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ANAMNESIS AND COMMON OCULAR CONDITIONS IN ANIMALS

Common Breeds Affected by Specific Eye Conditions

Dogs

  • Eye Irritation: Common in Poodles, Sheepdogs, and Maltese.

  • Cataracts: Found in Cocker Spaniel, Labradors, Poodles, Boston Terriers, and Siberian Huskies.

  • Lens Luxation: Affects Beagles.

  • Progressive Retinal Atrophy: Seen in Golden Retrievers, Labrador Retrievers, and Siberian Huskies.

  • Ectropion: Common in Basset Hounds, Clumber Spaniels, Cocker Spaniels, Springer Spaniels, Boxers, Bull Terriers, and Bulldogs.

  • Entropion: Seen in American Staffordshire, Yorkies, Irish Setters, Retrievers, Boxers, Bulldogs, Cocker Spaniels, Springer Spaniels, and Clumber Spaniels.

  • Trichiasis: Found in Bulldogs, Pugs, Boxers, and Shar Peis.

  • Diamond Eye: Affects Great Danes, Mastiffs, Saint Bernards, Bernese Mountain Dogs, and Newfoundlands.

Cats

  • Siamese Cats: Prone to nystagmus, strabismus, glaucoma, and progressive retinal atrophy.

  • British Shorthair: Susceptible to cataracts, glaucoma, eye infections, and irritations.

  • Persians: At risk for corneal sequestra, trichiasis, entropion, and ocular irritation.

ANAMNESIS AND CLINICAL HISTORY

Important Factors to Assess

  • Environment: Identify where the animal resides and if it lives with other animals.

  • Systemic Diseases: Consider conditions like diabetes, high blood pressure, hyperadrenocorticism, hypothyroidism, kidney disease, calicivirus, herpesvirus, distemper virus, and leishmania.

  • Previous Ocular Pathologies: Document any past ocular conditions and their treatments.

  • Symptom Onset: Determine when symptoms started and if they are acute or chronic. Investigate potential causes.

SIGNS OF OCULAR ISSUES

  • Blepharospasm: Characterized by half-closed eyelids.

  • Rapid Blinking: An indication of discomfort.

  • Visible Third Eyelid: Suggests possible problems.

  • Inflammation: Identified by redness and swelling.

  • Epiphora: Excessive tearing.

  • Pawing at the Eye: Indicates irritation or pain.

  • Colored Discharge: Yellow, green, or red discharge indicates infection or irritation.

  • Conjunctival Redness and Swelling: Extreme redness and swelling of conjunctiva.

  • Avoidance of Bright Lights: Suggests photophobia.

ANATOMY OF THE EYE

Key Structures

  • Orbit: Contains extraocular muscles, nerves, blood vessels, the lacrimal gland, the optic nerve, and the eye globe.

  • Annexes: Includes eyelids, nictitating membrane, lacrimal glands, and meibomian glands.

  • Conjunctiva: The mucous membrane lining parts of the eye.

  • Eyeball Layers:

    • Sclera and Cornea: Outer protective layer.

    • Uveal Tract: Comprises the iris, ciliary body, and choroid.

    • Retina: Contains photoreceptor cells for vision.

  • Optic Nerve: Transmits visual information to the brain.

  • Eye Compartments:

    • Aqueous Humor: Fluid in the anterior chamber.

    • Vitreous Humor: Gel-like substance filling the vitreous chamber.

EYELID ANATOMY AND FUNCTIONS

Structure

  • Components: Tissue flaps with conjunctiva on the inner surface and haired skin on the outer surface. Contains muscle (orbicularis oculi and levator muscles), meibomian glands (which secrete the lipid component of tears), and cilia (eyelashes).

Functions

  • Distributes tears across the eyeball surface.

  • Protects the eye from mechanical damage.

EYELID ALTERATIONS

Common Conditions

Ptosis (Blepharoptosis)

  • Description: Droopy eyelids, primarily the upper eyelid.

