**Question:** Histopathologically reversal lines are seen in

A. Charcot-Leyden crystals
B. Schirmer's test
C. Descemet's membrane
D. Descemet's striae

**Correct Answer:** D. Descemet's striae

**Core Concept:**
Reversal lines are characteristic histopathological features observed in certain pathological conditions. Descemet's striae and Charcot-Leyden crystals are both types of inclusion bodies, but they differ in their origin and significance.

**Why the Correct Answer is Right:**
Descemet's striae are seen in Descemet's membrane, which is an extracellular matrix layer within the cornea. They represent the accumulation of glycoproteins and proteoglycans due to the loss of corneal endothelial cells. This loss results from various conditions, such as Fuchs' endothelial dystrophy or age-related changes. Descemet's striae reflect the structural alterations in the cornea and thus are relevant in understanding corneal pathophysiology.

**Why Each Wrong Option is Incorrect:**

A. Charcot-Leyden crystals: These are eosinophil granule proteins that form needle-shaped crystals in eosinophilic infiltrates, primarily seen in allergic conditions or parasitic infections. They are not related to the cornea or Descemet's striae.

B. Schirmer's test: This test measures the amount of tear production and is not related to histopathological findings in the cornea.

C. Descemet's membrane: Descemet's membrane is the correct answer, but the striae are not directly associated with this structure. Descemet's striae represent alterations in the extracellular matrix, not the membrane itself.

**Clinical Pearl:**
Understanding reversal lines in histopathology helps in differentiating between various corneal diseases, such as Fuchs' endothelial dystrophy, where Descemet's striae are present, and conditions like bacterial keratitis, where no reversal lines are seen. This distinction aids in diagnosing the underlying pathology and selecting appropriate treatment strategies for patients.