Williams

What is the pinna and its function?

Funnel-shaped part of the ear that collects sound and directs it to the tympanic membrane via the external ear canal.

Describe the external ear canal and its features.

• Shape: L-shaped (short vertical outer section, longer horizontal inner section)

• Glands: Lined with apocrine (ceruminous) and sebaceous glands

• Examination: Complete view requires an otoscope

What is the middle ear function, structure, and connection?

• Function: Amplifies vibrations from the external ear and transmits them to the inner ear

• Structure: Air-filled tympanic cavity, 3 auditory ossicles (malleus, incus, stapes), and tympanic membrane

• Connection: Linked to the pharynx by the Eustachian tube, which maintains normal middle ear pressure

Where is the inner ear located and what structures are involved?

• Location: Inside the petrous part of the temporal bone

• Structures:

  • Cochlea – hearing

  • Vestibule – balance

  • Three semicircular canals – balance and spatial orientation

What are the functions of the cochlea, vestibule, and semicircular canals, and which nerve supplies them?

• Cochlea: Contains nerves that transmit electrical impulses for hearing

• Vestibule & semicircular canals: Maintain balance and equilibrium

• Nerve supply: Vestibulocochlear nerve (CN VIII) transmits sound and balance information to the brain

What are the two main types of deafness?

• Neurologic/Sensorineural: Inner ear, auditory nerve, or brain abnormalities

• Conduction: Pinna, ear canal, tympanic membrane, auditory ossicles, or middle ear issues (e.g., wax, infections)

What are the most common forms of deafness?

• Inherited congenital sensorineural

• Acquired later-onset sensorineural (e.g., ototoxicity)

• Acquired later-onset conductive (e.g., chronic otitis externa/media)

Which animals have higher incidence of congenital deafness?

• White-haired, blue-eyed cats

• Many dog breeds (sensorineural deafness; avoid using for breeding)

What are common acquired causes of deafness?

• Ear canal occlusion or middle/inner ear destruction

• Trauma to petrous temporal bone

• Loud noises

• Demyelinating conditions

• Ototoxic drugs (e.g., aminoglycosides)

• Cochlear degeneration in older dogs

What are common congenital causes of deafness?

• Toxic or viral damage to the developing fetus

• Merle or white coat colors

How is deafness diagnosed in animals?

• History: Not responding to commands, wrong direction when called, excessive sleeping

• Otic exam: Check ear canal, tympanic membrane, signs of infection or obstruction

• Neurological exam: Evaluate cranial nerves

• Radiography: Assess middle/inner ear structures, temporal bone

• BAER test: Brainstem Auditory Evoked Response detects electrical activity in cochlea and auditory pathways

What factors affect the prognosis of deafness?

• Cause of deafness (congenital, acquired, sensorineural, conductive)

• Progression of the disease

• Time of diagnosis (earlier is better)

• Ability to correct the underlying problem (e.g., treat infection, remove obstruction)

How can insects and parasites affect the pinna?

• Cause redness, swelling, and pruritus

• Damage is from direct bites or hypersensitivity reactions

• Examples: fly strike, sarcoptic mange, demodectic mange

What immune-mediated diseases can affect the pinna?

• Examples: Pemphigus, Atopy, Food allergy

• Diagnosis: Confirmed via biopsy of primary lesions

How does frostbite affect the pinna and how is it treated?

• Location: Poorly insulated areas like ear tips

• Signs: Pain, swelling, redness, possible tissue sloughing

• Treatment: Gentle warming and supportive care

What are common pinna skin disorders?

• Seborrhoea/Dermatosis: Oily skin at ear edges or ear edge skin disease

• Trauma

• Tumours: Squamous cell carcinoma, mast cell tumor, histiocytoma, melanoma

What are primary causes of otitis externa (OE)?

Factors that cause disease in a normal ear and change the ear environment, allowing secondary infections:

• Allergy

• Autoimmune (e.g., pemphigus)

• Endocrine disorders

• Epithelialization disorders

• Foreign bodies

• Immune-mediated (e.g., drug reactions)

• Parasites

• Viral infections

What are secondary causes of otitis externa?

Factors that cause disease in an already abnormal ear:

• Bacteria

• Fungi/Yeast overgrowth

• Medication reactions

• Overcleaning

What are predisposing and perpetuating factors in otitis externa?

• Predisposing factors: Present before disease develops, e.g., ear conformation, excessive moisture, prior otitis media, treatment effects

• Perpetuating factors: Occur as a result of inflammation, e.g., ear canal edema, tympanic membrane changes (dilated/ruptured)

How is otitis externa diagnosed?

