What fluid fills the space between the lens and the retina?

The correct answer is that the vitreous humor fills the space between the lens and the retina. The vitreous humor is a transparent gel-like substance that occupies the vitreous chamber of the eye, which is located behind the lens and in front of the retina. This gel maintains the shape of the eye, providing structural support, and also helps in the transmission of light to the retina.

The vitreous humor is important for the overall health of the eye because it contains nutrients for the retina and helps to keep the retina in place against the choroid layer. Additionally, it acts as a shock absorber for the eye.

Other options like aqueous humor refer to the fluid found in the anterior chamber of the eye, between the cornea and the lens. Serous fluid is not a specific fluid in the context of the eye, and synovial fluid is associated with the lubrication of joints rather than any part of the eye. Understanding the role and location of these fluids is essential for grasping the anatomy of the eye and how its components function together.