Ocular Anatomy Flashcards
(180 cards)
1
Q
Fibrous tunic
A
Consists of cornea, limbus, sclera
2
Q
Functions of the Cornea
A
Protection of interior structures, clarity of vision, and refraction of light coming into eye
3
Q
Parts of the Cornea
A
Outermost epithelium
Stroma
Descemet’s membrane
Innermost endothelium
4
Q
Corneal epithelium properties
A
- Multilayered: superficial cells, wing cells, basal cells
- Great regenerative capacity
5
Q
Stroma properties
A
- Makes up 90% of corneal thickness
- Composed of regular (parallel) strands of collagen- form lamellae
- Largely acellular (except keratocytes + wandering leukocytes)
- Highly organized ECM (proteoglycans, GAGs, mult. Types of collagen)
6
Q
Corneal endothelium properties
A
- Monolayer of hexagonal cells
- Low regenerative capacity
- Acts as metabolic “pump” to maintain equilibrium of corneal fluid
7
Q
Point of corneal decompensation
A
When corneal endothelial cells are low in concentration and cannot handle workload of pumping out corneal fluid; there’s a leak
8
Q
Descemet’s Membrane properties
A
- Basement membrane of corneal epithelium
- Thickens with age
- Made up of various collagen types
9
Q
Describe corneal innervation
A
- Branches from Trigeminal nerve (CN V)
- Concentrated superficially
- NOT found in Descemet’s membrane
- Very dense anterior sensory neural networks (subbasal plexus)
10
Q
What properties allow for corneal clarity?
A
Avascular, anhydrous, absence of pigment, non-keratinized anterior epithelium, regular arrangement and small size of stromal collagen fibrils
11
Q
What issue(s) can corneal edema cause?
A
Fluid accumulation can disrupt the focused manner in which light refracted through cornea, body will compensate with pigment repositioning in cornea, which can cause blindness
12
Q
Superficial corneal ulcer
A
When only corneal epithelium is missing; most painful due to nerve exposure
13
Q
Deep corneal ulcer
A
Epithelium and stroma missing; remainder of cornea is extremely fragile
14
Q
Iris prolapse
A
All layers of cornea are missing/ulcerated
15
Q
Limbus properties
A
- Transition zone of cornea and sclera
- Epithelia of conjunctiva and cornea are contiguous
- Source of stem cells for epithelial regeneration
- Contains vasculature
- Can be pigmented
16
Q
Sclera properties
A
- Posterior aspect of fibrous coat
- Dense, irregular CT and collagen fibers
- White with variable amounts of pigment
- Blood vessels + nerves pass through
- In non mammals, contains cartilaginous support/bony ossicle for protection and enhanced refraction
17
Q
Layers of Sclera
A
Lamina fusca- innermost margin
Sclera proper- majority of tissue
Episclera- loose exterior CT
18
Q
Lamina cribrosa
A
Anatomic sieve through which retinal ganglion cell axons exit the globe and coalesce to form the optic nerve; becomes weak point in glaucoma
19
Q
Adnexa
A
Supporting structures of the eye; orbit, eyelids, conjunctiva, third eyelid, nasolacrimal system
20
Q
Properties of the orbit
A
- Made up of several different bones
- Has species-specific foramina and fissures through which vessels and nerves communicate with the orbit
- Complete (herbivores) or incomplete (carnivores)
- Orbital ligament forms connection in incomplete orbits
- Location within skull determines degree of binocular vision
- Breed/individual differences in depth = degree of protection for globe
21
Q
Orbital fascia
A
Periorbita (periosteum)
Tenon’s capsule (fascia that covers globe itself)
Fascial sheaths of extraocular muscles (EOM)
22
Q
Extraocular Muscles
A
Rectus muscles: lateral, medial, dorsal, ventral
Oblique muscles: superior (dorsal) and ventral (inferior)
Retractor bulb is: pulls eye back
23
Q
Functions of the eyelids
A
- Protect the globe
- Distribute tear film
- Pump spent tears into NL apparatus
- Help control amount of light entering eye
24
Q
Properties of the eyelids
A
- Contains skin, orbicularis oculi m., tarsal plate w/ glandular tissue (develops portion of tear film), palpebral conjunctiva
- May or may not have cilia (eyelashes)
- Richly vascular
25
Eyelid musculature and their innervations
Orbicularis oculi- closes palpebral fissure; CN 7 (facial n.)
