Chapter 13 Ocular Diseases
DISEASES OF THE ORBIT
Inflammatory Orbital Diseases
Orbital Cellulitis
Etiology.
Puncture wounds and lacerations of the eyelids or conjunctiva that allow opportunistic bacteria to invade orbital soft tissue are the most common cause of orbital cellulitis. Hooking the eyelid on a sharp object or stanchion lock can result in a puncture wound of the palpebral conjunctiva or eyelid. Migration of plant origin fibrous foreign bodies from the oral cavity also may result in orbital cellulitis. Severe ocular infections that progress from endophthalmitis to panophthalmitis may then infect orbital soft tissue. Chronic inflammation in the orbit from cellulitis or foreign bodies may allow orbital or retrobulbar abscess formation.
Signs.
Acute orbital cellulitis patients have rapid onset of a warm, painful swelling of the orbital region, lids, and nictitans, chemosis of the conjunctiva, and a degree of exophthalmos. Fever is usually present, and the exophthalmos may allow exposure keratitis to occur as the globe is pushed outward to such an extent that the lids no longer protect the central cornea (Figure 13-1).
Figure 13-1 Orbital cellulitis secondary to a laceration of the palpebral conjunctiva. Swelling of the orbit and lids, and conjunctival chemosis and exposure keratitis are present.
Chronic orbital cellulitis or orbital abscess results in a more insidious but painful exophthalmos with soft-tissue swelling that may be more localized. Fever is inconsistent.
Diagnosis.
Acute ophthalmic signs coupled with fever suggest acute orbital cellulitis. Definitive diagnosis is aided by the physical finding of an entry wound in the eyelid or conjunctiva. Orbital ultrasound evaluation helps rule out neoplasia or presence of a foreign body, and tissue aspirates may reveal large numbers of neutrophils. A complete blood count (CBC) is worthwhile but may be normal or show a mild neutrophilia.
Chronic orbital cellulitis or abscessation must be differentiated from orbital neoplasia and chronic frontal sinusitis (see following discussion). A complete physical examination, percussion of sinuses, orbital ultrasound, and radiographs may be required in confusing cases. Serum globulin levels may be elevated to greater than 5.7 g/dl in cases that last longer than 2 weeks, suggesting chronic inflammation or abscessation.
Treatment.
Acute orbital cellulitis is managed with systemic broad-spectrum antibiotics. Although penicillin may be effective because Arcanobacterium pyogenes is a likely causative organism, ampicillin may be a better choice. Nonsteroidal antiinflammatory agents (NSAIDs) such as aspirin (240 to 480 grains orally, twice daily) provide analgesia and mild antiinflammatory action. Warm compresses of the orbit are very helpful in reducing orbital and lid swelling, thereby lessening the degree of exophthalmos. Compresses may be applied two or three times daily for 5 minutes if labor is available. Topical antibiotic ointment or lubricant should be applied liberally to the cornea to prevent exposure keratitis. If no ulceration of the cornea has occurred, sterile ocular lubricating ointments or mastitis ointments may be used prophylactically. If exposure ulceration has occurred, the eye should be treated topically several times daily with a broad-spectrum antibiotic ointment to control infection and 1% atropine ointment to provide cycloplegia.
The prognosis for acute orbital cellulitis is good if medical and nursing care can be provided. Most cases resolve within 5 to 7 days with the aforementioned therapy.
Chronic orbital cellulitis or abscessation requires localization of the lesion to allow surgical drainage. Needle aspirates or ultrasound-guided needle aspirates confirm the location of the infection before drainage. Knowledge of the skull and orbit anatomy is helpful in avoiding injury to important structures when attempting to lance an orbital abscess (Figure 13-2). Most abscesses harbor A. pyogenes. Therefore systemic penicillin (22,000 U/kg once daily) should be used for 1 to 2 weeks following surgical drainage of the lesion. Gentle flushing of the abscess cavity should be performed once or twice daily, and warm compresses should be used if exophthalmos is severe enough to raise concern of exposure keratitis. Recurrent orbital abscesses or chronic cellulitis will dictate more intensive diagnostic work, including ultrasonography, radiographs, and culture-sensitivity testing to rule out foreign bodies and resistant organisms.
