Chapter 13 Ocular Diseases
DISEASES OF THE ORBIT
Inflammatory Orbital Diseases
Orbital Cellulitis
Inflammation of the Tissues Adjacent to the Orbit
Diagnosis.
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.
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 13-4 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.
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.
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.
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.
DISEASES OF THE EYELIDS
Inflammatory Diseases
Etiology and Signs
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).
Neoplastic Diseases
Etiology and Signs
Lymphosarcoma rarely infiltrates the eyelids as a diffuse lid swelling with conjunctival chemosis.