**Question:** Cataract is seen in following except –

A. Vitamin C deficiency
B. Hyperthyroidism
C. Diabetes mellitus
D. Hypothyroidism

**Core Concept:** Cataract is a condition characterized by clouding of the lens of the eye, leading to visual impairment or loss. It can be caused by various factors, including aging, trauma, hereditary disorders, or systemic conditions.

**Why the Correct Answer is Right:**

1. Vitamin C deficiency: Vitamin C is essential for maintaining the integrity of collagen, a structural protein in the lens. Deficiency can lead to cataract formation due to impaired collagen synthesis and increased oxidative stress.

2. Hyperthyroidism (excessive thyroid hormone production): Although thyroid hormones are involved in eye development and growth, they do not directly cause cataract formation. This option is incorrect because the excess hormones do not directly impact lens transparency.

3. Diabetes mellitus: Diabetes can lead to microvascular complications, including retinal damage and increased vascular permeability. However, the lens itself is not directly affected by diabetes, making this option incorrect.

4. Hypothyroidism (insufficient thyroid hormone production): Similar to hyperthyroidism, hypothyroidism does not directly cause cataract formation. Hormone imbalances do not impact lens transparency.

**Why Each Wrong Option is Incorrect:**

A. Vitamin C deficiency: While vitamin C is essential for lens health, hypothyroidism does not directly impact lens transparency, making this option incorrect.

B. Hyperthyroidism: As mentioned earlier, thyroid hormones do not directly cause cataract formation in the lens. This option is incorrect.

C. Diabetes mellitus: While diabetes can lead to microvascular complications, the lens itself is not directly affected, making this option incorrect.

D. Hypothyroidism: Similar to the other options, hypothyroidism does not directly cause cataract formation in the lens, making this option incorrect.

**Clinical Pearl:**

Cataract can be caused by various factors, including aging, trauma, and systemic conditions such as diabetes and hypothyroidism. However, in this question, we have established that hypothyroidism does not directly cause cataract formation in the lens. It is essential for students to understand the direct involvement of hypothyroidism in lens transparency to avoid confusion with other causes of cataract.