Inflammation of the Tissues Adjacent to the Orbit
Etiology.
Chronic frontal sinusitis in dairy cattle leads to inflammatory bony expansion of the frontal sinus with ipsilateral exophthalmos that may be mild to moderate. Chronic sinusitis most commonly results from previous (months to years) dehorning or ascending respiratory infections of the sinus. A. pyogenes or mixed infections usually are found after dehorning, whereas Pasteurella spp. are most common in ascending respiratory tract infections.
Sporadic infections of the maxilla and other bones of the skull caused by Actinomyces bovis may occasionally cause bony expansion into the orbit, resulting in an exophthalmos.
Maxillary sinusitis also may be so severe as to expand into the ventral orbit, causing apparent ocular disease and exophthalmos. Infected tooth roots are the most common cause of maxillary sinusitis in adult dairy cattle.
Neoplasia of the frontal sinus, maxillary sinuses, or respiratory pharynx may expand the affected structures such that the orbit is compromised and ipsilateral exophthalmos with orbital swelling results. Carcinomas, fibrosarcomas, and adenocarcinomas have been diagnosed.
Signs.
Mild to marked unilateral exophthalmos associated with bony expansion of the ipsilateral frontal or maxillary sinus, depression, mild ocular discharge, and fever constitute the major signs in chronic sinusitis (see Chapter 4). Fever may be transient or intermittent, depending on patency of the frontomaxillary-nasal drainage. When purulent material cannot escape, bony expansion of the sinus and fever are more constant. Purulent material can escape through sinus openings into the nasal cavity and cause unilateral purulent nasal discharge. Chronic infection causes extreme softening of the bones surrounding the sinuses and allows for variation in the appearance of the skull. The caretaker may report that the animal’s skull appears swollen on some days but normal on others.
A. bovis lesions that impinge or extend into the orbit are obvious bony swellings that eventually ulcerate and form draining tracts.
Sinus or skull tumors that compromise the orbital space lead to exophthalmus, ocular discharge, ipsilateral nasal discharge, and fetid breath. Inspiratory dyspnea is more common with neoplasia than infection, although fever is less common with neoplasia. Postorbital lymphosarcoma is especially common in dairy cattle.
Diagnosis.
Diagnosis may be obvious following physical examination or may require radiographs, ultrasonography, aspirates for cytology, cultures, or biopsy to confirm specific diseases.
Radiographs are useful to confirm sinusitis, and aspirates for cytology and culture allow appropriate antibiotic selection. Biopsies are essential when presence of neoplasia is suspected. Radiographs are very useful to detect cheek/tooth root abnormalities in chronic maxillary sinusitis patients.
Treatment
Frontal Sinusitis
Trephining of the skull in at least two areas is necessary to provide adequate drainage and lavage of chronic frontal sinusitis in adult cattle. Trephine holes should be 1.75 to 2.5 cm in diameter and drilled at the cornual area (former area of horn) and 3.75 to 4.50 cm off the skull midline along a transverse line drawn through the caudal bony orbit (see Figures 4-10 and 4-11,A and B). Some references suggest a third opening dorsocaudal to the orbit, but in Dr. Rebhun’s experience, this was associated with complications such as entering the orbit. Calves and heifers do not have an extensive frontal sinus except at the cornual area, and trephining the sinus of heifers less than 15 to 18 months of age may lead to invasion of the calvarium.
Successful treatment usually requires 2 weeks of local therapy, systemic antibiotics, and analgesics.
Maxillary Sinusitis
Treatment of maxillary sinusitis requires differentiation of primary sinusitis, tooth root infections in the cheek, sinus cysts, and neoplasia. In dairy cattle, bad teeth that result in sinusitis usually are grossly abnormal, fractured, loose, or missing. Diseased teeth should be removed, and a trephine hole should be drilled into the sinus to allow lavage into the nasal or oral cavity (depending on cause). Because the maxillary sinus has less of a labyrinth-like anatomy than does the frontal sinus, one hole may be drilled using a 1.0- to 2.0-cm trephine or with a large Steinmann pin to allow placement of polyethylene or plastic tubing in the sinus to facilitate daily flushing. Culture of the purulent material in the sinus is essential for selection of appropriate systemic antibiotic therapy. Analgesics may relieve some of the pain associated with eating and thus improve appetite.
