The prism cover test (PCT) is an objective measurement and the gold standard in measuring strabismus, i.e. ocular misalignment, or a deviation of the eye.It is used by ophthalmologists, orthoptists, and optometrists in order to measure the vertical and horizontal deviation and includes both manifest and latent components. Manifest is defined by the eye deviating constantly or intermittently, whereas latent is where the deviation is normally controlled but becomes present when the eyes are dissociated. A PCT reveals the total deviation and cannot distinguish between latent and manifest strabismus as you are using an alternate cover test.