What does fluorescein stain primarily affect in the cornea?

Fluorescein stain is primarily used to evaluate the integrity of the corneal epithelium, which is the outermost layer of the cornea. When applied, fluorescein dye binds to areas of the cornea where the epithelium is damaged or missing, allowing for visualization under a blue light. This staining demonstrates defects such as abrasions or ulcers, thus confirming its primary role in assessing the corneal epithelium's status.

The corneal stroma, which lies beneath the epithelium, does not take up fluorescein in the same way because it is typically protected by an intact epithelial layer. However, if there is significant damage or loss of the epithelium, the stroma may become affected or visible due to underlying conditions, but fluorescein itself does not primarily target the stroma.

Fluorescein does affect the corneal epithelium as it highlights areas of damage, but the emphasis of the question pertains specifically to where the staining process is concentrated. Understanding this distinction highlights the importance of the corneal epithelium in ocular health and disease, underscoring fluorescein stain's role in providing critical information about injuries or diseases affecting this layer