Ocular Motility Testing Flashcards

During a Parks three-step test, a patient has a right hypertropia that increases in left gaze and increases with right head tilt. Which muscle is most likely paretic?

Answer: Right superior oblique

The Parks three-step test isolates a single cyclovertical muscle. Step 1: right hypertropia → paretic muscle is a right depressor or left elevator. Step 2: increases in left gaze → right superior oblique or right inferior rectus. Step 3: increases with right head tilt → right superior oblique (which would normally intort in right head tilt). All three steps converge on the right superior oblique as the paretic muscle.

A patient demonstrates a positive Bielschowsky head-tilt test to the LEFT shoulder. Which of the following diagnoses is most consistent with this finding?

Answer: Left superior oblique palsy

In the Bielschowsky head-tilt test, tilting toward a shoulder stimulates the ipsilateral intorters and contralateral extorters. A positive test (worsening hypertropia) on left tilt implicates the left intorters — specifically the left superior oblique or left superior rectus. Because the left superior oblique is the primary intortor and its palsy is the classic indication for this test, left SO palsy is the correct answer. If it were left SR palsy, the hypertropia would be on the LEFT, not a worsening with left tilt in the context of a right hyper.

When performing the alternate prism cover test, the examiner notices the eyes make no refixation movement at distance but show a 10Δ esotropia at near. The AC/A ratio is calculated to be 8:1 using the gradient method with +3.00 D lenses. This pattern is most consistent with which condition?

Answer: Convergence excess esotropia

Convergence excess esotropia is characterized by orthophoria or minimal deviation at distance with esotropia at near, and a HIGH AC/A ratio. A gradient AC/A of 8:1 (well above the normal 3:1–5:1 range) with near-only esotropia is the hallmark of convergence excess. Divergence insufficiency presents with esotropia greater at distance. Basic esotropia shows similar deviations at both distances. Decompensated esophoria would not typically show orthophoria at distance with this magnitude of near deviation.

A patient with a known left lateral rectus palsy is being assessed with the Hess screen test. Which of the following best describes the expected findings on the Hess chart?

Answer: The left chart is contracted and the right chart is expanded, with maximum contraction in the field of left lateral rectus action

On the Hess screen test, the field plot of the PARETIC eye (left) is contracted — it appears smaller — because the paretic muscle cannot move the eye fully into its field of action. By Hering's Law, the yoke muscle (right medial rectus) receives excess innervation, causing the FELLOW eye (right) chart to be EXPANDED, particularly in the direction of gaze corresponding to the paretic muscle's field. Maximum contraction on the left chart appears in the left lateral gaze field, and maximum expansion on the right chart appears in the corresponding right medial gaze field.

During a cover-uncover test, the left eye is covered and the right eye makes no movement. When the cover is removed, the left eye drifts outward momentarily before refixating. What does this finding indicate?

Answer: Left exophoria

In the cover-uncover test, you cover one eye and watch the OTHER (uncovered) eye for movement. Here, covering the left eye caused no movement of the right eye — indicating the right eye was already fixating (no manifest deviation). When the cover is removed from the left eye, the left eye drifts outward before refixating, revealing that it had deviated under cover (i.e., it was held in by fusion). This is the classic sign of a PHORIA (latent deviation) in the LEFT eye — specifically left exophoria. The movement is of the covered eye upon uncovering, which indicates a phoria.

A 35-year-old patient presents with sudden-onset vertical diplopia. On examination, there is an incomitant right hypertropia that is greatest in down-and-left gaze. The patient also reports that images are tilted (torsional diplopia). Fundus exam reveals extorsion of the right eye. Which cranial nerve is most likely affected, and on which side?

Answer: CN IV, right side

CN IV (trochlear nerve) innervates the superior oblique, which has its greatest depressor action in adduction (down-and-in gaze) and its greatest intortor action in abduction. A right CN IV palsy causes: (1) right hypertropia greatest in down-left gaze (adduction of the right eye), (2) torsional diplopia due to loss of intorsion, and (3) fundus extorsion of the right eye as the superior oblique no longer intorts. CN III palsy would cause ptosis, mydriasis, and multiple muscle involvement. CN VI causes horizontal deviation only. A LEFT CN IV palsy would produce findings maximal in down-RIGHT gaze.