**Core Concept**
Vigabatrin is an antiepileptic medication that acts as an irreversible inhibitor of GABA transaminase, the enzyme responsible for the breakdown of GABA (gamma-aminobutyric acid) in the brain. By preventing GABA degradation, vigabatrin increases the concentration and duration of action of GABA, which has a calming effect on neuronal activity.

**Why the Correct Answer is Right**
Vigabatrin is specifically used for treating epilepsy, particularly in patients with resistant partial seizures or infantile spasms. Its mechanism of action is based on the inhibition of GABA transaminase, which leads to an increase in the concentration of GABA in the synaptic cleft. This results in a decrease in excitatory neurotransmission and an increase in inhibitory neurotransmission, ultimately leading to a reduction in seizure frequency. Vigabatrin's effect on GABA levels is dose-dependent and reversible upon discontinuation of the medication.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is left blank, so we'll address the other options.
**Option B:** This option is incorrect because vigabatrin is not primarily used for treating bipolar disorder; it is used for treating epilepsy.
**Option C:** This option is incorrect because vigabatrin is not used for treating depression; it is used for treating epilepsy.

**Clinical Pearl / High-Yield Fact**
Vigabatrin is known to cause visual field defects as a side effect, particularly in patients with a history of glaucoma or other eye disorders. It is essential to monitor patients on vigabatrin for visual field defects and to use the medication with caution in patients with pre-existing eye conditions.

**Correct Answer: B. Infantile spasms.**