No treatment is practical or possible for most sinus tumors in cattle.
Actinomycosis (lumpy jaw) is best treated with sodium iodide and very long-term antibiotic therapy with penicillin (20,000 U/kg twice daily). Organic iodides, although commonly used in practice, are of unproven efficacy.
Neoplastic Disease
The most common orbital tumor in dairy cattle is lymphosarcoma. Tumors may be unilateral or bilateral and cause progressive acquired exophthalmos with exposure keratitis or proptosis (Figure 13-3). Because some Jersey, Ayrshire, and Holsteins cows have relative bilateral exophthalmos (i.e., are “bug-eyed” as a normal appearance), early detection of acquired exophthalmos may be difficult for the average caretaker. Therefore severe exophthalmos and exposure damage to the globe secondary to orbital lymphosarcoma may be reported to be acute by the caretaker. This history implies a higher likelihood of orbital cellulitis than neoplasia. However, thorough physical examination to detect other neoplastic target areas and absence of fever usually allows a proper diagnosis. In fact, even though the retrobulbar lymphoid masses obviously have been present and enlarging for some time before pathologic exophthalmos, the pathology may appear very acute once the degree of exophthalmos prevents the eyelids from completely protecting the central cornea. At this point, exposure damage and desiccation of the central cornea coupled with severe blepharospasm, chemosis, and lid swelling dramatically worsen the appearance of the eye (Figure 13-4). A visual eye with moderate exophthalmos but without exposure keratopathy may change to a blind, proptosed eye with complete corneal desiccation in less than 48 hours.
Figure 13-3 Bilateral pathologic exophthalmos and chemosis caused by retrobulbar neoplasia in a cow with widespread lymphosarcoma.
Figure 13-4 Retrobulbar lymphosarcoma causing exophthalmos, chemosis, and severe exposure keratopathy.
Diagnosis depends on finding other evidence of lymphosarcoma in the patient. Enlarged lymph nodes, melena, cardiac abnormalities, uterine masses, or neurologic signs also may be present. In some patients, the retrobulbar masses are the signal lesions, and other lesions may be undetectable. In this instance, blood for a CBC and bovine leukemia virus (BLV) agar gel immunodiffusion or enzyme-linked immunosorbent assay test is indicated to add supportive data. Most cattle with clinical lymphosarcoma test positive for BLV. This test is supportive but not conclusive because most BLV-positive cattle never develop tumors. Unlike cases with an orbital abscess, serum globulins and inflammatory markers are often normal in cattle with lymphosarcoma. Aspirates from the retrobulbar region may be helpful in some affected cattle. In questionable cases, the proptosed globe should be enucleated to alleviate the cow’s pain and allow collection of tumor material from the orbit for cytology or histopathology. The lymphoid tumors can be palpated along the periorbita and in the orbital cone in most affected cattle. Although the globe usually is free of tumor, rare cases have had conjunctival, corneal, lid, or scleral involvement.
In confirmed cases, the only indication for treatment would be in extremely valuable cattle that are in the last trimester of pregnancy or candidates for embryo transfer in the near future. Enucleation is palliative to relieve the cow’s pain and reduce the possibility of panophthalmitis and orbital cellulitis. Cattle with confirmed orbital lymphosarcoma usually die within 3 to 6 months as a result of diffuse lymphosarcoma. Therefore further treatment is not warranted. Pregnant cattle with confirmed lymphosarcoma masses seldom live through more than 2 to 3 months of gestation. Those that do live to term tend to deliver small, nonviable calves. Embryo transfer attempts in cows with confirmed lymphosarcoma frequently are unsuccessful because of the cow’s catabolic state.
