Certified Paraoptometric (CPO) Practice Exam 2025 - Free Paraoptometric Practice Questions and Study Guide

The thick jelly-like substance that fills the eyeball behind the lens is called vitreous humor. This gel-like material helps maintain the shape of the eyeball and provides a medium for light to pass through without scattering. It also plays a role in supporting the retina and keeping it in place. The vitreous humor is crucial for proper vision, as it ensures that light is transmitted efficiently to the retina where images are processed.

Other substances mentioned, such as aqueous humor, are found in the front part of the eye, between the cornea and the lens, and serve different functions related to the eye's hydration and intraocular pressure. Corneal gel and uveal fluid are not terms typically used to describe the contents within the eye, which makes vitreous humor the correct choice in this context.