two cone photo-pigment sub-types are present.
2. In Monochromatism, there is complete absence of colour vision.
* This can be caused by Blue Cone Monochromatism,
with the presence of only blue L-cones.
* Or by Rod Monochromatism,
in which there is a total absence of all cone photo-receptors.
* Patients with Blue Cone Monochromatism have normal day light visual acuity,
* whereas Patients with Rod Monochromatism have no functional day vision.
46
What is meant by the term "refraction"
- When light is passing through one medium into another
- The velocity changes
47
What is the "indec of refraction"- what does it tell us?
Index of refraction (n)= speed of light in a vacuum/ speed of light in a medium
- n tells us how much the light changes speed
- All substances have an index of refraction and can be used to identify the material.
48
What are the "Refraction Facts"?
1. As light goes from one medium to another, the velocity CHANGES
2. As light goes from one medium to another, the path changes (light bends)
49
What exactly is light doing when it reaches a new medium?
Some of the light reflects off the boundary and some of the light refracts through the boundary.
50
Angle of incidence = Angle of Reflection, true or false?
TRUE
51
Angle of Incidence > or < the Angle of refraction depending on the direction of the light, true or false?
TRUE
52
What are the 2 basic types of lens?
Convex and Concave
53
What do convex and concave lenses do to light?
A converging lens (convex) takes light rays and brings them to a point.
A diverging lens (concave) takes light rays and spreads them outward.
54
What is meant by "Emmetropia"?
Emmetropia is the ABSENCE of refractive errors in the eye
- There is adequate correlation between axial length and refractive power
- Parallel light rays fall on the retina (no accommodation)
55
What is "Ametropia"?
The opposite of Emmetropia
- Ametropia is a state where refractive error is present, or when distant points are no longer focused properly to the retina
- Mismatch between axial length and refractive power
Parallel light rays don’t fall on the retina (no accommodation)
56
What are the different forms of Ametropia?
Near-sightedness (Myopia)
Farsightedness (Hyperopia)
Astigmatism
Presbyopia
57
What is myopia?
Parallel rays converge at a focal point ANTERIOR to the retina
Causes: (not clear , genetic factor)
- excessive long globe (axial myopia) : more common
- excessive refractive power (refractive myopia)
58
What are the symptoms of myopia?
- Blurred distance vision
- Squint in an attempt to improve uncorrected visual acuity when gazing into the distance
- Headache
(no issues reading)
59
How can myopia be treated?
a. Correction with diverging lenses (negative lenses)
b. Correction with contact lens
c. Correction by removing the lens to reduce refractive power of the eye
60
What is "hyperopia"?
Parallel rays converge at a focal point POSTERIOR to the retina
CAUSES: (not clear, inherited)
- excessive short globe (axial hyperopia) : more common
- insufficient refractive power (refractive hyperopia)
61
What are the symptoms of hyperopia?
- Visual acuity (sharpness) 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 (inflammation of the eyelid and conjunctiva)
- Amblyopia (Lazy eye (amblyopia) is reduced vision in one eye caused by uncorrected fibre optics in one eye.)– uncorrected hyperopia > 5D
62
How is hyperopia treated?
a. Correction with converging (positive lenses)
b. Correction with positive lens + cataract extraction
c. Correction with contact lens
d. Correction with intraocular lens
63
What is Astigmatism?
Astigmatism means your eye is shaped more like a rugby ball than a football, so light is focused at more than 1 place in the eye (cornea has an irregular conformation; steeper/ flatter regions create new focal points
Parallel rays come to focus in 2 focal lines rather than a single focal point
64
What is the cause of Astigmatism?
Heredity
Cause : 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)
65
What are the symptoms of Astigmatism?
Asthenopic symptoms (headache , eyepain)
blurred vision
distortion of vision
head tilting and turning (attempting to compensate for irregular shape)
66
How is Astigmatism treated?
Regular astigmatism : cylinder lenses with or without spherical lenses (convex or concave), Sx
Irregular astigmatism : rigid cylinder lenses, surgery
67
What is the "Near Response Triad"
The near/accommodative response is a three-component reflex that assist in the redirection of gaze from a distant to a nearby object. It consists of a pupillary accommodation reflex, lens accommodation reflex, and convergence reflex
68
What is the role of the Pupillary miosis in the near response triad?
Pupillary Miosis (Sphincter Pupillae) to increase depth of field
69
What is the role of the Convergence in the near response triad?