Levator palpebrae superioris- raises upper lid; CN 3
Muller's muscle- raises upper lid; sympathetic innervation
Retractor anguli oculi- supports and keeps lateral canthus extended
26
Palpebral fissure
Juncture where upper and lower lids meet
27
Canthus
Juncture where both medial parts of eyelids meet (medial canthus) or where both lateral parts meet (lateral canthus)
28
Meibomian (tarsal) glands
- Contribute portion of tear fluid
- Line eyelid margin
- Compound acinar; holocrine sebum-producing
29
Main concern with eyelid trauma
Globe exposure
30
Properities of Eyelashes (cilia)
- Function: protection and surveillance
- Absent in cats
- Found along free margin of upper or upper/lower eyelids
- They exit external to glandular openings of the margin
31
Distichiasis
Corneal irritation associated with eyelash insult
32
Spectacle
Fused, transparent eyelids that are shed concurrent with skin and found on snakes
33
Properties of Conjunctiva
- Mucosal lining assoc. with eye and eyelids
- Stratified to pseudostratified columnar epithelium + goblet cells on top of loose CT
- Richly vascular
34
3 regions of the conjunctiva
Palpebral (exterior)
Fornix (reflection point)
Bulbar (interior)
35
Functions of the conjunctiva
- Produces mucin component of tear film
- Immune surveillance
- CALT (conjunctiva-associated lymphoid tissue)
36
What is conjunctivitis?
Inflammation of the conjunctiva; non-specific clinical findings
37
Properties of the third eyelid (nictitating membrane)
- Semilunar fold of conjunctiva surrounding a T-shaped cartilaginous support
- Has a gland at base of the cartilage
38
Functions of the third eyelid
- Tear production (aqueous portion) and distribution
| - Protect globe
39
What is cherry eye?
- Prolapse of third eyelid gland
- Gland protrudes over free border of TE and becomes inflamed/enlarged
- Weak fascial attachments
- Common in young dogs, Cockers, bulldogs/brachiocephalics, (uncommon in cats)
40
Nasolacrimal System Secretory Components
- Meibomian glands and conjunctival goblet cells
| - Orbital lacrimal glands and third eyelid glands
41
Nasolacrimal System Drainage Components
- Puncta at medial canthus
- Lacrimal sac and duct
- Nasal puncta
42
Properties of Lacrimal glands
Tubuloalveolar glands, serous secretions, orbital lacrimal gland, nictitans gland
43
Functions of tears
- Cleanse and lubricate ocular surface
- Provide nutrition and O2
- Antimicrobial defense
- Maintains optically uniform surface
44
Makeup of Tears
Aqueous component- Lacrimal glands
Lipid component- meibomian glands
Mucin component- conjunctival goblet cells
45
What is keratoconjunctiva sicca (chronic dry eye)?
-Quantitative deficiency of aqueous tears, resulting in significant ocular irritation, conjunctivitis/inflammation, and compensatory mucoid discharge
46
What is epiphora?
Increased tear production (causes pain/irritation) and decreased tear drainage (could be due to NL obstruction)
47
3 structures of the vascular tunic (uvea)
Iris, ciliary body, choroid
48
Functions of the uvea
- Nourish interior (O2 and glucose)
- Productions and outflow of AqH
- Immune responses
- Lens accomodation
49
Properties of the Iris
- Anterior portion of the uvea that forms diaphragm in front of lens
- Central aperature = pupil
50
3 zones of iris
Pupillary zone, ciliary zone, collarette (in between)
51
Functions of the iris
=controls amount of light entering eye (pupil)
| -enhances visual resolution
52
What is a unique feature of the iris?
It is not covered entirely by epithelium
53
What is the most common iris color?
Some shade of brown, but can vary from brown to blue
54
How does iridal pigment mature in non-mammals?
Blue color comes with maturation of pigments
55
What does iris color change typically indicate?
