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172 Cards in this Set

  • Front
  • Back
What forms the orbital margin?
The frontal, lacrimal, maxillary, & zygomatic bones and the orbital ligament laterally
What is the medial wall of the orbit formed by?
Parts of the frontal, presphenoid, and lacrimal bones
What is the ventral wall of the orbit formed by?
Zygomatic salivary glands and the pterygoid muscles
What primarily forms the dorsal and lateral walls of the orbit?
Temporal muscle
What is the periorbita?
Cone-shaped sheath of CT that encloses the eyeball and its muscles, vessels, and nerves
Where does the periorbita contact the bone?
Medially at the periosteum of the orbit
What does the caudal apex of the periorbita attach to?
To the bony margin of the optic canal and the orbital fissure (here it continues with the dura intracranially)
What does the periorbita do rostrally?
It widens to blend with the periosteum of the face
Where is the lacrimal gland located?
On the medial side of the orbital ligament within the periorbita
Where does the lacrimal gland empty into?
Small ducts empty their secretion into the conjunctival sac at the dorsal fornix
Where is the levator palpebrae superioris muscle located?
It is a superficial muscle beginning at the apex of the orbit, extending over the dorsal rectus, and inserting as a flat tendon in the upper eyelid.
Which nerve innervates the levator palpebra superioris muscle?
Oculomotor nerve
What are the 7 extrinsic muscles of the eyeball?
2 obliquus muscles, 4 rectus muscles, and a retractor bulbi
Where do the extrinsic muscles insert into?
All insert on the sclera, near the equator of the eyeball
What are the 4 rectus muscles?
Dorsal rectus, medial rectus, ventral rectus, and lateral rectus
Where do the 4 rectus muscles originate?
They originate around the optic canal and orbital fissure
Which nerves innervate the rectus muscles?
Lateral rectus is innervated by abducent nerve. Dorsal, medial, and ventral rectus muscles are innervated by oculomotor nerve.
What is the function of the dorsal & ventral rectus muscles?
Rotate the eyeball around a horizontal axis thru the equator
What is the function of the medial and lateral rectus muscles?
Rotate the eyeball around a vertical axis thru the equator
Where is the retractor bulbi found?
It can be seen in the spaces b/w the rectus muscles. It consists of 4 fascicles that surround the optic nerve (a dorsal pair & a ventral pair)
What nerve innervates the retractor bulbi?
Abducent nerve
What are the 2 obliquus muscles?
Dorsal & ventral oblique muscles
Where is the dorsal oblique muscle found?
It ascends on the dorsomedial side of the extraocular muscles dorsal to the medial rectus
What does the dorsal oblique muscle's tendon pass through?
It forms a long tendon rostrally that passes thru a groove in the trochlea. The trochlea is a cartilaginous plaque attached at the level of the medial angle of the eye to the wall of the orbit
Where does the tendon of the dorsal oblique muscle attach?
It attaches to the sclera under the tendon of insertion of the dorsal rectus muscle
What nerve innervates the dorsal oblique muscle?
The trochlear nerve
Where does the ventral oblique muscle originate and where does it insert?
Arises from the rostral border of the palatine bone and inserts on the sclera at the insertion of the lateral rectus muscle
What is unique about the ventral oblique muscle when compared to the other extrinsic muscles?
It is the only extraocular muscle that does not arise from the apex of the orbit
What nerve innervates the ventral oblique muscle?
Oculomotor nerve
What is the dorsal & ventral oblique muscles' function?
They rotate the eyeball around a longitudinal axis thru the center of the eyeball
What does the third eyelid contain?
Third eyelid contains lymph nodules on its bulbar conjunctival surface and a superficial gland
What are the 3 layers of the eyeball wall?
Fibrous coat, vascular coat, and internal coat
What is the external fibrous coat composed of? And how much of it is composed by each?
Cornea & sclera. Cornea forms the anterior 1/4 of the fibrous coat. Sclera forms the posterior 3/4 of the fibrous coat.
What is the corneoscleral junction called?
Limbus
Characteristics of cornea?
Transparent and circular
Characteristics of sclera?
Dense and opaque, dull gray-white
What covers the sclera anteriorly?
Bulbar conjunctiva
What does the middle vascular coat (the uvea) consist of?
From posterior to anterior: the choroid, ciliary body, and iris
What is the iris made of?
