## 4 Discussion  
In the present study, we evaluated the change in tear osmolarity and the MMP-9 level after FLACS. We found that tear osmolarity did not change up to 1 month after surgery. MMP-9 increased with significance at D1, returned to its preoperative level at W1, and then decreased significantly by M1. There was no significant change in the overall OSDI score after FLACS. However, the ocular discomfort subscale score was aggravated significantly at M1. These results suggest that the aggravated or persistent symptoms of ocular discomfort that are commonly reported by patients after FLACS may be due to factors other than an increase in tear film osmolarity or inflammatory conditions. Dry eye disease is a multifactorial disease of the ocular surface that is accompanied by increased tear osmolarity and inflammation of the ocular surface [30]. In addition to slit-lamp evaluation, tools to diagnose dry eye disease include corneal fluorescein staining, tear film break-up time, the Schirmer test, and validated questionnaires, such as the ocular surface disease index (OSDI). However, the poor association between the signs and symptoms of dry eye disease is well known [31; 32]. The recent development of point-of-care diagnostics in diagnosing dry eye disease, such as tear osmolarity and MMP-9 testing have shown high sensitivity and specificity [10; 11; 12; 13]. Previous studies recommend using these point-of-care diagnostic tools in evaluating ocular surface disease before performing cataract surgery [14; 33]. Despite the development of these new diagnostic tools, only a few studies have evaluated the changes in tear osmolarity after cataract surgery [16; 17]. No study has investigated the changes in MMP-9 after conventional cataract surgery. To the best of our knowledge, this is the first study to evaluate the changes in tear osmolarity and MMP-9 after FLACS. It is widely accepted that patients experience ocular discomfort or symptoms of dry eye syndrome after cataract surgery [7; 34; 35; 36]. In line with previous studies, we also found that patients experience aggravated ocular discomfort 1 month after FLACS. Ocular discomfort after cataract surgery has been attributed primarily to the development or aggravation of dry eye syndrome [9; 37; 38; 39; 40]. However, previous studies have shown that not all signs of dry eye syndrome are aggravated after cataract surgery. [PERSON] et al. investigated the changes in the ocular surface and dry eye symptoms after FLACS and found that most signs of dry eye returned to their baseline level within 3 months postoperatively, although symptoms of dry eye disease remained aggravated [41]. Additionally, [PERSON] et al. [16] reported that tear osmolarity did not increase after conventional cataract surgery and they suggested that ocular surface discomfort after cataract surgery is not attributable to an increase in tear osmolarity. Despite the aggravation of ocular discomfort after FLACS, our study also found that there was no change in tear osmolarity after FLACS. Moreover, MMP-9, an important indicator of ocular surface inflammation, decreased 1 month after the surgery while the ocular surface discomfort scale score increased. If ocular discomfort after cataract surgery is due to the development or aggravation of dry eye disease, tear osmolarity or MMP-9 would be expected to be increased after surgery. However, our results suggest that the ocular discomfort patients experience after FLACS may be due to an etiology other than the development or aggravation of dry eye disease because there was no change in tear osmolarity, and there was a decrease in MMP-9 level. The ocular discomfort that patients experience after FLACS may include symptoms such as pain, which is shared with symptoms of dry eye disease. Damage to the trigeminal nerves by inflammation after surgery and the corneal incisions could be the cause of the pain [42]. Previous studies have also proposed that persistent postsurgical pain (PPP) may present as dry eye symptoms after cataract surgery [43; 44].