Anatomy of the Eye Flashcards
(151 cards)
1
Q
What are the 2 main components of the eye?
A
Eyeball and adnexa (accessory structures)
2
Q
What are the 6 accessory structures of the eye?
A
- Eyelids
- Conjunctiva
- Lacrimal apparatus
- Orbital soft tissues
- Vessels and nerves
- Extrinsic muscles of the eye
3
Q
What is the collective function of the eye adnexa?
A
Protection of the eyeball
4
Q
What is the specific function of the lacrimal apparatus?
A
Helps to moisten the eye surface; barrier against infection
5
Q
What is the orbit?
A
A conical cavity containing the eyeball and ocular adnexa
6
Q
What 5 structures form the orbital margin?
4 bones and ligament
A
- fronta bone
- lacrimal bone
- maxilla bone
- zygomatic bone
- orbital ligament laterally (in dogs)
7
Q
The medial wall of the orbit is formed by what 3 bones?
A
- frontal
- presphenoid
- lacrimal
8
Q
The ventral wall of the orbit includes what 2 structures?
A
- Zygomatic salivary gland
- the pterygoid muscles
9
Q
The dorsal and lateral walls of the orbit are formed primarily by what muscle(s)?
A
largely the temporalis muscle
10
Q
How many eyelids are there?
A
3: upper, lower, and 3rd
11
Q
What is lagophthalmos?
A
Inability to completely close the eyelid
12
Q
What is entropion vs ectropion?
A
- Entropion: inward folding of the eyelid
- Ectropion: outward folding of the eyelid
13
Q
What is the official name for the 3rd eyelid?
A
Nictitating membrane
.
14
Q
Describe the 3rd eyelid.
A
- Thin fold of MM that is located at about the ventromedial aspect of the eyelid
- Situated between the eyeball and palpebra
15
Q
What are the 3 functions of the 3rd eyelid?
A
- Provides protection to the eye
- aids in oxygen supply to the eye
- aids in tear production via the 3rd eyelid gland
16
Q
What are the species differences pertaining to the 3rd eyelid?
A
- Present in dogs, cats, horses, and camels
- Less developed in pigs
- Absent or rudimentary in ruminants and rodents
17
Q
Why would you temporarily suture the eye closed?
A
Provides protection and prevents drying during or after surgery
18
Q
Why does the 3rd eyelid come up during surgery?
A
The retractor bulbi muscle is relaxed and muscle tone that would normally keep it retracted is lost
19
Q
What is Haw’s syndrome?
A
Collapse of the 3rd eyelid in which it protrudes over the eyeball; usually not serious and sometimes resolves on its own
20
Q
How is Haw’s syndrome treated?
A
Mostly resolves on its own, but can also prescribe eyedrops
21
Q
Describe the 3rd eyelid gland.
A
Seromucous gland at the base of the 3rd eyelid with a T-shaped cartilage that keeps it in place
22
Q
The 3rd eyelid gland produces what % of the tears of the eyeball?
A
30-50%
23
Q
What is cherry eye?
A
Prolapse of the 3rd eyelid usually seen in dogs under the age of 2
24
Q
How is cherry eye treated?
A
Can be surgically removed, but treatment with antibiotics or tucking it back in preferred first in order to preserve the gland
25
What can occur if cherry eye is not treated?
- Can cause dry eye and stop tear production if not treated
- Treatment within 3 months can help prevent it from occurring on the other side
26
Describe the location of the levator palpebrae superioris.
Extends over the dorsal rectus muscle
27
What is the ORIGIN of the levator palpebrae superioris?
Orbit
28
What is the INSERTION of the levator palpebrae superioris muscle?
Upper eyelid
29
What is the ACTION of the levator palpebrae superioris?
Elevates the upper eyelid
| Opens the eye?
30
What is the INNERVATION of the levator palpebrae superioris?
Oculomotor nerve
31
What are the meibomian glands?
Specialized glands that produce oily substances that resist evaporation of the tears
32
Where are meibomian glands located?
Within the tarsal plate which is a fibrous plate that supports the margin of the eyelid
33
What is another name for meibomian glands?
Tarsal glands
34
What is the function of the conjunctiva?
Mucous membrane that lines the eyeball and eyelid and acts as barriers to infection and foreign particles
| 2 parts: palpebral conjuctiva, bulbar conjuctiva
35
What is the name of the conjunctiva that lines the eyeball?
Bulbar conjunctiva
36
What is the name of the conjunctiva that lines the eyelid?
Palpebral conjunctiva
37
How are the palpebral and bulbar conjunctiva related?
They are continuous and fold over one another
38
How do you administer an optic nerve block?
