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Ophthalmology > Ocular Anatomy > Flashcards

Ocular Anatomy Flashcards

1
Q

Fibrous tunic

A

Consists of cornea, limbus, sclera

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2
Q

Functions of the Cornea

A

Protection of interior structures, clarity of vision, and refraction of light coming into eye

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3
Q

Parts of the Cornea

A

Outermost epithelium
Stroma
Descemet’s membrane
Innermost endothelium

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4
Q

Corneal epithelium properties

A
  • Multilayered: superficial cells, wing cells, basal cells

- Great regenerative capacity

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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)
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6
Q

Corneal endothelium properties

A
  • Monolayer of hexagonal cells
  • Low regenerative capacity
  • Acts as metabolic “pump” to maintain equilibrium of corneal fluid
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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

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8
Q

Descemet’s Membrane properties

A
  • Basement membrane of corneal epithelium
  • Thickens with age
  • Made up of various collagen types
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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)
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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

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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

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12
Q

Superficial corneal ulcer

A

When only corneal epithelium is missing; most painful due to nerve exposure

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13
Q

Deep corneal ulcer

A

Epithelium and stroma missing; remainder of cornea is extremely fragile

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14
Q

Iris prolapse

A

All layers of cornea are missing/ulcerated

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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
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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
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17
Q

Layers of Sclera

A

Lamina fusca- innermost margin
Sclera proper- majority of tissue
Episclera- loose exterior CT

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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

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19
Q

Adnexa

A

Supporting structures of the eye; orbit, eyelids, conjunctiva, third eyelid, nasolacrimal system

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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
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21
Q

Orbital fascia

A

Periorbita (periosteum)
Tenon’s capsule (fascia that covers globe itself)
Fascial sheaths of extraocular muscles (EOM)

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22
Q

Extraocular Muscles

A

Rectus muscles: lateral, medial, dorsal, ventral
Oblique muscles: superior (dorsal) and ventral (inferior)
Retractor bulb is: pulls eye back

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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
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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
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25
Q

Eyelid musculature and their innervations

A

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

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26
Q

Palpebral fissure

A

Juncture where upper and lower lids meet

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27
Q

Canthus

A

Juncture where both medial parts of eyelids meet (medial canthus) or where both lateral parts meet (lateral canthus)

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28
Q

Meibomian (tarsal) glands

A
  • Contribute portion of tear fluid
  • Line eyelid margin
  • Compound acinar; holocrine sebum-producing
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29
Q

Main concern with eyelid trauma

A

Globe exposure

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30
Q

Properities of Eyelashes (cilia)

A
  • 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
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31
Q

Distichiasis

A

Corneal irritation associated with eyelash insult

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32
Q

Spectacle

A

Fused, transparent eyelids that are shed concurrent with skin and found on snakes

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33
Q

Properties of Conjunctiva

A
  • Mucosal lining assoc. with eye and eyelids
  • Stratified to pseudostratified columnar epithelium + goblet cells on top of loose CT
  • Richly vascular
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34
Q

3 regions of the conjunctiva

A

Palpebral (exterior)
Fornix (reflection point)
Bulbar (interior)

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35
Q

Functions of the conjunctiva

A
  • Produces mucin component of tear film
  • Immune surveillance
  • CALT (conjunctiva-associated lymphoid tissue)
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36
Q

What is conjunctivitis?

A

Inflammation of the conjunctiva; non-specific clinical findings

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37
Q

Properties of the third eyelid (nictitating membrane)

A
  • Semilunar fold of conjunctiva surrounding a T-shaped cartilaginous support
  • Has a gland at base of the cartilage
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38
Q

Functions of the third eyelid

A
  • Tear production (aqueous portion) and distribution

- Protect globe

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39
Q

What is cherry eye?

A
  • 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)
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40
Q

Nasolacrimal System Secretory Components

A
  • Meibomian glands and conjunctival goblet cells

- Orbital lacrimal glands and third eyelid glands

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41
Q

Nasolacrimal System Drainage Components

A
  • Puncta at medial canthus
  • Lacrimal sac and duct
  • Nasal puncta
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42
Q

Properties of Lacrimal glands

A

Tubuloalveolar glands, serous secretions, orbital lacrimal gland, nictitans gland

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43
Q

Functions of tears

A
  • Cleanse and lubricate ocular surface
  • Provide nutrition and O2
  • Antimicrobial defense
  • Maintains optically uniform surface
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44
Q

Makeup of Tears

A

Aqueous component- Lacrimal glands
Lipid component- meibomian glands
Mucin component- conjunctival goblet cells

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45
Q

What is keratoconjunctiva sicca (chronic dry eye)?

