Mr A has post-operative cataract surgery and is using Tobradex and Yellox. When two different eye preparations must be used at the same time, what is the recommended interval between drops?

• A. Immediately after
• B. Leave an interval of at least 5 minutes
• C. Wait 30 minutes
• D. Never rinse between drops

Answer: (B)

Spacing two eye drops is important because the tear film can wash away the first drop if another is instilled too soon, reducing how much of the drug stays on the ocular surface. Allowing a short interval gives the first drop time to spread, coat the eye, and begin absorption by the ocular tissues, so the second drop isn’t diluted or prematurely cleared. In the post-operative setting with Tobradex (tobramycin/dexamethasone) and Yellox, waiting at least five minutes between drops ensures both medications achieve their intended effect without interfering with each other. Instilling immediately after would wash out the first drop; waiting 30 minutes is longer than necessary and can complicate dosing; never rinsing between drops doesn’t resolve the underlying issue of washout. Five minutes is the practical, evidence-aligned interval.