What does 'O.S.' denote in terms of medication application?

The abbreviation 'O.S.' stands for "oculus sinister," which is Latin for "left eye." In the context of medication administration, this term specifies that a medication or treatment is intended for use in the left eye. This designation is particularly relevant in ophthalmic practices, where precise instructions are critical for patient safety and effective treatment.

In contrast, the other choices reference different forms of medication application that do not align with the definition of O.S. For example, placing medication in the stomach pertains to oral administration but is indicated by different terminology. The right eye is denoted by "O.D." or "oculus dexter," and taking medication orally typically uses phrases like "per os" (often abbreviated as p.o.). Understanding these abbreviations is essential for medication aides to ensure correct administration and prevent potential medication errors.