Cover test

The cover test and Aufdecktest (also: Cover-Test/Uncover-Test ) is the main and most common method of examination in ophthalmology for the detection of strabismus. Requirement for its use is always that the patient is able to fix the object. During the investigation, near no light as possible, but an image or a letter should be presented to enable the Naheinstellungsmechanismus of the eye (accommodation). To cover usually a round plastic disk with a short handle will be used.

Unilateral cover test

If there is a manifest squint, a Fixierobjekt can not be viewed by both eyes simultaneously. With the unilateral cover test is not squinting eye is covered and the patient asked the same time, continue to fix the same object in this situation. To this end, the squinting eye must be necessarily aligned with a corresponding saccade to the object. This saccade is called adjustment movement. There is a central fixation, this corresponds, in this case, the adjusting movement of the objective degree of squint angle.

Alternating cover test

In mutual covering the eyes binocular vision is interrupted, preventing any form of latent or manifest squint with the corresponding adjustment movements visible. Exceptions to this rule is a special form of microstrabismus, and possibly severe amblyopia. In some cases it is necessary to perform the alternate cover test longer to compensatory movements merger to bring to subside and trigger adjustment movements.

Aufdecktest

When Aufdecktest the shared eye is observed in the first place. This may lead to fusion movements or even common adjustment movements with the other eye. Also the absence of a movement. However, the assessment is always dependent on the result of Monolateral Abdecktests and the present fixation conditions.

Measurement of squint angles

The cover test is in addition to the purely qualifying process an important instrument for the measurement of squint angles. To this end, prisms are used in the investigation in free space, both in distance and proximity, are used. These prisms are to be used either as a single prism or prism by means of bar (horizontal or vertical arrangement varies strong prisms).

Unilateral Prismenabdecktest

Here, a prism is held before the non-leading, so squinting eye and covers the lead eye at intervals and released. The prism effect will be adjusted until no adjusting movement is obtained.

Simultaneous Prismenabdecktest

Here it is necessary to estimate the extent of the squint angle as accurately as possible already before covering. Then the examiner an appropriate prism must keep the (usually a single prism) before the squinting and the cover before the dominant eye, paying attention to adjustment movements. The prism power is increased and the test repeated until no further adjustment movements can be performed. For dynamic look angles and deferred components that change their extent with the degree of dissociation of the research method, this is an effective method to determine the smallest manifest squint angle. It should therefore not need to be repeated too often, what an appropriate experience presupposes.

Alternating Prismenabdecktest

The alternating Prismenabdecktest a prismatic bar is held against the eye whose difference is to be measured, and at the same time are alternately covered with the cover the right and left eyes. The eye behind the prism strip is observed for the setting movements and the prism power adjusted until they are neutralized. As the largest squint angle can be determined with this method, it can happen that you have to hold prisms before both eyes, until no more adjustment movements occur.