- Insert the needle below the lower margin of the eyeball; can bend the needle so that it assumes the natural curvature of the eyeball
- 4 separate injections at 3, 6, 9, and 12 o'clock
39
How can you desensitize all of the nerves of the eyeball at once in large animals?
Insert the needle into the foramen orbitorotundum at the intersection of the zygomatic process of the frontal bone and the zygomatic arch
40
What is another name for the orbitorotundum nerve block?
Peterson's nerve block
41
What is conjunctivitis?
Inflammation of the conjunctiva characterized by a pinkish coloration of the eye
42
Describe the difference between a canthus and a commissure.
- Canthus: point at which the upper and lower eyelids meet; medial and lateral
- Commissure: broader area where the upper and lower eyelid meet; medial and lateral
43
What are the 5 components of the lacrimal apparatus?
- Lacrimal gland
- Gland of the 3rd eyelid
- Lacrimal canaliculi
- Lacrimal sac
- Nasolacrimal duct
44
What are the lacrimal gland and the gland of the 3rd eyelid responsible for and what are they innervated by?
Responsible for the production of tears and they are innervated by branches of the facial nerve
45
Where is the lacrimal gland located?
Deep to the orbital ligament and periorbita on the lateral side of the eyeball
| anterior & dorsolateral to the eyeball
46
How do tears travel that are produced by the lacrimal gland?
They are transported via the lacrimal ducts to the conjunctival sac
47
What is the conjunctival sac?
Space between the eyelid and eyeball
48
What is responsible for distribution of tears from the conjunctival sac via blinking?
Eyelids
49
Where does drainage of the eye begin?
Lacrimal puncta
50
What does the lacrimal puncta open into?
Lacrimal canaliculi
51
Describe the lacrimal canaliculi in dogs vs horses.
Relatively small in horses; relatively large and easily cannulated in dogs
52
Describe the flow of drainage of the eye.
Lacrimal puncta -> lacrimal canaliculi -> merge into lacrimal sac -> nasolacrimal duct
53
What occupies the wall of the nasolacrimal duct and what is its function?
Lymphoreticular tissue which is responsible for production of lymphocytes
54
What 2 bones does the nasolacrimal duct pass through?
Maxilla and lacrimal bone
55
What is the nasal opening to the nasolacrimal duct used for in horses?
Used to flush the tear ducts in horses since their lacrimal puncta and canaliculi are smaller
56
What is epiphora?
Excessive tearing of the eyes
57
What does a blocked tear duct bring about?
Discomfort and dried material in the eye region that attracts flies
58
What 5 things can cause a blocked tear duct?
* accumulation of excess debris
* tumor
* congenital
* trauma
* dental abscess
59
What is blepharitis?
Inflammation of the eyelid
60
What is a Schirmer tear test used for?
To check the volume of tear production in the eye
61
What is the lacrimal caruncle?
- Triangular shaped area at the medial canthus only
- Small and pinkish and contains both oil and sweat glands
62
What are the 3 structures you can expect to find near the medial canthus of the eye?
* Lacrimal caruncle
* lacrimal duct
* 3rd eyelid
63
What 5 structures make up the lateral margin of the orbit?
* Zygomatic bone
* lacrimal bone
* maxilla
* orbital ligament
* frontal process of the zygomatic bone
64
What 3 bones make the medial margin of the orbit?
* lacrimal bone
* frontal bone
* presphenoid
65
What can you find behind the eyeball?
Fat and tissue that helps protect the eye
66
What is the periorbita?
* Cone-shaped structure of CT and smooth muscle
* contains the extraocular muscles, blood vessels, nerves, fat, etc.
* also called the periosteum of the orbit
67
What is the action of the dorsal and ventral oblique muscles of the eye?
Move the eyeball medially in an oblique course
68
What are the innervations of the dorsal and ventral oblique muscles of the eye?
Dorsal: trochlear n.
Ventral: oculomotor n.
69
What is the action of each of the rectus muscles of the eye?
Movement in the direction of the name of the muscle;
i.e. dorsal rectus: upward movement of the eye, lateral rectus: lateral movement of the eye, etc.
70
What are the rectus muscles of the eye innervated by?
Lateral: abducens nerve
Medialis: oculomotor
Dorsal & ventral: oculomotor nerve
71
What is the insertion of the 4 rectus muscles?
Near the corneoscleral junction
| .
72
Where does the retractor bulbi muscle insert?
More towards the posterior end of the sclera
73
Describe the location of the retractor bulbi muscle.
- Covered by fat in between two rectus muscles
- Covers the optic nerve
74
What is the action of the retractor bulbi muscle?
