Question

Based on the following eye examination image, what is the most likely finding?

• A. RAPD
• B. Adie's tonic pupil
• C. 3rd cranial nerve Palsy
• D. Optic nerve damage

Hint:

Pupillary Reflex Pearls:
- RAPD (Marcus Gunn pupil): Demonstrated via the Swinging Flashlight Test $\rightarrow$ Paradoxical pupillary dilation when light swings to the diseased eye.
- Location of lesion: Afferent pathway (retina or optic nerve anterior to optic chiasm).
- Pupil size at rest: Pupils are of EQUAL size in ambient room light (no baseline anisocoria).

Answer 1

The Correct Option is A

Concept:
Relative Afferent Pupillary Defect (RAPD), also known as the Marcus Gunn pupil, is a physical examination finding detected using the Swinging Flashlight Test, indicating asymmetric or unilateral dysfunction in the afferent visual pathway anterior to the optic chiasm.
Explanation:
• In a normal swinging flashlight test, shining light into either eye produces equal, brisk, and symmetric pupil constriction in both the illuminated eye (direct light reflex) and the contralateral eye (consensual light reflex).

• When light is rapidly swung from the normal unaffected eye to the abnormal affected eye with an afferent conduction defect:
1. The diseased eye perceives a decreased stimulus intensity compared to the normal eye.
2. The brainstem interprets this as a reduction in illumination.
3. Consequently, instead of constricting, both pupils paradoxically dilate when light shines into the affected eye.

• This paradoxical bilateral pupillary dilation upon illumination of the abnormal eye during the swinging flashlight test is the clinical definition of a Relative Afferent Pupillary Defect (RAPD).

• Common causes of RAPD in children include unilateral optic neuritis, severe asymmetric glaucoma, optic nerve hypoplasia, optic glioma, and extensive unilateral retinal detachment or ischemic retinopathy.

• An efferent defect (such as 3rd cranial nerve palsy) causes an anisocoric, fixed, and dilated pupil that does not respond consensually, rather than bilateral paradoxical dilation on swinging flashlight test.
Final Answer:
The swinging flashlight test demonstrating paradoxical dilation of both pupils when light is shifted to the affected eye is diagnostic of a Relative Afferent Pupillary Defect (RAPD).