**7. Mechanisms of IPL for prevention of damage to the ocular surface**

A better explanation of the mechanisms of IPL leads to a better treatment plan. Regarding several mechanisms, it would be nice to describe as follow:

Demodex folliculorum and Bacillus oleronius are common inhabitants of human hair follicles and sebaceous glands occasionally found in ocular rosacea. IPL increases mitochondrial activity and wound healing, decreasing lid marginal bacteria and Demodex by photocoagulation, improving elastosis, and connective tissue disorganization that occurs with MGD rosacea to relieve pain (**Figure 3**).

#### **7.1 Effects on mucin and corneal nerve**

Mucin plays many essential roles on the ocular surface, including maintaining lacrimal fluid, lubricating the ocular surface to facilitate flat blinking, forming a smooth spherical surface for clear vision, providing an ocular surface shield and trapping and eliminating contaminants and debris [41–43]. The tear film is divided into two layers, with the aqueous layer containing secreted mucin MUC5AC scattered across [42]. Xue et al. discovered no improvements in MU5AC expression after IPL procedures Utilizing conjunctival impression cytology,. IPL therapy has little effect on the density of nerve fibers and dendritic cells in the corneal sub-basal layer, according to research [44].

### **7.2 Pro- and anti-inflammatory molecule effects, as well as matrix metalloproteinase suppression**

Factors that influence tear film stability and osmolarity can cause ocular injury and trigger an inflammatory cascade that leads to a strong immunological reaction, leading to further ocular surface injury, causing a self-perpetuating inflammatory loop [45]. By upregulating anti-inflammatory cytokines, downregulating proinflammatory cytokines, or both, IPL can disrupt the inflammatory cycle. Dry eye's inflammatory cascade is highly complex and little known. Nevertheless, at least part of IPL's positive effect on DED patients may come from messing with the pathology's inflammatory cycle's positive feedback loop [46]. Interference with the inflammatory process by modulating anti-inflammatory factors and Matrix Metalloproteinase (MMP), lowering the turnover of skin epithelial cells, reducing the rate of severe obstruction of the meibomian glands, and improving the levels of active oxidative species all aid in the prevention of dry eye symptoms.

#### **Figure 3.**

*IPL treats MGD; IHMGEC: Immortalized human MG epithelial cells; SREBP-1: Sterol regulatory elementbinding protein 1.*