Disease (in most domestic species) -neoplasia or inflammation
56
Pupil shape variety
Vertical slit = cats, reptiles, amphibians
Round = carnivores/predators
Horizontal ellipse- Herbivores
57
What is the corpora nigra (granula iridica)?
Hypertrophy of posterior uveal pigmentation that acts as a shade and to dissuade scatter and improve resolution
58
Difference between pupillary size control in mammals and non-mammals?
Mammals cannot voluntary control pupil size (under smooth muscle control); non-mammals have some skeletal muscle control
59
What causes persistent pupillary membranes to occur?
When pupillary membrane, of which the center regresses upon forming the pupil remains and leads to opacities
60
Functions of the ciliary body
Blood aqueous barrier, produces AqH, involved in AqH drainage, generates intraocular pressure, and serves as anchor for fibers that suspend the lens
61
Parts of the ciliary body
```
Pars plicata (ciliary processes)
Pars plana (flattened posterior zone)
```
62
Functions of aqueous humor
Fills anterior and posterior chambers, supplies nutrition and is a waste sink to lens and cornea, production and outflow maintains IOP, light refraction
63
How is the aqueous humor produced?
Actively produced by selective transport by carbonic anhydrase and Na+K+ATPase; also passive diffusion and ultrafiltration of blood plasma
64
How does aqueous humor outflow work?
AqH returns to systemic vascular system, primarily via conventional pathway, but alternative uveoscleral pathway is present
65
What causes glaucoma?
A collapsed idriocorneal angle, b/c normal aqueous drainage cannot occur and fluid buildup leads to loss of resolution
66
Functions of ciliary musculature
Facilitates AqH outflow, contributes to lentricular accomodation, and spasms when there is intraocular inflammation
67
Portions of the uvea
Anterior- iris
Middle- ciliary body
Posterior- Choroid
68
Properties of Choroid
Lies b/t sclera and retina, is continuous with ciliary body, main source of O2 and nutrition for outer retina, heavily pigmented, and site of alternative AqH outflow
69
Layers of the Choroid
```
Suprachoroidea
Large vessel layer
Medium-sized vessel layer
Tapetum
Choriocapillaris
```
70
Properties of tapetum
-Reflective structure located in dorsal choroid that allows retina "second chance" to interact with photons
71
Species-specific differences in the tapetum structure
Carnivores- cellular; iridocytes form rodlets w/ high levels of zinc + riboflavin
Herbivores- fibrous, acellular, highly organized collagen
72
Purpose of blood ocular barriers
Maintains ocular privilege, limits damage to ocular structures by systemic conditions
73
Important uvea facts
-Provides interior structures with O2
-Produces AqH
-Regulates light entering eye
-Some CB muscle fibers insert into ICA
When CB contracts, ICA is opened and AqH outflow is increased.
-With intraocular inflammation, the CB musculature
spasms (= pain)
74
What shape is the lens?
Biconvex (generally)
75
What structures support the crystalline lens?
Zonules attached to ciliary body
76
What embryological structure does the lens develop from?
Presumptive lens ectoderm-->Lens placode-->Lens vesicle
77
What are suture lines?
Chunks of fibers that have junctures located on the lens; mostly Y-shaped; opacities denote cataract/clinical condition
78
What is the unique cellular makeup of the lens nucleus?
From inside out:
Embryonal- primary nerve fibers formed in development
Fetal-secondary n. fibers formed while fetus is in utero
Adult- tertiary n. fibers formed out of the womb
79
What is nuclear sclerosis?
A normal aging phenomenon where lens thickens and impairs lentricular ability to accommodate path of light entering the eye; can result in loss of depth perception and presbyopia (farsightedness)
80
What assists with lenticular transparency?
Highly organized fibers
Maintained in avascular (anaerobic) environment
Fibers are kept dehydrated
Large % of soluble proteins (crystallins)
81
What is a cataract?
An opacity of the lens
82
What is phacoemulsification?
Placement of a probe into the lens that uses ultrasonic waves to break up proteins causing opacity in the lens
83
What are zonules?
