A recent study investigated the association between levels of matrix metalloproteinase-9 (MMP-9), a common marker of inflammation in tears, and changes to the meibomian glands accompanying soft contact lens (CL) wear. The researchers found that the early years of CL wear are associated with increased expression of MMP-9, possibly indicating low-level inflammation during this phase of wear.

The researchers collected flush tears from three cohorts: (1) CL wearers who had worn lenses on a daily basis for different durations (short: 2±1 years, moderate: 5±1 years and long experience: 10±2 years); (2) a group of previous CL wearers who had ceased wear for at least six months; and (3) healthy non-wearers as a control group. From the 100 participants, the study calculated the concentration ratio of MMP-9 to its inhibitor, tissue inhibitor of metalloproteinase-1 (TIMP-1).

MMP-9 concentrations and the MMP-9:TIMP-1 ratio were significantly different between groups, while the concentration of TIMP-1 did not vary statistically between study groups. A post-hoc analysis revealed that only CL wearers with a short experience had MMP-9 concentrations that were significantly high compared with non-wearers (23.1ng/mL and 4.1ng/mL, respectively). When comparing MMP-9:TIMP-1 ratios, the team found it was only significantly greater in CL wearers with a short experience (about a six-fold increase) compared with non-wearers, CL wearers with moderate experience and previous wearers.

The concentration of MMP-9 falling to a level that is no longer significant in the following years of CL wear compared with non-wearers suggests that some adaptation may take place. The researchers note that although the disturbance to the MMP-9 levels was not enough to cause significant changes morphologically, it is unclear what effects these have downstream. They believe that further research will reveal whether the factors together may play role in the inflammatory cascade seen in meibomian gland dysfunction.