## 4 Discussion
They found that PPP could manifest in 32-34% of patients up to 6 months postoperatively. Additionally, the administration of multiple eyedrops which contain preservatives may cause toxic effects and pain [9; 34; 40]. There also may be other etiologies to explain the postsurgical ocular discomfort after FLACS, which require further investigation. Because ocular discomfort after FLACS may be explained by an etiology other than dry eye disease, it will be important to assess tear osmolarity and MMP-9 to evaluate and manage postsurgical ocular discomfort appropriately. Our study found that abnormal MMP-9 levels and the number of eyes with abnormal results decreased significantly compared to the baseline level 1 month after surgery. This is thought to be due to the use of topical corticosteroids after the surgery. Topical corticosteroids cause a significant decrease in the MMP-9 level in patients with dry eye [45]. This may be explained by the suppression of cytokine expression, mitogen-activated protein kinase (MAPK) signaling pathways, c-Jun N-terminal kinase (JNK), and extracellular signal regulated kinase (ERK) in the corneal and limbal epithelial cells [46; 47]. Therefore, we may interpret a decreased MMP-9 level after cataract surgery as reflecting decreased inflammation of the ocular surface. However, cytokines and enzymes, such as interleukin-1\(\beta\), interleukin-6, caspase 3, transglutaminase 2, interferon-\(\gamma\), and tumor necrosis factor-\(\alpha\), are also known to be released during dry eye disease [48]. There is a chance that our study may not have detected ocular surface inflammation since only MMP-9 has been measured in this study [49]. We also observed an increase in MMP-9 1 day after FLACS. This was probably caused by several factors, such as damage to the cornea, inflammation, or mechanical trauma due to the use of a suction ring. [PERSON] et al. [50] explained that the higher risk of dry eye symptoms after FLACS compared to conventional cataract surgery may be due to the difference in the use of a suction ring during the femtosecond laser procedure. Previous studies have shown that the use of a suction ring during laser in situ keratomileus causes damage to the conjunctival epithelium and a loss of goblet cells [51; 52; 53; 54]. Inflammatory conditions and a decrease in mucin secretion may have stimulated the production of MMP-9 after FLACS. However, whether this is only observed after FLACS or also after conventional cataract surgery needs further investigation. There were no significant changes in tear osmolarity after FLACS. Several studies have shown conflicting results regarding changes in tear osmolarity after conventional cataract surgery. The study of [PERSON] et al. [55] resulted in a significant increase in tear osmolarity up to 4 weeks after surgery. [PERSON] et al. [15] showed an increase in tear osmolarity in the early postoperative period that normalized to baseline level compared to the preoperative tear osmolarity. Dissimilarly, [PERSON] et al. [16] showed no significant changes in tear osmolarity before and after cataract surgery. Our results also did not show increased tear osmolarity after FLACS. These studies have used topical corticosteroids after cataract surgery for 4 weeks. Normalization of tear osmolarity may be due to the use of topical corticosteroids. [PERSON] et al. [56] treated patients with moderate to severe dry eye disease with topical 1% methylprednisolone for 8 weeks and found a significant decrease in tear osmolarity compared to baseline level. Further investigation regarding the effects of corticosteroid on tear osmolarity after cataract surgery is needed. It is noteworthy to mention that there was no difference in postoperative tear osmolarity, MMP-9 level, or OSDI scores between those with normal and abnormal results of preoperative tear osmolarity and MMP-9 tests. [PERSON] et al.