**Core Concept**
Binocular single vision (BSV) is the ability to fuse two images from each eye into a single perception, enabling depth perception and three-dimensional vision. This is achieved through the coordination of extraocular muscles, the convergence of the eyes, and the suppression of the image from one eye by the brain.

**Why the Correct Answer is Right**
The cover-uncover test is a simple, bedside method to assess BSV. It involves covering one eye and asking the patient to fixate on a near object. The uncovered eye is then covered, and the covered eye is uncovered, and the patient is asked to continue fixation. A normal response is that the patient maintains fixation without any noticeable diplopia or nystagmus. This test relies on the patient's ability to suppress the image from the covered eye and maintain fusion with the image from the uncovered eye.

**Why Each Wrong Option is Incorrect**
**Option A:** The Maddox rod test is used to assess for strabismus and to detect the presence of a squint. It involves placing a Maddox rod over the patient's eye, which creates a streak of light instead of a point source. This test is not used to assess BSV.
**Option B:** The Worth 4-dot test is used to assess for binocular vision and to detect the presence of a squint. It involves placing a red filter over one eye and a green filter over the other eye, and then shining a light through the filters to create a red dot in one eye and a green dot in the other eye. This test is not used to assess BSV.
**Option C:** The cover test is used to assess for strabismus by measuring the amount of deviation between the two eyes at near and far distances. While it is related to BSV, it is not a direct test of BSV.

**Clinical Pearl / High-Yield Fact**
The cover-uncover test is a simple and effective bedside test for assessing BSV, and it can be used to detect the presence of a squint or strabismus.

**Correct Answer: C. Cover test.**