Squamous cell carcinoma may occur in an orbital location but usually is preceded by lid, conjunctival, or corneal squamous cell carcinoma. Orbital squamous cell carcinomas are locally invasive, tend to metastasize, and have a grave prognosis. Carcinomas of respiratory epithelial origin also have been observed in older dairy cattle (more than 8 years of age). These tumors are slow growing over months to years; cause progressive unilateral exophthalmos, inspiratory stridor, and reduced airflow in the ipsilateral nasal airway; and may cause ipsilateral Horner’s syndrome (see Figures 4-5 and 4-6). Although prognosis is poor, affected cattle may be productive for 1 to 3 years with these slow-growing tumors.
Figure 13-5 Right-sided Horner’s syndrome in a cow secondary to a perivascular reaction in the right jugular vein region. Ipsilateral ptosis and dryness of the muzzle are present.
Figure 13-6 Microphthalmia in a Guernsey calf. The calf also had congenital absence of the tail and a ventricular septal defect.
Cattle sent to slaughter with severe ocular or orbital neoplasia are condemned when the eye is destroyed, has draining pus, is obscured by neoplasia, has bony involvement, or is associated with lymph node enlargement or emaciation.
Neurologic Diseases
Horner’s syndrome is the most common neurologic disease of the orbit observed in dairy cattle. The features of ptosis, mild miosis, and ipsilateral facial warmth coupled with dryness of the muzzle and nares are well described. Horner’s syndrome in cattle is most commonly caused by injury to the cervical vagosympathetic trunk by carotid artery hematomas, cellulitis of the neck, or direct injury by traumatic venipuncture of the jugular vein (Figure 13-5). Other causes are rare, but the syndrome has been observed with skull tumors (e.g., squamous cell carcinoma, carcinoma, and adenocarcinoma) that invade the orbit causing upper respiratory dyspnea and decreased air flow from one or both nostrils, as well as Horner’s syndrome.
DISEASES OF THE GLOBE
Developmental Diseases of the Globe
Etiology and Signs
Developmental malformations of the globe result in megaglobus or microphthalmos (Figure 13-6). Anophthalmos, absence of all ocular tissue, is seldom an appropriate term because histologic section of orbital tissue in suspected anophthalmos cases almost always produces some evidence of ocular tissue, thus making microphthalmos the proper term. Congenital microphthalmia may be unilateral or bilateral in calves. Physical, toxic, and infectious causes have been suggested but seldom are confirmed to explain all sporadic microphthalmia. In utero infection with bovine virus diarrhea virus (BVDV) during the middle trimester occasionally has resulted in microphthalmia.
Genetic causes of microphthalmia appear common in dairy cattle. In Guernsey and Holstein calves, the defect has been linked with cardiac and tail anomalies. Most commonly these calves have a ventricular septal defect and wry tail, as well as unilateral or bilateral microphthalmia. Tail defects other than wry tail have been observed in some Guernsey and Holstein calves with microphthalmia and/or ventricular septal defect. These include absence of a tail, short tail, absence of some sacral vertebrae in addition to coccygeal vertebrae, and atresia ani coupled with absence of vertebrae (see Figure 13-6). In Guernseys, these malformations are thought to be caused by a recessive trait, but in Holsteins, the exact mode of inheritance is unknown.
Congenital megaglobus results from anterior cleavage abnormalities or multiple congenital anomalies producing glaucoma in utero. Dr. Rebhun observed several calves with anterior cleavage anomalies. The lens placode had not separated from the surface ectoderm during the development of those eyes. Subsequent influx of mesodermal tissue forming the corneal stroma, endothelium, Descemet’s membrane, and iris surrounds the lens. The resulting absence of an anterior chamber causes congenital glaucoma and buphthalmos. All cases to date have been unilateral, and the affected eye is noticeably buphthalmic at birth, with corneal edema, central dense opacity (lens in cornea), and no discernable anterior chamber (Figures 13-7 and 13-8).
Figure 13-7 Congenital buphthalmos and glaucoma in the right eye of a calf with an anterior cleavage defect.
Figure 13-8 The lens can be observed as a dense circular opacity within the cornea of a calf with an anterior cleavage anomaly. Corneal edema radiates from the lens opacity.