Convergence (medial recti from both eyes) to align both eyes towards a near object
70
What is the role of Accomodation in the near response triad?
Accommodation (Circular Ciliary Muscle) to increase the refractive power of lens for near vision
71
What is presbyopia?
- Naturally occurring loss of accommodation (focus for near objects)
- Onset from age 40 years
- Distant vision intact (near vision affected- can't read close up)
72
How is presbyopia corrected?
Corrected by reading glasses (convex lenses) to increase refractive power of the eye
a) Spectacle lenses
b) Contact lenses
Vision remains intact until cataracts kick in
73
How is presbyopia?
Treatment
- convex lenses in near vision
* Reading glasses
* Bifocal glasses
* Trifocal glasses
* Progressive power glasses
74
What types of spectacle lenses are there?
Monofocal lenses : spherical lenses , cylindrical lenses
Multifocal lenses
75
Compare spectacle lenses with contact lenses
Contact lenses have higher quality of optical image and less influence on the size of retinal image than spectacle lenses (can't move the lens closer/ further from the eye)
76
For what reasons do people need contact lenses?
indication : cosmetic , athletic activities , occupational , irregular corneal astigmatism , high anisometropia , corneal disease
77
What are disadvantages of contact lenses?
disadvantages :
- careful daily cleaning and disinfection
- expense
complication:
- infectious keratitis
- giant papillary conjunctivitis
- corneal vascularization
- severe chronic conjunctivitis
78
What are intraocular lenses?
- replacement of cataract crystalline lens
- give best optical correction for aphakia (absence of crystaline lens) , avoid significant magnification and distortion caused by spectacle lenses
disadvantage= lens do not correct/ help with reading
79
What are the different surgical corrections you can have?
1. Keratorefractive surgery :RK, AK, PRK, LASIK, ICR, thermokeratoplasty
2. Intraocular surgery : clear lens extraction (with or without IOL), phakic IOL
80
Describe the process of Lasik surgery
1. Pre operative eye
2. Initial cutting of corneal flap
3. Cutting of corneal flap
4. Flipping of corneal flap
5. Photorefractive treatment (laser)
6. Corneal stroma reshaped post laser
7. Corneal flap back in position
8. Treatment completed
81
What is ICL, (the Staar intra-collamer lens)?
It is inserted into the eye on top of the natural lens for correction of myopia and astigmatism
82
What is a disadvantage of ICL?
ICL= The Staar intra-collamer lens (ICL)
- Natural lens eventually becomes opaque; leads to cataract
83
Describe the process of clear lens extraction/ intraocular surgery
- Same as cataract extraction
- Implantation of artificial lens
- Patients lose accomodation (need reading glasses)
1. Use a phaco tip to break up & suck out the natural lens
2. Insert the artificial intraocular lens
84
What is the role of the visual pathway in the neurology of the visual system?
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.
85
What are the main 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
86
Describe the structure of the visual pathway starting from the retina
Retina ->
First Order Neurons: Rod and Cone Retinal Photoreceptors->
Second order Neurons: Retinal Bipolar Cells->
Third Order Neurons ("proper neurons"):
Retinal Ganglion Cells
*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
87
What is the optic chiasma?
53% Ganglion Fibres cross at Optic Chiasma:
Crossed Fibres – originating from nasal retina, responsible for temporal visual field
Uncrossed Fibres – originating from temporal retina, responsible for nasal visual field
88
How would a lesion anterior to the optic chiasma affect vision?
Lesions anterior to Optic Chiasma affect visual field in one eye only
89
How would a lesion posterior to the optic chiasma affect vision?
Lesions posterior to Optic Chiasma affect visual field in both eyes:
Right sided lesion – Left Homonymous Hemianopia in Both Eyes
Left sided lesion – Right Homonymous Hemianopia in Both Eyes
90
How would a lesion at the optic chiasma affect vision?
Damages crossed ganglion fibres from nasal retina in both eyes
Temporal Field Deficit in Both Eyes – Bitemporal Hemianopia
91
What are the types of disorders of the visual pathway?
Normal
Monocular blindness
Bitemporal Hemianopia
Rigjht nasal hemianopia
Homonymous hemianopia
Quadrant- anopia
Macular sparing
92
What is the cause of Bitemporal Hemianopia
Typically caused by enlargement of Pituitary Gland Tumour
93
What is the cause of homonymous hemianopia
Stroke (Cerebrovascular Accident)
94
What is Homonymous Hemianopia with Macular Sparing
Damage to Primary Visual Cortex
- Often due to stroke
- Leads to Contralateral Homonymous Hemianopia with Macula Sparing
- Area representing the Macula receives dual blood supply from Posterior Cerebral Arteries from both sides
95
What is the role of Pupillary Function
Regulates light input to the eye like a Camera Aperture
96
How does the pupil change in light?
