The Ear & Eye

What structures make up the external ear, and how can it respond to injury?

The external ear consists of the auricle/pinna and the external acoustic meatus(ear canal), and it terminates at the tympanic membrane. Responses to injury include:

• Inflammation

• Epithelial and adnexal hyperplasia

• Fibrosis

• Osseous metaplasia/heterotopic ossification

• Neoplasia

What is otitis externa and what is the histologic makeup of the external acoustic meatus?

Inflammation of the external acoustic meatus. The EAM is dermatologic tissue lined by:

• Keratinized stratified squamous epithelium

• Thin dermis

• Sebaceous glands

• Hair follicles

• Ceruminous glands, which are more abundant medially than laterally

What categories of causes should be considered for otitis externa?

• Predisposing causes

• Primary causes

• Secondary causes

What are the predisposing cause of otitis externa?

Conformation, excessive moisture, treatment effects, neoplasia and polyps, systemic disease

What are the primary causes of otitis externa?

Parasites, hypersensitivity reactions, keratinization disorders, foreign body, glandular disorders, autoimmune disease, vascular disease

What are the secondary causes of otitis externa?

Bacteria such as Staphylococcus, Proteus, Pseudomonas, E. coli, Klebsiella, and yeasts such as Malassezia and Candida albicans

What are the key features of Dermatophilus congolensis infection of the external ear?

• Can affect any species

• Zoonotic

• Often transferred during nursing from dam

• Traumatized inguinal skin of lactating dams can transmit infection to ears of nursing offspring

• Flagellated zoospores invade epidermis, germinate into filamentous organisms, and damage/separate keratinocytes

Histology of Dermatophilus congolensis infection of the external ear?

• Intraepidermal pustular dermatitis

• Superficial perivascular dermatitis

• Folliculitis

What chronic responses to injury can occur in the external ear: Epithelial and adnexal hyperplasia?

• Glandular change with increased ceruminous glands

• Mentioned in Cocker Spaniels

What chronic responses to injury can occur in the external ear: Fibrosis?

• Chronic lymphocytes

• Fibroblasts

• Collagen

• Can lead to stenosis

What chronic responses to injury can occur in the external ear: Osseous metaplasia/heterotopic ossification?

Abrupt ossification arising from the auricular perichondral scaffold

What chronic responses to injury can occur in the external ear: Neoplasia?

• Squamous cell carcinoma

• Sebaceous gland tumors

• Melanocytic tumors

• Histiocytoma

• Plasmacytoma

• Mast cell tumor

• Ceruminous gland tumor in cats

• Trichoblastoma

What is an aural hematoma?

• Caused by ear discomfort leading to head shaking

• Head shaking creates shearing forces on blood vessels

• Can fracture auricular cartilage

• Hemorrhage collects:

  • Intraparachondrially

  • Subparachondrially

• Common in:

  • Pigs

  • Dogs

  • Cats

• If untreated:

  • Heals by fibrosis

  • Causes a malformed auricle

Aural plaques

• Also called:

  • Equine ear papillomas

  • Papillary acanthoma

  • Hyperplastic dermatitis of the ear

• Seen in horses under 1 year

• Caused by Equus caballus papillomavirus (EcPV)

• Spread by fly bite

• Important histologic feature:

  • Koilocytes → giveaway that this is due to a virus

Feline ceruminous cystomatosis → “a cat has lots of little cysts coming from the ear wax glands.”

• Benign lesion

• Cystic, non-neoplastic proliferation of ceruminous glands

• Located on:

  • Medial auricle

  • Ear base

  • May extend into the EAM

• Especially seen in:

  • Abyssinian cats

  • Persian cats

• Cause is unknown

What is otognathia?

• Rudimentary accessory mouth

• Located at the base of the pinna

• Seen in:

  • Sheep

  • Cattle

• Orifice may be:

  • Blind

  • Continuous with the pharynx

• May contain:

  • Rudimentary teeth

  • Mandible-like bones

  • Lateral tongue extensions

What are the main components and important features of the middle ear?