Convergent strabismus with or without associated relative exophthalmos has been described as an inherited trait in Jersey and Shorthorn cattle. It also has been observed occasionally in Ayrshires, Holstein, and Brown Swiss cattle (Figure 13-9). Bilateral relative exophthalmos (“bug-eyed cows”) is a condition that has been observed in several dairy breeds and probably is a genetic trait. Exophthalmos in these cows does not progress to a pathologic state or exposure keratitis because the eyelids still cover the cornea adequately. However, pigment migration occurs over the bulbar conjunctiva and peripheral cornea as a result of exposure of the globe to dust, air, or debris in some affected cattle.
Figure 13-9 Severe convergent strabismus and congenital exophthalmos in a Holstein. The temporal bulbar conjunctiva has become pigmented as a result of chronic exposure.
(Photo courtesy Dr. Kit Blackmore.)
Congenital nystagmus has been observed in several breeds and is common in Holsteins. The nystagmus is a rapid pendular nystagmus that is horizontal and constant. It persists throughout the animal’s life and does not seem to interfere significantly with vision. The heritability or mode of inheritance is unknown. The trait also has been observed commonly in a herd of purebred Guernseys.
Treatment
Enucleation is indicated for calves with unilateral congenital megaglobus because the affected eyes become grotesque and soon suffer exposure damage. Enucleation has been successful in these cases, and the relatively rare incidence rules against inheritance. Microphthalmic globes usually are not treated, but if no other anomalies exist, the owner may elect to raise a calf with unilateral microphthalmos. Chronic conjunctivitis occurs in some microphthalmic patients and, if persistent and severe, may dictate enucleation to stop chronic discharge and fly irritation, thereby aiding patient comfort.
Acquired Diseases
Acquired megaglobus may follow severe intraocular inflammation of exogenous or endogenous cause. Infectious bovine keratoconjunctivitis (IBK), trauma, and uveitis are the usual causes of anterior synechiae, lens luxation, and adhesions that disturb aqueous outflow, thereby creating glaucoma. Endophthalmitis and panophthalmitis secondary to septic uveitis or ocular perforation may also cause megaglobus. If megaglobus is severe enough to cause exposure keratitis, the affected globe should be enucleated to prevent eventual perforation or panophthalmitis. Adult dairy cattle with severe megaglobus treated by enucleation become comfortable and return to anticipated production within several days (Figure 13-10). Therefore it is important that acquired megaglobus is not diagnosed erroneously as a retrobulbar neoplasia.
Figure 13-10 Acquired megaglobus following severe pinkeye in a Holstein cow. Enucleation of this eye resulted in rapid improvement in appetite and production as a result of resolution of pain and irritation caused by the enlarged globe.
Less frequently, megaglobus follows intraocular neoplasia or granulomatous infections of the uveal tract. Squamous cell carcinoma is the most frequent tumor to invade the globe, and tuberculosis must be considered when a granulomatous infection of the globe is diagnosed.
Phthisis bulbi (shrinking of the globe) follows ocular perforations, chronic uveal inflammation, and severe pinkeye complications such as corneal perforation and iris prolapse. If a phthisical globe is sterile and nonpainful, it may be ignored. However, if chronic conjunctivitis, facial dermatitis from discharges, and fly irritation affect the cow’s production, enucleation should be performed.
DISEASES OF THE EYELIDS
Congenital Diseases
Ancillary or supernumerary nasolacrimal duct openings have been reported in 13 Brown Swiss calves and 1 Holstein calf. These calves had a depigmented, hairless puncta located a few centimeters from the medial canthus in addition to the normal puncta in the upper and lower lid margins. The lesion is likely to be inherited, but this has not been proven.
Neurologic Diseases
Unilateral facial nerve palsy causing ptosis and exposure keratitis is common in calves affected with otitis media/interna and adults affected with listeriosis. Trauma may cause facial nerve injuries resulting in neuroparalytic keratitis in bovine patients of any age. The most common cause of bilateral eyelid paralysis in cattle is “stanchion trauma” wherein a cow pulls back against a stanchion until her head is trapped along the temporal ridge between the ears and orbit. The result is a bilateral traumatic palpebral nerve paralysis.
