Ocular Motility Testing Flashcards

During the Parks-Bielschowsky three-step test, a patient demonstrates left hypertropia in primary position, worsening of the left hypertropia in right gaze, and further worsening of the left hypertropia on left head tilt. Which muscle is most likely paretic?

Answer: Left superior oblique

Step 1: Left hypertropia implicates left eye depressors (LSO, LIR) or right eye elevators (RSR, RIO). Step 2: Worsens in right gaze — in right gaze the left eye is adducted, where the LSO has maximal depressor action; and the right eye is abducted, where the RSR has maximal elevator action. This narrows the suspects to LSO or RSR. Step 3: Worsens on left head tilt — on left tilt the left eye must intort, a function of the LSO. If the LSO is paretic, it cannot respond, and the left hypertropia increases. This confirms left superior oblique palsy.

A patient presents with right hypotropia following blunt orbital trauma. Forced duction testing demonstrates resistance to passive elevation of the right eye. Active force generation testing of the right superior rectus shows near-normal force. Which interpretation is most accurate?

Answer: Mechanical restriction of the right inferior rectus consistent with orbital floor entrapment

Forced duction testing assesses passive movement. Resistance to elevation indicates a mechanical tether preventing the eye from moving upward — most consistent with inferior rectus entrapment in an orbital floor fracture. The near-normal active force generation of the superior rectus confirms the muscle itself is intact and functional; it simply cannot overcome the restriction. If the superior rectus were paretic, forced duction would be unrestricted (the eye would move passively without resistance), and active force generation would be reduced.

A 5-year-old presents with intermittent vertical strabismus of the right eye. On alternate cover testing, the right eye elevates when occluded. When the occluder is removed, the right eye descends to resume fixation, but the left eye shows no corresponding downward movement. Which condition does this finding most specifically support?

Answer: Right dissociated vertical deviation (DVD)

The defining feature of dissociated vertical deviation (DVD) is that it does not obey Hering's law of equal innervation. In true strabismus, uncovering the elevated eye causes it to descend while the fellow eye simultaneously elevates (a yoke response). In DVD, when the right eye descends upon uncovering, the left eye shows NO conjugate movement downward or upward — there is no corresponding shift. This violation of Hering's law is pathognomonic for DVD and distinguishes it from true hypertropia or inferior oblique overaction.

A patient is diagnosed with left superior oblique palsy. During double Maddox rod testing, one rod is placed before each eye with the cylinder axes oriented vertically (producing horizontal streaks). Which torsional finding is most expected in the left eye?

Answer: Excyclotorsion (extorsion) of the left eye, because the superior oblique is the primary intortor

The superior oblique is the primary intortor of the eye. With left SO palsy, its intorsion function is lost, and the unopposed inferior oblique (an extortor and elevator) causes the left eye to excyclotort. On double Maddox rod testing, the horizontal streak seen by the left eye appears tilted relative to the right eye's streak — the angular difference between the two streaks quantifies the degree of excyclotorsion. Bilateral excyclotorsion >10° per eye raises suspicion for bilateral SO palsy.

A clinician measures the AC/A ratio using both the gradient method (±2 D lenses at 40 cm) and the calculated (heterophoria) method (phorias at 6 m and 40 cm). The calculated method yields a significantly higher AC/A ratio than the gradient method. What is the most likely explanation for this discrepancy?

Answer: The calculated method includes proximal convergence in the near phoria measurement, inflating the AC/A value

The calculated method derives AC/A from phorias measured at two different distances. The near phoria incorporates proximal convergence — vergence driven by the perception of nearness itself, independent of accommodation. This proximal component inflates the near phoria and therefore inflates the resulting AC/A. The gradient method changes accommodation via lenses at a FIXED distance, keeping proximal convergence constant and canceling it out of the equation. It therefore isolates the true accommodative convergence per diopter of accommodation, yielding a lower and more accurate AC/A ratio.

In which clinical scenario is the Krimsky test most clearly advantageous over the Hirschberg corneal reflex test for estimating the angle of strabismus?

Answer: A patient with dense amblyopia and eccentric fixation in the deviating eye

The Krimsky test places prisms in front of the FIXING eye and increases power until the corneal light reflex appears centered in the DEVIATING eye. Because the examiner is observing the deviating eye's reflex rather than requiring that eye to fixate accurately, the Krimsky test remains valid even when the deviating eye has eccentric fixation due to amblyopia. The Hirschberg estimates deviation by observing the reflex position in both eyes simultaneously; if the deviating eye fixates eccentrically, the reflex position misrepresents the true angle. Corneal scarring of the fixing eye (option D) would prevent prism neutralization and impair the Krimsky test rather than benefit it.