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

## **Why the Correct Answer is Right**
The correct answer, **D. Upward and temporal**, describes the typical direction of lens dislocation in Marfan syndrome. This occurs due to the weakness of the zonular fibers (or suspensory ligaments of the lens) which are primarily composed of fibrillin-1. In Marfan syndrome, mutations in the FBN1 gene lead to abnormal fibrillin-1 protein, causing these zonular fibers to be fragile and prone to rupture. As a result, the lens often dislocates upward and temporally due to the loss of support.

## **Why Each Wrong Option is Incorrect**
- **Option A:** Downward and nasal - This is incorrect because, although lens dislocation in Marfan syndrome can occur in various directions, the most common and characteristic direction is upward and temporal, not downward and nasal.
- **Option B:** Only nasal - This option is too restrictive and incorrect because it doesn't account for the typical upward component of the dislocation seen in Marfan syndrome.
- **Option C:** Only temporal - This option is also incorrect because it fails to acknowledge the upward directionality that is commonly observed alongside the temporal displacement.

## **Clinical Pearl / High-Yield Fact**
A key clinical pearl is that Marfan syndrome patients are at risk for ectopia lentis (lens dislocation), which can lead to vision disturbances. The upward and temporal dislocation is a classic finding. Additionally, these patients are also at risk for retinal detachment and require regular ophthalmological follow-up.

## **Correct Answer:** D. Upward and temporal.