Circular and radial smooth muscle
Where is the choroid located?
The choroid is the posterior portion of the vascular coat & is firmly attached to the sclera. It is pigmented and lines the internal surface of the sclera as far anterior as the ciliary body posterior to the lens.
What is the junction of the choroid and the ciliary body called? And what does it look like?
Ora serrata, seen as an undulating line in the overlying retina
What is the posterior or deep portion of the eyeball called?
Fundus
What is the light-colored, reflective area in the dorsal part of the fundus called?
Tapetum lucidum
What is the tapetum lucidum's function?
It is a specialized layer of cells in the choroid behind the retina that reflects light rays
What is the brown-black portion of the interior of the eyeball called?
Nontapetal area or nontapetal nigrum
What is the ciliary body's function?
It contains numerous muscle bundles that function in the regulation of the shape of the lens
What are ciliary processes?
Longitudinal folds marking the internal surface of the ciliary body. These processes surround but do not attach to the lens at its equator.
What suspends the lens from the ciliary processes?
Zonular fibers
What does contraction of the ciliary muscle do?
Contraction pulls the ciliary body & processes toward the lens. This relaxes the tension on the zonular fibers attached to the lens. Relaxing this tension allows the elastic lens to become more spherical and accomodate for near vision.
What is the space b/w the cornea and the iris called?
Anterior chamber
What is the narrow cavity b/w the iris and the lens called?
Posterior chamber
Where is the aqueous humor produced? And how does it drain?
It is continuously produced by ciliary epithelium covering the ciliary processes. It circulates thru zonulary fibers into posterior chamber b4 passing thru pupil into anterior chamber. Then drained thru trabecular meshwork at iridocorneal angle, where it passes into the venous system via the venous scleral sinus.
What is the pectinate ligament?
The iridocorneal angle is transversed by a meshwork of fibers referred to as the pectinate ligament.
Failure in the drainage of the aqueous humor thru the iridocorneal angle results in increased IOP, known as ___________
Glaucoma
What does the internal coat of the eye consist of?
The retina and its associated blood vessels and the nerves surrounding the vitreous body
What are the 3 parts of the retina?
Pars optica retinae, pars ciliaris retinae, and pars iridica retinae
Where is the pars optica retinae located? And what does it contain?
It covers the internal surface of the choroid from the point where the optic nerve enters to the level of the ciliary body (ora serrata). It contains the light-sensitive rods & cones, the bipolar cells, and the ganglion cells.
Where is the pars ciliaris retinae located? And what does it consist of?
It is a thin non-light receptive portion of the retina extending anteriorly from the ora serrata over the posterior surface of the ciliary body. It is 2 layers thick & forms the blood-aqueous barrier, thru which aqueous fluid is secreted into the posterior chamber.
Where is the pars iridica retinae located? And what does it consist of?
It is the anterior continuation of the pars ciliaris retinae on the posterior surface of the iris. It is a double cell layer consisting of pigment cells, which give the iris its color, and myoepithelial cells, which form the dilator pupillae.
Where does the optic nerve enter thru?
Optic nerve enters the posterior aspect of the eyeball at the optic disc. The optic disk is found in the interior region of the tapetum lucidum or at or below the inferior border.
What does the auricle (pinna) made of?
Cartilage
Which nerve innervates the muscles that move the pinna?
CN VII (facial)
What is the external acoustin meatus made of?
It has both cartilaginous & osseous parts. The vertical part & most of the horizontal part of the canal are cartilaginous, but the deepest part is osseous.
What kind of glands line the external acoustic meatus?
Sebaceous & ceruminous
What are ceruminous glands responsible for?
For the production of wax. The function of wax is to trap foreign bodies as well as to keep the tympanic membrane moist & pliable.
What is the main blood supply to the ear?
External carotid artery.
Caudal auricular a. arises from external carotic a. @ the base of the annular cartilage, medial to the parotid salivary gland & deep to the caudal auricular muscles. This a. gives off the lateral, intermediate, & medial auricular arteries.
What nerves give sensory innervation to the pinna & external ear canal?
Trigeminal, facial, vagus, & second cervical nerves
What does the middle ear consist of and where is it housed?
The middle ear is housed in the temporal bone, and it is a small air-filled space called the tympanic cavity.