Signs of neuroparalytic keratitis include lacrimation, ptosis, absence of palpebral response, and progressive corneal exposure damage. Treatment requires therapy for primary diseases and protection of the cornea with frequent application of antibiotic ointments or tarsorrhaphy. Cattle with facial nerve paralysis appear to be much less likely to develop corneal ulcers than in many other species. Treatment of stanchion paralysis requires warm compresses, systemic antiinflammatories, and protection of the cornea with ocular lubricants or broad-spectrum antibiotic ointment if indicated.
Flashing or protrusion of the nictitans in tetanus patients is a passive rather than active movement of the nictitans. Tetany of the retractor oculi muscles pulls the globe caudally in the orbit, allowing passive prolapse of the nictitans.
Inflammatory Diseases
Etiology and Signs
In dairy cattle, trauma to the eyelids occurs from blows to the head by other cattle or handlers, or from the cow crashing into feed troughs, stanchions, and chutes. Infection of the eyelids can result from neglected lacerations or puncture wounds from similar causes. The eyelids can be severely swollen as a result of hemorrhage or inflammation because cattle have abundant eyelid skin with a great amount of tissue elasticity. This elasticity affords the surgeon a great deal of tissue to work with if surgical or plastic repair is necessary.
Signs of trauma or laceration are obvious. Cellulitis of the eyelids and secondary orbital cellulitis are possible in neglected or dirty wounds. Lid swelling and ocular discharge accompany most traumatic injuries.
Less common causes of lid inflammation include actinobacillosis granulomas appearing at the site of previous eyelid injury and demodectic mite infestation.
Allergic reactions commonly result in eyelid swelling and conjunctival edema (chemosis). These signs usually but not always are accompanied by other systemic signs such as urticaria, skin wheals, facial swelling, and other mucocutaneous junctional swellings. Allergic reactions may occur secondary to iatrogenic administration of antibiotics, intravenous (IV) fluid, blood transfusions, and biologics. Similar reactions accompany individual animal sensitivities to various feedstuffs, plants, and milk allergy (see Chapter 7).
Treatment
Conservative measures such as cold or hot compresses, cleaning and dÃ(c)bridement of damaged tissue, local and systemic antibiotic therapy, drainage of abscesses, and protection of the cornea with topical antibiotic ointments suffice in most cases. NSAIDs and corticosteroids are avoided unless soft tissue swelling is severe; corticosteroids are contraindicated in pregnant cattle. Lacerations of the eyelid may be closed using a two-layer technique with absorbable sutures (2-0) in the lid stroma and nonabsorbable sutures (2-0 or 3-0) in the skin. It is not necessary to suture the conjunctiva. Topical and systemic antibiotics for 5 to 7 days are indicated postoperatively to help prevent infection and subsequent wound dehiscence.
Actinobacillosis granulomas should be debulked, and the cow should be treated with 20% sodium iodide (30 g/1000 lb body weight IV) followed by 30 g of oral organic iodide powder once daily for 14 days.
Allergic reactions require treatment with avoidance or correction of the primary cause, antihistamines, antiinflammatories, or epinephrine (see Chapter 7).
Neoplastic Diseases
Etiology and Signs
Fibropapillomas or “warts” are the most common tumor to involve the eyelid of calves and young cattle. In most instances, the tumors are raised, firm masses with a gray crusty covering (see Figure 7-1).
Lymphosarcoma rarely infiltrates the eyelids as a diffuse lid swelling with conjunctival chemosis.
Squamous cell carcinomas are the most common tumor to affect the eyelids and nictitans (or third eyelid) of adult cattle. White-faced beef cattle and Holsteins that are mostly white or have nonpigmented lid margins or nictitans are at risk. In predominantly dairy practice, most bovine patients with squamous cell carcinoma (“cancer eye”) are Holsteins. The tumors are pink, raised or ulcerated, cobblestone in appearance, and most commonly appear in middle-aged (5 to 10 years) cows. True squamous cell carcinoma of the eyelid usually is preceded by precursor lesions that are epitheliomas or a wartlike growth on the eyelid or eyelid margin.
Treatment
Fibropapillomas normally are self-limiting within 4 to 6 months and do not require treatment. Persistent or large fibropapillomas (Figure 13-11) may interfere with eyelid function or cause corneal injury and require surgical treatment via cryosurgery or sharp dissection.
