Diseases of the Conjunctiva

Chapter 133 Diseases of the Conjunctiva

Cecil P. Moore

ANATOMY AND PHYSIOLOGY

• Conjunctival mucosa covers the inner aspect of the eyelids, the front and back of the membrana nictitans, and the anterior sclera. Conjunctiva extends from the lacrimal caruncle nasally to the lateral canthus temporally.
• Normal conjunctiva is semitransparent and appears moist and glistening. Numerous small, branching blood vessels are visible within the conjunctiva.
• Sensory innervation to the conjunctiva is via ophthalmic and maxillary branches of the trigeminal nerve.
• The conjunctiva serves as a protective external physical, secretory, and immunologic barrier for the eye.
• Epithelial goblet cells within the conjunctiva produce mucus that contributes to the preocular tear film, harbors immunoglobulin, and traps foreign material and surface debris.

CONJUNCTIVITIS

The term conjunctivitis describes nonspecific inflammation of the ocular mucous membrane. Conjunctivitis is the most common cause of “red eye” in animals. To accurately assess the small animal patient presented with conjunctivitis, recognize inherent species differences in susceptibility and establish whether the disorder is primary or secondary. For example, feline conjunctivitis is generally caused by a primary ocular infection. Canine conjunctivitis, by contrast, usually is secondary to ocular surface irritants, tear film deficiencies, or foreign bodies.

Additional pertinent information regarding conjunctival disease is found in other chapters in this book. Conjunctival disease is often associated with viral infections, diseases of the cornea (see Chapter 134), diseases of the lacrimal apparatus (see Chapter 139), and diseases of the eyelids (see Chapter 132).

Etiology

Causes of conjunctivitis are numerous. Frequently, more than one etiologic factor plays a role in the clinical course of the disease.

Key Point

Regardless of the primary cause, bacterial infection is a common complicating factor in conjunctivitis.

Infectious Agents

• Infectious agents cause severe conjunctivitis in cats by infecting epithelial cells. Feline herpesvirus and Chlamydophila felis cause the most serious and common ocular infections in cats (see Chapter 11). Mycoplasma felis, Staphylococci species, Streptococci species, and coliform organisms are bacterial causes of usually less severe forms of feline conjunctivitis.
• Gram-positive aerobic bacteria are most commonly isolated from cases of canine conjunctivitis. Opportunistic bacterial infections are common in dogs following conjunctival irritation from other causes. Canine distemper virus (see Chapter 13) causes conjunctivitis and dacryoadenitis in dogs.

Tear Film Deficiency

• Tear film deficiency results in dehydration of the ocular surface with accompanying inflammation of the conjunctiva and cornea. Aqueous tear deficiency, or keratoconjunctivitis sicca, occurs more frequently in dogs than in cats (see Chapter 139).
• Although less common than aqueous deficiency, inadequacy of the lipid or mucous components may, when present, complicate the surface disease.
• Poor eyelid conformation, as with exophthalmos and/or lagophthalmos, potentiates exposure and drying, which may be further complicating factors.

Foreign Bodies

• Foreign bodies of the conjunctiva can include plant components, synthetic material, or metallic substances. Plant awns and weed seeds may become embedded in the fornices of the conjunctiva or migrate under the conjunctiva or behind the third eyelid. Embedded plant material is quite reactive and stimulates an intense pyogranulomatous inflammation.
• By contrast, synthetic material, such as glass or plastic, and certain metals, such as lead and stainless steel, are minimally reactive. Depending upon the location and rigidity of the material, conjunctival foreign bodies may cause direct frictional irritation and result in surface ulceration.

Trauma

• Trauma to the conjunctiva may be blunt, resulting in bruising of an intact membrane or penetrating with puncture or laceration.
• Conjunctival lacerations 5 mm in length or larger, or when the nictitans is involved, may require suturing.
• Otherwise, bruises, focal punctures, or smaller lacerations usually resolve uneventfully with symptomatic treatment.

Key Point

In cases of conjunctival trauma, examine the eye thoroughly for the presence of foreign bodies and intraocular lesions.

Chemical Irritants

• Chemical irritants that damage the conjunctiva include noxious gases, alkalis, and acids. Alkaline substances (e.g., lye, fresh lime, or ammonia) cause the most serious injuries.
• When chemical injury has occurred, flush the eye copiously with saline or tap water and evaluate for associated corneal and/or anterior uveal involvement.

Environmental Irritants

• Environmental irritants, such as dust, particles of sand or plant material, wind, and solar irradiation, are additional causes of conjunctivitis in small animals.
• These are particularly common causes in hunting dogs and outdoor working dogs.

Immune-Mediated Conjunctivitis

• Immune-mediated conjunctivitis results from acute allergic chemosis, atopy (see Chapter 46), follicular conjunctivitis, and conjunctivitis resulting from eosinophilic or plasmacytic infiltrates.
• An immune-mediated ulcerative conjunctivitis occurs in Doberman pinschers.

Proliferative Diseases

• Proliferative diseases are categorized as non-neoplastic or neoplastic.

Non-Neoplastic Disease

• Episcleritis and idiopathic granulomatous disease are the main non-neoplastic proliferative conjunctival disorders (see Chapter 134).
• Conjunctival epithelial hyperplasia, granulation tissue, and pigmentary infiltrates are additional examples of non-neoplastic proliferative conditions.

