We thank Dr. Scott for his interest in our article. Through our clinical research on the use of povidone–iodine in ophthalmologic surgeries, we know that preoperative topical antibiotic and povidone–iodine irrigation do not eliminate the bacterial flora present on the eye surface. Repeated intraoperative irrigation with povidone–iodine achieves transient sterilization of the surgical field, reducing the risk of intraocular inoculation of microorganisms to a minimum, which we think greatly reduces the risk of endophthalmitis. We believe that our method can be applied widely to vitreoretinal procedures including intravitreal injection, vitrectomy, and surgery for retinal detachment.
Povidone–iodine is a low-cost antiseptic agent with no antibiotic-resistance issue and is rapidly bactericidal and used worldwide. The bactericidal effect of povidone–iodine peaks at 0.1% and requires a shorter contact time for 0.1% to 1.0% solutions (15 seconds) compared with 2.5% to 10% solutions (30 to 120 seconds). However, diluted povidone–iodine is not stable. Therefore, 5% to 10% povidone–iodine is used widely in the operating room for routine skin and hand disinfection because of its higher stability and easy storage. For conjunctival irrigation, we use 1% povidone–iodine freshly prepared before surgery. Indeed, a freshly prepared 1% solution can be used even more effectively than the 10% solution for periorbital skin and hand disinfection.
The povidone–iodine concentrations that are highly bactericidal and nontoxic to ocular tissues range from 0.05% to 0.5%. As ophthalmic applications, 0.05% povidone–iodine (Ophtecs, Kobe, Japan) is used for disinfecting the contact lens and lens case, whereas an ophthalmic preparation containing 0.4% povidone–iodine is used for the treatment of adenoviral conjunctivitis, because the concentration tends to decrease after instillation. Povidone–iodine has been shown to be bactericidal not only to bacteria, but also to Candida species, viruses, and acanthamoebae, and also has been shown to be active against biofilms. For instance, if 0.4% povidone–iodine instillations before and after cataract surgery reliably can prevent infections caused by microbial flora in the surgical field, this will be a superior alternative to topical antibiotics also from the viewpoint of not generating antibiotic-resistant bacteria. However, that depends on how much free iodine is present in the anterior chamber. In our study, we measured iodide ion in the anterior chamber and found the concentration to be 0.008%. Although we did not measure free iodine, the concentration should be even lower. Therefore, by instilling 0.4% povidone–iodine, it may be difficult to achieve a free iodine concentration of 0.05% in the anterior chamber for a given period. Obviously, the free iodine concentration in the anterior chamber should be measured to provide solid evidence. We would like to encourage the author to continue in his research of optimal ophthalmic formulations and applications that are more effective and less toxic.