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.