Heterophoria

Measurement of Ocular Deviations

Heterophoria

❚ A deviation kept latent by the fusion reflex

❚ Prevent fusion to measure phoria

❚ Dissociation of the eyes required

Dissociation of Eyes

❚ Cover test❚ Diplopia or displacement tests (vertical ∆)❚ Distortion tests (Maddox Rod)❚ Independent objects (Maddox Wing)

Cover Test

❚ Simplest method❚ Objective assessment❚ Used at any distance❚ Only test to distinguish between phoria

and tropia❚ Use on ALL patients

Cover Test

❚ Patient fixates on smallest letter seen by poorest eye (eg R6/6 L6/12)

❚ Accommodative stimulus required❚ Less than 6/18 use spot light❚ Use an opaque occluder❚ Don’t go too quickly

Cover Test

❚ Cover/uncover: allows diagnosis of phoria or tropia

❚ Alternate cover: allows size and direction to be determined

Alternative Cover Test

❚ Do not allow binocular fixation❚ Move cover from one eye to the other❚ If deviation present it will be seen as a re-

fixation eye movement❚ Will NOT distinguish between a phoria

and a tropia

Cover/uncover Test

❚ Cover placed before 1 eye and then removed❚ Observe the uncovered eye for movement; if

movement is present then patient has a squint

❚ If a squint is present there cannot be a phoria

Strabismus: Cover Fixing Eye

Strabismus: Uncover

Strabismus: Cover deviating eye

Cover/uncover Test

❚ Observe occluded eye when covered; eye drifts out for XOP and in for SOP

❚ Observe occluded eye when cover removed; eye moves in for XOP and out for SOP

Phoria: SOP

Hering’s Law

❚ Innervation to synergist muscles of the 2 eyes is equal

Esophoria with Hering Response

Technique

❚ Ensure eye is completely covered❚ At near move fixation target prior to

cover to ensure fixation❚ Observe latency and speed of recovery❚ Estimate size❚ Measure size using prism bar

Prism Cover Test

Prism Bar

❚ Base Out for SOP and SOT

❚ Base In for XOP and XOT

Displacement Test

❚ Vertical Prism

Distortion Test

❚ Maddox Rod❚ Can be used for vertical and horizontal

deviations

Maddox Rod

Maddox Rod

❚ Place rod before right eye❚ Use spot light and dim room lights❚ Ask “ is red line to the left or right of the

spotlight?”❚ If rod is to the right SOP❚ If rod to the left XOP❚ Use prism to align rod and spotlight

Maddox Rod

Esophoria

Esophoric Projection

Exophoria

Exophoric Projection

Maddox Rod

Independent Objects

❚ Maddox Wing

Summary

❚ Cover test only way to distinguish between phoria and tropia

❚ Perform on all patients with and without Rx

❚ Work in systematic manner❚ Do not rush the diagnosis❚ Use appropriate tets