Ophthalmacrosis of the chick

A peculiar enlargement of the eyes of certain groups of chickens has been observed by a number of poultry researchers at The University of Tennessee Agricultural Experiment Station and elsewhere. This condition of eye enlargement, referred to as ophthalmacrosis in this study, is characterized in the live bird by an elongation of the eye. The space between the inner canthus and the edge of the iris is increased; thus, resulting in a much greater exposure of the sclera or white of the eye. This gives the eye the appearance of being slanted. The eyeball itself is greatly enlarged, and the apparent increase in vitreous humor results in an outer displacement of the lens against the cornea with the obliteration of the anterior chamber.

The few reports found in the literature pertaining to the enlargement of the eyes of chickens attribute the development of the condition to excessive exposure to light (Jensen, 1957, Lauber et al., 1961, McCluskey and Arscott, 1967). However, the studies made by Shirley and Voitle, The University of Tennessee Agricultural Experiment Station, dating back to 1955 (unpublished), show that this eye enlargement not only occurs when the birds are exposed to constant light, but to an even greater extent in constant darkness. This indicates that light per se is not the causative factor, but that the absence of a diurnal light-dark cycle may account for the eye abnormality.

This poses the question of the physiological processes involved in the maintenance of the osmotic integrity of the ocular fluids and their regulation by the photoperiod. Can the dynamics of the ocular fluids be added to the list of several physiological functions of animals now known to be under the influence of photoperiodism?

The experiments reported herein were designed to determine certain physiological relationships involved in ophthalmacrosis of chickens.