Incidence of microbial keratitis associated with overnight orthokeratology: a multicenter collaborative study

To investigate the incidence of microbial keratitis among Japanese patients wearing orthokeratology (ortho-k) lenses Retrospective multicenter study This study was conducted at 4 hospitals in Japan and involved 1438 patients who had been prescribed ortho-k lenses and had worn them for at least 3 months. Data on patient demographics, lens characteristics, lens care systems, and presence of microbial keratitis were extracted from the medical records. Duration of ortho-k lens wear was calculated from the original fitting date to the patient's last visit, with the total years of lens wear used as person-years of lens wear. The incidence of microbial keratitis was calculated by dividing the number of infected cases by the total person-years of lens wear for all enrolled participants. Among the 1438 patients, 753 were male and 685 were female, with a mean age of 12.7 ± 5.4 years. The mean duration of ortho-k lens wear was 5.2 ± 4.5 years, and the mean lens power was -3.52 ± 1.41 D. The total person-years of lens wear for all enrolled patients was 7415. Four cases of microbial keratitis were identified, resulting in an overall incidence of microbial keratitis of 5.4 (95% CI: 1.0–9.8) per 10,000 patient-years among ortho-k lens wearers. This study represents the largest sample size to date for estimating the incidence of microbial keratitis associated with ortho-k lenses. The incidence was similar to or slightly lower than that of previous studies on ortho-k-related microbial keratitis and also comparable to that of daily wear soft contact lenses.