In light: pupil constriction
- the iris circular muscle contracts,
and constricts the pupillary aperture.
-Small pupil reduces the amount of light entering into the eye,
and thus reduces the rate of photo-pigment bleaching.
- decreases spherical aberrations and glare
- increases depth of field
- Pupillary constriction mediated by parasymapthetic nerve (within CN III)
97
How does the pupil change in darkness?
In dark: pupil dilatation
- This is mediated by the sympathetic nerve,
activating the iris radial muscle (radial muscles contract)
- increases light sensitivity in the dark by allowing more light into the eye
- pupillary dilatation mediated by sympathetic nerve
98
Describe the afferent pathway of pupillary reflex
The pupillary light reflex is an autonomic reflex that constricts the pupil in response to light, (afferent: sensory information from eye to brain)
Pathway: Afferent pupillary fibers start at the retinal ganglion cell layer (Rod and Cone photoreceptors synapsing on Bipolar Cells synapsing on Retinal Ganglion Cells)
- They then travel through the optic nerve, optic chiasm, and optic tract,
- Pupil-specific ganglion cells exits at posterior third of optic tract before entering the Lateral Geniculate Nucleus
- They then travel to the pretectal area of the midbrain
- which sends fibers bilaterally to the efferent Edinger-Westphal nuclei. (Afferent (incoming) pathway from each eye synapses on Edinger-Westphal Nuclei on both sides in the brainstem)
It is important to note that afferent pathway from either eye, stimulates the efferent pathway on both eyes.
This means only one eye needs to be stimulated with light, to elicit pupillary constriction response in both eyes.
99
Describe the efferent pathway of pupillary reflex
The pupillary light reflex is an autonomic reflex that constricts the pupil in response to light, (efferent: motor information from brain to eye)
[continued from the afferent pathway]
- From the Edinger- Westphal nucleus, efferent pupillary parasympathetic preganglionic fibers travel on the oculomotor nerve
- to synapse in the ciliary ganglion
- which sends parasympathetic postganglionic axons in the short posterior ciliary nerve
- to innervate the iris sphincter smooth muscle (pupillary sphincter)
- a direct and consensual pupillary response is produced
100
Compare direct reflex vs consensual reflex
Direct Light Reflex –Constriction of Pupil of the light-stimulated eye
Consensual Light Reflex – Constriction of Pupil of the other (fellow) eye
101
How are we able to have consensual reflex?
Consensual Light Reflex – Constriction of Pupil of the other (fellow) eye
beacuse:
Afferent pathway on either side alone will stimulate efferent (outgoing) pathway on both sides
102
How would a right afferent defect affect contriction?
E.g. damage to optic nerve
- No pupil constriction in both eyes when right eye is stimulated with light
- Normal pupil constriction in both eyes when left eye is stimulated with light
103
How would a right efferent defect affect pupil constriction ?
E.g. Damage to Right 3rd Nerve (oculomotor 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
104
What is the "Swinging Torch Test"?
Test used to demonstrate partial pupillary response when one eye (afferent pathway) is damaged:
- The best way to demonstrate this weaken response,
is to stimulate one eye at a time,
alternating between the right and the left eye
- Both Pupils constrict when light swings to left undamaged side
- Both Pupils paradoxically dilate when light swings to the right damaged side
105
What structures facilitate the movement of the eye?
Facilitated by the six extraocular muscles innervated by the three cranial nerves (III (oculomotor, IV trochlear and VI abducens)
106
What is "duction" ?
Eye Movement in One Eye
107
What is "Version"?
Simultaneous movement of both eyes in the same direction such as gazing to the right, Dextroversion,
or gazing to the left, Levoversion.
108
What is "Vergence"?
Simultaneous movement of both eyes in the opposite direction
109
What is "convergence"?
Simultaneous adduction (inward) movement in both eyes when viewing a near object
110
What is meant by "Saccade"?
Eye movement can also be characterized by its speed.
Saccade refers to short fast burst eye movement,
up to 900 degrees per second.