  • Associated with: Horner’s syndrome presenting with ptosis, miosis, enophthalmos, dry eye, and third eyelid protrusion.

Ectropion

  • Description: Lower eyelid rolls outward or is everted. Exposed conjunctival tissues lead to drying and irritation, with a risk of recurring bacterial infections.

  • Breeds at Risk: Cocker Spaniel, Saint Bernard, Basset Hound, Mastiff, Bulldog, Newfoundland, Chow Chow, Springer Spaniel.

Entropion

  • Description: Eyelid rolls inward, leading to hair rubbing against the cornea causing pain and possible corneal ulcers.

  • Breeds at Risk: Akita, American Stafford, Bulldog, various Spaniels, Dalmatian, Retriever, Gordon Setter, Irish Setter, Great Dane, Pomeranian, Pug, Pekingese, Shar Pei, Shih Tzu, Bull Terrier, Poodles, and Weimaraners.

Trichiasis

  • Description: Eyelashes emerge normally but are directed towards the eyeball.

  • Breeds at Risk: Pekingese, Cocker Spaniel, Pugs, and Bulldogs.

Distichiasis

  • Description: Extra eyelashes emerge through the duct of the tarsal gland towards the cornea.

  • Breeds at Risk: Cocker Spaniels, Longhaired Dachshunds, English Bulldogs, Golden Retrievers, Poodles, and Pekingese.

Ectopic Cilia

  • Description: Single or multiple hairs grow through the inner eyelid surface.

  • Breeds at Risk: Dachshunds, Lhasa Apso, Shih Tzus, Boxers, and Shetland Sheepdogs.

Blepharitis

  • Description: Inflammation of the eyelids causing redness, swelling, and itchiness.

  • Symptoms: Dogs may exhibit blepharospasm and discharge from the eye. Predominantly affects dogs with prominent facial folds and brachycephalic breeds.

Lagophthalmos

  • Description: Inability to fully close eyelids, risking dryness and trauma to the cornea.

Symblepharon

  • Description: Adhesion between conjunctival surfaces and the cornea due to severe conjunctival inflammation.

Chalazion

  • Description: Inflammation of a meibomian gland leading to clogged openings and sebum build-up within the gland.

Hordeolum (Stye)

  • Description: Bacterial infection of the meibomian gland leading to localized swelling.

NICTITATING MEMBRANE

Structure and Function

  • Anatomy: Composed of a T-shaped piece of cartilage covered by conjunctiva. Contains the gland of the third eyelid, which produces up to half of the tear film in dogs. Contains lymphoid follicles beneath the bulbar surface.

  • Functions:

    • Tear production and distribution

    • Corneal protection

  • Dangers: Removal or disease of the third eyelid may result in corneal drying, chronic keratitis, conjunctivitis, and decreased tear production.

NICTITATING MEMBRANE ALTERATIONS

Conditions

Protrusion

  • Description: Abnormal elevation of the third eyelid, often a sign of underlying issues.

Cherry Eye

  • Description: Prolapse of the third eyelid gland resulting in a red, swollen mass at the medial canthus of the eye.

  • Breeds at Risk: Cocker Spaniels, Bulldogs, Boston Terriers, Beagles, Lhasa Apso, Shih Tzu, and Burmese and Persian cats.

CONJUNCTIVA

Anatomy

  • Structure: Thin mucous membrane lining the inner surfaces of the eyelids, the third eyelid, and the anterior portion of the eye globe.

  • Tissue Types:

    • Bulbar Conjunctiva: Whitish in color.

    • Palpebral Conjunctiva: Pinkish hue.

Color Alterations

  • Congestion: Red coloration indicates irritation or inflammation.

  • Cyanosis: Violet hue indicating lack of oxygen.

  • Paleness: Suggests anemia.

  • Jaundice: Yellow indicates increased bilirubin due to liver disorders.