Ligaments that suspend the lens from the equator to the ciliary body musculature; can become dysplastic with age/inflammation
84
What is the structure seen when a lens is dislocated?
Aphacic crescent
85
Properties of the vitreous humor?
Largest structure of the eye that is a hydrogel of hyaluronic acid and 98-99% water
86
3 vitreous components
```
Primary = hyaloid vascular system
Secondary= contains Mittendorf's dot
Tertiary = lens fibers connecting to CB
```
87
What is a clinical condition involving the vitreous?
Persistent hyperplastic primary vitreous
88
What is the ocular fundus?
The interior surface of the eyeball that is visible through the ophthalmoscope.
89
What do you typically look for during a fundus examination?
Vessels coming out of the optic disc; attenuation, clotting, irregularities
90
Function of the retina
Transform light energy (photons) into an electrical signal (transduction)
91
Function of the lens
Accommodation or changing path of light entering the eye
92
Properties of the retina
- Multilayered
- Most metabolically active tissue in body (per wt/unit)
- High O2 consumption
93
How many layers of cells are involved in the sensory neural circuit of the retina?
10
94
What is the path of light traveling through the eye?
Light passes through the entire retina prior to stimulating photoreceptors at the back of the eye, which stimulates a cascade effect from back to front
95
What is the purpose of the tapetum?
It's a reflective structure that allows photoreceptors a "second chance" at stimulation; improves night vision
96
Order of retinal neural tissues from exterior to interior
```
Tapetum (part of choroid)
Retinal pigmented epithelium
Photoreceptors
Outer nuclear layer
Inner nuclear layer
Ganglion cell layer
Vitreal chambers
```
97
What are the two photoreceptors found in the retina?
Rods and cones
98
What are the differences between rods and cones?
Cones function in color vision, detail, and acuity
| Rods function in low-light vision (low acuity/no color)
99
What occurs during the process of phototransduction?
Conversion of light energy absorbed by photopigments in rods and cones into electrical energy (nerve impulse) by generating a cascade of enzymatic reactions that decrease neurotransmitter release, resulting in bipolar cell, then ganglion cell responses, and nerves impulses are carried to brain optic nerve fibers
100
What are the main molecules/chemicals involved in phototransduction?
Rhodopsin (-->retinal + opsin)
Transducin
cGMP
Na+/K- ion channels
101
What forms the optic nerve (CN II)?
Axons of the retinal ganglion cells coalesce at the lamina cribrosa and posterior to the globe
102
What types of cells support the optic nerve (CN II)?
Astrocytes and oligodendrocytes
103
What is the only part of the CNS that is directly visible to the examiner?
The optic nerve (through the optic disc)
104
What is the pathway of a nerve impulse traveling from the medial side of the left eye?
Leaves the eye via the left optic nerve, information is exchanged at the optic chiasm, follows down the right optic tract to the right lateral geniculate nucleus of the thalamus, down the right optic radiation, and to the right visual cortex of the brain
105
What is decussation?
The percentage of crossing of optic nerve fibers at the optic chiasm (differs in species)
106
What percentage of ocular blood flow do the retina and choroid receive, respectively?
Retina- 4%
| Choroid- 85%
107
Which organ receives more blood flow, the brain or the retina/choroid?
Retina and choroid (10 x more)
108
What are the four types of retinal vasculature patterns?
Holangiotic
Paurangiotic
Merangiotic
Anangiotic
109
What is holangiotic vasculature patterning and what types of animals is it found in?
-Prominent vascular supply both dorsally and ventrally; e.g. dogs, cats, people
110
What is the macula?
Region of the retina containing a higher percentage of photoreceptors (typically darker circular region visualized adjacent to optic disc)
111
What is paurangiotic vasculature patterning and what types of animals is it found in?
-A few small vessels or capillaries restricted to the region of the optic disc; requires heavier reliance on choroid for nutrients; e.g. horses, some marsupials
112
What is merangiotic vasculature patterning and what types of animals is it found in?
Small part of retina provided with obvious blood vessels along horizontal plane; e.g. rabbits
113
What is anangiotic vasculature patterning and what types of animals is it found in?
No visible vessels; e.g. birds, reptiles
114
What is pecten?
