Three avian eye enlargement protocols as myopia models: effects of pharmacological intervention

Myopia is a prevalent condition threatening vision in half or more of the individuals in some subpopulations and at some ages. The etiology is unknown. It is not even clear whether myopia has several possible causes or only one, whether the condition is inherited or acquired. Suggested counter measures have ranged from behavior modification during the growing years through various medications, to surgical intervention. It is suggested that answers to these questions must lie in research exploring how the eye develops, how it serves its owner. A common finding in most cases of myopia is that the eyeball is too long axially, thus the image from a distant object comes to sharp focus in front of, rather than at, the retina. Accommodation increases the refractive power of the eye and is counterproductive in a myope. Nonetheless, one suggested treatment has been to suppress accommodation by paralyzing the ciliary muscles. Another theory suggests that high intraocular pressure causes eye enlargement, thus the anti-glaucoma drugs have sometimes been recommended. We report here some trials involving drugs given to chicks with light-induced avian glaucoma, a syndrome characterized by moderate to severe myopia, and elevated intraocular pressure.