It can be a voluntary or involuntary movement,
useful for:
- acquiring new external target/ stimuli
- scanning saccade, e.g. scanning text when reading a book,
- Predictive saccade e.g. tracking objects
- performing eye movement guided by memory,
in the absence of external stimuli.
111
What is meant by "Smooth Pursuit"?
Eye movement can also be characterized by its speed.
Smooth Pursuit is a slow sustain movement,
up to 60 degrees per second.
- Driven by motion of a moving target across the retina.
112
What are the extraocular muscles?
Six muscles
- Attach eyeball to orbit
- Straight and rotary movement
Four straight muscles
1. Superior rectus
2. Inferior rectus
3. Lateral rectus
4. Medial rectus
(5 of the 6 muscles come out of a cone from the back of the orbit. The inferior oblique comes in nasally. )
113
What is the role of the superior and inferior rectus?
Superior rectus
Attached to the eye at 12 o’clock
Moves the eye up.
Inferior rectus
Attached to the eye at 6 o’clock
Moves the eye down.
114
What is the role of the Lateral rectus?
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)
115
What is the role of the medial rectus?
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)
116
What is the role of the superior oblique?
Attached high on the temporal side of the eye.
Originates at the orbital apex and passes under the Superior Rectus.
Moves the eye in a diagonal pattern down and out
Travels through the trochlea (trochlea is attached to nasal bone)
117
What is the role of the inferior oblique?
Attached low on the nasal side of the eye.
Passes over the Inferior Rectus.
Moves the eye in a diagonal pattern - up and out.
118
What extraocular muscles are innervated by CNIII the oculomotor nerve?
As the Third Cranial nerve enters into the orbit,
it divides itself into superior and inferior branches.
Superior Branch:
1. Superior Rectus – elevates eye
2. levator palpebrae superioris - raises eyelid (not shown)
Inferior Branch:
3. Inferior Rectus – depresses eye
4. Medial Rectus – adducts eye
5. Inferior Oblique – elevates eye
6. Parasympathetic Nerve – constricts pupil
119
What extraocular muscles are innervated by the trochlear nerve CN IV?
Superior Oblique – depresses eye
120
What extraocular muscles are innervated by CNVI the abucens?
Lateral Rectus – abducts eye
121
Which eye movements help test for which eye structures?
To test the function of the six extra-ocular muscles,
we need to isolate the action of each of them,
by maximizing the action of the muscle to be tested,
and minimizing the action of all other muscles.
Lateral Rectus muscle action is best tested in the abducted position.
Medial Rectus muscle action is best tested in the adducted position.
Superior Rectus muscle action is best tested in the elevated and abducted position.
Inferior Rectus muscle action is best tested in the depressed and abducted position.
Inferior Oblique is best tested in the elevated and adducted position.
Superior Oblique is best tested in the depressed and adducted position.
122
What is "supraversion" and supraduction?
Supraversion is the elevation of both eyes,
elevation of one eye, right or left eye is supraduction.
123
What is "infraversion" and "infraduction"?
Infraversion is the depression of both eyes,
depression of one eye, right or left eye is infraduction
124
What is "Dextroversion"?
Dextroversion, or right gaze,
involves simultaneous right eye abduction,
and left eye adduction.
125
What is "levoversion"?
Levoversion, or left gaze,
involves simultaneous left eye abduction,
and right eye adduction.
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What is "torsion"?
rotation of eye around the anterior-posterior axis of the eye
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What is third nerve palsy?
When there is a complete third nerve palsy,
only muscles not innervated by the third cranial nerve in the affected eye are working:
- 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)
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What is sixth nerve palsy?
Sixth nerve palsy presents with deficit in abduction in the affected eye.
- Affected eye unable to abduct and deviates inwards
- Double vision worsen on gazing to the side of the affected eye
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What is meant by "Nystagmus"
Nystagmus refers to oscillatory movement of the eye,
which can be physiological or pathological.
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What is Opto-kinetic Nystagmus Reflex?
Opto-kinetic Nystagmus is a form of physiological nystagmus, triggered by the presentation of a constantly moving grating pattern.
- 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.
- This results in cycles of slow phase smooth pursuit,
alternating with fast phase reset saccade in the opposite direction.
The presence of Opto-kinetic Nystagmus signifies that the subject has sufficient visual acuity to perceive the grating.
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When is Optokinetic Nystagmus Reflex tested?
Opto-kinetic Nystagmus is useful in testing pre-verbal children visual acuity.
The presence of Opto-kinetic Nystagmus signifies that the subject has sufficient visual acuity to perceive the grating.
