**Core Concept**
Telecanthus refers to an abnormal increase in the distance between the medial canthi (the medial corners of the eyes), which can be caused by various factors including congenital conditions, trauma, or surgical interventions. This condition is often evaluated in the context of other craniofacial and orbital abnormalities.

**Why the Correct Answer is Right**
The correct answer, D, reflects the definition of telecanthus as an increase in the intercanthal distance, which is the distance between the medial canthi, while the interpupillary distance remains normal. This occurs due to an abnormal separation of the medial orbital walls, which can be caused by various factors such as congenital conditions, trauma, or surgical interventions. The intercanthal distance is measured between the medial canthi, whereas the interpupillary distance is measured between the centers of the pupils.

**Why Each Wrong Option is Incorrect**
**Option A:** Narrow medial epicanthus is actually a characteristic of hypotelorism, which is the opposite of telecanthus, where the distance between the medial canthi is decreased.

**Option B:** Widely separated medial orbital wall is a contributing factor to telecanthus, but it is not the definition of the condition itself.

**Option C:** Lateral epicanthal fold thickened is not directly related to the definition of telecanthus, which involves the medial canthi.

**Clinical Pearl / High-Yield Fact**
Telecanthus can be a subtle sign of underlying craniofacial abnormalities, and a thorough evaluation of the patient's orbital and facial anatomy is essential to determine the underlying cause of this condition.

**✓ Correct Answer: D. Increases in intercanthal distance with normal interpupillary distance**