Choroid Choroid The choroid, also known as the choroidea or choroid coat, is the vascular layer of the eye, containing connective tissues, and lying between the retina and the sclera. The human choroid is thickest at the far extreme rear of the eye (at 0.2 mm), while in the outlying areas it narrows to 0.1 mm. The choroid provides oxygen and nourishment to the outer layers of the retina. Along with the ciliary body and iris, the choroid forms the uveal tract. The structure of the choroid is generally divided into four layers (classified in order of furthest away from the
Iris cyst a shadow with a tumor but almost never with a cyst. Ultrasound B-scan (USB) uses wavelengths of 10-20MHz to form an image of the eye. USB can be used to identify the extension of the iris cyst in either the anterior or posterior chamber. It can also be used to identify midzonal cysts behind the iris and to determine whether there is ciliary body involvement. The preferred method to determine ciliary body involvement however, is not USB but ultrasound biomicroscopy. Ultrasound biomicroscopy, (UBM) has a higher resolution than USB an di t also using soundwaves with a higher frequency from