To create a 0.2% povidone-iodine solution for corneal surfaces, which dilution is used?

• A. 1:10
• B. 1:50
• C. 1:100
• D. 1:5

Answer: (B)

To obtain a final 0.2% povidone-iodine solution from a stock of 10%, you need to dilute by a factor of 50. That’s because 0.2% is 1/50 of 10%. A 1:50 dilution means 1 part stock mixed with 49 parts diluent, giving a total of 50 parts. So, for example, mix 1 mL of 10% povidone-iodine with 49 mL of sterile saline to make 50 mL of 0.2% solution.

This concentration is used on the corneal surface to balance antimicrobial effectiveness with reduced ocular toxicity. Dilutions like 1:10 (about 1%), 1:100 (about 0.1%), or 1:5 (roughly 2%) would not give the intended 0.2% strength and could be either irritating or under-detectant, respectively.