  • Petechia: Reddish spots indicating blood presence due to coagulopathies.

CONJUNCTIVA ALTERATIONS

Conditions

Chemosis

  • Description: Manifestation of conjunctival edema.

Conjunctivitis

  • Description: Inflammation of the conjunctiva leading to redness and discomfort.

Dermoid

  • Description: Area of normal haired skin located abnormally on the eye.

  • Breeds at Risk: German Shepherd, Dachshund, St. Bernard.

Epiphora

  • Description: Continuous shedding of tears. May be bilateral (indicating infection or irritation) or unilateral (suggesting foreign body or trauma).

Keratoconjunctivitis Sicca (KCS)

  • Description: Inadequate aqueous tear production by lacrimal glands often linked with conditions such as hypothyroidism, distemper, and immune-mediated diseases.

  • Breeds at Risk: Boston Terrier, Spaniels, English Bulldog, Pekingese, Pug, Samoyed, West Highland White Terrier, Yorkshire Terrier, Miniature Schnauzer.

  • Diagnosis: Schirmer Test to measure tear production.

    • Physiological values:

    • Dogs: 15-25 ext{ mm}

    • Cats: 10-20 ext{ mm}

EYEBALL ALTERATIONS

Conditions

Buphthalmos

  • Description: Enlarged globe due to elevated intraocular pressure (IOP).

Microphthalmia

  • Description: Smaller-than-normal eyeball for the breed.

  • Breeds at Risk: Australian Shepherds, Great Danes, Beagles, Collies, Dobermans, Portuguese Water Dogs, Akitas, Miniature Schnauzers, Labrador Retrievers, Cavalier King Charles Spaniels.

Enophthalmos

  • Description: Globe appears sunken within the orbit.

Exophthalmos

  • Description: Abnormal protrusion of the eyeball; physiological in brachycephalic breeds.

Proptosis

  • Description: Sudden anterior displacement of the globe.

Strabismus

  • Description: Deviation of one or both ocular axes due to decreased function of the ocular muscles, originating from congenital issues or nerve injury.

  • Breeds at Risk: Siamese, Himalayan, and Persian cats, as well as Irish Wolfhound, Shar Pei, Golden Retriever, and Akita dogs.

Nystagmus

  • Description: Involuntary, convulsive movements of the eyeball.

CORNEA

Structure

  • Anatomy: The most anterior, convex, and transparent section of the outer layer of the eye.

  • Limbus: Junction where the cornea, bulbar conjunctiva, and sclera converge.

  • Layers of the Cornea:

    • Epithelium: Anterior layer attached to its basement membrane; lipophilic.

    • Stroma: Comprises 90% of corneal thickness; hydrophilic.

    • Descemet's Membrane: A single cell layer that is also lipophilic.

    • Endothelium: Regulates ion movement from the stroma to the aqueous humor, maintaining stroma hydration.

CORNEAL ALTERATIONS

Conditions

Corneal Ulcers

  • Description: Superficial defects involving damage to the corneal epithelium.

Descemetocoele

  • Description: Deep defects affecting both the epithelium and stroma.

Corneal Edema

  • Description: Swelling due to water retention; cornea appears blue or cloudy. Common in older animals.

Keratitis

  • Description: Inflammation resulting in a white or foggy appearance with blood vessel proliferation.

Pannus

  • Description: Elevated pink mass on the cornea that may flatten and darken as the disease progresses.

  • Breeds at Risk: Middle-aged German Shepherds and Belgian Tervurens.

UVEA

Anatomy and Function

  • Structure: The uvea is the vascular component of the eyeball consisting of the iris, ciliary body (anterior uvea), and choroid (posterior uvea).

  • Function: Produces aqueous humor and plays a key role in maintaining the blood-aqueous barrier. Diseases affecting uveal structures may compromise this barrier.

