16 Microphthalmia, or a congenitally small eye, is one of the more frequent ophthalmic anomalies in food animals (Figure 16.1). Congenital eye anomalies occur in 3.5% of lambs, 5.5% of pigs, and 18.7% of calves. In calves, microphthalmia is the most frequent eye defect. Microphthalmia is inherited, viral (calves – bovine viral diarrhea virus; lambs – bluetongue virus), or nutritional (pigs – vitamin A deficiency), as well as combined with other ocular and systemic anomalies. Figure 16.1 (A) Microphthalmia in a goat. Note the elevated nictitans, enophthalmia, and mydriasis. (B) Marked microphthalmia in a white Shorthorn calf with the palpebral fissures less than 50% of normal size. Clinically, microphthalmia occurs in one or both eyes and is characterized by a smaller than normal palpebral fissure, nictitans protrusion, and a small globe. Pupillary abnormalities, congenital cataracts, and retinal dysplasia and detachments can also occur. Strabismus, or the deviation of the eye, occurs most frequently in cattle (Figure 16.2). Esotropia, or convergent strabismus, is inherited in the Jersey, German Brown Swiss, Holstein, Ayrshire, and Shorthorn breeds. It can be transmitted as a recessive (Jersey and Shorthorn cattle) or dominant trait (German Brown Swiss cattle). These eyes can also appear to be exophthalmic. Acquired strabismus, usually esotropia, also develops as a sign of polioencephalomalacia (PEM) and listeriosis in cattle. Figure 16.2 (A) Inherited strabismus in a Holstein cow. Note the exposed lateral bulbar conjunctiva and esotropia (convergent strabismus).(B) Congenital strabismus and microphthalmia in a Hereford. Orbital neoplasms produce slow and progressive exophthalmia, strabismus, conjunctival hyperemia, and nictitans protrusion, and with advanced exophthalmia can also cause impaired blink, exposure keratitis, vision impairment, and even blindness. Orbital neoplasms in cattle are usually unilateral as with squamous cell carcinomas, but can be bilateral in lymphoma (Figure 16.3). Figure 16.3 (A) Lymphoma and squamous cell carcinoma are the most common forms of orbital neoplasia in cattle. In this Holstein cow, systemic lymphoma has involved the retrobulbar tissues and resulted in exophthalmia. (B) Extensive size and invasion of the orbital bones with squamous cell carcinoma in this Hereford cow. Dermoids affect the eyelids, conjunctiva, nictitating membrane, or cornea (Figure 16.4). In food animals, calves are most frequently affected, and dermoids are inherited in the Hereford breed. One or both eyes are affected. A white, black, or colored mass with long coarse hair extending from its surface will be present upon examination of the irritated eye. Recommended treatment, when pain and disfigurement are present, is superficial keratectomy. Limited scarring results after surgery. Figure 16.4 Corneoconjunctival dermoid in Jersey calf involving the ventromedial bulbar conjunctiva and cornea. Note the brown mass and the long coarse hair protruding from its surface. Entropion in food animals occurs most frequently in lambs, and a considerable percentage (up to 80%) of the flock can be affected. The entropion affects one or both eyes, and either the upper or lower eyelids, or both (Figure 16.5). Clinical signs range from mild blepharospasm, lacrimation, nictitating membrane protrusion, and conjunctivitis with serous exudates to severe blepharospasm with mucopurulent conjunctivitis and corneal ulceration. Persistent entropion with corneal ulceration can lead to corneal perforation and iris prolapse. Figure 16.5 Entropion in the most common ophthalmic disease in sheep. In this lamb entropion affects the entire lower eyelid and had caused a ventral corneal ulcer. Note the corneal vascularization. To treat entropion in immature animals, the eyelid margins are everted to the normal position (away from the cornea) using vertical mattress sutures or skin staples. Permanent surgical correction with the Hotz–Celsus procedure used in small animals should be delayed until the animal has approximated its adult size. The eyes of lambs have excellent healing ability, and a completely opaque but nonperforated cornea can clear within several weeks. Sheep and goats present with similar forms of infectious keratoconjunctivitis (Figure 16.6). Chlamydophila psittaci and the Mycoplasma spp. (M. conjunctivae, M. mycoides var. capri, and M. conjunctivae var. ovis) are the most commonly implicated pathogens. Other microorganisms have been isolated, such as Branhamella ovis, Escherichia coli, and Staphylococcus aureus, but these are often found in mixed infections or concurrent with the main pathogens. Chlamydophila is most prevalent during lambing and when lambs are present, and adults can be affected repeatedly (over years) suggesting limited immunity. Polyarthritis can also occur with the keratoconjunctivitis. The disease