COA Ocular Motility and Alignment 2 — Questions and Answers

Question 1: During the cover-uncover test, the examiner covers the right eye. The left eye moves outward (temporally) to pick up fixation. This finding MOST likely indicates:

Left esotropia (Correct answer)
Left exotropia
Right hypertropia
Orthophoria

Correct answer: Left esotropia

If the uncovered (left) eye moves outward when the right eye is covered, the left eye was turned inward (esotropia) before coverage. The outward refixation movement reveals a manifest inward deviation of the left eye.

In the cover-uncover test, each eye is covered and uncovered separately while the patient fixates on a target. If the UNCOVERED eye moves to pick up fixation, a manifest strabismus (tropia) is present. Movement direction is opposite to deviation: if the uncovered left eye moves outward (abducts), it was previously deviated inward — left esotropia. If the uncovered left eye moves inward, left exotropia is present. No movement of the uncovered eye suggests no manifest deviation (orthotropia or correctly fixed). The alternate cover test reveals both manifest and latent deviations (phorias).

Question 2: In ocular motility testing using the H pattern (nine cardinal positions of gaze), which muscle is being evaluated when the patient looks to the right and UP?

Right inferior oblique (IO) and left superior rectus (SR)
Right superior rectus (SR) and left inferior oblique (IO) (Correct answer)
Right lateral rectus (LR) and left medial rectus (MR)
Right superior oblique (SO) and left inferior rectus (IR)

Correct answer: Right superior rectus (SR) and left inferior oblique (IO)

In right and up gaze, the right superior rectus is the primary elevator and the left inferior oblique is the primary elevator of the fellow eye in that conjugate gaze position. The superior rectus and inferior oblique are yoke muscles (Hering's law) for upgaze.

The six cardinal positions of gaze each have a yoke muscle pair per Hering's law of equal innervation. Right and up: right SR + left IO. Right and down: right IR + left SO. Pure right: right LR + left MR. Left and up: left SR + right IO. Left and down: left IR + right SO. Pure left: left LR + right MR. In the H-pattern motility test, underaction or overaction in a specific gaze direction helps localize the paretic or hyperactive muscle. This is core JCAHPO COA knowledge for assessing extraocular muscle function.

Question 3: A patient reports diplopia that is WORSE when looking down and to the left. Which cranial nerve palsy is MOST likely?

Right CN III (oculomotor) palsy
Left CN VI (abducens) palsy
Right CN IV (trochlear) palsy (Correct answer)
Left CN IV (trochlear) palsy

Correct answer: Right CN IV (trochlear) palsy

The right superior oblique (CN IV) primarily depresses and intorts the eye. Diplopia that worsens in downgaze (especially when adducted, i.e., looking left with the right eye) is the classic presentation of a right CN IV palsy.

The trochlear nerve (CN IV) innervates the ipsilateral superior oblique muscle. The superior oblique's primary action is intorsion; secondary action is depression (most effective when the eye is adducted). CN IV palsy causes ipsilateral hypertropia (vertical diplopia) worst when looking down and inward. The Parks-Bielschowsky three-step test — (1) which eye is higher? (2) worse in left or right gaze? (3) worse with head tilt left or right? — helps localize CN IV palsy. The patient often compensates with a contralateral head tilt. CN IV palsy can be congenital or acquired (trauma is common).

Question 4: The Hirschberg test estimates the angle of strabismus by observing corneal light reflections. If the corneal reflex appears at the pupil margin of the right eye and centered in the left eye, approximately how many prism diopters of deviation is estimated?

5–10 prism diopters
15–20 prism diopters (Correct answer)
30–45 prism diopters
60–80 prism diopters

Correct answer: 15–20 prism diopters

In the Hirschberg test, a decentered corneal light reflex at the pupil margin corresponds to approximately 15 prism diopters (pd) of deviation. Each millimeter of decentration equals approximately 15 pd (some sources use 7° or 22 pd/mm depending on reference).

The Hirschberg corneal reflex test is a quick gross estimate of strabismus angle. With a penlight held at ~33 cm, a centered reflex = orthophoria. Displacement toward the pupil margin ≈ 15 pd (1 mm); mid-iris ≈ 30–35 pd; limbus ≈ 60 pd. The right eye reflex displaced toward the pupil margin represents approximately 15–20 pd of right exotropia or esotropia, depending on direction. For precise measurement, the Krimsky prism reflex test (neutralizing the reflex with prisms) or the prism and alternate cover test is needed. Hirschberg is most useful for uncooperative patients or quick screening.

Question 5: Which test best evaluates for a latent deviation (phoria) that is only revealed when binocular fusion is disrupted?

Cover-uncover test
Hirschberg corneal reflex test
Alternate cover test (Correct answer)
Maddox rod test only

Correct answer: Alternate cover test

The alternate cover test rapidly moves the occluder from eye to eye, preventing fusion and revealing both manifest (tropia) and latent (phoria) deviations. The cover-uncover test reveals only manifest deviations.

A phoria is a latent tendency for ocular misalignment controlled by fusional vergence. To measure it, fusion must be disrupted. The alternate cover test (ACT) moves the occluder alternately between eyes without allowing binocular viewing. Any eye movement observed when the cover is moved reveals the total deviation (phoria + tropia). The cover-uncover test (performed by covering and uncovering one eye at a time) reveals only manifest tropias — if no movement occurs of the uncovered eye, a tropia is absent (but a phoria may remain). The Maddox rod or von Graefe dissociation tests are also used for phorias but require additional equipment.

Question 6: A child is found to have a right esotropia measuring 30 prism diopters by the prism and alternate cover test. The child is 3 years old. What is the MOST important reason to treat this promptly?

To prevent astigmatism from developing
To prevent amblyopia from developing in the deviated eye (Correct answer)
To strengthen the extraocular muscles
To reduce intraocular pressure

Correct answer: To prevent amblyopia from developing in the deviated eye

In young children, strabismus causes the brain to suppress the input from the deviated eye to avoid diplopia. Prolonged suppression during the critical period of visual development leads to amblyopia (lazy eye) — a reduction in best corrected visual acuity that can become permanent if untreated.

The critical period for visual development extends from birth through approximately 7–9 years (peak plasticity 0–3 years). Constant esotropia causes the cortex to suppress the image from the deviated eye to avoid diplopia. This prolonged suppression interrupts normal visual development, resulting in amblyopia — decreased BCVA in the suppressed eye that cannot be corrected by glasses alone. Treatment includes glasses (if accommodative component), patching or penalization of the fellow eye, and possibly surgery. Early intervention (before age 7) provides the best prognosis for visual recovery. Amblyopia is the leading cause of unilateral vision loss in children.

COA Ocular Motility and Alignment 2

During the cover-uncover test, the examiner covers the right eye.
The left eye moves outward (temporally) to pick up fixation.
This finding MOST likely indicates: