The claim that viral keratitis is an infectious eye disease is a matter of established medical terminology and direct definition, requiring no citation of specific studies.
The claim asserts that viral keratitis is a contagious eye infection. Keratitis is by definition an inflammation of the cornea, and viral keratitis specifically refers to a viral infection of the cornea. Because this is a definitional medical fact about what the condition is, it represents common knowledge and does not require empirical citation.