• Tympanic membrane

• Tympanic cavity

  • Air-filled

  • Surrounded by bone

  • Communicates with the pharynx via the auditory tube

• Auditory tube

  • Allows migration of infectious organisms

• Guttural pouches in horses

  • Enlarged diverticula of the auditory tube

What species differences exist in the tympanic bulla and what is mucoperiosteum?

• Septum bulla

  • Thin bony septum partially dividing the tympanic cavity

• Cats

  • “Complete” septum

  • Dorsolateral and ventromedial compartments

• Dogs

  • Incomplete septum

  • Single cavity

• Bovids, goats, camelids

  • Septate

  • Multiple compartments

• Horses

  • No prominent septum

• Mucoperiosteum

  • Fused mucosa and periosteal lining of the bony middle ear surfaces

What ossicles are found in the middle ear?

• Malleus

• Incus

• Stapes

What is otitis media?

• Inflammation of the middle ear

• Involves inflammation of the mucoperiosteum

How can otitis media develop, and what organisms are associated with it?

• Descending infection

  • From the external auditory meatus

  • Often occurs from otitis externa in dogs

• Systemic/hematogenous infection

  • Mycoplasmopsis bovis in cows

  • M. hyorhinis in pigs

  • Histophilus somni in cows

• Ascending infection via the auditory tube

  • Trueperella pyogenes in pigs and cows

  • Pasteurella multocida in pigs and cows

What diseases affect the auditory tube and guttural pouch?

• Salpinx / salpingitis

• Guttural tympany (air)

  • Due to obstruction of outflow via the auditory tube

• Empyema (pus)

• Aspergillus infection

  • Especially on the dorsal and caudal wall

• Carotid hemorrhage

  • Important complication

What are the key features of primary ciliary dyskinesia affecting the middle ear?

Genetic abnormal cilia movement

• Seen in dogs under 1 year

• Causes:

  • Cough

  • Persistent nasal discharge

• Due to ineffective mucociliary clearance → cilia do not work

• Ciliated epithelial cells normally clear fluid and debris in the auditory tube

Results in:

• Unilateral otitis media

• Bilateral otitis media

• Sterile gelatinous material in the tympanic cavity

Aural (nasopharyngeal) polyp

• Most common in cats under 2 years

• Less frequent in dogs

• Reported in one horse

• Proposed causes:

  • Chronic upper respiratory infection

  • Otitis media

  • Ascending middle ear infection

  • Congenital defects

• Gross appearance:

  • Pedunculated

  • Polypoid

  • Smooth surface

• Develops from ciliated epithelium in the middle ear

• May:

  • Remain confined to the middle ear

  • Extend through the auditory tube and obstruct the pharynx

  • Extend through a ruptured tympanic membrane into the EAM

• In the EAM, may be visualized as a mass

Tympanokeratoma

• Previously called:

  • Epidermoid inclusion cyst

  • Aural cholesteatoma

• Seen in:

  • Dogs

  • Horses

• Develops secondary to chronic inflammation

• Chronic inflammation causes squamous metaplasia

• Respiratory epithelium becomes stratified squamous epithelium

• Contains:

  • Keratin debris

  • Cholesterol

What neoplasms can affect the middle ear or guttural pouch region?

• Squamous cell carcinoma

  • Frequent in cats

  • Can arise in the guttural pouch of horses

• Adenocarcinoma

What is otitis interna and what are its complications?

• Also called labyrinthitis

• Inflammation of the inner ear

• May be accompanied by osteomyelitis of the petrous temporal bone

• Usually extends from otitis media via the cochlear window

• Sequelae include retrograde spread through the internal auditory meatus, causing:

  • Meningitis

  • Encephalitis

What are important causes of congenital hearing loss and deafness?

• Albinotic congenital deafness

• Due to dysfunction of intermediate cells

• Causes abnormal endolymph

• Leads to degeneration of cochlear hair cells

• Can be:

  • Unilateral

  • Bilateral

Affects:

• Up to 50% of white-coated, blue-eyed cats

• About 30% of Dalmatians with MITF mutation

• About 90% of horses with endothelin B receptor mutation in lethal white foal syndrome

What are acquired causes of hearing loss and deafness?