Retracts the eyeball
75
All of the extrinsic muscles of the eye insert where?
On the sclera
76
Blood is supplied to the eye by what 2 arteries?
Internal and external ophthalmic arteries
77
The internal ophthalmic artery branches from what parent artery?
Internal carotid
78
How does the internal ophthalmic artery get to the eyeball?
Goes to the eyeball by coursing together with the optic nerve through the optic canal
79
The internal ophthalmic artery supplies what portion of the eye?
Internal structures such as the retina; very important for vision
80
The external ophthalmic artery branches from what parent artery?
The maxillary artery which branches from the external carotid artery
81
How does the external ophthalmic artery get to the eyeball?
Exits through the orbital fissure
82
The external ophthalmic artery supplies what portion of the eye?
External structures of the eye such as the palpebra, eyelids, conjunctiva, and extrinsic muscles
83
What are the features that distinguish between right and left eyeballs?
* Optic nerve: slightly towards the medial aspect of the eye
* Orbit looks more rounded on the medial side
84
What are the different tunics/layers of the eye?
- External layer (/outer layer/fibrous layer)
- Middle layer (uvea/vascular layer)
- Internal layer (retina/nervoud)
85
What are the 2 components of the external layer of the eye?
* Sclera
* Cornea
86
What are the 3 components of the middle layer of the eye?
* ciliary body
* iris
* choroid
87
What are the components of the inner layer of the eye?
Retina
88
Describe the sclera.
- White, dense, opaque
- Lots of CT
- Anterior portion covered by bulbar conjunctiva
- Posterior portion provides attachment for extraocular muscles
- Penetrated by nerves and blood vessels
89
What are the 3 functions of the sclera?
* Forms the framework of the eyeball
* protection
* helps maintain internal pressure of the fluid within the eye
90
Describe the cornea:
- Transparent
- Anterior portion of the eyeball
91
What is the function of the cornea?
Allows for passage of light to the retina and controls the amount of light that comes in via refraction
92
What are the 5 layers of the cornea from outside to inside?
Anterior epithelium → anterior limiting lamina → substantia propria → posterior limiting lamina → posterior epithelium
93
What is the procedure for enucleation in cats given that the orbit is deeper than in other species?
Take a needle and drain at least 1 mL of fluid from the eye first in order to give space to work around the extrinsic musculature
94
What is the name of the meeting point of the cornea and sclera?
Limbus
95
What is the significance of the limbus?
- Contains the pathways of aqueous humor outflow
- Site of surgical incision for corneal transplant, cataract, and glaucoma surgeries
96
What is the vertex?
The highest point of the cornea
97
What is the shape of the cornea in different species?
Dogs and cats: round
Ungulates: oval
98
What are 4 different pathologies commonly associated with the external layer of the eye?
- Corneal opacity: moon blindness
- Keratitis: inflammation of the cornea
- Corneal ulcer
- Equine recurrent uveitis
| .
99
The middle layer of the eye is composed mainly of what 2 things?
Vessels and smooth muscles
100
Describe the iris.
- Pigmented diaphragm that can be seen through the cornea- gives colored appearance
- Surrounds a central opening called the pupil
- Responsible for pupillary constriction and dilation via radial and circular muscles
101
The radial muscles of the iris are responsible for what?
Pupil dilation (sympathetic)
102
The circular muscles of the iris are responsible for what?
Pupil constriction (parasympathetic)
103
What is the iridocorneal angle?
Point of drainage of the aqueous humor
104
Describe the shape of the pupil in different species.
Cats, ruminants, horses: oval
Dogs: round
105
Describe the function of the coloration of the iris.
Due to melanin pigment and is able to absorb and control light
106
How is sight affected in the case of albinism?
Iris is non-melanated and so all of the light is allowed to pass: no protection present and creates problems with vision
107
Describe the choroid.
Thin, vascular, pigmented layer on the posterior part of the vascular tunic
108
What are the 4 layers of the choroid from outside to inside?
Suprachoroid → vascular layer (thickest) → choroidopapillary → basal lamina
109
What exists between the vascular layer and the choroidopapillary of the choroid?
The tapetum lucidum
110
What are the 2 components of the tapetum lucidum?
* Guanine
* crystalline rods that consist of zinc and cysteine
* which are highly refractive
111
What is the function of the tapetum lucidum?
Provides light-sensitive retinal cells with a 2nd opportunity for photon-receptor stimulation; enhances visual sensitivity at low light levels
112
What is the color of the tapetum lucidum in different species?
Yellow in cats
Green in dogs
Blue/green in horses/ruminants
113
What species does not have a tapetum lucidum?
