Chapter 7
Conjunctiva

Anatomy and Physiology

Conjunctiva is the mucous membrane lining the eyelids and the anterior sclera, and the nictitating membrane in those species having one.

Palpebral

Lines eyelid - thick, opaque and red; its redness, especially of the lower eyelid, often is mistaken as abnormal.

Bulbar conjunctiva

Thin, semitransparent, and colorless (however, in many animals there is normal melanosis, of various degrees - animals with heavily melanotic skin or hair usually have some melanin in conjunctiva - increases with age). Blood vessels in the bulbar conjunctiva can be differentiated from those in underlying sclera by moving the conjunctiva (e.g., with forceps): conjunctival vessels will move, those in sclera will not. These blood vessels are sensitive to irritation and easily become congested.

The white sclera and Tenon's capsule can be seen deep to the bulbar conjunctiva.

Occasionally, a large scleral vein will penetrate the sclera at the limbus and be present in the conjunctiva. This will concern the client, but is of no clinical significance to the patient. These vessels are more prevalent in small breed dogs.

Fornix

The area where the palpebral conjunctiva reflects to become the bulbar conjunctiva is called the conjunctival fornix. The space between the palpebral and bulbar conjunctiva (which can be widened by reflecting the eyelid from the globe) is called the conjunctival cul-de-sac.

Glands

The conjunctiva contains goblet cells and accessory lacrimal glands which add to the tear film (Moore, et al.). It also contains lymphoid tissue.

Microbiology

There is a mixture of bacterial and fungal flora in the normal conjunctiva of most animals (Gerding, et al.; Gerding, et al.; Urban, et al.; Wolf, et al.; Zenoble, et al.). Most of the bacteria are gram-positive which means that the culturing of an overwhelming number of gram-negative organisms suggests an abnormal condition.

Healing

Normal conjunctiva heals rapidly following surgery or other injury. Simple lacerations can heal within 24 hours.

Indicator of systemic status

The conjunctiva is a useful indicator of systemic problems such as icterus, anemia, and hemorrhagic diseases.

Congenital Abnormalities

Dermoids

More common in the dog than in other species, particularly in St. Bernard and Dalmatian dogs. Among cats, more common in Burmese and Siamese. Also seen as a heritable trait (autosomal recessive and polygenic) in Hereford cattle (Barkyoumb and Leipold).

Site of involvement usually the lateral canthus or limbus in dogs. Additional sites in cattle include third eyelid, medial canthus and eyelid.

Appearance

Dogs - usually thick with all the characteristics of skin including hair. They often do not cause much trouble, other than epiphora, if the hair is long and soft. If the hair is short and stiff, there may be considerable irritation; this usually is associated with dermoids which are thin and flat.

Horses - usually flat with a rough surface; hairs usually are short, stiff and not always easily appreciated. There often is considerable irritation when the individual blinks.

Cattle - similar to dog.

Treatment

Surgical excision. Use similar techniques as if a neoplasm; small conjunctival incisions do not need suturing; large incisions should be closed with fine, absorbable suture.

Extension of conjunctiva over the cornea

Rarely seen in nonhuman animals. Appears as a thin band of conjunctiva covering the peripheral part of the cornea. In most cases does not cause problems for the patient and should be left alone. In severe cases , surgical excision may be tried.

Pterygium is a condition seen in people. This is a band of conjunctiva which extends over the medial aspect of the cornea. It requires surgical excision, but can recur.

Acquired Abnormalities

Conjunctivitis

Inflammation of the conjunctiva. Alone or in combination with other conditions, it is the most common eye disease in all species.

General signs

Erythema of conjunctiva - due to capillary and other vessel dilatation.

Chemosis (edema of conjunctiva) - this may be so great that folds of edematous conjunctiva may protrude from the palpebral fissure; although this appears grotesque, the degree of chemosis is not necessarily related to the seriousness of the problem.

Discharge - if serous, suggests allergy, irritant, or very early infection; becomes mucopurulent with time in most situations that do not resolve regardless of cause (however, infections more likely to be mucopurulent). If there is sicca, the discharge will be thick and mucoid.

Conjunctivitis alone is not particularly painful; a certain amount of discomfort may be present in most patients. Certain causes, such as a foxtail foreign body, may be associated with extreme pain.

Follicles - hyperplasia of the normally present lymphoid tissue as a result of chronic irritation; not an abnormality in itself.

Cause

Infections - may be restricted to the eye or be part of a systemic disease (Campbell and Otis; Hopkins, et al.; Jacobson, et al.; Nasisse, et al.; Rogers, et al.). Remember to evaluate the entire patient.

Bacterial: Bacteria normally are present in the conjunctival sacs of most individuals. Thus, bacterial involvement in conjunctivitis may be secondary. Whether opportunistic or pathogenic, the bacteria should be controlled (Hughes and Pugh).

