Change in Prostaglandin Expression Levels and Synthesizing Activities

We read with great interest the recently published study by Shim et al, which the authors described as a cross-sectional, case-control, clinical trial. As a single study, such a design is not possible because cross-sectional, case-control, and clinical trials are 3 distinct types of study designs. The authors conducted a cross-sectional analysis to investigate the associations of ocular irritation scores and concentrations of prostaglandin E2 to prostaglandin D2 in adult eyes with dry eye disease. In addition, in a separate analysis, eyes of the participants with dry eye disease were compared with those without the disease to identify possible risk factors, including tear film breakup time, fluorescein staining, tear sampling, intraocular pressure, and threshold of ocular irritation. Because study participants were selected based on their disease status (dry eye disease), this is better described as a case-control study. The authors report that the controls were age- and gender-matched to the cases, which suggests that this is a matched, case-control study. Although the study participants did not differ by age or gender (See Supplemental Table 1 in Shim et al), this does not indicate the groups were intentionally matched. Therefore, we believe that this was an unmatched study, given that a different number of cases and controls were enrolled and the analyses were based on an unmatched study design. Last, data from a mouse eye model were used to investigate the association of various celecoxib solution concentrations and ocular tissue levels in control mice compared with mice with induced dry eye disease. This is better described as a clinical trial mouse model.