• History: Include dermatologic history

• Physical exam

• Otoscopic exam: May require sedation

• Cytology: Identify organisms

  • Cocci: Staph or Strep

  • Rods: Pseudomonas aeruginosa, E. coli, Proteus mirabilis

  • Yeast: Malassezia pachydermatis

What are additional diagnostic tools for otitis externa?

• Microbial culture and sensitivity – identifies pathogens and effective antibiotics

• Histopathology – evaluates underlying tissue changes

• Imaging (Radiography, CT, MRI) – assesses middle/inner ear involvement or chronic disease

How is otitis externa treated?

• Ear cleaning – remove debris and discharge

• Antibiotics

  • Topical: Broad-spectrum, sometimes with glucocorticoids

  • Systemic: Based on cytology and/or culture & sensitivity (e.g., cephalexin for cocci, fluoroquinolones for rods)

• Systemic glucocorticoids: For severe inflammation

• Antifungals: Topical or systemic (e.g., clotrimazole, nystatin, thiabendazole, ketoconazole, itraconazole)

How are ticks, mites, and chronic ear infections managed in otitis externa?

• Acaricides: Treat ticks and mites

• Systemic medications: Used for chronic infections or suspected otitis media

• Ear cleansing caution: If tympanic membrane might be ruptured, use saline or Tris-EDTA instead of harsher cleaners

What is the maintenance therapy for otitis externa?

• Ear cleaning: As needed, usually 1–2 times per week

• Hair management: Clip hairs in ear canal only if they cause problems

• Keep ears dry to prevent recurrence

What can happen if otitis media is left untreated?

It can progress to otitis interna (OI)

What are the clinical signs of otitis media (OM)?

• Behavioral: Head shaking, tilting or rotating head toward affected side, scratching affected ear

• Neurologic: Facial nerve paralysis (ear/lip droop, collapse of nostril)

• Autonomic signs: ± Horner’s syndrome (miosis, ptosis, enophthalmos, 3rd eyelid prolapse)

What are the clinical signs and complications of otitis interna (OI)?

• Vestibulocochlear dysfunction: Hearing loss, head tilt, circling, falling toward affected side, general incoordination

• Severe complications: Infection can extend → meningitis, meningoencephalitis, or abscess formation

How is otitis media (OM) diagnosed?

• Otoscopic exam: Bulging, discoloured, or ruptured tympanic membrane

• Imaging:

  • Radiography: Osseous changes in tympanic bulla, fluid in tympanic cavity

  • CT or MRI for detailed assessment

• Note: Always check both ears

How common is otitis media (OM) in chronic otitis externa cases?

• Occurs in >50% of chronic otitis externa cases

• >70% of these cases have an intact tympanic membrane

How is chronic or refractory otitis media (OM) treated?

• Systemic antibiotics

• Acaricides (if parasites involved)

• Treat underlying otitis externa (OE)

• Myringotomy – drain and flush middle ear

• Bulla osteotomy / Total ear canal ablation – for severe or unresponsive cases

What is important about ear canal tumors in dogs?

• Benign vs malignant: More likely benign in dogs

• Prognosis: Invasion into tympanic bulla or surrounding tissues → poorer prognosis

What are the clinical signs of ear canal tumors?

• Otic discharge

• Head shaking or scratching

• Aural haematomas

• Deafness

• Vestibular signs (head tilt, circling)

• Facial nerve palsy/paralysis, ± Horner’s syndrome

What are common ear tumors in dogs?

• Sebaceous gland tumor

• Mast cell tumor

• Histiocytoma

• Ceruminous gland adenoma/adenocarcinoma

• Squamous cell carcinoma (SCC)

• Hemangiosarcoma

• Melanocytic tumors

• Basal cell tumors

What are common ear tumors in cats?

• Nasopharyngeal polyps

• Squamous cell carcinoma (SCC)

• Ceruminous gland adenocarcinomas

How are ear tumors typically treated?

Surgical excision – main treatment for most benign and malignant ear tumors

What are the key steps in eye examination?

• History – onset, duration, discharge, vision changes, trauma, systemic disease

• Restraint – gentle handling; sedation if needed for painful or fractious animals

• Equipment – ophthalmoscope, pen torch/bright light, fluorescein stain, tonometer, slit lamp (if available)

What anesthetics may be used for eye examination?

• Xylocaine (lidocaine) – local anesthetic for corneal/conjunctival procedures

• Rompun (xylazine) – systemic sedation, may help in uncooperative animals

• Proparacaine hydrochloride ophthalmic solution – topical eye anesthetic for diagnostic procedures

How is the auriculopalpebral nerve block performed in horses and what is it for?

• Purpose: Blocks motor innervation to orbicularis oculi, preventing blinking → allows examination or surgery of the eye/eyelid.