• Acoustic noise trauma

• Radiation

• Ototoxicity

  • Aminoglycosides

  • Platinum-containing chemotherapy agents

  • Furosemide

  • Salicylates

• Primary target:

  • Hair cells

What are the major structures involved in eye form and function?

• Globe (bulbi)

• Optic nerve (CN II)

• Accessory structures / adnexa:

  • Eyelids

  • Lacrimal apparatus

    • Sac

    • Duct

  • Orbital connective tissue

  • Extraorbital muscles

What are the major abnormalities of eyeball size?

• Small eye

  • Microphthalmia = congenital

  • Phthisis bulbi = acquired

• Large eye

  • Buphthalmus

  • Typically associated with glaucoma

What is the normal flow of aqueous humor?

• Produced by the ciliary body

• Enters the posterior chamber

• Passes through the pupil

• Enters the anterior chamber

• Drains through the iridocorneal / filtration angle

• Then passes through:

  • Pectinate ligaments

  • Trabecular meshwork

  • Corneoscleral meshwork

  • Scleral vasculature

horses enter through posterior chamber

What is glaucoma?

• Accumulation of aqueous humor

• Causes increased intraocular pressure

What are the major signs of glaucoma?

• Buphthalmus

• Retinal changes

  • Atrophy

  • Cupping of the optic disc

  • Degeneration of the optic nerve (in severe cases)

• Uveal changes

  • Retraction and collapse of the filtration angle

• Corneal changes

  • Edema from endothelial loss

  • Striae from breaks in Descemet’s membrane

  • Exposure keratitis

do not need all of these to diagnose glaucoma

What are the three major mechanisms of glaucoma?

1. Increased fluid production

2. Altered flow at the pupil

3. Reduced outflow

   • Most common mechanism

How can increased aqueous humor production cause glaucoma?

• Inflammation, especially anterior uveitis, breaks down the blood-aqueous barrier

• This increases ciliary body vascular permeability

• Protein and fluid leak into aqueous humor

• In dogs:

  • Ciliary body neoplasms can increase production

• In cats:

  • Hypertension can increase ciliary body perfusion

What lesion can alter aqueous flow at the pupil and contribute to glaucoma?

Anterior synechia

What pupil-flow abnormalities can lead to glaucoma?

Posterior synechia with iris bombe

What is primary glaucoma due to obstructed outflow?

Most common

• Can be congenital

• Caused by goniodysgenesis

What is an important cause of secondary glaucoma due to obstructed outflow?

From inflammation

• Preiridial fibrovascular membrane (PIFM)

What are the causes and related lesions of PIFM?

• Cytokine mediated

• Especially associated with VEGF

• Associated conditions:

  • Uveitis

  • Retinal detachment

  • Ciliary body tumor

• Related lesion:

  • Retrocorneal fibrovascular membrane

  • Similar to PIFM

  • Occurs on the posterior limiting lamina / Descemet membrane

What findings may accompany obstructed outflow glaucoma with PIFM?

• Preiridial fibrovascular membrane

• Hyphema → inc blood in anterior chamber

• Exudates → cellular debris

• Plasmoid aqueous → too much protein, cells cannot settle

What are other causes of secondary glaucoma with obstructed outflow?

• Neoplasia

• Lens luxation

layers of the cornea

• Anterior epithelium

• Anterior limiting lamina

• Proper substance / stroma

• Posterior limiting lamina

• Posterior endothelium

• Tear film lies externally

• Aqueous humor lies internally

What are the major categories of corneal disease?

• Keratitis

• Ulceration

• Neoplasia

What infectious causes of keratitis are discussed?

Infectious keratoconjunctivitis by Moraxella bovis

• Bacterial adhesins attach to corneal epithelium

• Cytotoxins cause epithelial ulceration

• Causes neutrophilic inflammation

Feline herpesvirus-1

• Viral replication causes epithelial necrosis

• Causes ulceration

• Can lead to chronic keratitis

• Can cause corneal scarring

• Sequela of FHV-1

  • Corneal sequestru = Necrosis of corneal stroma, Pigment accumulation

  • Forms a well-demarcated plaque

Corneal sequestrum in a cat → FHV-1

• Necrosis of corneal stroma with accumulation pigment (well demarcated plaque)