UVEA ALTERATIONS

Conditions

Uveitis

  • Description: Inflammation of the uveal tract, causing a breakdown of the barrier between the eye and its blood supply, resulting in a hazy appearance.

Synechiae

  • Description: Adhesions between the iris and cornea (anterior synechiae) or the lens (posterior synechiae), usually due to uveitis inflammation.

ANTERIOR CHAMBER

Anatomy and Examination

  • Location: Between the cornea and the iris.

  • Contents: Contains aqueous humor produced by the ciliary body.

  • Examination: Conducted using a slit lamp with directed light to assess normal (optically empty) or pathological conditions (Tyndall phenomenon; aqueous flare indicating the presence of proteins or white blood cells).

GLAUCOMA

Description

  • Definition: An ocular disease characterized by increased intraocular pressure (IOP).

  • Measurement: IOP assessed using a tonometer.

  • Fluid Dynamics: Excess fluid drains between the cornea and iris, specifically through the iridocorneal angle. Obstruction here causes increased IOP.

  • Types:

    • Primary Glaucoma: Common in Akitas, Dalmatians, Alaskan Malamutes, Poodles, Basset Hounds, Samoyeds, Shar Peis, Beagles, Miniature Pinschers, Terriers, and Spaniels.

    • Secondary Glaucoma: Can be caused by conditions like uveitis, lens luxation, or tumors.

  • Normal IOP: Range between 15-25 ext{ mmHg}.

PUPIL

Function and Reflexes

  • Structure: Rounded opening in the center of the iris that permits light to enter the eye, reaching the retina.

  • Pupillary Reflex: Includes direct and consensual responses, assessing optic and oculomotor nerve function.

  • Terms:

    • Miosis: Contraction of the pupil.

    • Mydriasis: Dilation of the pupil.

    • Anisocoria: Condition where pupils are not equal in size.

LENS

Structure and Function

  • Description: Transparent, biconvex structure.

  • Anatomy: The anterior surface fills the pupil, while the posterior surface contacts the vitreous.

  • Components: Central nucleus surrounded by lens fibers encased in an elastic envelope.

  • Suspensory Ligaments: Holds the lens in place to focus light onto the retina.

LENS ALTERATIONS

Conditions

Lens Luxation

  • Description: Weakening or rupture of the lens support ligaments, causing dislocation.

  • Types:

    • Posterior Luxation: Lens falls backward, potentially causing retinal detachment.

    • Anterior Luxation: Lens shifts forward, blocking fluid drainage and raises IOP.

  • Breeds at Risk: Terrier breeds, Shar Peis, and Border Collies.

Cataract

  • Description: Opacity of the lens or its capsule.

  • Types:

    • Inherited: Common in American Cocker Spaniels, Labrador Retrievers, Poodles, Boston Terriers, Springer Spaniels, and Rottweilers.

    • Secondary: Associated with diabetes mellitus, malnutrition, trauma, or uveal inflammation.

Sclerosis

  • Description: Denser and tightly packed lens cells.

RETINA

Function and Examination

  • Function: Converts light into neurological signals, perceived as vision by the brain.

  • Observation: Conducted using an ophthalmoscope, either direct (high amplification, limited view) or indirect (lower amplification, broader view).

CANINE FUNDUS

Anatomy

  • Tapetal Zone: Superior and central area; colors include green, blue, yellow, and orange.

  • Non-Tapetal Zone: Inferior and peripheral; colors are reddish and brown.

  • Vascular Pattern: Characterized by 3-4 retinal veins emerging from the optic disc center along with smaller arteries.

  • Optic Disc: Entry point of the optic nerve.

CANINE FUNDUS ALTERATIONS

Conditions

  • Haemorrhages: Indicates vascular or traumatic damage.

  • Inflammations: May signify infectious or immune-mediated processes.

  • Retinal Detachment: Separation of the retina from the underlying layer.

  • Tumours: Lesions that can impair visual function.