Which of the following clinical issues does fluorescein evaluate?

Fluorescein is a vital diagnostic tool in veterinary ophthalmology, particularly effective for evaluating corneal integrity. When applied to the cornea, fluorescein dye will stain areas where the epithelial layer is compromised, such as in cases of corneal ulceration. A corneal ulcer appears as a bright green area when viewed under cobalt blue light, clearly indicating where the corneal epithelium is absent or damaged. This property makes fluorescein crucial for diagnosing and assessing the severity of corneal ulcers.

While fluorescein can help assess other aspects of the eye, such as tear film stability and corneal perforation, its primary and most reliable use is in diagnosing corneal ulceration. The other clinical issues mentioned, like corneal pigmentation, conjunctival redness, and eyelid margins, do not rely on fluorescein staining and would require alternative diagnostic methods to evaluate those conditions accurately.