## Core Concept
Marfan's syndrome is a genetic disorder that affects the body's connective tissue. It has widespread effects on various systems, including the musculoskeletal, cardiovascular, and ocular systems. Ocular manifestations include lens subluxation, which is a key feature.

## Why the Correct Answer is Right
The correct answer, **D. Upward and temporal**, describes the typical direction of lens subluxation in Marfan's syndrome. This occurs due to the weakness of the zonular fibers (or suspensory ligaments of the lens) caused by the genetic defect in fibrillin-1, a protein crucial for the formation of elastic fibers found in connective tissue. The weakened zonular fibers lead to a loss of lens stability, causing the lens to sublux, most commonly in the upward and temporal direction.

## Why Each Wrong Option is Incorrect
- **Option A:** Downward and nasal. This is incorrect because, although lens subluxation in Marfan's syndrome can occur in various directions, the most common and characteristic direction is upward and temporal, not downward and nasal.
- **Option B:** Upward and nasal. This direction is less commonly associated with Marfan's syndrome. While upward subluxation can occur, the typical direction also involves a temporal component.
- **Option C:** Downward and temporal. This is not the typical direction for lens subluxation in Marfan's syndrome. The characteristic direction involves upward displacement.

## Clinical Pearl / High-Yield Fact
A key clinical feature of Marfan's syndrome is the **ectopia lentis**, which refers to the displacement or malposition of the eye's lens. This can lead to vision problems and is one of the major criteria for the diagnosis of Marfan's syndrome. Clinicians should always consider Marfan's syndrome in patients presenting with lens subluxation, especially if there are other systemic features suggestive of the disorder.

## Correct Answer: D. Upward and temporal.