Squint Cover Tests Video
A cover test or cover-uncover test is an objective determination of the presence and amount of ocular deviation. It is typically performed by orthoptists, ophthalmologists andoptometrists during eye examinations.
The two primary types of cover tests are:
- the alternating cover test
- the unilateral cover test (or the cover-uncover test).
The test involves having the child (typically) focusing on a near object. A cover is placed over an eye for a short moment then removed while observing both eyes for movement. The “lazy eye” will deviate inwards or outwards. The process is repeated on both eyes and then with the child focusing on a distant object.
The cover test is used to determine both the type of ocular deviation and measure the amount of deviation. The two primary types of ocular deviations are the tropia and the phoria. A tropia is a misalignment of the two eyes when a patient is looking with both eyes uncovered. A phoria (or latent deviation) only appears when binocular viewing is broken and the two eyes are no longer looking at the same object.
The unilateral cover test is performed by having the patient focus on an object then covering the fixating eye and observing the movement of the other eye. If the eye was exotropic, covering the fixating eye will cause an inwards movement; and esotropic if covering the fixating eye will cause an outwards movement. The alternating cover test, orcross cover test is used to detect total deviation (tropia + phobia).