Chapter 133 Diseases of the Conjunctiva
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.
CONJUNCTIVITIS
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
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.
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.
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.
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.
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.
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.
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.
Proliferative Diseases
Non-Neoplastic Disease
• Episcleritis and idiopathic granulomatous disease are the main non-neoplastic proliferative conjunctival disorders (see Chapter 134).
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.
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).
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
Physical Examination
Perform physical examination to rule out multisystemic diseases (see Chapter 1).
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.
• 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.
