**Core Concept**
Diplopia, also known as double vision, is a symptom that occurs when the brain receives two different images from each eye, making it difficult to focus on a single object. This condition is often associated with disorders affecting the extraocular muscles or their innervation.

**Why the Correct Answer is Right**
Paralytic squint, also known as paralytic strabismus, is a type of squint that occurs due to weakness or paralysis of one or more extraocular muscles. This can be caused by various factors, such as cranial nerve palsies (e.g., third, fourth, or sixth nerve palsy), which disrupt the normal coordination between the extraocular muscles. As a result, the brain receives images from each eye that are not aligned, leading to diplopia. The affected eye may also undergo compensatory movements, such as hypertropia or hypotropia, which can further exacerbate the diplopia.

**Why Each Wrong Option is Incorrect**

* **Option A:** Concomitant squint refers to a squint that is present at all distances and is usually due to a misalignment of the extraocular muscles. However, it does not typically cause diplopia, as the brain learns to suppress the image from the deviated eye.
* **Option B:** Non-paralytic squint, also known as non-paralytic strabismus, is a type of squint that occurs due to a misalignment of the extraocular muscles, but it is not caused by paralysis or weakness of the muscles. This type of squint is often present at birth or develops during childhood and may not cause diplopia.
* **Option D:** Latent squint, also known as latent strabismus, is a type of squint that occurs when one eye deviates inward or outward when the other eye is covered. However, it does not cause diplopia, as the brain suppresses the image from the deviated eye.

**Clinical Pearl / High-Yield Fact**
The cover-uncover test is a useful clinical tool for diagnosing latent squint. In this test, the examiner covers one eye and asks the patient to look straight ahead. If the uncovered eye deviates inward or outward, it indicates the presence of latent squint.

**✓ Correct Answer: C. Paralytic squint**