• Technique: Inject local anesthetic subcutaneously over the auriculopalpebral nerve (runs over zygomatic arch, just cranial to the base of the ear).

• Effect: Temporary paralysis of eyelid closure without affecting sensation of the cornea.

When does an eye exam begin?

As soon as the animal enters the room – observe behavior, posture, and vision responses.

What are the four tests for vision?

1. Menace response – learned blinking response; only in older animals.

2. Obstacle test – place objects in the pathway, call the animal to see if it avoids them.

3. Cotton ball test – drop a cotton ball from above to check reaction.

4. Placement test – place objects at varied heights and observe paw placement/reaction.

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What are the external observations in an eye exam?

Check eye symmetry, discharge, eyelid margins, and lumps/bumps.

How do you test for infection in the third eyelid?

• Swab for culture and sensitivity.

• Cytology via eye scraping using topical anesthetic.

How is dry eye (Keratoconjunctivitis Sicca, KCS) tested in dogs?

Schirmer tear test – measures tear production; compare to normal reference values.

How are corneal issues assessed?

• Opacity, depressions, lacerations, scratches – use fluorescein dye.

• Stroma – hydrophilic layer between epithelium and endothelium absorbs dye, revealing damage.

What is the normal pupil shape in different species?

• Dog: round

• Cat: vertical slit

• Horse/Cattle (large animals): rectangular with pupillary masses (corpora nigra)

What are pupillary masses (corpora nigra)?

Dark masses on the pupil margin in horses and cattle; help regulate light entry and reduce glare.

What should you check in the lens during an eye exam?

Look for opacity (cataracts), luxation, or subluxation.

When should pupil dilation be avoided?

If increased intraocular pressure (glaucoma) is suspected.

How do you check eye pressure?

Use tonometry tests, e.g., Tonopen or Schirmer tonometry.

What are the three main eye tests for small animals?

1. Schirmer test – measures tear production (dry eye).
2. Intraocular pressure (tonometry) – checks for glaucoma.
3. Menace response – tests vision and learned blink reflex.

What is Tonovet used for?

Measures intraocular pressure (tonometry) to check for glaucoma.

How is Tonovet used?

Place probe gently on the cornea after calibration, usually without topical anesthesia. Follow manufacturer directions for accuracy.

What is PLR?

Pupillary light reflex – checks if pupils constrict in response to light.

What are common pupil-dilating agents?

Atropine and Tropicamide – used to dilate pupils for eye exams.

Difference between direct and indirect ophthalmoscope?

• Direct ophthalmoscope: anatomically correct view, high magnification, clinician must be close, can be difficult with glasses.

• Indirect ophthalmoscope: upside-down/back-to-front image, lower magnification, but shows entire fundus.

What structures can be viewed behind the eye during ophthalmoscopy?

Optic nerve, tapetal fundus, retinal vessels

How does the optic nerve head and tapetum appear in different animals?

• Dog: Normal optic nerve head, tapetum present

• Cat: Brightest tapetum

• Horse: Non-tapetal fundus

What is the order of a complete eye exam?

• History & light source use

• Adnexa & anterior segment (focal light)

• Conjunctival/corneal culture

• Schirmer Tear Test (before liquids)

• Tonometry (intraocular pressure)

• Pupil dilation (if safe)

• Conjunctival/corneal cytology (with topical anesthetic)

• Evaluation of posterior nictitans

• Lens & fundus examination

• Fluorescein stain (last—blocks view if done earlier)

Does the PLR (pupillary light reflex) involve the visual cortex?

No. The PLR bypasses the visual cortex and is a reflex mediated entirely by the midbrain.

What is the parasympathetic pathway of the pupillary light reflex?

1. Light stimulus → detected by retinal photoreceptors (rods & cones).

2. Signal travels via optic nerve (CN II) to the pretectal nucleus in the midbrain.

3. Pretectal nucleus sends signals bilaterally to the Edinger-Westphal nuclei (parasympathetic).

4. Preganglionic parasympathetic fibers travel via oculomotor nerve (CN III) to the ciliary ganglion.

5. Postganglionic fibers innervate the sphincter pupillae muscle, causing pupil constriction.

Where are light signals first detected in the eye?

By retinal photoreceptors (rods & cones).

Through which nerve do light signals travel to the brain?

Optic nerve (CN II) to the pretectal nucleus in the midbrain.

Which nucleus sends signals bilaterally to the Edinger-Westphal nuclei?

Pretectal nucleus.

Which nerve carries preganglionic parasympathetic fibers to the ciliary ganglion?

Oculomotor nerve (CN III).

What causes the pupil to constrict in the PLR?

Postganglionic fibers from the ciliary ganglion innervate the sphincter pupillae muscle.