A pigmented, vascular structure found in bird retinas that acts as an extraretinal blood supply
115
What are some adaptations of the avascular (anangiotic) retina?
Thin, short outer segments, glycogen storage (Muller cells), absence of tapetum and retinal taper, or extraretinal blood supply (pecten, conus papillarus, choroidal papillae)
116
What causes retinal detachment and where does it typically occur?
Vitreal contraction or formation of inflammatory bands in the vitreous creates tension that can tear or detach the retina; typically occurs between the retinal pigmented epithelium and the sensory retinal layer
117
What determines an animal's visual field?
Whether it's predator or prey, position of orbit/globe relative to midline, and pupil size and shape
118
Who typically has a wider visual field, the predator or the prey?
Prey
119
What is acuity?
The exactness or sharpness of an image
120
What properties/structures enhance vision in dim light?
Large relative proportion of rods (scotopic vision), tapetum, and pupil size and shape (smaller = better)
121
True or False: Animals can only see in black and white
False; most mammals are dichromates (2 types of cones), they cannot perceive red, and colors are muted
122
What wavelengths can dogs/cats see at?
```
429-432 nm (Blue)
555 nm (Yellow-green)
```
123
What wavelengths can horses see at?
```
428 nm (Blue)
539 nm (Green)
```
124
What aspects of vision are animals (dogs) better at than humans?
Better flicker detection (motion), superior night (dim light) vision, larger visual fields (peripherals)
125
What aspects of vision are animals (dogs) worse at than humans?
Reduced color perception and acuity (13-16% that of humans)
126
Which neurologic systems are involved in normal vision and ocular health?
Visual sensory system (CN II), autonomic nervous system (parasympathetic + sympathetic), oculomotor system (CN III, IV, VI, VII, VIII), and trigeminal somatic sensory system (CN V)
127
Which cranial nerves are involved in vision/ocular health?
II-VIII; Optic (II), Oculomotor (III), Trochlear (IV), Trigeminal (V), Abducens (VI), Facial (VII), Vestibulocochlear (VIII)
128
Functions of CN II- Optic n.
Sensory (carries visual info) from retina to cortex
129
Functions of CN III- Oculomotor n.
Motor to several extraocular mm. and levator palpebrae superioris m.; parasympathetic hitchhikers
130
Functions of CN IV- Trochlear n.
Motor to superior oblique m.
131
Functions of CN V- Trigeminal n.
Sensory from eyelids, cornea, lacrimal gland
132
Functions of CN VI- Abducens n.
Motor to lateral rectus m. and retractor bulbi m.
133
Functions of CN VII- Facial n.
Motor to eyelids and other facial mm.
134
Functions of CN VIII- Vestibulocochlear n.
Sensory for vestibular component of ocular movements
135
What are the two parts of a reflex response?
Afferent (sensory) and efferent (motor)
136
What processes does the visual sensory system consist of?
Photoreceptors converting light energy to electrical energy (transduction), modulation of electrical signal by various retinal cells, and electrical impulses leave retina by ganglion cell fibers
137
Pathway of the visual sensory system
Retinal ganglion cell axons become optic nerve-->decussation (+/-) occurs at optic chiasm--> optic tract --> ganglion synapses in the dorsolateral or lateral geniculate nucleus--> output to visual cortex
138
Where can electrical signals go?
To the visual cortex (visual pathways)- 80% n. fibers
| To the midbrain (pupillary light reflexes aka PLRs)- 20%
139
3 structures where opacities can obscure light so it doesn't reach retina appropriately
Cornea, uvea (uveitis), lens
140
What are the three subcortical effects?
1. Through pretectal nucleus to Edinger-Westphalia nucleus--> PLR
2. To superior follicular-->saccadic (tracking) eye, correlation of sensory info
3. To others--> control optokinetic reflexes, circadian rhythms, endocrine activity of hypothalamus
141
Potential problems with vision
Opacity obscuring light to retina, retinal dysfunction (lack of transduction), optic nerve dysfunction (lack of transmission), cortical problems (info processing/recognizing issue)
142
What goes on physiologically in glaucoma?
