Why Motility Testing Matters
Motility testing evaluates the alignment of the eyes and the full range of extraocular muscle function. As a CPOA, you will help position patients, provide fixation targets, occlude eyes as directed, and document findings. Understanding the tests allows you to assist smoothly and recognize when results are unusual and need immediate reporting to the doctor.
Hirschberg Corneal Light Reflex Test
The Hirschberg test is the simplest and fastest method for estimating ocular alignment. The examiner shines a penlight at the patient's face from about 33 cm away and observes where the light reflex falls on each cornea:
- Normal (orthophoria): The light reflex is centered symmetrically in both pupils.
- Esotropia: The reflex is displaced temporally (toward the outer edge of the cornea) in the deviating eye.
- Exotropia: The reflex is displaced nasally (toward the inner cornea) in the deviating eye.
Quantification: each millimeter of reflex displacement from center equals approximately 15 prism diopters of deviation.
💡 Clinical Tip: The Hirschberg is a quick screening test, especially useful for very young children, uncooperative patients, or patients with severely limited vision who cannot maintain fixation for formal cover testing.
Bruckner Test
The Bruckner test uses the ophthalmoscope (or a retinoscope) from a distance to simultaneously view both red reflexes. In strabismus, the deviating eye produces a brighter, lighter-colored red reflex compared to the fixating eye. The Bruckner test is particularly useful for detecting strabismus in infants and toddlers who cannot cooperate with other tests.
Cover-Uncover Test
The cover-uncover test detects and distinguishes manifest deviations (tropias) from latent deviations (phorias).
Procedure
- Patient fixates a target at distance (6 meters) or near (33 cm).
- The examiner covers one eye and watches the fellow (uncovered) eye for movement.
- If the fellow eye moves to pick up fixation when the other is covered, a tropia is present (the uncovered eye was deviating).
- The cover is removed; if the uncovered eye moves to re-establish fixation, a phoria is present (the covered eye drifted during occlusion).
- Repeat for the other eye.
CPOA Role in Cover Testing
- Hold the fixation target at the correct distance (typically an accommodative target at near, a projected letter at distance).
- Hand the occluder to the doctor or provide it at the correct position.
- Document findings as dictated by the doctor.
Alternate Cover Test (Prism and Cover Test)
The alternate cover test breaks fusion completely by rapidly alternating the cover between the two eyes, maximizing any deviation. Used to measure the total deviation (phoria + tropia combined). Prisms are placed in front of the deviating eye until no eye movement occurs when the cover alternates -- the prism power that neutralizes the movement is the deviation magnitude.
Ocular Motility (Range of Motion)
The doctor tests full range of motion in all six cardinal positions of gaze (H pattern). The CPOA may hold or move the fixation target:
- Move the target slowly and smoothly to each cardinal position.
- Hold each position long enough for the doctor to assess full excursion.
- Watch the patient's eyes -- if they break fixation or blink excessively, pause and restart.
Documenting EOM Function
- Full EOMs OU: Normal -- no restriction or limitation in any direction.
- Restriction: "LR OD 50% -- restricted abduction." or "SO OS -- limited in downgaze with adduction."
⚠️ Common Mistake: Moving the fixation target outside the comfortable head position. Patients can appear to have limited motility because they are turning their head to follow the target rather than rotating their eyes. Always remind the patient to keep their head still and move only their eyes.
Convergence (Near Point of Convergence)
The near point of convergence (NPC) is the closest point at which the patient can maintain binocular fixation (both eyes pointing at the same target). Tested by slowly bringing a fixation target toward the nose from arm's length. The CPOA moves the target steadily toward the patient's nose until:
- The patient reports double vision, or
- One eye is observed to break away outward (exodeviation).
A normal NPC is 5-8 cm from the nose. A receded NPC (>10 cm) is a common sign of convergence insufficiency.
Key Takeaways
- Hirschberg test estimates alignment by corneal light reflex position -- quick, no patient response needed.
- Cover-uncover test detects tropias (movement when fellow eye is uncovered) and phorias (movement when covered eye is uncovered).
- Alternate cover test with prisms measures total deviation magnitude in prism diopters.
- The CPOA provides fixation targets, assists with occlusion, and documents EOM and alignment findings.
- Remind patients to hold their head still and move only their eyes during motility testing.
- Normal near point of convergence is 5-8 cm; greater than 10 cm suggests convergence insufficiency.