Comparison Between Continuous and Pulsed Oral Doxycycline Treatment Protocols for Refractory Meibomian Gland Dysfunction

The goal of this observational study (spontaneous, non-randomised, prospective cohort, phase IV) is to compare the efficacy and safety of two different oral doxycycline treatment protocols (LCP - Low dose continuous protocol \& FPP - Full dose pulsed protocol) for meibomian gland dysfunction (MGD) in patients with refractory MGD (OSDI \> 13 after at least 2 months treatment with warm compresses and lacrimal substitutes - first-line therapy). Systemic doxycycline doesn't have a standardized treatment protocol and this is why those patients are treated as in normal clinical practice. The main questions it aims to answer are: Which treatment protocol has a greater impact on patient symptoms during the follow-up (OSDI score reduction)? Which treatment protocol has a greater impact on patient signs during the follow-up (TBUT and corneal staining variations)? Which treatment protocol is safer (in terms of adverse events rate)? Participants will be visited every 3 months (V0-V1-V2-V3) with signs and symptoms assessment (TBUT, corneal staining, OSDI score) after being treated for 3 months with the assigned doxycycline treatment protocol (LCP or FPP).