affects predominately the conjunctiva (epiphora, chemosis, and conjunctival hyperemia), and serous progressing to mucopurulent conjunctival exudates. Conjunctival lymphoid follicles can develop in the third week of infection when clinical signs are regressing. The corneal disease does not affect all sheep and consists of interstitial (deep) keratitis, corneal vascularization, and pigmentation. Diagnosis can be made using conjunctival scrapings and cytology. The disease is generally self‐eliminating, but systemic tetracyclines can shorten the clinical signs. Figure 16.6 Chlamydophila infectious keratoconjunctivitis in a ram. Note the interstitial keratitis and corneal edema. Both sheep and goats are also affected with mycoplasmal infectious keratoconjunctivitis, and this disease is generally more severe than that caused by Chlamydophila. The disease starts as a conjunctivitis that then extends to the peripheral cornea as microabscess formation. Initial clinical signs include eyelid swelling, conjunctival hyperemia, epiphora, and blepharospasm (Figure 16.7). Soon, keratitis with both superficial and deep vascularization develops with the formation of microabscesses. The conjunctival exudates range from serous (early) to mucopurulent (late). Infrequently, and in severely affected eyes, corneal ulceration, iridocyclitis with hypopyon, and panophthalmitis develop. Figure 16.7 (A) Early mycoplasmal infectious keratoconjunctivitis in a young goat. Note the circumferential corneal neovascularization and corneal infection. (B) Mycoplasmal infectious keratoconjunctivitis in a goat. Note the conjunctival exudates, marked corneal vascularization, corneal edema, and corneal microabscesses below the dorsal blood vessels. A secondary iridocyclitis is also present. (C) More advanced mycoplasmal keratoconjunctivitis. The entire cornea is opaque and surrounded by corneal vascularization. The disease has progressed to panophthalmitis. Diagnosis is made by means of clinical signs and cytology (intracytoplasmic coccobacillary to ring‐shaped bodies). For treatment, topical and intramuscular tetracyclines are recommended. These mycoplasmal organisms have also been associated with mastitis, arthritis, and pleuropneumonia. Infectious bovine keratoconjunctivitis (IBK) occurs worldwide, and affects all breeds of cattle (Figure 16.8). The infection rates vary by season, but can be as high as 63% in cows and 75% in calves. Older, previously exposed cattle generally develop a milder form of the disease, suggesting some immunity develops and persists. The Bos indicus are more resistant than the Bos taurus breeds. Although many different bacteria have been implicated, the hemolytic and piliated form of Moraxella bovis is known to cause the disease. Transmission occurs via flies, animal handlers’ hands, or direct contact. The nonhemolytic and nonpiliated forms of M. bovis appear to be normal inhabitants of the bovine conjunctival sac. The nonpathogenic M. bovis appears to undergo conversion to the pathogenic form quickly when exposed to greater ultraviolet radiation during the early summer months. Figure 16.8 The clinical appearance of infectious bovine keratoconjunctivitis (IBK) varies depending on the stage of the disease. (A) Early IBK with intense conjunctivitis, and a central large corneal ulcer and edema with corneal vascularization. (B) Another case of IBK. Note the abscessed cornea, corneal edema, and peripheral vascularization. (C) More advanced IBK with corneal ulceration perforation and iris prolapse. The pigmented iris is protruding within the necrotic corneal ulcer. Considerable edema and vascularization involve the surrounding cornea.(D) IBK with a healing corneal ulcer. There is faint fluorescein retention in the central ulcer. A faint to small corneal opacity will result. The initial early clinical signs include marked lacrimation, blepharospasm, photophobia, conjunctival hyperemia, and chemosis. Within 24–48 hours a central small pale yellow corneal abscess forms that quickly sloughs leaving a shallow corneal ulcer. The corneal ulcer can expand in size and depth, and a secondary iridocyclitis develops. Superficial corneal vascularization starts within a few days, and within 5–7 days the entire cornea is vascularized leading to healing of the corneal ulcer. Within 2 weeks the corneal ulcer is usually healed, and by 1–2 months only a faint central corneal scar remains. Infrequent complications of IBK include corneal perforation and iris prolapse, panophthalmitis, and secondary glaucoma. Fortunately, M. bovis
Food and Fiber Animal Ophthalmology
Diseases of the Orbit
Diseases of the Eyelids
Diseases of the Conjunctiva and Cornea
Chlamydophila Infectious Keratoconjunctivitis in Sheep and Goats
Mycoplasma Infectious Keratoconjunctivitis
Infectious Bovine Keratoconjunctivitis
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