Characteristics of corneal microcysts in Hong Kong children wearing orthokeratology.

PURPOSE: To report the characteristics (prevalence, severity, and location) of corneal epithelial microcysts and investigate associated risk factors in children wearing orthokeratology (ortho-k) lenses. METHOD: Ninety-five myopic children wearing ortho-k lenses (examined by one of three independent investigators from March to September 2020) were included in this retrospective cross-sectional study. Pertinent data at baseline before ortho-k treatment and at the aftercare visits (the first visit when the microcysts were observed for children with microcysts, and the last visit before October 2020 for children without microcysts) were retrieved and analysed. RESULTS: A microcystic response was observed in 52.6% of children wearing ortho-k lenses. Children with high myopia (≥ 5.00 D) had a higher prevalence (100.0%, 23/23) and severity (69.5% (16/23) > grade 2 Efron scale) compared to children with low myopia (≤ 4.00 D) (prevalence of 37.5% (27/72) and 7.0% (5/72) > grade 2, p < 0.001). Microcysts were predominantly (86.0%) observed in the region of the inferior pigmented arc, typically originating in the inferior mid-peripheral cornea, and expanding over time into a semi- or whole annulus. Baseline myopia and topographical change at the treatment zone centre were significantly greater (p < 0.05) in low myopic children with microcysts (univariate analyses). CONCLUSIONS: During the COVID-19 pandemic, probably due to lifestyle changes, microcysts were frequently observed in children wearing ortho-k lenses and were associated with higher baseline myopia. Practitioners should examine ortho-k wearers with caution using a slit lamp with high magnification and illumination, especially the mid-peripheral cornea. The use of highly oxygen permeable lenses and frequent aftercare are necessary for ortho-k wearers, especially those with higher myopia.

Repeatability of corneal biomechanical measurements in children wearing spectacles and orthokeratology lenses.

PURPOSE: To determine the repeatability of corneal hysteresis (CH) and corneal resistance factor (CRF) measurements in children wearing spectacles and children under orthokeratology (ortho-k) therapy using the Ocular Response Analyzer (ORA). METHODS: CH and CRF were measured twice at a 10-min interval using ORA on the same day in both eyes of 25 children (mean age = 10.6 ± 1.2 years) wearing spectacles and 34 children (mean age = 10.9 ± 1.0 years) wearing ortho-k lenses. Four measurements were obtained from each eye in each set of measurements. Only data from the right eyes were analyzed. RESULTS: No significant between-measurement differences in CH and CRF were found in either group of subjects (paired t-tests, p > 0.05) and no correlations were found between the mean differences and their means (Pearson's correlations, -0.09 < r < 0.21, 0.24 < p < 0.85). The 95% limits of agreement (LA) were -1.87 mmHg to +2.59 mmHg and -1.53 mmHg to +1.41 mmHg for CH and -1.86 mmHg to +2.22 mmHg and -1.45 mmHg to +1.57 mmHg for CRF in the spectacle and ortho-k groups, respectively. A significant between-group difference in CRF was found (unpaired t-tests, p = 0.02). CONCLUSIONS: Repeatability of CH and CRF measurements using the ORA is within ± 2 mmHg in children wearing spectacles or ortho-k lenses. We suggest that the ORA can be used to monitor long-term corneal biomechanical changes during ortho-k treatment.