COA Practice Test 2026 – Complete Guide for JCAT Certified Ophthalmic Assistant Exam

The transparent gel-like substance filling the eyeball is known as vitreous humor. This gel is located in the posterior segment of the eye, filling the space between the lens and the retina. Its primary function is to help maintain the shape of the eyeball, provide support to the retina, and allow light to pass through to the retina without obstruction.

In contrast, aqueous humor is a clear fluid found in the anterior chamber of the eye, which is essential for nutrient supply to the avascular structures of the eye, like the lens and cornea. The corneal stroma is a layer of the cornea and plays a role in maintaining corneal transparency and refractive properties, while the retinal pigment epithelium is a layer of cells that nourishes the retinal visual cells and is involved in the recycling of visual pigments. Collectively, these structures support the eye's function but do not fill the eyeball like vitreous humor.