Pigs
114
What is the thickest layer of the vascular tunic?
Ciliary body; between the choroid and the iris
115
What is the function of the ciliary body?
- Produces fluid of the eye (aqueous humor)
- Processes anchor zonular fibers; the suspensory ligaments for the lens
- Secondarily alter the shape of the lens through their attachment to zonular fibers
116
The crown of the ciliary body is made up of what?
Smooth muscles
117
What are the 3 layers of the retina neuron?
- Photoreceptors (outer)
- Bipolar neurons (middle)
- Ganglion neurons (inner)
118
The layers of the retina arise from what?
Diencephalon
119
What is the function of the retina?
Image formation
120
Describe the photoreceptor layer of the retina.
- Light sensitive layer
- Controls the amount of light that goes into the eye
- Made up of rods (beams of light) and cones (color and sharpness)
121
Describe the bipolar neurons of the retina.
- Interneurons
- Middle layer that receives impulses from the rods and cones and passes it to the neuronal ganglia
122
Describe the ganglion neurons of the retina.
Passes the impulse to the optic nerve to be sent to the brain
123
How do ruminants + horses see color?
Cannot differentiate red and blue
124
Which species has the best color differentiation?
Pigs
125
What is the optic disk?
- Blind spot: no image is formed
- No rods or cones
- Axons of the ganglia are leaving the retina of the eyeball as the optic nerve
126
What is the scotoma?
Point where the optic disk begins
127
Describe the shape of the lens.
Biconvex
128
What is the function of the lens?
Transmits and focuses light onto the retina
129
What are the boundaries of the lens?
- Bounded posteriorly by vitreous body
- Bounded anteriorly by aqueous humor
130
What is a cataract?
Condition in which the lens becomes clouded
131
How are cataracts corrected?
Phacoemulsification: Surgical correction involves removal of the lens and replacement with an artificial plastic lens
132
What are 4 causes of cataracts?
* Age
* diabetes
* long term use of steroids
* genetics
133
What are cataracts a result of?
A build up of crystallin proteins within the lens of the eye
134
What are the chambers of the eye?
- Anterior: between sclera and cornea
- Posterior: between iris and ciliary body/lens
- Vitreous: between lens and retina
135
Describe the anterior and posterior chambers of the eye.
- Contains aqueous humor produced by the ciliary body
- Helps maintain integrity of cornea and lens, which are avascular
136
Describe the vitreous chamber of the eye.
- Contains gel-like substance called the vitreous humor
- Makes up 80% of the volume of the eye
137
True or false: aqueous humor is constantly produced and replaced.
True
138
How is the aqueous humor of the eye recycled into circulation?
Via the scleral venous plexus at the iridocorneal junction
139
Does the vitreous humor regenerate?
No
140
Given that the vitreous humor does not replenish itself, what happens when there is a problem with it?
Problems require surgical removal and replacement with artificial material: vitrectomy
141
What is the clinical significance of the vitreous humor?
Can be used in place of blood post mortem to provide a true picture in terms of forensics, etc. if needed
142
What is glaucoma?
When the ciliary body produces aqueous humor but there is a blockage in the iridocorneal junction which leads to an increase in pressure of the anterior chamber
143
How is glaucoma treated?
Eyedrops or removal of excess fluid buildup via the limbus
144
What is asteroid hyalosis?
Build up of deposits called 'asteroid bodies' within the vitreous
145
What are the 3 methods of enucleation?
* Transpalpebral
* subconjunctival
* exenteration
146
When would you perform a transpalpebral enucleation?
Done when you suspect tumor or infection and want to prevent it from spreading
147
Describe how to perform a transpalpebral enucleation.
- Suture the eyelids first and make incisions at least one cm away from the suture line.
- Progress incision into the orbit in order to remove entire eyeball including muscles and conjunctiva.
- Suture the remaining skin closed over the socket after removal.
148
Why don't you want to apply traction or pull on the eyeball during enucleation?
You risk damaging the optic chiasm and subsequently the other eyeball; want to instead clamp and transect the nerve/blood vessels at the back of the eye and leave a stump.
149
When would you perform a subconjunctival enucleation?
In the case of trauma without infection; more recommended for cosmetic purposes to prevent the sunken in appearance post-op.
150
Describe the protocol for a subconjunctival enucleation.
- Incision begins at the corneoscleral junction/limbus and continuing caudally, removing a portion of the conjunctiva.
- Transect muscles from their insertion on the eyeball, but they remain attached on the orbit and are not removed.
- In this method, we preserve a portion of the conjunctiva and the extraocular muscles.
151
Which method of enucleation is considered to be less invasive?
Subconjunctival
