Which of the following structures will NOT stain with fluorescein?

Fluorescein is a useful dye in veterinary ophthalmology, particularly for assessing the integrity of the corneal surface and detecting corneal ulcers or lesions. When fluorescein is applied to the eye, it stains only certain ocular structures based on their permeability and the presence of certain cells.

The corneal epithelium is the outermost layer of the cornea and acts as a barrier to fluorescein dye. When the epithelium is intact, fluorescein will not penetrate through it, and therefore, it will not stain the corneal epithelium. This characteristic allows veterinarians to use fluorescein to identify epithelial defects, as any breach in the epithelium will allow the dye to penetrate and stain the underlying corneal stroma but not the epithelium itself.

In contrast, the corneal stroma, which lies beneath the epithelial layer, is made up of collagen and is permeable to fluorescein when there is an epithelial defect. Structures such as the anterior chamber and pupil do not stain with fluorescein because they contain aqueous humor, which does not interact with the dye in the same way the corneal tissue does.

In summary, the corneal epitheli