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Zorluk: OrtaPhysical Examination Findings

A 2727-year-old woman presents to the clinic complaining of acute-onset blurry vision in her left eye that began two days ago. She also reports mild pain in the same eye when looking in different directions. She has no significant past medical history and takes no medications. Vital signs are within normal limits. Visual acuity is 20/2020/20 in the right eye and 20/20020/200 in the left eye. During the physical examination, the physician performs a swinging flashlight test. When the light is shone directly into the right eye, both pupils constrict briskly. When the light is rapidly moved to shine into the left eye, both pupils appear to dilate. Which of the following is the most likely anatomic location of the lesion responsible for this physical examination finding?

  1. Left optic nerveCevap
  2. B
    Left oculomotor nerve
  3. C
    Optic chiasm
  4. D
    Left primary visual cortex
  5. E
    Left superior cervical ganglion

Cevap

The correct anatomic location is the left optic nerve, indicated by the presence of a relative afferent pupillary defect.
The patient's physical examination demonstrates a relative afferent pupillary defect (RAPD), also known as a Marcus Gunn pupil. During the swinging flashlight test, shining light into the healthy right eye causes brisk bilateral pupillary constriction, verifying that the right afferent (optic nerve, CN II) and bilateral efferent (oculomotor nerve, CN III) pathways are intact. When the light is rapidly moved to the affected left eye, the diminished afferent signal from the damaged left optic nerve leads to a reduced parasympathetic drive to the Edinger-Westphal nuclei. Because the intense consensual constriction from the right eye is withdrawn, the reduced afferent signal from the left eye makes both pupils appear to dilate. This finding definitively localizes the lesion to the afferent visual pathway anterior to the optic chiasm on the affected side, which is the left optic nerve. The clinical presentation of acute monocular vision loss with pain on eye movement in a young woman strongly suggests optic neuritis, a classic cause of this examination finding.

Adım Adım Çözüm

1
Analyze the clinical presentation.
The patient is a young woman with acute, painful, unilateral vision loss, which strongly suggests optic neuritis.
Establishing the most likely underlying pathology helps guide the anatomic localization of the physical examination findings.
2
Interpret the initial phase of the swinging flashlight test.
Brisk bilateral constriction when light is shone in the right eye indicates that the right afferent pathway and bilateral efferent pathways are fully intact.
This establishes a baseline that the motor components (pupillary constrictor muscles) and their direct neural supply are functioning.
3
Interpret the second phase of the swinging flashlight test.
Bilateral dilation when the light is moved to the left eye confirms a Relative Afferent Pupillary Defect (RAPD), or Marcus Gunn pupil.
The brain perceives less light coming from the left eye compared to the right eye, resulting in decreased parasympathetic output to both pupils, causing them to dilate from their previously constricted state.
4
Localize the lesion based on the reflex arc.
The defect must lie in the afferent visual pathway anterior to the optic chiasm on the affected side.
An RAPD is pathognomonic for a lesion in the ipsilateral optic nerve (CN II).

Anahtar Kavram

A relative afferent pupillary defect (RAPD) manifests as bilateral pupillary dilation when a light is swung from the normal eye to the affected eye, indicating a lesion in the ipsilateral optic nerve.
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Physical Examination Findings

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