Chapter 8 Ocular disorders

Introduction

Disorders of the eye are relatively easily seen and photographed. The disorders may be congenital, nutritional, infectious, traumatic, or neoplastic in origin. Examples of each are illustrated. Some conditions, e.g., infectious bovine keratoconjunctivitis (IBK), occur worldwide, and may be a significant cause of economic loss. Pain associated with the active phase of disease restricts feeding and leads to weight loss. If sight is lost, affected animals are less able to forage, particularly under extensive ranch conditions, and they are more susceptible to predators.

Congenital disorders

Although by definition congenital abnormalities are present at birth, some may not be recognized until the calf is much older. Strabismus (squint) is a typical example. Congenital disorders may be genetic, and therefore inherited, or they may be caused by environmental factors. Some abnormalities have more than one cause. For example, congenital cataract may be inherited, or it may have been caused by maternal BVD infection during pregnancy. The cause of many abnormalities is unknown. Congenital disorders in organs other than the eye are described in Chapter 1.

BVD/MD, discussed under “Alimentary disorders” (p. 54) can give rise to congenital or acquired ocular changes. Congenital BVD/MD can cause teratogen-induced retinal necrosis and degeneration, focal capsular cataract, as well as optic nerve gliosis, microphthalmos (see below) and optic neuritis. 8.1 shows retinal changes in a calf associated with the teratogenic effects of BVD/MD virus. There is marked attenuation of many retinal blood vessels, retinal hyper-reflectivity and a patchy yellow pigmentary disturbance.

8.1 Retinal dysplasia in BVD

Anophthalmos (anophthalmia); microphthalmos (microphthalmia)

Definition

anophthalmos is a developmental absence of the eye; microphthalmos is an abnormal smallness of one or both eyes.

Clinical features

the two examples illustrate both abnormalities. The left eye of the Guernsey heifer in 8.2 has a small orbit and there is no evidence of the globe. Note that the entire orbit appears collapsed and smaller, compared with the normal right eye. This condition can be inherited. A Jersey cow with microphthalmos (8.3) and prolapse of orbital fat had possibly had an insult to the eye in calfhood, leading to this shrunken globe (phthisis bulbi).

8.2 Anophthalmos in left eye of heifer (Guernsey)

8.3 Microphthalmos in cow (Jersey)

Cataract

Definition

opacity of the lens or its capsule, or both, present at birth or acquired from trauma or systemic disease.

Clinical features

both eyes of the 4-day-old Hereford crossbred calf in 8.4 were affected and the animal was totally blind. In other animals, only one eye may be affected, or the cataract may not cause total loss of vision. Congenital cataract is not normally progressive. Cattle cope with blindness remarkably well and can be reared in confinement systems. They quickly learn to remain within the group, although handling can be difficult. Blind dairy cows will learn to follow the herd to and from pasture. Congenital cataract may be inherited, or may result from the teratogenic effects of maternal BVD infection during early/mid pregnancy. 8.5 shows a congenital nuclear cataract in a young Friesian calf.