A

-Quantitative deficiency of aqueous tears, resulting in significant ocular irritation, conjunctivitis/inflammation, and compensatory mucoid discharge

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46
Q

What is epiphora?

A

Increased tear production (causes pain/irritation) and decreased tear drainage (could be due to NL obstruction)

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47
Q

3 structures of the vascular tunic (uvea)

A

Iris, ciliary body, choroid

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48
Q

Functions of the uvea

A
  • Nourish interior (O2 and glucose)
  • Productions and outflow of AqH
  • Immune responses
  • Lens accomodation
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49
Q

Properties of the Iris

A
  • Anterior portion of the uvea that forms diaphragm in front of lens
  • Central aperature = pupil
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50
Q

3 zones of iris

A

Pupillary zone, ciliary zone, collarette (in between)

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51
Q

Functions of the iris

A

=controls amount of light entering eye (pupil)

-enhances visual resolution

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52
Q

What is a unique feature of the iris?

A

It is not covered entirely by epithelium

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53
Q

What is the most common iris color?

A

Some shade of brown, but can vary from brown to blue

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54
Q

How does iridal pigment mature in non-mammals?

A

Blue color comes with maturation of pigments

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55
Q

What does iris color change typically indicate?

A

Disease (in most domestic species) -neoplasia or inflammation

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56
Q

Pupil shape variety

A

Vertical slit = cats, reptiles, amphibians
Round = carnivores/predators
Horizontal ellipse- Herbivores

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57
Q

What is the corpora nigra (granula iridica)?

A

Hypertrophy of posterior uveal pigmentation that acts as a shade and to dissuade scatter and improve resolution

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58
Q

Difference between pupillary size control in mammals and non-mammals?

A

Mammals cannot voluntary control pupil size (under smooth muscle control); non-mammals have some skeletal muscle control

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59
Q

What causes persistent pupillary membranes to occur?

A

When pupillary membrane, of which the center regresses upon forming the pupil remains and leads to opacities

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60
Q

Functions of the ciliary body

A

Blood aqueous barrier, produces AqH, involved in AqH drainage, generates intraocular pressure, and serves as anchor for fibers that suspend the lens

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61
Q

Parts of the ciliary body

A 
Pars plicata (ciliary processes)
Pars plana (flattened posterior zone)
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62
Q

Functions of aqueous humor

A

Fills anterior and posterior chambers, supplies nutrition and is a waste sink to lens and cornea, production and outflow maintains IOP, light refraction

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63
Q

How is the aqueous humor produced?

A

Actively produced by selective transport by carbonic anhydrase and Na+K+ATPase; also passive diffusion and ultrafiltration of blood plasma

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64
Q

How does aqueous humor outflow work?

A

AqH returns to systemic vascular system, primarily via conventional pathway, but alternative uveoscleral pathway is present

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65
Q

What causes glaucoma?

A

A collapsed idriocorneal angle, b/c normal aqueous drainage cannot occur and fluid buildup leads to loss of resolution

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66
Q

Functions of ciliary musculature

A

Facilitates AqH outflow, contributes to lentricular accomodation, and spasms when there is intraocular inflammation

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67
Q

Portions of the uvea

A

Anterior- iris
Middle- ciliary body
Posterior- Choroid

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68
Q

Properties of Choroid

A

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

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69
Q

Layers of the Choroid

A 
Suprachoroidea
Large vessel layer
Medium-sized vessel layer
Tapetum
Choriocapillaris
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70
Q

Properties of tapetum

A

-Reflective structure located in dorsal choroid that allows retina “second chance” to interact with photons

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71
Q

Species-specific differences in the tapetum structure

A

Carnivores- cellular; iridocytes form rodlets w/ high levels of zinc + riboflavin
Herbivores- fibrous, acellular, highly organized collagen

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72
Q

Purpose of blood ocular barriers

A

Maintains ocular privilege, limits damage to ocular structures by systemic conditions

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73
Q

Important uvea facts

A

-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
Q

What shape is the lens?

