**Core Concept**
The alternate cover test evaluates the presence of a latent or manifest strabismus by detecting movement discrepancies between the eyes during fixation, distinguishing between concomitant and paralytic squints based on the nature of deviation and the timing of movement.

**Why the Correct Answer is Right**
The alternate cover test is specifically designed to detect and differentiate between concomitant and paralytic squints. In concomitant squint, both eyes move together in the same direction and magnitude, and the deviation is only visible when one eye is covered. In paralytic squint, there is a fixed deviation due to a palsy of one extraocular muscle, and the test reveals a persistent deviation even when the other eye is covered. The test works by alternating coverage of each eye while the patient fixates on a target, allowing observation of any movement discrepancies that indicate muscle dysfunction or lack of coordination.

**Why Each Wrong Option is Incorrect**
Option A: The cover-uncover test detects manifest strabismus but cannot reliably differentiate between concomitant and paralytic squints because it only identifies deviation at rest and does not assess movement patterns.
Option C: The direct cover test is used to detect latent strabismus but does not provide the dynamic movement assessment needed to distinguish between types of squints.
Option D: This is incorrect because the alternate cover test is a valid and clinically used method for such differentiation.

**Clinical Pearl / High-Yield Fact**
Always perform the alternate cover test before the cover-uncover test in patients with suspected strabismus—this test is superior in detecting true paralytic squints due to its dynamic movement assessment.

✓ Correct Answer: B. Alternate covertest