***TASK*** the task is to summarize an input biomedical literature in six sentences 
    ***INPUT*** the input is a biomedical literature 
    ***OUTPUT*** the output is the summary of an input biomedical literature in six sentences 
    ***DOCUMENTATION*** 
    ***EXAMPLES*** 
    Input: Laser-assisted in situ keratomileusis ( LASIK ) is commonly used to correct refractive defects . The procedure frequently results in dry eye symptoms , usually of short but sometimes longer duration . This study was design ed to assess dry eye and ocular tolerability after  LASIK in patients treated with a preservative-free lacrimal substitute ( Hylabak ® ) or preserved lacrimal substitute ( Systane ® ) .  In a single-center , investigator-masked , prospect i ve , noninferiority , clinical study , patients undergoing LASIK surgery were r and omized to receive Hylabak or Systane eye drops ( one drop in each eye four times daily for 3 months ) . Fluorescein test scores were the primary efficacy variable and were similar on day 1 ( mean 0.26 and 0.28 for Hylabak and Systane , respectively ) . At the final visit ( day 84 ± 3 ) the fluorescein scores had improved to 0.11 and 0.04 , respectively . The difference was not significant and thus noninferiority was established . A trend of more rapid improvement in the Hylabak group was evident . Both treatments were well tolerated and there were no serious adverse events , discontinuations for adverse events or other safety-related reasons , and no systemic adverse events . The results suggest that Hylabak is not less effective than Systane in reducing the symptoms of dry eye after LASIK surgery Purpose This study aim ed to compare the efficacy of two sustained-release formulation of artificial tear drops . Patients and methods This is a r and omized patient-masked clinical trial , a total 88 patients into two group A ( n = 41 ; with single dose of artificial tear , containing dextran 70 , 1 mg/ml and hypromellose , 3 mg/ml hydroxypropyl methylcellulose ( HPMC )  and group B ( n = 47 ; with multidose of artificial tear , containing 0.3 g HPMC and 0.1 g of dextran 70 , with 0.01 % benzalkonium chloride ( BAK ) as preservative ) were completed the study . The ocular surface disease index ( OSDI ) question naire , tear break up time ( TBUT ) , corneal and conjunctival staining and Schirmer test , were performed . Repeated measures ANOVA was used to assess the differences among the two products . A p-value less than 0.05 was considered significant . Results The mean of age of the participants in the Group A and B was 44.08 ± 6.29 ( range , 33–58 years ) years and 45.83 ± 8.42 ( 31–60 years ) , respectively . In comparing two groups before the intervention , the OSDI scores , the TBUT scores , the conjunctival and corneal staining scores and the Schirmer scores did not show statistically significant differences ( p = 0.339 , p = 0.640 , p = 0.334 , p = 0.807 and p = 0.676 , respectively ) . After 4 weeks , the OSDI scores , conjunctival and corneal staining scores showed improvement in compare to those before the intervention ( p < 0.001 ) . But , the differences for the Schirmer test score and TBUT score was not significant ( p = 0.115 , p = 0.013 , respectively ) . Conclusion Our outcomes indicated that improvement occurred with use of both products but there was no statistically significant difference between them Benzalkonium chloride ( BAC ) is the most common preservative in ophthalmic preparations . Here , we investigated the  corneal alternations in rabbits following exposure to BAC . Twenty-four adult male New Zeal and albino rabbits were r and omly divided into three groups . BAC at 0.01 % , 0.05 % , or 0.1 % was applied twice daily to one eye each of rabbits for 4 days . The contralateral untreated eyes were used as control . Aqueous tear production and fluorescein staining scores of BAC-treated eyes were compared with those of controls . The structure of the central cornea was examined by in vivo confocal microscopy . Expression of mucin-5 subtype AC ( MUC5AC ) in conjunctiva was detected by immunostainig on cryosections . Corneal barrier function was assessed in terms of permeability to carboxy fluorescein ( CF ) . The distribution and expression of ZO-1 , a known marker of tight junction , and reorganization of the perijunctional actomyosin ring ( PAMR ) were examined by immunofluorescence analysis . Although there were no significant differences between control and BAC-treated eyes in Schirmer scores , corneal fluorescein scores and the number of conjunctival MUC5AC staining cells , in vivo confocal microscopy revealed significant epithelial and stromal defects in all BAC-treated corneas . Moreover , BAC at 0.1 % result ed in significant increases in central corneal thickness and endothelial CF permeability , compared with those in control eyes , and endothelial cell damage with dislocation of ZO-1 and disruption of PAMR . Topical application of BAC can quickly impair the whole cornea without occurrence of dry eye . A high concentration of BAC breaks down the barrier integrity of corneal endothelium , concomitant with the disruption of PAMR and remodeling of apical junctional complex in vivo Background Dry eye disease ( DED ) is multifactorial , affecting 5–34 % of the global adult population and reducing quality of life . The artificial tears or lubricants are the therapy most used for the treatment of DED , due to their low side effect profile , which attempt to modify the properties of the tear film . The aim of the present study was to evaluate the clinical efficacy of a fixed combination of xanthan gum and chondroitin sulfate preservative free