What is the difference between versions and ductions in motility testing?

Versions are conjugate (both eyes together) movements in the same direction, testing the coordinated action of yoked muscle pairs. Ductions are monocular movements performed with the fellow eye occluded, isolating one eye's muscles to detect restrictions or paresis. Versions are tested first as a screening tool; ductions are used to clarify deficits found on versions by isolating one eye.

How does the Hirschberg test detect strabismus?

The Hirschberg test shines a penlight at the patient from arm's length and observes where the corneal light reflex falls in each eye simultaneously. Normally, the reflex is centered or slightly nasally displaced on each cornea. If the reflex is displaced temporally on one eye, that eye is esotropic (turned in); if displaced nasally, the eye is exotropic (turned out). Each 1 mm of reflex displacement corresponds to approximately 15-20 prism diopters of deviation.

What does the cover-uncover test detect?

The cover-uncover test detects manifest deviations (tropias). The examiner covers one eye and observes the uncovered eye. If the uncovered eye makes a movement to take up fixation, it was not fixating the target while both eyes were open, indicating a manifest strabismus (tropia). If the uncovered eye does not move, it was already fixating, meaning no manifest deviation is present (though a phoria may still be present).

Motility Testing: CPO Exam Guide

Why Motility Testing Matters

Motility testing evaluates the range and coordination of eye movements. It detects muscle weaknesses, nerve palsies, restrictions, and strabismus. As a CPO, you perform initial motility screening, including versions and the Hirschberg test, and document findings before the physician performs the detailed cover and prism tests.

Versions vs. Ductions

Versions: conjugate (both eyes together) movements in the same direction. Used to assess the coordinated action of yoked muscle pairs. Tested by having the patient follow a target through the six cardinal positions and nine positions of gaze.
Ductions: monocular movements with the other eye occluded. Isolate the action of one eye's muscles to determine if a deficit is due to restriction or muscle paresis.

Testing Versions

The standard version test follows an H-pattern (or full nine positions):

Ask the patient to follow your target (penlight, fixation stick) without moving their head
Move the target to the right, then right-up, then right-down
Return to center, then move to the left, left-up, left-down
Observe for: full range of movement, smoothness, onset of diplopia, asymmetry, or nystagmus
Rate each position as full (normal), restricted, or absent

Have patients hold their head still while following the target. Many patients automatically turn their head rather than moving their eyes. You can lightly stabilize the head by asking them to hold their chin level, or simply reminding them to move only their eyes.

Hirschberg Test

The Hirschberg corneal reflex test provides a quick estimate of the angle of strabismus by observing where a penlight reflection falls on each cornea simultaneously:

Normal: the light reflex is centered (or slightly nasal) on both corneas simultaneously
Displaced reflex: if the reflex is displaced temporally on one cornea, the eye is esotropic; if displaced nasally, the eye is exotropic
Estimation: each 1 mm of reflex displacement from center corresponds to approximately 15-20 prism diopters of deviation

The Hirschberg test is a rough estimate, not a precise measurement. It is useful for screening and for patients who cannot cooperate with formal cover testing (young children, cognitively impaired patients). Formal prism and alternating cover test is needed for quantitative measurement.

Cover Test Basics

The physician performs the formal cover test, but understanding it helps you document findings accurately:

Cover-uncover test: cover one eye and observe the uncovered eye for movement to take up fixation. A shift indicates that the uncovered eye was not fixating (manifest deviation, or tropia).
Alternating cover test: rapidly alternate covering each eye; observe the eye that was covered for a corrective movement as it is uncovered (reveals phorias and tropias).
Prism cover test: neutralizes the deviation with prisms to quantify the angle in prism diopters.

Documenting Motility Findings

Standard documentation uses a grading scale from -4 (complete absence of movement into a field) to 0 (full movement). You may also note:

Which positions are limited or overacting
Presence of nystagmus in specific gaze positions
Patient-reported diplopia in specific positions

Testing versions in only the horizontal directions. Always test all six cardinal positions (right, right-up, right-down, left, left-up, left-down) plus upgaze and downgaze in primary position. Vertical muscle deficits from conditions like thyroid eye disease or CN IV palsy are missed if only horizontal versions are tested.

Key Takeaways

Versions test both eyes together (conjugate); ductions test each eye separately
Test six cardinal positions plus upgaze and downgaze in the H-pattern
Hirschberg: corneal reflex position estimates angle of strabismus (1 mm = ~15-20 PD)
Cover-uncover detects tropias; alternating cover reveals phorias and tropias
Document restrictions on a -4 to 0 scale and note diplopia in specific positions