Dimensional and Physiological Lesions in the Chick Eye as Influenced by the Light Environment 1

Domestic chickens reared under continuous light (24L/0D) develop a series of eye lesions culminating in elevated intraocular pressure and blindness (1-3). This light-induced avian glaucoma is characterized by enlargement of the globe (as evidenced by increased eye weight), reduction in anterior chamber depth, and impaired outflow facility (3). Recently we have shown that in preglaucomatous eyes lactic dehydrogenase (LDH) leakage from the cornea is one of the earliest detectable lesions, and that preliminary morphological damage as well can be detected by 4 wk of age (4). That systemic pathways are involved in the genesis of light-induced avian glaucoma was suggested by a study which showed that bilateral eye enlargement occurs even when light is excluded from one eye of birds reared under 24L/0D (5). Eye enlargement can also be induced in the domestic chicken by greatly reducing the intensity of the environmental light (6, 7). This finding raises the possibility that total exclusion of light from the eye may also have some effect on eye morphology. The present study involved experiments addressed to the following questions: (a) are all the early ocular morphological changes seen in 24L/0D birds present bilaterally when light is excluded from one eye (Experiment I)? (b) if so, are the effects on the covered eye a result of 24L/0D acting via an extra ocular system(s), or are they induced only by lack of light to the eye (Experiment II)? In addition, we have measured aqueous and corneal LDH levels (Experiment III) and here report enzyme changes in 24L/0D birds reared to 8 wk of age, an extension of earlier findings. Materials and Methods. White Rock chicks (fast growing, broiler type) were reared in light- and temperature-controlled environmental chambers (24 × 24 × 18 in. high).