Viral: Particularly herpesvirus (Campbell and Otis; Jacobson, et al.) and adenovirus. With herpes, there may be corneal and conjunctival ulcerations with adhesions of conjunctiva to itself or to cornea; a pseudo diphtheritic membrane may be present. Sneezing and other signs of upper respiratory disease may be present.

Chlamydophila : Especially in cats (Campbell and Otis; Sykes, Jane E.) and sheep (Hopkins, et al.). Begins with epiphora, but changes to mucopurulent discharge over several days. The conjunctiva becomes thickened and hyperemic. In cats, sneezing also may be present.

Mycoplasma: Especially in cats (Campbell and Otis) and cattle; also seen in pigs (Rogers, et al.). Begins with epiphora, but changes to mucoid after several days. Papillary hypertrophy occurs. Occasionally there are pseudo membranes.

Mycotic: Uncommon. Usually associated with corneal infection.

Rickettsia: In sheep and goats.

Parasitic:

Thelazia sp. - occurs in domestic and free-living animals. Usually see a mild conjunctivitis and epiphora; many patients show no signs; occasionally get secondary keratitis; these must be removed manually, however the patient likely will become re-infested through the insect vector who transmits the larvae.

Onchocerca cervicalis - often a granulomatous conjunctivitis in the horse.

Face flies - spread bacteria or fomites among horses and cattle.

Demodectic mange - when in the eyelids, may see conjunctivitis in dogs.

Flukes in ostriches (Greve and Harrison).

Allergic: Seasonal usually, and may be accompanied by upper respiratory signs. Some topical medications such as neomycin, penicillin, or pilocarpine may be allergenic when used chronically. Tetracaine may cause an immediate hypersensitivity reaction with marked chemosis; this infrequent reaction is transient and not harmful.

Physical irritation: By foreign bodies, or growths from the eyelids.

Decreased tear production: Keratoconjunctivitis sicca.

Eosinophilic: This is related to the condition seen in the cornea. Although termed eosinophilic conjunctivitis, the actual cause is not known (Pentlarge).

Diagnostic procedures

Cultures: See elsewhere.

Conjunctival scrapings: See elsewhere for scrapings or cytology or other references (Campbell and Otis; Lavach, et al.). Using Giemsa stain, the following may be seen in cats infected by these organisms

Herpesvirus - neutrophils and occasional epithelial inclusion bodies.

Chlamydophila - neutrophils and basophilic intracytoplasmic inclusion bodies in epithelial cells (these are gone by 7-10 days).

Mycoplasma - neutrophils and basophilic pleomorphic coccobacilli on surface of epithelial cells.

Conjunctival stain: See elsewhere.

Schirmer tear test: See elsewhere.

Immunofluorescent antibody test for herpes: It has been shown that the use of topical fluorescein prior to collection of samples for this test will interfere by causing a false positive result (daSilva Curiel, et al.). This may occur even if the fluorescein is washed away with saline. Therefore, you should take scrapings before you instill fluorescein if you suspect herpes infection and you want to have this test done.

Treatment

Eliminate obvious causes such as foreign bodies. Provide specific therapy for any primary disease (e.g., systemic) as well as symptomatic treatment.

Cleanse eye with an eyewash, after doing diagnostic tests if these are necessary.

Antimicrobials - use at least 4 times a day. Although it would be desirable to do a culture and sensitivity and use a specific antibiotic, in reality, it is just as effective to use a broad spectrum antibiotic (or mixture); most patients will improve on this regimen; those who do not can be cultured.

In cats, the following may be tried for these organisms:

Herpesvirus - idoxuridine or vidarabine can be used, but usually ineffective for conjunctival infection; may be good for corneal involvement; may want to use steroids towards end of healing process to minimize scarring; recurrence common.

Chlamydophila - treatment only effective when epithelial cells have ruptured; use topical tetracycline for at least 4 weeks; do not use steroids.

Mycoplasma - most ophthalmic preparations other than neomycin are effective; treat for 7-10 days; do not use steroids.

Anti-inflammatory - corticosteroids often are used in combination with antibiotics to reduce the inflammatory response particularly in the case of allergies or physical irritants; generally should not be used in viral or mycoplasma infections.

Antihistamines - sometimes effective for preventive treatment of allergies.

Decongestants - in the case of mild allergies or minor irritation, mild sympathomimetic agents such as naphazoline or weak phenylephrine preparations may be useful; these can be used periodically to control a seasonal or temporary condition.

