**Core Concept**
Bilateral inferior lens subluxation is a rare ocular condition characterized by the displacement of the crystalline lens in a downward direction in both eyes. This condition is often associated with a specific systemic disease.

**Why the Correct Answer is Right**
The correct answer is related to Marfan syndrome, a genetic disorder affecting the body's connective tissue. In Marfan syndrome, the lens subluxation is caused by the weakening of the suspensory ligaments (zonules) that hold the lens in place, leading to its downward displacement. The condition is often bilateral and can occur in both children and adults. The pathophysiology involves a mutation in the FBN1 gene, which codes for fibrillin-1, a protein essential for the formation of elastic fibers in connective tissue.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because Marfan syndrome is a more common cause of bilateral lens subluxation compared to other conditions like homocystinuria.
**Option B:** This option is incorrect because Weil's disease is a rare bacterial infection caused by Leptospira, and it is not typically associated with lens subluxation.
**Option C:** This option is incorrect because Ehlers-Danlos syndrome is a group of disorders affecting the body's connective tissue, but it is not the most common cause of bilateral inferior lens subluxation.

**Clinical Pearl / High-Yield Fact**
Marfan syndrome is often associated with other systemic features, including tall stature, arachnodactyly (spider-like fingers), and aortic root dilation. A high index of suspicion is necessary for early diagnosis and management.

**Correct Answer: D. Marfan syndrome**