Squamous cell carcinomas tend to be locally invasive and may metastasize in some neglected cases. This tumor requires aggressive early therapy to prevent progression, or the cow will be lost. Many therapeutic options exist for early, small squamous cell carcinoma of the eyelids, whereas enucleation, radical exenteration, or culling may be required for large lid lesions. Recognition of early tumor formation when the mass is less than 2.0 cm in diameter allows consideration of cryosurgery, radiofrequency hyperthermia, radiation (if available), sharp surgery, and immunotherapy. Large lid masses (greater than 5.0 cm in diameter) are less likely to be treated successfully because destruction or removal of this much lid tissue may lead to ocular exposure damage (Figure 13-12). These large tumors also are more likely to invade adjacent adnexal tissue, orbital ligaments, periorbita, and bone of the skull. Tumors at the medial canthus are extremely dangerous because they need to advance only 2.0 cm along the medial orbital ligament before entering the bony orbit.
Figure 13-12 Squamous cell carcinoma of the lower eyelid. The tumor is pink, raised, ulcerative, and has a white necrotic surface discharge. Chronic superficial keratitis is present as a result of tumor irritation of the cornea.
DISEASES OF THE CONJUNCTIVA
Developmental Diseases
Dermoids of the conjunctiva cause irritation to the cornea because of hair growth on the dermoid and require surgical removal. A full-thickness wedge resection of the involved conjunctiva and lid followed by a two-layer repair has given excellent results.
Inflammatory Diseases
Etiology and Signs
Moraxella bovis, the cause of IBK (i.e., pinkeye), is the most important bacterial disease of the conjunctiva and cornea in cattle. The organisms and IBK will be discussed in the section on the cornea.
Pasteurella and other bacteria may also cause mucopurulent conjunctivitis in cattle occasionally. Pasteurella conjunctivitis occurs in conjunction with severe Pasteurella pneumonia or septicemia in calves. The organisms are normal inhabitants of the upper respiratory tract in cattle and therefore accessible to the conjunctiva. Neisseria spp. have been isolated from cattle with conjunctivitis and infectious keratitis. Atypical (winter) outbreaks of IBK-like endemics have been blamed on these other bacteria, but overwhelming evidence supports M. bovis as the most likely causative organism. Calves with respiratory infections caused by Histophilus somni may have conjunctivitis, rhinitis, laryngitis, and pneumonia. Cattle affected with bacterial conjunctivitis have a serous or mucopurulent ocular discharge, conjunctival injection, and do not appear to have ocular pain.
Mycoplasma and ureaplasma have been isolated from the eyes of cattle during herd epidemics of conjunctivitis. Affected cattle do not appear ill, but 10% to 50% of the animals have a unilateral or bilateral ocular discharge and conjunctival hyperemia. The ocular discharge is serous initially but becomes mucopurulent after 1 to 4 days. No keratitis is associated with this problem.
Infectious bovine rhinotracheitis (IBR) virus, the herpes virus 1 of cattle, may cause a severe endemic conjunctivitis in nonvaccinated cattle. The conjunctivitis may be the only lesion observed in sick cattle or may occur in conjunction with the typical respiratory form of IBR. The disease has been observed in heifers and adult cattle. Typical lesions include severe conjunctival hyperemia, heavy ocular discharge that converts from serous to mucopurulent over 48 to 72 hours, and the presence of multifocal white plaques in the palpebral conjunctiva (Figure 13-14). The lesions may be unilateral or bilateral and affect 10% to 70% of the herd. The plaque lesions are pathognomonic for IBR. Affected adult cattle have high fever (105.0 to 108.0° F/40.56 to 42.22° C), depression, and decreased milk production. Milking cattle with the conjunctival form of IBR appear ill regardless of whether the respiratory form coexists. Heifers with the conjunctival form of IBR may have fever and mild systemic illness but seldom appear as sick as adult milking cattle. The reason for this difference is not known but may be related to the stress of lactation.
Figure 13-14 Multifocal white plaques on the palpebral conjunctiva as a result of acute infectious bovine rhinotracheitis virus conjunctivitis.
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