Spray treatment for birds - rather than stress these patients by restraining them, Dr. Cindi Bossart of Fort Lauderdale, Florida has developed a spray that has been helpful in treating conjunctivitis or chronic sinusitis (works well for secondary bacterial infections in birds infected with poxvirus); spray the following mixture 2-3 times a day - get the bird very wet (head, eye area - okay to go in mouth, helps systemically) - keep bird warm after spraying:

200 mg tylosin (Tylan® injectable)

150 mg gentamicin (Gentocin® injectable)

3 cc Flucort® (flumethasone); or you could use 8 mg dexamethasone (Azium® injectable)

3 cc Avitron® (a bird vitamin from 'pet' store), or 6 cc of Anjacome® (injectable vitamin)

1 quart water

Prognosis

Most patients with conjunctivitis usually respond well to treatment. If the signs persist for more than a few days, re-examine carefully; do culture and sensitivity and other diagnostic tests.

Neonatal conjunctivitis of kittens and puppies

Usually occurs before eyes open.

Cause

Various organisms (bacterial, viral, other) may cause genital infections in the mother and may result in infection of the litter at birth or neonatally. Bacteria, Chlamydophila, or virus should be considered.

Chlamydophila infection may arise from carrier queens or other cats in the household, after the kittens' eyes open.

Signs and appearance

Before the eyelids open - discharge beneath the eyelids causes swelling - discharge may be seen at the medial canthus before the eyelids open. There may be delayed opening of the eyelids.

After the eyelids open - similar signs to other conjunctivitis, but the purulent discharge is particularly sticky and may cause adherence of upper and lower eyelids.

There may be corneal ulceration or perforation by the time the eyelids open.

Some of these individuals are 'poor-doers' because of systemic illness.

Treatment

Open and cleanse the eyes; check cornea for presence of damage. The client should continue the cleansing periodically.

Use a broad spectrum antibiotic (ointment preferred).

Do not use corticosteroids unless keratitis is present and virus is not suspected as being the cause. If cornea is ulcerated, wait until re-epithelialized before initiating steroids.

Injuries

Lacerations

Numerous causes.

Signs - bloody tears, chemosis, pain (manifested as blepharospasm), erythema.

Treatment - in all cases, treat medically like a conjunctivitis.

Laceration of bulbar conjunctiva may expose the sclera. If clean, recent (within 6 hours), and large, suture with 6-0 or 7-0 absorbable suture, any pattern; will heal within few days. Small non-gaping wounds should not be sutured. Dirty, old wounds should be cleaned and allowed to heal by second intention.

Fornix wounds may be associated with protrusion of orbital fat. Remove the fat before suturing.

Palpebral conjunctival wounds usually need no suturing, but if part of a full thickness eyelid laceration, suture to add strength to the eyelid skin suture.

Subconjunctival hemorrhage

Causes: Associated with most trauma to the eye.

Also seen in clotting disorders or secondary to strangling (e.g., choke collars).

Treatment: Eliminate the cause, if still present.

Topical 1-2% epinephrine for active bleeding.

Benign neglect in cases where bleeding has stopped (most cases).

Topical corticosteroids if there appears to be irritation.

Prognosis: Does not cause any harm if uncomplicated - must determine the cause because this may alter the management.

Thoroughly examine the eye to see if there is intraocular or other damage.

Neoplasia

Most common in cattle, followed by horses, dogs, and cats.

Generally, manage as you would any other neoplastic disease. Impression smears and exfoliative cytology are particularly rewarding. Any tissue removed should be examined histologically, even if you do not suspect neoplastic disease.

Treatment is aimed at removing the mass without interfering with function or appearance. Most conjunctival neoplasms are efficiently removed if diagnosed early. In the case of squamous cell carcinoma, radiation therapy may be needed in addition to excision. Cryotherapy or diathermy also are useful, particularly in cattle.

Treat as conjunctivitis following your definitive treatment.

Cattle

Squamous cell carcinoma ('cancer eye') by far the most frequent . Related to regions of high actinic irradiation, and in individuals with hypomelanotic tissues. May also be related to presence of infectious bovine rhinotracheitis virus. There may be heritable or breed-related predisposition (e.g., Herefords) (Russell, et al.).

Often begins as hyperplastic plaque, progresses to keratoma, papilloma and, finally squamous cell carcinoma.

Usually seen in individuals over 4 years old with a peak at 8 years. Most begin at lateral limbal area. Most do not metastasize.

Horses

Squamous cell carcinoma most common . Lesions begin at limbal region or leading edge of third eyelid. Early lesions may appear simply as conjunctivitis. Angiosarcomas have been reported and are particularly aggressive and usually fatal (Hacker, et al.).

Dogs

Primary conjunctival neoplasms are uncommon, but you may see such types as hemangiomas , virus induced warts, melanomas (Collins, et al.), or histiocytomas .

Cats

Primary conjunctival neoplasms are rare, but squamous cell carcinoma is the most frequent of those which have been seen.