What does the middle ear connect to? And how?
Connected to the nasopharynx sinus via the auditory tube
What are the 3 parts to the middle ear?
Tympanic cavity, auditory tube opening, and the ossicles
What are the 2 windows on the medial wall of the tympanic cavity?
The vestibular window (dorsal) and the cochlear window (ventral)
The bulla is the most ventral portion of the middle ear. What is it believed to do?
To improve the perception of sound
Where does the opening of the auditory tube lie?
The osteum of the auditory tube lies in a rostrodorsomedial location in the tympanic bulla
What kind of cells line the auditory tube?
Pseudostratified ciliated columnar epithelium containing goblet cells
What is the auditory tube's function?
It opens into the nasopharynx & equalizes air pressure on either side of the tympanic membrane
What are the 3 ear ossicles?
Malleus, incus, and stapes
Where are the ossicles located?
They extend like a chain from the tympanic membrane and functionally connect the tympanic membrane with the vestibular (oval) window
What is the ossicles' function?
Vibrations of the tympanic membrane are transmitted thru the chain of these auditory ossicles to the perilymph fluid w/in the vestibule.
What is the vestibular window's function?
The vestibular window is approx. 18-20 times smaller in area than the tympanic membrane, contributing significantly to the amplification of sound waves by the ear ossicles
Which of the ossicles is the most lateral?
Malleus
Which of the ossicles is the most medial?
Stapes
What does the head of the malleus articulate with?
Incus
What does the handle (manubrium) of the malleus imbed into?
Tympanic membrane
What does the stapes articulate with?
The medial portion of the incus
What part of the stapes comes into direct contact with the perilymph fluid?
Its footplate (base of stapes) attachment in the vestibular window
What are the muscles of the middle ear?
Tensor tympani and stapedius
What does the tensor tympani muscle attach to?And what innervates it?
Tensor tympani muscle is a spherical muscle that attaches to the malleus by a short tendon. It is supplied by a branch of the trigeminal nerve.
What innervates the stapedius muscle?
Facial nerve
What is the function of the tensor tympani and stapedius muscles?
Reflex contraction of these muscles in response to loud noises results in fixation of the ear ossicles, damping vibrations. This protective reflex is called the tympanic reflex.
How long does it take for the tympanic reflex to occur?
40-160 milliseconds
What are the functions of the inner ear?
Receiving auditory signals and maintaining equilibrium
Where is the inner ear located?
Within the osseous labyrinth of the petrous part of the temporal bone
What are the 3 parts to the membranous labyrinth?
Cochlea, vestibule, and semicircular canals
What is the cochlea's function?
Cochlea is receptive to vibrations in endolymph
What is the function of the vestibular and semicircular canals?
Associated with the function of equilibrium
What is the vestibule divided into?
An utricle and a saccule
What are the 3 semicircular canals? And what are they connected to?
Designated as anterior, posterior, and lateral semicircular canals. Connected to the utriculus.
How does the eye embryologically form?
Optic sulcus on neural fold --> optic vesicle --> optic cup
Where does the optic nerve embryologically come from?
Optic stalk
Where does the optic vesicle come from?
The neuroectoderm surrounding the optic sulcus proliferates rostrolaterally to form a hollow diverticulum of the prosencephalon, the optic vesicle
What is the MIC?
The lowest concentration of antimicrobial that completely inhibits bacterial growth as detected by the unaided eye
What type of yeast is malassezia pachydermatis?
Parasitic yeast
How many types of malassezia are there?
7
Which is the only malassezia commonly associated with animal disease?
M. pachydermatis
What kind of animal disease is malassezia pachydermatis associated with?
Most often otitis externa and dermatitis in dogs
What is the cell wall of M. pachydermatis made of?
Glycoproteins, lipids, and chitin
What type of environment does M. pachydermatis grow in?
It is lipophilic so growth is improved when lipids are added to medium. It will grow in either aerobic or microaerophilic atmosphere.
Where does M. pachydermatis normally reside?
Lives on the skin and external ear canal of healthy animals, including dogs, cats, ferrets, pigs & rhinos
How is M. pachydermatis transmitted?
It is an opportunistic fungus, contributing to disease processes already in progress
What is a cataract?
Non-physiologic whitening or other cloudiness of the lens fibers &/or the lens capsule
What causes a cataract?