Pressure inside eye causes damage to nerve fibers going through lamina cribrosa, causing them to decompose, and pushes lamina up
143
Parts of a vision test
History (trauma, systemic disease, drugs), obstacle course, cotton ball test (does globe follow ball?), visual placing reaction (will animal extend both forelegs when bringing down towards table?), Menace response
144
What is the menace response?
Menacing hand movements in front of eye should cause dog to blink and/or retract the globe
- Afferent arm: CN II (Optic n.)- senses movement
- Efferent arm: CN VIII (Facial n.)- closes eyelids, CN VI (Abducens n.)- retracts globe
145
What is the difference between vision and functional evaluation?
Functional evals do no assess vision, but parts of visual pathway needs to be intact
146
What reflex tests are involved in functional evaluations?
Pupillary light reflex (PLR), Dazzle reflex test, electroretinogram (ERG), visual evoked potential (VEP)
147
What is involved in the pupillary light reflex (PLR) test?
Bright light in front of the eye--> should cause pupillary constriction
- Afferent arm: CN II (Optic n.)
- Efferent arm: CN III (Oculomotor n.)
148
What is involved in the Dazzle reflex test?
Bright light in front of the eye--> eyelid closure
Afferent arm: CN II (Optic n.)
Efferent arm: CN VII (Facial n.)
149
What is an electroretinogram (ERG)?
Recording of the electrical activity of the retina after a bright light flash
150
What is a visual evoked potential (VEP)?
Recording of the electrical activity of the occipital cortex after a bright light flash
151
What aspects are involved/assessed of the autonomic nervous system?
```
Pupil size
PLRs
Lacrimation
Eye position
Eyelid position
Third eyelid position
```
152
What is miosis and what branch of the ANS is it controlled by?
Constriction of the pupil; parasympathetic
153
What is mydriasis and what branch of the ANS is it controlled by?
Enlargement of pupil/dilation; sympathetic
154
What controls pupil size?
Balance between Parasympathetic and
| Sympathetic innervations of the iris
155
What is anisocoria?
Unequal pupil size
156
Properties of testing PLRs
```
Subcortical response
-Does not test vision
-In a dimly lit room
-Using a strong focal light source
-Afferent arm: retina, CN II
-Efferent arm: parasympathetic fibers along CN III
-Direct and consensual responses (constriction of the pupil)
-Nasal and temporal retinal fields
-->PLRs (and vision tests) help
to localize a lesion
```
157
What is a direct PLR response?
The PLR of the pupil receiving the beam of light
158
What are the parasympathetic pathways of the ANS?
```
Afferent Arm:
1-Photoreceptors
2- Optic n. (CN II),
O.chiasm (50-90% fibers decussate),
Optic tract
3- Pretectal nucleus (20% fibers leave)
Efferent Arm:
1- Pre ganglionic fibers CN III parasymp.,
Nucleus (80% fibers cross back)
-Parasymp. fibers along CN III
-Ciliary ganglion
2- Short ciliary nerve
-Iris sphincter muscle
```
159
What are the sympathetic pathways of the ANS?
Smooth orbital muscles, upper eyelid, dilator pupillae, third eyelid, lower eyelid
160
Two causes of pupil size change
1. Drug induced
- Mydriatic (atropine, phenylephrine)
- Miotics (pilocarpine, timolol, latanaprost)
2. Due to disease
161
Vision/PLR Rules of Thumb
- Visual with normal PLRs: A-OK
- Visual with absent PLRs: Efferent problem (CN 3
or iris sphincter) or mechanical or pharmacological interference
- Blind with normal PLRs: Something obscuring
vision (cataract) or cortical disease
- Blind with absent PLRs: Retina, Optic nerve
162
What are the ANS components of the neurology of lacrimation?
Afferent arm: CN V (ophthalmic/trigeminal n.)
| Efferent arm : parasympathetic fibers accompany peripheral branches of CN VII (Facial n.)
163
What test is used to determine if an animal is adequately producing tears?
Shirmer Tear Test (STT)
-Filter paper hooked over the middle of the
lower lid, 1 minute
-Assessment of the basal and reflex tear
production. Normal range in dogs: 15-25 mm/min
164
What are the sympathetic pathways of the ANS involved in lacrimation?