Corneal ulceration Tears provide nutrition to the cornea

• Minor epithelial defects heal by:

  • Epithelial sliding

  • Regeneration

• Ulceration may lead to:

  • Vascularization

  • Pigmentation

  • Descemetocele

    • Bulging of Descemet’s membrane / posterior limiting lamina

  • Iris prolapse

Uncomplicated ulcer heals in 3-5 days

Corneal neoplasms

Squamous cell carcinoma (pictures)

• Occurs in cattle, horses, cats, and dogs

• Associated with chronic UV exposure

• Most common at the corneoscleral / limbal junction

Limbal melanoma in dogs

• Arises from melanocytes at the corneoscleral junction

• Benign

What are the developmental and structural features of the lens?

• Lens is a modified epithelial structure

• Single layer of cuboidal epithelium is present only on the anterior lens

• Equator remains mitotically active

• Equator produces lens fibers throughout life

• Lens fibers are elongated epithelial cells

• Lens is avascular

• Lens depends on aqueous humor for nutrients

• Lens transparency depends on:

  • Highly ordered fibers

  • Proper dehydration state

  • Lack of organelles

Which part of the lens has no epithelium?

Posterior lens

What are lens fibers made up of?

elongated epithelial cells that lose nuceli + organelles

What is lens luxation?

Displacement of the lens due to zonular ligament failure

Anterior luxation of the lens

• Lens moves into the anterior chamber

• Emergency → leads to acute glaucoma

Posterior luxation of the lens

Lens falls into the vitreous

Causes of lens luxation

• Primary

  • Breed-related zonular degeneration

  • Example: terriers

• Secondary

  • Uveitis

  • Glaucoma

  • Trauma

Pathogenesis of lens luxation

Zonular breakdown → Loss of lens support → Increased lens mobility

Anterior lens luxation

How do diabetic cataracts develop?

• Caused by osmotic injury

• High glucose is converted to sorbitol via aldose reductase

• Sorbitol cannot diffuse out

• Sorbitol accumulates in the lens

• Water enters the lens

• Causes:

  • Fiber swelling

  • Fiber rupture

  • Opacity (cataract)

• Features:

  • Onset in days to weeks

  • Usually bilateral

  • Common in dogs

  • Rare in cats

What is feline post-traumatic ocular sarcoma?

• Also called:

  • Ocular posttraumatic lens tumor

  • FPTOS

• Develops after lens capsule rupture exposes lens proteins

• Chronic inflammation promotes neoplastic transformation

• Likely arises from:

  • Lens epithelial cells

  • Mesenchymal transformation

• Locally invasive:

  • Invades globe

  • Extends along optic nerve

  • Can metastasize

• Histology:

  • Spindle cell sarcoma

  • May have lens rupture or lens remnants

ocular posttraumatic lens tumor in a cat

• wide range of where the neoplastic cells will go

What structures make up the uvea?

• Uvea is the vascular tunic

• Anterior uvea

  • Iris

  • Ciliary body

• Posterior uvea

  • Choroid

• Blood-eye barrier is formed by endothelial cells of iridial vessels

What are the major types of uveal inflammation?

• Iritis

  • Iris

• Cyclitis

  • Ciliary body

• Anterior uveitis / iridocyclitis

  • Anterior segment

• Choroiditis

  • Choroid

• Panuveitis

  • Choroid + ciliary body + iris

• Ophthalmitis

  • All parts of the eye

What inflammatory patterns and causes are associated with uveal disease?

• Suppurative

  • Bacteria

  • FIP

• Lymphocytic plasmacytic

  • Idiopathic in cats

  • Malignant catarrhal fever in cattle, sheep, and goats → blue eye

• Granulomatous

  • Fungi

  • Yeasts

• Lens-induced

  • Phacolytic

    • Lens protein leaks out of an intact capsule

  • Phacoclastic

    • Lens ruptures

What neoplasms can affect the uvea?

• Anterior uveal melanoma

• Diffuse iris melanoma in cats

• Iris melanoma in dogs

• Ciliary body tumor

diffuse iris melanoma in a cat

iris melanoma in a dog

Ocular trauma caused by a foreign body

ciliary body tumor in a dog