True or False: Drugs that cause nystagmus usually don't affect pupil size.

The statement that drugs causing nystagmus usually don't affect pupil size is considered true. Nystagmus, which is an involuntary eye movement that can be characterized by a rapid oscillation of the eyes, is often induced by specific categories of drugs, particularly central nervous system depressants, stimulants, and certain hallucinogens. While nystagmus manifests as eye movement, the effect on pupil size can vary depending on the specific drug involved.

Many drugs that induce nystagmus, such as alcohol and some sedatives, often leave pupil size unaffected or cause only subtle changes. This means that while a subject may exhibit nystagmus due to drug influence, their pupils may remain normal in size, which can be a key observation during a drug evaluation.

It's important to note that there are exceptions where certain drugs or higher doses might impact pupil size, but the general principle remains that the presence of nystagmus does not typically correlate with significant changes in pupil size for the majority of substances that induce this particular ocular phenomenon. This distinction aids drug recognition experts in assessing impairment and identifying the specific substances that may be involved.