Chapter 13 Ocular Diseases

DISEASES OF THE ORBIT

Inflammatory Orbital Diseases

Orbital Cellulitis

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.

Figure 13-2 Drainage of a chronic orbital abscess in the retrobulbar region.

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.

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.

When orbital swelling is obvious, exophthalmos, lid swelling, and chemosis usually are present. Serous ocular discharge is present initially but may become mucopurulent with time. Affected cattle show signs of “headache,” holding the head extended, with eyelids partially closed. Affected sinuses sound duller than normal on percussion.

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.

Purulent material in the sinus should be cultured such that an appropriate antibiotic may be selected for systemic use. The most common isolates from adult cattle and bulls are A. pyogenes and Pasteurella sp. In extremely chronic cases, fluid pus may be replaced by a pyogranulomatous mass of tissue that fills the sinus. When the sinuses cannot be flushed, these patients have an extremely poor prognosis because they often develop fatal meningitis. Lavage of the sinus should be performed daily to flush away discharges and maintain patent trephine holes. Saline, dilute iodine solutions, and other nonirritating lavage solutions may be used. Analgesics such as aspirin (240 to 480 grains orally twice daily for an adult cow) are indicated to alleviate the pain associated with headache.

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.

Treatment for cervical lesions is symptomatic with topical and systemic antiinflammatory drugs. Prognosis is good for return to function. Tumors have a hopeless prognosis.

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.