Neoplasia

• Conjunctival neoplasms may be primary or secondary.
• Papillomas, squamous cell carcinomas, and hemangiomas are the most common primary tumors. Less common primary neoplasms are hemangiosarcomas, mastocytomas, and melanomas.
• Adenomas, adenocarcinomas, fibromas, fibrosarcomas, lymphomas, transmissible venereal tumors (TVTs) and melanomas are tumors that may secondarily involve the conjunctiva.

Iatrogenically Induced Conjunctivitis

• Iatrogenically induced conjunctivitis results when topically administered therapeutic agents or surgical manipulations cause conjunctival inflammation.
• A number of drugs may cause conjunctivitis because of irritation from their active ingredients, vehicles, or preservatives. For example, neomycin hypersensitivity may manifest as severe conjunctivitis after topical administration of triple antibiotic combination.
• Surgical procedures result in conjunctivitis from direct insult (e.g., manipulation, dissection, thermal injury, or exposure during or following surgery).

Other Eye Diseases

• Other eye diseases, either ocular surface disorders or intraocular diseases, are frequently associated with conjunctival inflammation.
• Surface diseases in which conjunctivitis is prominent include episcleritis, keratitis, and eyelid disease (e.g., chalazia, entropion, ectropion, and cilia disorders).
• Conjunctival inflammation occurs with uveitis and glaucoma, although deeper episcleral injection is also present and is a hallmark of these intraocular diseases.

Clinical Signs

• Hyperemia resulting from vasodilation of conjunctival vessels causes the appearance of a red eye. The redness is intensified when conjunctival hemorrhage or episcleral vascular injection is also present.
• Ocular discharge is characteristic of conjunctivitis and is serous, mucoid (catarrhal), or mucopurulent. The type of discharge may change as conjunctivitis progresses—from serous (mild) to mucopurulent (severe).
• Chemosis is swelling or “puffiness” of the conjunctiva caused by edema of the mucosa and submucosal tissues.
• Pain with conjunctivitis varies with the severity of the ocular disease. Squinting and tearing are characteristic of most cases of conjunctivitis. Photophobia and marked blepharospasm generally occur only when other eye disease is present, such as ulcerative keratitis or uveitis.
• Tissue proliferation is a variable finding of subacute or chronic conjunctival disease. Conjunctival lymphoid follicular hyperplasia may develop in dogs as a non-specific immune response to persistent antigenic stimulation. In cats, conjunctival follicles are associated with chlamydial conjunctivitis (see Chapter 11). Diffuse thickening of the conjunctiva may occur from epithelial hyperplasia or from chronic inflammatory cell infiltrates. Focal, acquired, proliferative lesions may be either granulomas or neoplastic.

Diagnosis

History

History pertinent to cases of conjunctivitis includes possible systemic illnesses, environment and habits, possible exposure to infectious or chemical agents, possible trauma, and previous ocular diseases, including notation of any medications administered.

Physical Examination

Perform physical examination to rule out multisystemic diseases (see Chapter 1).

Cultures

Culture and sensitivity testing is indicated for the definitive diagnosis and treatment of ocular infection. When culturing for fungi, Mycoplasma, Chlamydophila, or viral agents, consult with the diagnostic laboratory in advance regarding special requirements for submitting culture samples.

Key Point

When the need for cultures is anticipated, collect samples prior to applying topical agents or manipulating ocular surface tissues.

Ophthalmic Examination

Ophthalmic examination should be thorough and, in addition to confirming conjunctivitis, is aimed at identifying other forms of eye disease. Perform a complete ophthalmic examination.

• Inspect the external ocular surfaces and the anterior portion of the globe directly using a focal light source with magnification. The focused light is also used to check for pupil symmetry and light responses.
• Perform the intraocular examination with a focused light and an ophthalmoscope. Opacities of the normally clear ocular media (cornea, intraocular chambers, lens) are noted. Perform funduscopy to determine if abnormalities of the retina, choroid, or optic nerve are present.
• Measure aqueous tear production with Schirmer tear test strips as described in Chapters 131 and 139. Rule out aqueous tear deficiency because this is a common disorder in small animals, particularly in dogs, and results in chronic conjunctivitis with a tenacious mucopurulent ocular discharge.

Key Point

The Schirmer tear test strips measure reflex tear production. Evaluate prior to application of any local solutions, including topical anesthetic agents.

• Apply fluorescein stain to determine if surface ulceration is present. Establish nasolacrimal duct patency by allowing fluorescein stain to gravitate into the external nares.
• Following application of a topical anesthetic, examine for foreign bodies. Use blunt-tipped forceps to probe the conjunctiva fornices and to lift the third eyelid, allowing inspection of the posterior surface.
• Use tonometry to rule out other intraocular causes of red eye, for example, glaucoma (elevated pressure) and uveitis (low pressure). Applanation tonometry produces the most accurate intraocular pressure readings in small animal patients (see Chapters 131 and 137).

Cytology

• Cytology of conjunctival scrapings may provide a definitive diagnosis of inflammatory or neoplastic disease.
• Immunofluorescence testing of cytologic specimens can confirm viral or chlamydial infection.

Related posts:

  1. Feline Infectious Peritonitis (Feline Coronavirus)
  2. Borreliosis (Lyme Disease)
  3. Immune-Mediated Dermatoses
  4. Otitis Media and Otitis Interna

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Aug 27, 2016 | Posted by in SMALL ANIMAL | Comments Off on Diseases of the Conjunctiva

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