Question:easy
What is the most common eye manifestation of allergy to tubercular bacilli?
What is the most common eye manifestation of allergy to tubercular bacilli?
Show Hint
Think of the type IV hypersensitivity nodule at the limbus classically linked to TB antigen exposure.
Updated On: Jul 8, 2026
- Koeppe's nodules
- Posterior scleritis
- Phlyctenular conjunctivitis
- Optic neuritis
Show Solution
The Correct Option is C
Solution and Explanation
Step 1: Separate direct infection from allergy.
TB can affect the eye in two different ways: the germ can directly invade eye tissue (as in TB uveitis or choroiditis), or the eye can react to TB proteins without the germ being present there, which is a hypersensitivity or allergic response. The question asks about the second kind.
Step 2: Recall the hallmark hypersensitivity lesion.
A phlycten is a small raised nodule of lymphocytes that forms at the limbus (junction of cornea and conjunctiva) as a delayed immune reaction to circulating tubercular antigen. This is called phlyctenular conjunctivitis or keratoconjunctivitis, and it is the standard teaching example of ocular TB allergy.
Step 3: Go through the distractors.
Koeppe's nodules sit on the iris and mark active granulomatous uveitis, a direct inflammatory process, not a surface allergic reaction. Posterior scleritis is uncommon and mostly tied to autoimmune causes. Optic neuritis in TB usually comes from drug side effects or nerve compression, not allergy.
Step 4: Fit the answer to the question wording.
Since the question specifically says "allergy," the nodule that forms purely from immune sensitisation, the phlycten, fits best.
Step 5: Conclude.
\[ \boxed{\text{Phlyctenular conjunctivitis}} \]
TB can affect the eye in two different ways: the germ can directly invade eye tissue (as in TB uveitis or choroiditis), or the eye can react to TB proteins without the germ being present there, which is a hypersensitivity or allergic response. The question asks about the second kind.
Step 2: Recall the hallmark hypersensitivity lesion.
A phlycten is a small raised nodule of lymphocytes that forms at the limbus (junction of cornea and conjunctiva) as a delayed immune reaction to circulating tubercular antigen. This is called phlyctenular conjunctivitis or keratoconjunctivitis, and it is the standard teaching example of ocular TB allergy.
Step 3: Go through the distractors.
Koeppe's nodules sit on the iris and mark active granulomatous uveitis, a direct inflammatory process, not a surface allergic reaction. Posterior scleritis is uncommon and mostly tied to autoimmune causes. Optic neuritis in TB usually comes from drug side effects or nerve compression, not allergy.
Step 4: Fit the answer to the question wording.
Since the question specifically says "allergy," the nodule that forms purely from immune sensitisation, the phlycten, fits best.
Step 5: Conclude.
\[ \boxed{\text{Phlyctenular conjunctivitis}} \]
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