In cold caloric stimulation test, the cold water, induces movement of the eye ball in the following direction –
**Core Concept**
The cold caloric stimulation test is a method used to assess the vestibular function of the inner ear. When cold water is introduced into the ear canal, it causes a change in the temperature of the endolymph in the horizontal semicircular canal, leading to a displacement of the cupula and a subsequent stimulation of the vestibular nerve. This stimulation results in nystagmus, which is a rhythmic movement of the eyeball.
**Why the Correct Answer is Right**
The cold caloric stimulation test is used to assess the function of the lateral semicircular canal. When cold water is introduced into the ear canal, it causes a decrease in the temperature of the endolymph in the horizontal semicircular canal. This decrease in temperature leads to a decrease in the density of the endolymph, causing it to sink away from the ampulla of the canal. As a result, the cupula is displaced towards the ampulla, stimulating the vestibular nerve and causing the eyeball to move in a specific direction.
* In the case of a normal individual, the cold caloric stimulation test causes the eyeball to move in an **ipsilateral** direction (towards the stimulated ear) and **contralateral** direction (away from the stimulated ear).
* The nystagmus induced by the cold caloric stimulation test is usually followed by a secondary nystagmus in the opposite direction, which is called the **Alexander's law**.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because the cold caloric stimulation test does not cause the eyeball to move in the **ipsilateral** direction only.
**Option B:** This option is incorrect because the cold caloric stimulation test does not cause the eyeball to move in the **contralateral** direction only.
**Option C:** This option is incorrect because the cold caloric stimulation test does not cause the eyeball to move in a **random** direction.
**Clinical Pearl / High-Yield Fact**
The direction of nystagmus induced by the cold caloric stimulation test is an important clinical sign that can be used to assess the function of the vestibular system. It is essential to note that the direction of nystagmus can be affected by the position of the head and the presence of any underlying neurological conditions.
**Correct Answer: C.**