-1st order neurons
Diencephalic autonomic centers -->T1- T3 spinal segments
-2nd order neurons (preganglionic)
Leave spinal cord by T1- T3 roots
-->join vago-sympathetic trunk and cranial cervical ganglion
-3rd order neurons (postganglionic)
Fibers join the trigeminal nerve (CN V), through the middle ear, the ophthalmic n., the long ciliary n., iris dilator m., Muller m., 3rd eyelid
165
What do the sympathetic nerves of the lacrimal system innervate?
-Pupillary dilator muscle and smooth muscle in orbit and in upper, lower, and third eyelids
166
What are the sympathetic actions in the lacrimal system?
-Slight pupillary dilation, eyeball protrusion, widen palpebral fissure, third eyelid retraction
167
What is Horner's syndrome and what are its symptoms?
```
= sympathetic nerve paralysis (or denervation)
Symptoms:
- Miosis
-Protrusion of the 3rd eyelid
- Ptosis
- Enophthalmos
-(Sweating)
```
168
Etiology of Horner's Syndrome
Head or neck trauma, mediastinal disease, brachial plexus injury, orbit/middle ear
169
What two things are controlled by the oculomotor system?
Eye position and movement
170
What cranial nerves are involved in the oculomotor system?
CN III (Oculomotor n.)
-Dorsal (1), ventral (3), medial (2) rectus muscles
Inferior oblique muscle (6)
-CN IV (Trochlear n.)- Superior oblique muscle (5) – SO
-CN VI (Abducens n.)
-Lateral rectus muscle (ns) – LR 6
Retractor bulbi muscles (4)
171
What is strabismus?
Lack of parallelism of the visual axes of other eyes (due to oculomotor lesions)
172
What are the actions/innervations the oculomotor system?
Rectus mm.
- Dorsal globe- CN III- Elevates
- Ventral globe- CN III - Depresses
- Medial- CN III - Turns globe nasally
- Lateral- CN IV - Turns globe temporally
Retractor bulbi- CN VI- Retracts globe
Oblique mm.
- Dorsal- CN IV- Intorts globe
- Ventral- CN III- Extorts globe
173
What is nystagmus?
Rhythmical oscillation of the eyeballs
174
What is physiologic nystagmus?
```
To keep the visual target steady
during head movements
- Doll’s head reflex (vestibulo-ocular
reflex VOR)
-Afferent arm: CN VIII (vestibulo-
cochlear n.)
-Efferent arm: CN III, CN IV, CN VI
```
175
What is pathologic nystagmus?
-Vestibular disease (central or
peripheral)
-Lesion of CN VIII
176
What nerves are in charge of eyelid motor innervation?
Oculomotor nerve (CIII)
- Levator palpebrae superioris m. -elevates
the upper eyelid
Facial nerve (CN VII) (Auriculopalpebral branch)
- Orbicularis oculi m. -->eyelid closure
Sympathetic innervation (Associated with CN III)
- Muller m. --> elevates
177
Arms of the Palpebral reflex
Afferent arm: CN V
| Efferent arm: CN VII
178
Components of the trigeminal somatic sensory system
2 main branches of CN V
1. Ophthalmic nerve (CN V)
-Supraorbital n. (aka frontal n.) --> upper eyelid, forehead
-Nasociliary n. (infratrochlear n.) --> medial canthus, 3rd eyelid
-Long & short ciliary nn. --> ciliary body, cornea and iris
2. Maxillary nerve (CN V)--> Lateral canthus and lacrimal
gland, lower eyelid
179
What is the corneal blink reflex and how is it tested?
-Stimulation of the cornea --> closure of the lids,
retraction of the globe
-Afferent arm: CN V (Ophthalmic nerve)
-Efferent arm : CN VII (Facial nerve, Auriculo- palpebral branch) and CN VI (Abducens n.)
180
What are two types of regional nerve blocks done in horses?
- Akinesia: motor nerve block (CN VII)
| - Sensory Analgesia: sensory nerve block (CN V)
