**5. Differential diagnoses**

The differential diagnosis of PUK should include inflammatory conditions (e.g., marginal keratitis and catarrhal infiltrates, phlyctenulosis, rosacea-associated keratitis, MGD-associated keratitis, peripheral infectious keratitis, vernal keratoconjunctivitis). Furthermore, local damage from improperly fitted contact lenses, exposure keratitis, trichiasis, and lid malposition can implicate peripheral corneal diseases [4–6].


c. Compared to marginal keratitis, herpetic infection begins with an epithelial defect, and then subepithelial infiltrates appear. HSV-induced keratitis may be associated with minor pain due to decreased corneal sensation due to infected corneal neurons [42].

When diagnosing PUK, it is also important to consider noninflammatory corneal disorders associated with peripheral corneal thinning or opacification such as peripheral corneal degeneration, e.g., Terrien's marginal degeneration (TMD), senile furrow degeneration, pellucid marginal degeneration.


MU is a rare, idiopathic form of peripheral corneal ulceration. This can present as unilateral, slowly progressive lesions in older adults and bilateral, rapidly progressing ulcers in younger adults. MU occurs without a specific general underlying disease likely to cause PUK, and it is an exclusion diagnosis. MU is more common in Africa, China, and India; it shows an association with viral exposure (hepatitis C), helminthic infections, HLA-DR17, and DQ2 antigens. The pathological process begins with the involvement of the peripheral cornea, spreads circumferentially, and then centrally with overhanging edges. A distinctive feature of MU, unlike PUK, is the absence of scleritis and the pain being more intense, poorly tolerated, and inadequate in relation to the size of the ulceration [4, 13, 45, 46].
