The association between demodex infestation and ocular surface manifestations in meibomian gland dysfunction

AIM: To investigate the association between ocular demodex folliculorum infestation and ocular surface manifestations in meibomian gland dysfunction(MGD).METHODS: Eight-six patients with MGD were enrolled. All enrolled subjects were tested in the following sequence: ocular surface disease index(OSDI), slit-lamp biomicroscope examination, corneal surface regularity index(SRI) and surface asymmetry index(SAI), tear fluid collection, fluorescein tear film break-up time(F-BUT), corneal fluorescein staining(CFS), Schirmer I test(SIT) and demodex folliculorum counting. Tear matrix metalloproteinase(MMP)-9 activity was assessed using MMP-9 activity assay kit.RESULTS: Among 86 MGD patients, 40 were positive for demodex. The ocular demodex-positive group showed significantly increased scores of OSDI(25.96±13.74 vs 18.07±11.55, P=0.01), lid margin abnormality(2.38±0.87 vs 1.98±0.91, P=0.04) and CFS(1.28±2.00 vs 0.94±1.36, P=0.01) compared to the ocular demodex-free group. The tear MMP-9 activity was higher in the ocular demodex-positive group(102.9±32.4 ng/mL) than the ocular demodex-free group(46.2±19.2 ng/mL, P=0.03). There was no significant difference in meibum quality and expressibility, SRI, SAI, F-BUT and SIT between the two groups(P>0.05 for each). No significant correlation was noted between the number of demodex and ocular surface parameters in demodexpositive MGD group(P>0.05 for each).CONCLUSION: Ocular demodex folliculorum infestation may be associated with ocular discomfort and ocular surface damage in MGD.