In a "primary eye irritation" study in rabbits, the untreated eye is referred to as which term?

• A. Control
• B. Placebo eye
• C. Baseline eye
• D. Reference eye

Answer: (A)

In this type of study, the eye that does not receive the test material is used for comparison to see what irritation the substance itself causes. That untreated eye is called the control eye because it serves as the baseline reference against which the treated eye’s responses are measured. Using the other eye as an internal control helps account for differences between animals and for any systemic factors, making it clearer whether observed irritation is due to the test substance. Other terms like placebo, baseline, or reference eye aren’t the standard name for this purpose, so the correct term is control eye.