A

Biconvex (generally)

75
Q

What structures support the crystalline lens?

A

Zonules attached to ciliary body

76
Q

What embryological structure does the lens develop from?

A

Presumptive lens ectoderm–>Lens placode–>Lens vesicle

77
Q

What are suture lines?

A

Chunks of fibers that have junctures located on the lens; mostly Y-shaped; opacities denote cataract/clinical condition

78
Q

What is the unique cellular makeup of the lens nucleus?

A

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
Q

What is nuclear sclerosis?

A

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
Q

What assists with lenticular transparency?

A

Highly organized fibers
Maintained in avascular (anaerobic) environment
Fibers are kept dehydrated
Large % of soluble proteins (crystallins)

81
Q

What is a cataract?

A

An opacity of the lens

82
Q

What is phacoemulsification?

A

Placement of a probe into the lens that uses ultrasonic waves to break up proteins causing opacity in the lens

83
Q

What are zonules?

A

Ligaments that suspend the lens from the equator to the ciliary body musculature; can become dysplastic with age/inflammation

84
Q

What is the structure seen when a lens is dislocated?

A

Aphacic crescent

85
Q

Properties of the vitreous humor?

A

Largest structure of the eye that is a hydrogel of hyaluronic acid and 98-99% water

86
Q

3 vitreous components

A 
Primary = hyaloid vascular system 
Secondary= contains Mittendorf's dot
Tertiary = lens fibers connecting to CB
87
Q

What is a clinical condition involving the vitreous?

A

Persistent hyperplastic primary vitreous

88
Q

What is the ocular fundus?

A

The interior surface of the eyeball that is visible through the ophthalmoscope.

89
Q

What do you typically look for during a fundus examination?

A

Vessels coming out of the optic disc; attenuation, clotting, irregularities

90
Q

Function of the retina

A

Transform light energy (photons) into an electrical signal (transduction)

91
Q

Function of the lens

A

Accommodation or changing path of light entering the eye

92
Q

Properties of the retina

A
  • Multilayered
  • Most metabolically active tissue in body (per wt/unit)
  • High O2 consumption
93
Q

How many layers of cells are involved in the sensory neural circuit of the retina?

A

10

94
Q

What is the path of light traveling through the eye?

A

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
Q

What is the purpose of the tapetum?

A

It’s a reflective structure that allows photoreceptors a “second chance” at stimulation; improves night vision

96
Q

Order of retinal neural tissues from exterior to interior

A 
Tapetum (part of choroid)
Retinal pigmented epithelium
Photoreceptors
Outer nuclear layer
Inner nuclear layer
Ganglion cell layer
Vitreal chambers
97
Q

What are the two photoreceptors found in the retina?

A

Rods and cones

98
Q

What are the differences between rods and cones?

A

Cones function in color vision, detail, and acuity

Rods function in low-light vision (low acuity/no color)

99
Q

What occurs during the process of phototransduction?

A

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
Q

What are the main molecules/chemicals involved in phototransduction?

A

Rhodopsin (–>retinal + opsin)
Transducin
cGMP
Na+/K- ion channels

101
Q

What forms the optic nerve (CN II)?

A

Axons of the retinal ganglion cells coalesce at the lamina cribrosa and posterior to the globe

102
Q

What types of cells support the optic nerve (CN II)?

A

Astrocytes and oligodendrocytes

103
Q

What is the only part of the CNS that is directly visible to the examiner?

A

The optic nerve (through the optic disc)

104
Q

What is the pathway of a nerve impulse traveling from the medial side of the left eye?

A

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
Q

What is decussation?

A

The percentage of crossing of optic nerve fibers at the optic chiasm (differs in species)

106
Q

What percentage of ocular blood flow do the retina and choroid receive, respectively?

A

Retina- 4%

Choroid- 85%

107
Q

Which organ receives more blood flow, the brain or the retina/choroid?

A

Retina and choroid (10 x more)

108
Q

What are the four types of retinal vasculature patterns?

A

Holangiotic
Paurangiotic
Merangiotic
Anangiotic

109
Q

What is holangiotic vasculature patterning and what types of animals is it found in?

A

-Prominent vascular supply both dorsally and ventrally; e.g. dogs, cats, people

110
Q

What is the macula?

