**2. Mechanisms of damage**

### **2.1 Inflammatory changes with topical treatment**

The damage that occurs with topical treatment in glaucoma is the result of chronic inflammatory changes. A significant increase in macrophages, mast

cells and lymphocytes has been found in conjunctival biopsies, compared with biopsies of patients who have not received treatment. A significant increase in inflammatory markers has also been found, specifically IgE and Class II HLA-DR1 antigen. All of this suggests that topical treatment produces an inflammatory state on the ocular surface and even on the tenon. This was published in 1989 by Dr. Sherwood, he showed than this inflammatory state affects both the conjunctiva and the tenon [6]. Fibroblasts also were more prominent in the deeper conjunctiva and Tenon's capsule, this finding might be expected to enhance the risk of external bleb scarring after trabeculectomy or valve surgery. Also, this study, in patients who received long-term antiglaucomatous medical therapy, detected a significant decrease in the number of goblet cells in patients who received long-term antiglaucomatous medical therapy, this contributes to dry eye in glaucoma patients, in addition to other studies have explored the potential association between topical anti-glaucoma medications and meibomian gland dysfunction [7].

#### **2.2 Meibomian gland dysfunction in Glaucoma**

We know that Meibomian gland dysfunction (MGD) is a chronic diffuse eyelid margin disease that is associated with tear film instability, inflammation, and OSD. MGD is the most common cause of evaporative dry eye. The mechanism underlying the changes in the meibomian glands is unclear, some studies have reported that results by a chronic inflammation of the conjunctiva, altered by long-term anti-glaucoma eye drop use [6]. These chronic inflammation causes morphological and functional changes in the glands. Some studies have shown stagnation of meibum followed by the keratinization of orifices in the meibomian glands [8]. Arita et al., using non-contact meibography, compares a Two treated group with control, subgroup analysis revealed than the meibomian gland loss in the PG-treated eyes and β-blocker-treated eyes, that was significantly higher than in the corresponding controls [9].

#### **2.3 Changes in extracellular matrix**

In extracellular matrix (ECM) a pair of enzyme families called the matrix metalloproteinases (MMPs; a group of enzymes catalyzing the degradation of ECM) and the tissue inhibitors of metalloproteinase (TIMPs) are involved in the regulation and maintenance of the ECM. MMPs and TIMPs are involved in physiological mechanisms. ECM accumulation caused by changes of MMP and TIMP expression is significantly involved in the increased outflow resistance in glaucomatous eyes and changes in ECM metabolism of ocular surface tissue, specifically changes in conjunctival tissues, including a decrease in the number of epithelial goblet cells, and increase in subepithelial collagen deposition [10].

The topical treatment for glaucoma can cause damage to the ocular surface where different inflammatory pathways, which over time affect the globet cells and Meibomian glands among other ocular structures. This damage is due to both, the components of the drugs and the preservatives, of which the most used is BAK, However many studies indicate a direct correlation between the presence of preservatives and the symptoms experienced during antiglaucoma therapy. Most effects observed in glaucoma patients are therefore more likely to be due to the preservative than the active ingredients [11], however, It has been described specific alterations in the ocular surface from each family of drugs.
