The least likely systemic condition to cause keratoconjunctivitis sicca?

• A. Myasthenia Gravis
• B. Sjogren's
• C. SLE
• D. Thyroid Eye Disease

Answer: (A)

Keratoconjunctivitis sicca arises mainly from reduced tear production or unstable tear film, often due to autoimmune attack on lacrimal glands or lid-tear film dynamics. Sjogren's syndrome is the classic systemic disease that destroys lacrimal (and salivary) glands, leading to aqueous-deficient dry eye. SLE can involve the ocular surface and tear production through inflammatory processes, so dry eye can occur with it as well. Thyroid eye disease tends to contribute to surface dryness mainly through lid retraction and exposure, which worsens tear film distribution and increases evaporation.

Myasthenia gravis, however, is a neuromuscular junction disorder that causes fatigable weakness of voluntary muscles, including the eyelids and extraocular muscles. While it explains ptosis and diplopia, it does not characteristically impair lacrimal gland function or tear production, so it is least likely among these conditions to cause keratoconjunctivitis sicca.