A 26 year old female presents with insidious onset of diplopia on alternate cover test, the patient has a right hypertropia, worse on right head tilt and left gaze. Which muscle is paralysed
**Core Concept**
The patient's symptoms indicate a disorder of ocular motor function, specifically a problem with the vertical gaze muscles. The right hypertropia, which worsens on right head tilt and left gaze, suggests an imbalance in the yoke muscles responsible for vertical gaze.
**Why the Correct Answer is Right**
In the context of vertical gaze, the yoke muscles are the superior rectus and inferior oblique muscles for the left eye (contralateral to the hypertropia) and the superior oblique and inferior rectus muscles for the right eye. The patient's symptoms point towards a problem with the left superior oblique muscle, which is responsible for intorsion, abduction, and depression of the left eye. The left superior oblique muscle is innervated by the trochlear nerve (CN IV), which is the fourth cranial nerve. The correct answer is the muscle responsible for the patient's symptoms, which is the left superior oblique muscle.
**Why Each Wrong Option is Incorrect**
* **Option B:** The right inferior oblique muscle is not primarily responsible for vertical gaze and would not cause hypertropia.
* **Option C:** The left superior rectus muscle is involved in elevation, not intorsion or depression, and would not cause the patient's symptoms.
* **Option D:** The right inferior rectus muscle is involved in depression, not elevation or intorsion, and would not cause the patient's symptoms.
**Clinical Pearl / High-Yield Fact**
In cases of vertical gaze palsy, it's essential to remember the "Wallace's rule of 9," which states that in vertical gaze palsy, the affected muscle is usually the one innervated by the cranial nerve that is contralateral to the hypertropia.
**Correct Answer:** C. Left superior oblique muscle.