Which structure is located in both anterior and posterior chambers of the eye?

The aqueous humor is a clear fluid that is found in both the anterior and posterior chambers of the eye. The anterior chamber is located between the cornea and the iris, while the posterior chamber is situated behind the iris and in front of the lens. Aqueous humor serves several important functions: it helps maintain intraocular pressure, provides nutrients to the avascular structures of the eye like the lens and cornea, and assists in the removal of metabolic wastes.

The other structures mentioned do not fulfill the criteria of being present in both chambers. The cornea is the transparent front part of the eye and does not extend into the posterior chamber. The retina is located at the back of the eye, involved in the light detection process, and is not present in either of the chambers. The sclera is the white outer layer of the eyeball and encases the eye but does not reside within the anterior or posterior chambers themselves. Thus, the unique presence of aqueous humor in both areas makes it the correct answer.