**Core Concept**
Leber hereditary optic neuropathy (LHON) is a maternally inherited mitochondrial disease characterized by a progressive loss of central vision, typically affecting young adult males. The condition is caused by mutations in the mitochondrial DNA, which affects the energy production in retinal ganglion cells.

**Why the Correct Answer is Right**
The correct answer, C, is incorrect because Leber hereditary optic neuropathy is a maternally inherited disease, meaning it is passed down from mother to child through the mitochondria. Mitochondrial DNA is inherited solely from the mother, and therefore, males cannot transmit the disease. The disease typically affects young adult males, who are the offspring of affected mothers.

**Why Each Wrong Option is Incorrect**
**Option A:** Seen in the 2nd or 3rd decade of life - This is correct, as Leber hereditary optic neuropathy typically affects young adults, often between the ages of 15 and 35.

**Option B:** It is an example of gradual painless visual loss - This is also correct, as the disease is characterized by a gradual and painless loss of central vision.

**Option D:** No leak of dye is observed in fluorescein angiography - This is correct as well, as fluorescein angiography typically shows normal retinal vasculature in patients with Leber hereditary optic neuropathy.

**Clinical Pearl / High-Yield Fact**
Leber hereditary optic neuropathy is a classic example of a mitochondrial disease, which can be distinguished from other forms of optic neuropathy by its characteristic clinical features and family history.

**Correct Answer:**
✓ Correct Answer: C. Males can transmit the disease