A

Region of the retina containing a higher percentage of photoreceptors (typically darker circular region visualized adjacent to optic disc)

111
Q

What is paurangiotic vasculature patterning and what types of animals is it found in?

A

-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
Q

What is merangiotic vasculature patterning and what types of animals is it found in?

A

Small part of retina provided with obvious blood vessels along horizontal plane; e.g. rabbits

113
Q

What is anangiotic vasculature patterning and what types of animals is it found in?

A

No visible vessels; e.g. birds, reptiles

114
Q

What is pecten?

A

A pigmented, vascular structure found in bird retinas that acts as an extraretinal blood supply

115
Q

What are some adaptations of the avascular (anangiotic) retina?

A

Thin, short outer segments, glycogen storage (Muller cells), absence of tapetum and retinal taper, or extraretinal blood supply (pecten, conus papillarus, choroidal papillae)

116
Q

What causes retinal detachment and where does it typically occur?

A

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
Q

What determines an animal’s visual field?

A

Whether it’s predator or prey, position of orbit/globe relative to midline, and pupil size and shape

118
Q

Who typically has a wider visual field, the predator or the prey?

A

Prey

119
Q

What is acuity?

A

The exactness or sharpness of an image

120
Q

What properties/structures enhance vision in dim light?

A

Large relative proportion of rods (scotopic vision), tapetum, and pupil size and shape (smaller = better)

121
Q

True or False: Animals can only see in black and white

A

False; most mammals are dichromates (2 types of cones), they cannot perceive red, and colors are muted

122
Q

What wavelengths can dogs/cats see at?

A 
429-432 nm (Blue)
555 nm (Yellow-green)
123
Q

What wavelengths can horses see at?

A 
428 nm (Blue)
539 nm (Green)
124
Q

What aspects of vision are animals (dogs) better at than humans?

A

Better flicker detection (motion), superior night (dim light) vision, larger visual fields (peripherals)

125
Q

What aspects of vision are animals (dogs) worse at than humans?

A

Reduced color perception and acuity (13-16% that of humans)

126
Q

Which neurologic systems are involved in normal vision and ocular health?

A

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
Q

Which cranial nerves are involved in vision/ocular health?

A

II-VIII; Optic (II), Oculomotor (III), Trochlear (IV), Trigeminal (V), Abducens (VI), Facial (VII), Vestibulocochlear (VIII)

128
Q

Functions of CN II- Optic n.

A

Sensory (carries visual info) from retina to cortex

129
Q

Functions of CN III- Oculomotor n.

A

Motor to several extraocular mm. and levator palpebrae superioris m.; parasympathetic hitchhikers

130
Q

Functions of CN IV- Trochlear n.

A

Motor to superior oblique m.

131
Q

Functions of CN V- Trigeminal n.

A

Sensory from eyelids, cornea, lacrimal gland

132
Q

Functions of CN VI- Abducens n.

A

Motor to lateral rectus m. and retractor bulbi m.

133
Q

Functions of CN VII- Facial n.

A

Motor to eyelids and other facial mm.

134
Q

Functions of CN VIII- Vestibulocochlear n.

A

Sensory for vestibular component of ocular movements

135
Q

What are the two parts of a reflex response?

A

Afferent (sensory) and efferent (motor)

136
Q

What processes does the visual sensory system consist of?

A

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
Q

Pathway of the visual sensory system

A

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
Q

Where can electrical signals go?

A

To the visual cortex (visual pathways)- 80% n. fibers

To the midbrain (pupillary light reflexes aka PLRs)- 20%

139
Q

3 structures where opacities can obscure light so it doesn’t reach retina appropriately

A

Cornea, uvea (uveitis), lens

140
Q

What are the three subcortical effects?

A
  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
Q

Potential problems with vision

A

Opacity obscuring light to retina, retinal dysfunction (lack of transduction), optic nerve dysfunction (lack of transmission), cortical problems (info processing/recognizing issue)

142
Q

What goes on physiologically in glaucoma?

A

Pressure inside eye causes damage to nerve fibers going through lamina cribrosa, causing them to decompose, and pushes lamina up

143
Q

Parts of a vision test

A

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
Q

What is the menace response?

A

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
Q

What is the difference between vision and functional evaluation?

A

Functional evals do no assess vision, but parts of visual pathway needs to be intact

146
Q

What reflex tests are involved in functional evaluations?

