Microbial keratitis (MK) is a devastating and potentially sight-threatening condition that is especially concerning for children, who may have numerous cumulative years of exposure to risk. Although published examples of MK associated with overnight orthokeratology (ortho-k) have reported data from children, children are not necessarily at greater risk (Bullimore and Johnson, 2020). More children than adults may be wearing overnight ortho-k lenses for myopia management. Thus, it is not possible to compare the risks of overnight ortho-k in children to the risks in adults.

Povidone-iodine disinfecting solution has been investigated in multiple studies. One study evaluated the frequency of adverse events with povidone iodine disinfecting solution in daily wear soft contact lens wearers over a three-month period (Tan et al, 2018). Ocular signs and symptoms during lens wear were assessed at baseline and after one and three months of solution use. Contact lens cases were assessed for the frequency of microbial contamination and for the types of microbes by culture and by the use of 16S rRNA sequencing.

The povidone-iodine disinfecting solution was well tolerated. Corneal staining was reduced (0.5 ± 0.5 at three months of use) compared with the habitual multipurpose disinfecting system (1.1 ± 1.0). Other clinical signs were similar. No cases of solution-induced corneal staining were observed. There was a low rate of adverse events (0.8% per 100 participant-months). Contact lens case contamination was low; 30% of cases did not have culturable microbes. There were low frequencies of Gram-positive (49%) and fungal (8%) contamination and a low level—but higher compared with published data of other disinfecting solutions—of Gram-negative bacteria. In this study, the levels of adverse events were low. Contact lens cases were significantly less frequently contaminated than with other types of disinfecting solutions.

Efficacy in Ortho-k Wearers

A recent study evaluated lens cleaning routines, lens and lens case contamination, and the effect on conjunctival colonization using a povidone iodine-based rigid lens disinfecting solution (Cheung et al, 2021). Children ages 6 to 10 years undergoing ortho-k treatment were randomized to four lens cleaning routines. Lenses were cleaned with and without the use of daily and/or weekly cleaners. The children’s parents performed lens cleaning.

Conjunctival colonization was evaluated prior to lens wear and at one, three, and six months after lens wear commenced. Lenses and lens cases were evaluated for contamination. MALDI-TOF mass spectrometry was used to identify organisms. At baseline, conjunctival colonization was present in 24 (32%) of the 76 participants who completed the study. Of the remaining 52 participants, 34 repeatedly did not yield any growth. Those who were positive at baseline were statistically more likely to be colonized after commencement of lens wear.

In general, after six months of lens wear, the colonization rate was reduced to 15%—a significant value for participants who were originally colonized. There was no evidence of Pseudomonas aeruginosa in any culture. In this study, contamination rates of both lenses and lens cases were minimal, with few isolations of ocular pathogens. There were no significant differences between cleaning regimens for conjunctival colonization or for contamination of lenses or cases.

In conclusion, povidone iodine-based solution may effectively disinfect ortho-k lenses regardless of the cleaning routine adopted in the current study. This study demonstrated that povidone iodine-based solution may improve the safety of overnight lens wear, as most samples did not have pathogens in the conjunctiva, lenses, and lens cases. CLS

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