What are the contributions of the choroid & sclera?
A novel finding in the chick that has since been corroborated in other animals is that the choroid can rapidly modulate its thickness, in so doing, varying the position of the retina and thus the state of focus of the eye. Traditionally, the vascular choroid has assigned the far similar role of supplying surrounding tissues with nutrients. “Choroidal accommodation” can lead to increases in thickness of over 100 m? in a day in the chick. We understand relatively little about the mechanisms underlying these thickness changes and their regulation. Choroidal blood flow changes occur in the same direction as the thickness changes, yet precede them, raising the possibility that they trigger the latter. The thickened choroids have increased protein and water content, with the main expansion taking place mainly in the outer layers where lacunae, lymphatic-like vessels, reside. The sclera constitutes the outer support structure of the eye, and also contributes to defocus compensation although i
