Which is a listed cause of secondary MGD in dogs?

• A. Surgical excision of the gland of the third eyelid
• B. Fungal infection of the eyelid
• C. Periocular radiotherapy
• D. Stevens-Johnson syndrome

Answer: (A)

Secondary MGD in dogs occurs when another factor disrupts the tear film or eyelid environment, leading to dysfunction of the Meibomian glands. The gland of the third eyelid adds a significant portion of tears; removing it changes tear film balance and the health of the eyelid margin. This iatrogenic change can promote stagnation, obstruction, and inflammation of the Meibomian glands, producing secondary MGD.

The other scenarios describe conditions that cause ocular surface disease through different mechanisms (surface infections, radiotherapy-related dry eye, or systemic mucocutaneous reactions) but are not listed as direct causes of secondary MGD. Therefore, surgical excision of the gland of the third eyelid is the correct listed cause.