Cover Test

Cover test

Objective measurement of ocular alignment

Performed with fixation target, occluder, and prisms

Ocular alignment

Ability of eyes to fixate on the same target

Strabismus

Deviation of one of the eyes during binocular viewing

Heterophoria (phoria)

Deviation of the eyes that only manifests when fusion is disrupted

When eye is occluded eye goes to resting position

Exo

Eye rests out temporally

Eso

Eye rests in nasally

Hyper

Eye rests up

Hypo

Eye rests down

Orthophoria

Eyes are aligned even when fusion is disrupted

Unilateral CT

Detects presence of strabismus, both eyes must be allowed to view between every cover

Performed first

Look at eye that is not being covered as the other is covered

Alternate CT

Measures magnitude of tropia or the direction and magnitude of phoria, one eye is always covered

Uses prisms

Look at eye as it is uncovered

If no strab is seen on UCT…

ACT is measuring magnitude and direction of a phoria

If a strab is seen on UCT…

ACT is measuring magnitude of a tropia

Selecting the correct target

2-3 lines bigger than the WORSE seeing eye

Single letter with sharp edges

V pattern

Tests for alternating strabismus

Alternating strabismus

Either eye can be the strabismic eye

Constant strabismus

Eyes never fuse together when viewing OU

What does the prism do?

Image will shift toward the apex so that the eye doesn’t move from its natural resting position

Vertical deviations

Can be tropias or phorias

Eyes move in opposite directions on ACT

Best observed for consistent flights of the lashes on uncover during ACT

Hyper deviation

Eye moves down on uncover

Hypo deviation

Eyes move up on uncover

Hyper deviation is neutralized with…

BD prism

Hypo deviation is neutralized with…

BU prism

What if a pt has a diagonal movement?

Neutralize the bigger movement first and then stack prism in the other direction to neutralize all movement

Document each direction separately