Is there a relationship between keratoconus and ocular Demodex mites?

BACKGROUND: The background of this study was to evaluate the relationship between keratoconus (KC) occurrence and ocular Demodex infestation together with the effects of Demodex on the ocular surface. METHODS: Thirty-eight eyes of 20 KC patients (KC group) and 40 eyes of 20 age- and sex-matched healthy subjects (control group) were included in this cross-sectional study. Demodex species (folliculorum/brevis), clinical symptoms such as eye rubbing, Ocular Surface Disease Index (OSDI), corneal topography findings, tear break-up time (TBUT), and Schirmer test scores were evaluated. KC eyes were also divided into two subgroups according to KC severity and presence of Demodex. Demodex was detected using conventional light microscopy. RESULTS: The mean age was 25.90 ± 7.01 years in the KC group, and 26.52 ± 8.94 years in the control group (P = 0.731). While unexpectedly no Demodex were detected in the control group, Demodex were detected in the KC group, including 8 eyes (21.1%) with Demodex folliculorum, and 10 eyes with D. folliculorum + Demodex brevis (26.3%) (P < 0.001). As the KC severity worsened, the percentage of eyes with Demodex mites increased (43.8% in the mild/moderate subgroup and 66.7% in the severe subgroup, P < 0.001). The number of rubbing eyes and OSDI scores were significantly higher, and TBUT levels were significantly lower in the KC Demodex + and Demodex − subgroups than the control group (P < 0.001 for all), but there is no significant difference between the KC Demodex + and Demodex − subgroups regarding ocular surface parameters (P = 1.0). CONCLUSIONS: Although the number of patients is relatively small and there is no follow-up data after Demodex treatment, KC and ocular Demodex infestation seem to be associated. Demodex-related inflammation and associated eye rubbing may contribute to KC progression.