**Question:** Which of the following is the least common corneal dystrophy -

A. Fuchs' dystrophy
B. Granular dystrophy
C. Pellucid marginal degeneration
D. lattice dystrophy

**Core Concept:** Corneal dystrophies are a group of inherited disorders characterized by the accumulation of abnormal substances within the cornea. They can lead to vision impairment and corneal opacities. Corneal dystrophies can be broadly categorized into four types:

1. Fuchs' dystrophy: This is a common age-related corneal dystrophy affecting the endothelial layer, leading to corneal edema, and vision impairment.
2. Granular dystrophy: This is another common dystrophy characterized by the accumulation of granular deposits in the corneal stroma, leading to corneal clouding and vision impairment.
3. Pellucid marginal degeneration: This is a rare dystrophy affecting the peripheral cornea, leading to progressive thinning and transparency of the cornea. It primarily affects individuals aged 50 years and above.
4. Lattice dystrophy: This is a common dystrophy characterized by the formation of lamellar precipitates in the corneal stroma, leading to corneal clouding and vision impairment.

**Why the Correct Answer is Right:** D. Lattice dystrophy is the least common corneal dystrophy among the given options. It is characterized by the formation of lamellar precipitates in the corneal stroma, leading to corneal clouding and vision impairment.

**Why Other Options are Incorrect:**

A. Fuchs' dystrophy is a common age-related corneal dystrophy affecting the endothelial layer, leading to corneal edema and vision impairment.
B. Granular dystrophy is another common dystrophy characterized by the accumulation of granular deposits in the corneal stroma, leading to corneal clouding and vision impairment.
C. Pellucid marginal degeneration is a rare dystrophy affecting the peripheral cornea, leading to progressive thinning and transparency of the cornea. It primarily affects individuals aged 50 years and above.

**Clinical Pearl:** Corneal dystrophies can present as a range of symptoms, including vision impairment, corneal clouding, and ocular discomfort. Early diagnosis and treatment are crucial to prevent corneal ulceration and perforation. In cases of suspected corneal dystrophy, referral to an ophthalmologist is essential for a proper diagnosis and management plan.