Reduced oxygen uptake & thus an increased water uptake by lens. This causes swelling at first and then dehydration, followed by shrinkage.
What can lead to secondary cataract?
Uveitus, lens luxation, retinal dysplasia, and heredital retinal degeneration
How does a diabetic cataract form?
Increase in conc. of glucose in aqueous, capsule, & lens cell membrane is insulin-independent. Excessive glucose is metabolized resulting in increased conc. of intracellular sorbitol, which cannot pass the lens cell membranes& produces significant osmotic gradient. Lens swells.
Treatment for mature cataract?
Lens extraction
When is enucleation performed?
Intraocular neoplasia, severe perforating ocular trauma w/ disruption & loss of ocular contents, uncontrollable endophthalmitis, intractable ocular pain
What is glaucoma?
Decreased retinal ganglion cell sensitivity & function, ganglion cell death, optic nerve axonal loss, optic nerve head cup enlargement, blindness, INCREASE IN IOP
Is glaucoma curable?
No
What neurotransmitter may play a role in pathogenesis of glaucoma?
Glutamate as it is toxic for the ganglion cells
What causes the elevated IOP?
Obstruction to aqueous flow
At what level is IOP considered to be elevated?
20-30 mmHg is moderately elevated.
At what level does IOP cause irreparable damage?
If pressure is elevated above 40 mmHg for as little as 48 hours
What kind of glaucoma does open irido-corneal angle cause?
Primary glaucoma
What is the most frequent form of primary glaucoma in cats?
Open pectinate ligament glaucoma
What characterizes open pectinate ligament glaucoma?
No abnormality in the pectinate ligament. Irido-corneal angle is not abnormally narrow and there are no symptoms indicative of a secondary glaucoma.
Diff. b/w hydrophthalmos and buphthalmos?
Hydrophthalmos is globe enlarged by water. Buphthalmos is globe enlargement, in general.
What does buphthalmos cause to the Descemet's membrane?
Tearing of the Descemet's membrane, via which water leaks into the corneal stroma. This results in curvilinear streaks in the cornea due to the elastic recoil that accompanies the tearing. The resulting stripes resemble cracks in ice. They remain visible as scar striae, even after the IOP has been normalized.
What does a definite buphthalmos imply?
That nerve fibers are irreversibly damaged, the functional connection with the brain is interrupted, and the eye is therefore blind and will remain blind. Exception is if pressure rise was subclinical over long period of time.
What does KCS stand for?
Keratoconjunctivitis sicca (dry eye)
What is KCS?
Inflammatory condition of the ocular surface caused by pathologic reduction in the aqueous component of the tear film
What can cause KCS?
Improper distribution of tears b/c of improper eyelid structure/function, ocular enlargement that prevents eyelids from closing, lacrimal gland adenitis, or systemic dz such as hypothyroidism, hyperadrenocorticism, diabetes mellitus
How is KCS diagnosed?
Classified as KCS when Schirmer tear test reads less than 10 mm/min with concomitant ocular surface pathologic findings
What are the 2 types of KCS?
Deficiency in tear duct and tear evaporation
What kind of KCS do brachycephalic dogs tend to have?
KCS due to tear evaporation. Caused by lagophthalmos (failure of complete eyelid closure). Results in central area of tear film deficiency or in dogs which deficiency in tear film lipids leads to increased tear loss thru evaporation
What does deficiency in tear duct lead to?
Pathologically reduced aqueous tear production leads to ocular pathologic findings of corneal vascularization, pigmentation, and frank ulcerations
Mechanism of tear hyposecretion?
Inflammatory changes in KCS leads to reduction tear prod. Efferent denervation impairs lacrimal secretion. SInce the eye is constantly bathed in protective/nourishing tear film, the partial or complete removal of the tear film can affect corneal homeostasis.
Insufficient glandular tissue of membrane & lacrimal glands found w/ biopsy results of those w/KCS. What are the 3 stages of inflammatory dz seen in glands?
Stage 1: minimal #s of periductal & periacinal lymphocytes.
Stage 2: lymphatic nodules, squamous metaplasia of ductal epithelial lining
Stage 3: replacement of glandular elements w/fibrous CT & mod. # of mononuclear inflammatory cells
Clinical signs of KCS?
