1. Subjects
This study is a retrospective review of clinical records conducted at Yeouido St. Mary’s Hospital, Seoul, South Korea. This study adhered to the tenets of the Declaration of Helsinki and approval for retrospective review of clinical records was obtained from the Institutional Review Board (IRB) of the Catholic University of Korea (SC21RISI0001, Seoul, South Korea). Written informed consent obtained from parents/legal guardians for study participation was waived by IRB of the Catholic University of Korea (SC21RISI0001, Seoul, South Korea) because of the retrospective nature of the study.
The study included pediatric population aged 7 to 17 years who visited the Yeouido St. Mary’s Hospital between September 2018 and December 2020. Subjects with a history of intraocular or eyelid surgery, ocular infectious (viral or bacterial) or inflammatory diseases, giant papillary conjunctivitis (GPC), as well as those diagnosed with dermatologic diseases including pediatric rosacea or allergic diseases and/or taking medications such as antihistamines, were excluded. Patients who showed any signs or symptoms of dry eye disease (DED) or MGD were also excluded.
The control group comprised of subjects who visited the clinic for the prescription of Ortho-K and they did not have a history of lens wear, irrespective of whether they wore glasses. Subjects in the Ortho-K group had been using the lenses for at least 4 months. The final cohort comprised 79 patients of control group and fifty-three patients of Ortho-K group. Right eye of each patients were used in the analysis.
2. Lenses
We prescribed rigid gas-permeable contact lenses with a reverse geometry design (Lucid LK; Lucid Korea, Seoul, South Korea) to all subjects and checked the lens-fitting according to the manufacturer’s guidelines. All patients wore the lenses for at least seven continuous hours while sleeping and immediately removed the lenses on awakening. The treatment policy at our lens clinic is that we neither prescribed the lens to the candidate subjects nor discontinued its use in the Ortho-K group participants with symptoms of DED or MGD16-19. Thorough opthalmic examination were performed at any time of visits.
3. Data collection
Information of the LipiView II Ocular Surface Interferometer (Tear Science Inc. Morrisville, NC, USA) was used for the evaluation of the lipid layer thickness (μm), and the percentage of incomplete blinks (incomplete blink rate).
Both the upper and lower eyelids were everted and MGs were observed using a noncontact meibography system. Partial or complete loss was scored according to the meiboscores for the upper and lower eyelids eyelids from the LipiView images as follows20: 0, no gland dropout; 1, dropout with less than 25% of the loss; 2, dropout with 26% to 50% loss; 3, dropout with 51% to 75% loss; and 4, dropout with more than 75% loss.
4. Statistical Analysis
We used propensity score (PS) weighting to compare between the variables21,22. We assessed the PS between the control and Ortho-K groups, using ordinal logistic regression based on the baseline covariates, including age, BCVA, axial length, and astigmatism. In addition, we used the inverse probability technique (IPTW) to balance the baseline covariates among the two groups during time-to-event analyses using stabilized weights calculated from the PS23. Comparisons of demographic characteristics (age, gender, BCVA, axial length, and astigmatism) and parameters measured by the LipiView (incomplete blink rate, average lipid layer thickness, and meiboscores of lower and upper eyelids) between the two groups were analyzed using paired t-tests. Pearson’s correlation analysis was used to determine the relationship of parameters measured by the LipiView with the duration of Ortho-K lens wear. A p-value of <0.05 was considered statistically significant.