Staph marginal keratitis is caused by an inflammatory reaction on the cornea due to bacteria that normally reside on the eyelids. What is the primary source of these bacteria?

• A. Bacteria on the eyelids
• B. Fungi on the eyelids
• C. Viruses in tears
• D. Allergic reactions of the eyelid skin

Answer: (A)

Staph marginal keratitis arises from an inflammatory reaction of the cornea to antigens from bacteria that normally inhabit the eyelids. The primary source of these bacteria is the eyelid margin skin and lash area—staphylococcal flora that reside on the lid margins and around the meibomian glands. Blepharitis or increased eyelid bacterial load can amplify this reaction, linking the lid flora directly to the corneal infiltrates. The other options don’t fit because fungi on the lids, viruses in tears, or eyelid skin allergies are not the usual bacterial source driving this corneal reaction.