A child age 5 years, presents with loss of vision and mild proptosis of left eye. On examination direct light reflex is absent but consensual is present in left eye. He is –
**Core Concept**
The child's presentation suggests an afferent pupillary defect (APD), a condition where the direct pupillary light reflex is abnormally weakened or absent in response to light shone into the affected eye. This is typically due to a disruption in the afferent pathway of the pupillary light reflex, which involves the optic nerve, optic chiasm, and optic tract.
**Why the Correct Answer is Right**
The absence of the direct light reflex but presence of the consensual light reflex in the left eye indicates an afferent pupillary defect. This is because the consensual reflex involves the efferent pathway, which is intact. The afferent pathway involves the optic nerve, which carries visual information from the eye to the brain. In this case, the optic nerve is likely affected, leading to the absence of the direct light reflex. The presence of the consensual reflex suggests that the efferent pathway, which involves the oculomotor nerve (cranial nerve III), is intact.
**Why Each Wrong Option is Incorrect**
* **Option A:** This option is not relevant to the clinical presentation of an afferent pupillary defect.
* **Option B:** This option may be a distractor, but it is not directly related to the clinical presentation of an afferent pupillary defect.
* **Option C:** This option could be a distractor, but it is not directly related to the clinical presentation of an afferent pupillary defect.
* **Option D:** This is a distractor, as it does not accurately describe the clinical presentation of an afferent pupillary defect.
**Clinical Pearl / High-Yield Fact**
Afferent pupillary defects can be caused by a variety of conditions, including optic nerve damage, optic chiasm lesions, and optic tract lesions. It is essential to perform a thorough ophthalmological examination, including pupillary reflex testing, to diagnose and manage APD.
**Correct Answer: B. Optic neuritis.**