Which of the following is the least common stromal type of corneal dystrophy?
**Core Concept**
The question is testing the knowledge of corneal dystrophies, a group of rare, inherited disorders that affect the cornea, leading to progressive vision loss. Corneal dystrophies can be classified into two main categories: epithelial and stromal, based on the layer of the cornea affected.
**Why the Correct Answer is Right**
The correct answer is **B. Macular dystrophy**. Macular corneal dystrophy is a rare, autosomal recessive disorder caused by mutations in the CHST6 gene, which encodes for the enzyme choroid plexus-specific chondroitin sulfate N-acetylgalactosaminyltransferase. This enzyme is responsible for the sulfation of chondroitin sulfate in the corneal stroma, leading to the accumulation of unsulfated chondroitin 6-sulfate in the cornea. This accumulation causes the corneal stroma to become cloudy and vision loss.
**Why Each Wrong Option is Incorrect**
**Option A:** Lattice corneal dystrophy is a more common stromal type of corneal dystrophy, characterized by the accumulation of amyloid deposits in the corneal stroma.
**Option C:** Fuchs' endothelial corneal dystrophy is an epithelial type of corneal dystrophy, characterized by the degeneration of the endothelial cells of the cornea, leading to corneal edema.
**Clinical Pearl / High-Yield Fact**
It's essential to distinguish between epithelial and stromal corneal dystrophies, as the treatment and prognosis differ significantly between the two.
**Correct Answer:** B. Macular dystrophy.