A

Pupillary light reflex (PLR), Dazzle reflex test, electroretinogram (ERG), visual evoked potential (VEP)

147
Q

What is involved in the pupillary light reflex (PLR) test?

A

Bright light in front of the eye–> should cause pupillary constriction

  • Afferent arm: CN II (Optic n.)
  • Efferent arm: CN III (Oculomotor n.)
148
Q

What is involved in the Dazzle reflex test?

A

Bright light in front of the eye–> eyelid closure
Afferent arm: CN II (Optic n.)
Efferent arm: CN VII (Facial n.)

149
Q

What is an electroretinogram (ERG)?

A

Recording of the electrical activity of the retina after a bright light flash

150
Q

What is a visual evoked potential (VEP)?

A

Recording of the electrical activity of the occipital cortex after a bright light flash

151
Q

What aspects are involved/assessed of the autonomic nervous system?

A 
Pupil size
PLRs
Lacrimation
Eye position
Eyelid position
Third eyelid position
152
Q

What is miosis and what branch of the ANS is it controlled by?

A

Constriction of the pupil; parasympathetic

153
Q

What is mydriasis and what branch of the ANS is it controlled by?

A

Enlargement of pupil/dilation; sympathetic

154
Q

What controls pupil size?

A

Balance between Parasympathetic and

Sympathetic innervations of the iris

155
Q

What is anisocoria?

A

Unequal pupil size

156
Q

Properties of testing PLRs

A 
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
Q

What is a direct PLR response?

A

The PLR of the pupil receiving the beam of light

158
Q

What are the parasympathetic pathways of the ANS?

A 
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
Q

What are the sympathetic pathways of the ANS?

A

Smooth orbital muscles, upper eyelid, dilator pupillae, third eyelid, lower eyelid

160
Q

Two causes of pupil size change

A
  1. Drug induced
    - Mydriatic (atropine, phenylephrine)
    - Miotics (pilocarpine, timolol, latanaprost)
  2. Due to disease
161
Q

Vision/PLR Rules of Thumb

A
  • 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
Q

What are the ANS components of the neurology of lacrimation?

A

Afferent arm: CN V (ophthalmic/trigeminal n.)

Efferent arm : parasympathetic fibers accompany peripheral branches of CN VII (Facial n.)

163
Q

What test is used to determine if an animal is adequately producing tears?

A

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
Q

What are the sympathetic pathways of the ANS involved in lacrimation?

A

-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
Q

What do the sympathetic nerves of the lacrimal system innervate?

A

-Pupillary dilator muscle and smooth muscle in orbit and in upper, lower, and third eyelids

166
Q

What are the sympathetic actions in the lacrimal system?

A

-Slight pupillary dilation, eyeball protrusion, widen palpebral fissure, third eyelid retraction

167
Q

What is Horner’s syndrome and what are its symptoms?

A 
= sympathetic nerve paralysis (or denervation)
Symptoms: 
- Miosis
-Protrusion of the 3rd eyelid
- Ptosis
- Enophthalmos
-(Sweating)
168
Q

Etiology of Horner’s Syndrome

A

Head or neck trauma, mediastinal disease, brachial plexus injury, orbit/middle ear

169
Q

What two things are controlled by the oculomotor system?

A

Eye position and movement

170
Q

What cranial nerves are involved in the oculomotor system?

A

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
Q

What is strabismus?

A

Lack of parallelism of the visual axes of other eyes (due to oculomotor lesions)

172
Q

What are the actions/innervations the oculomotor system?

A

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
Q

What is nystagmus?

A

Rhythmical oscillation of the eyeballs

174
Q

What is physiologic nystagmus?

A 
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
Q

What is pathologic nystagmus?

A

-Vestibular disease (central or
peripheral)
-Lesion of CN VIII

176
Q

What nerves are in charge of eyelid motor innervation?

A

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
Q

Arms of the Palpebral reflex

A

Afferent arm: CN V

Efferent arm: CN VII

178
Q

Components of the trigeminal somatic sensory system

A

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
Q

What is the corneal blink reflex and how is it tested?

A

-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
Q

What are two types of regional nerve blocks done in horses?

A
  • Akinesia: motor nerve block (CN VII)

- Sensory Analgesia: sensory nerve block (CN V)

Ophthalmology (1 decks)

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