Dry nose, slightly sticky mucoid/mucopurulent discharge, and conjunctival hyperemia
Does lens luxation occur more frequently in dogs or cats?
Dogs
In what dog breeds is lens luxation a recessive hereditary dz?
JRT, Tibetan Terrier, Welsh Terrier, Border Collie, Shar Pei
How can anterior lens luxation lead to glaucoma?
The lens and/or vitreous can block the drainage of the aqueous in the pupil or at the level of the drainage angle, resulting in secondary glaucoma
What can a completely dislocated lens likely lead to?
Diffuse cataract, presumably b/c of its inadequate access to aqueous humor
What almost always causes secondary lens luxation?
Manifestation of blunt trauma, that causes avulsion of the zonules, or excessive stretching of zonules within a globe that has become greatly enlarged secondary to glaucoma
What is the most significant consequence to lens luxation (esp. anterior lens luxation)?
Glaucoma
What is the earliest recognizable sign of lens luxation?
Leakage of vitreous, which hangs over the edge of the pupil and into the anterior chamber like very thin white clouds
What can be seen if the lens is completely displaced ventroposteriorly?
The fundus of the eye
How is lens luxation treated?
Removal of lens (intracapsular) [immediately b4 glaucoma forms]
What is phacolytic uveitis?
Lens protein is beginning to disintegrate and leak through the intact lens capsule
What is phacoclastic uveitis?
immune-mediated disease in response to the release of large amounts of intact lens protein though a traumatically ruptured lens capsule
What is the pathogenesis of the inflammatory component of phacoclastic uveitis?
Probably an immunologic response to release of large amounts of strongly antigenic lens protein into the aqueous humor. It overwhelms the immune tolerance, resulting in suppurative reaction.
Which ectoparasite causes 50% of otitis externa cases in cats?
Otodectes cynotis
What bacteria is normal flora in dog ears?
Staph. epidermis, Staph. intermedius, Micrococcus spp.
What bacteria is acute otitis externa usually associated with?
Staph. intermedius
What CS does rupture of tympanic membrane cause?
Significant reduction in hearing ability, but not deafness.
Ruptured tympanic membrane heals through a process called:
Epithelial migration
What are the 2 parts of the tympanic membrane?
Pars flaccida and pars tensa
What is eardrum healing dependent on?
Presence of adequate blood supply/oxygen
Where is aqueous humor produced?
Pars ciliaris retinae
What is the normal IOP in a dog?
15-30 mmHg
What controls the secretion of aqueous humor?
Sodium-potassium activated adenosine triphosphatatase in the ciliary processes
Where are the lacrimal glands located?
Dorsal and lateral to each eye
Tears produced in response to relative constant ____________ nerve stimulation via ________ nerve
Parasympathetic
Facial
How do tears drain?
Lacrimal puncta drain teats away from surface. Orbicularis muscle contracts, causing lacrimal sacs to expand, creating internal pressure change. Tears flow down 2 small ducts to lacrimal sac, then down single nasolacrimal duct to nasal cavity. Tears drain to back of throat.
Where is aqueous humor produced?
Pars ciliaris retinae
What are the 3 layers of the tear film?
Inner mucous layer, middle aqueous layer, and outer lipid layer
What is the normal IOP in a dog?
15-30 mmHg
What are the 3 layers made of?
Inner mucous layer is mucin from goblet cells in conjunctiva. Middle aqueous layer is from lacrimal glands. Outer lipid layer is oily layer from Meibomian glands.
What controls the secretion of aqueous humor?
Sodium-potassium activated adenosine triphosphatatase in the ciliary processes
Where are the lacrimal glands located?
Dorsal and lateral to each eye
Tears produced in response to relative constant ____________ nerve stimulation via ________ nerve
Parasympathetic
Facial
How do tears drain?
Lacrimal puncta drain teats away from surface. Orbicularis muscle contracts, causing lacrimal sacs to expand, creating internal pressure change. Tears flow down 2 small ducts to lacrimal sac, then down single nasolacrimal duct to nasal cavity. Tears drain to back of throat.
What are the 3 layers of the tear film?
Inner mucous layer, middle aqueous layer, and outer lipid layer
What are the 3 layers made of?
Inner mucous layer is mucin from goblet cells in conjunctiva. Middle aqueous layer is from lacrimal glands. Outer lipid layer is oily layer from Meibomian glands.