Keratoglobus lesions in the eyes of rearing broiler breeders

This report describes the occurrence of keratoglobus lesions in a rearing flock of broiler breeder grandparent stock (female line), and its ophthalmological and ocular pathomorphological features. Keratoglobus is known as a recessive sex-linked (Z chromosome) trait in some lines of chickens. The first cases were encountered at 5 weeks of age. At the end of the rearing period a total of 1.5% of the flock was affected. In the flock and affected birds, no signs of any other disease were detected. Compared to eyes of healthy flock mates, the most prominent symptom was ocular protrusion due to bulging and thinning of the cornea, and increase in anterior chamber depth. In addition, there were mononuclear, granulocytic and plasma cell infiltrates in the iris and corpus ciliare, and mild to minimal exudate in the anterior chamber in all cases examined. Although the corneal epithelium and collagen bundles appeared normal on electron microscopy, the corneal endothelium showed some loss of cells and the keratocytes some degenerative changes. The cornea had not lost its transparency and did not show any signs of inflammation, whereas the conjunctiva contained mononuclear infiltrations. Other eye structures did not show any clinical or pathological changes. The pathogenesis of keratoglobus lesions in chickens is unknown. Although a hereditary origin seems probable, it is not known whether the inflammatory changes found caused the presented pathology or were secondary to the extreme corneal bulging.