on the ocular surface of patients with dry eye disease during 60 days of intervention . Methods A phase III , double-blind , masked , controlled , multicenter , clinical trial of 148 subjects , r and omized to either a fixed combination of xanthan gum 0.09 % and chondroitin sulfate 0.1 % ( XG/CS ) ophthalmic solution ( n = 76 ) or a fixed combination of polyethylene glycol 400 0.4 % and propylene glycol 0.3 % ( PEG/PG ) ( n = 72 ) . Subjects self-dosed four times daily during 60 days . Follow-up was set on days 2 , 7 , 15 , 30 and 60 . Assessment s of anterior/posterior segment ocular signs were performed . The outcome measures included Schirmer test , tear film break-up time and OSDI score . Security variables included intraocular pressure , lisamine green and fluorescein ocular surface stains . Results The primary efficacy endpoints were similar between groups at baseline . After intervention time Schirmer test increased in both groups compared to baseline , XG/CS ( 6.4 ± 2.2 vs 11.0 ± 6.6 ; p = 0.002 ) and PEG/PG ( 6.5 ± 2.5 vs 10.5 ± 5.6 ; p = 0.019 ) respectively . Similar results were reported in the tear film break-up time in XG/CS ( 5.5 ± 2.1 vs 7.4 ± 2.9 ; p = 0.027 ) and PEG/PG ( 5.2 ± 2.0 vs 7.4 ± 2.7 ; p = 0.046 ) respectively . The OSDI score decreased to normal values in both groups , XG/CS ( 19.3 ± 7.4 vs 7.3 ± 5.9 ; p = 0.001 ) and PEG/PG ( 19.3 ± 7.5 vs 7.9 ± 8.2 ; p = 0.001 ) respectively . There was no significant difference between treatments for any parameter . Moreover , both groups decreased the presence of burning sensation , tearing , foreign body sensation , conjunctival hyperemia and photophobia . The adverse events were not related to the interventions . Conclusions Xanthan gum/chondroitin sulfate preservative free showed similar clinical efficacy , evaluated with OSDI score , TBUT and Schirmer test compared to polyethylene glycol/propylene glycol in the treatment of dry eye disease . Trial registration Clinical Trials.gov : NCT01657253 . Date of registration May 19 , 2014 PURPOSE To compare the antioxidant and inflammatory cytokine activities in tears of patients with dry eye syndrome treated with preservative-free versus preserved eye drops . METHODS A total of 100 patients with moderate to severe dry eye syndrome were r and omly divided into two groups . Fifty patients ( group 1 ) were treated four times with preservative-free 0.1 % sodium hyaluronate and 0.1 % fluorometholone eye drops in the first month and with preservative-free 0.1 % sodium hyaluronate and 0.05 % cyclosporine eye drops in the second and third months . Another 50 patients ( group 2 ) were treated with preserved eye drops on the same schedule . Ocular Surface Disease Index , corneal fluorescein staining , Schirmer I test , tear film breakup time , impression cytology , and antioxidant and inflammatory cytokine activities in tears were evaluated . RESULTS Treatment with preservative-free eye drops led to significant improvements in symptoms , tear film breakup time , Schirmer I score , and impression cytologic findings compared to treatment with preserved eye drops ( P < 0.05 ) in patients with dry eye syndrome . There was a statistically significant decrease in the IL-1β , IL-6 , IL-12 , and TNF-α concentrations and a statistically significant increase in the catalase , peroxiredoxin 2 , superoxide dismutase 2 ( SOD 2 ) , and thioredoxin mean fluorescence intensity ( MFI ) of tears in the preservative-free group at 1 , 2 , and 3 months compared to initial values , respectively ( P < 0.05 ) . CONCLUSIONS Treatment with preservative-free eye drops is effective against the dry eye syndrome . Preservative-free eye drops seem to be more effective than preserved eye drops in decreasing ocular inflammation and in increasing antioxidant contents in tears of patients with dry eye syndrome OBJECTIVE To investigate the effects of timolol maleate with preservative and its preserved ( PV ) and nonpreserved vehicles ( NPV ) ( benzalkonium chloride ) on the blood-aqueous barrier and angiographic cystoid macular edema ( CME ) in early postoperative pseudophakia . PATIENTS AND METHODS Patients with ocular hypertension , normal tension glaucoma , and primary open-angle glaucoma who underwent surgery for cataracts . The study included a double-masked trial for timolol , PV , and NPV and a single-masked trial on the effect of diclofenac sodium and fluorometholone acetate on all three . The patients were divided into 6 groups , each of which were simultaneously administered the following different combinations of compounds : timolol and diclofenac ( group A ) , timolol and fluorometholone ( group B ) , PV and diclofenac ( group C ) , PV and fluorometholone ( group D ) , NPV and diclofenac ( group E ) , and NPV and fluorometholone ( group F ) . The 6 groups were then compared using a laser flare cell meter to determine the degree of disruption of the blood-aqueous barrier and fluorescein angiography to investigate angiographic CME . The differences in mean daily fluctuations in intraocular pressure were compared on the preoperative baseline day and for 5 weeks postoperatively . Twice daily administration of 0.5 % timolol maleate or the vehicles was started 2 days before surgery , and continued until 5 weeks after surgery . Diclofenac or fluorometholone drops were instilled in the eyes 4 times preoperatively , on the day of surgery , and 3 times daily for 5 weeks postoperatively . RESULTS The flare amount was higher on the third and seventh days in group B than in group D , but was the same after the seventh day . The incidence of angiographic CME was the same between both groups . These 2 factors were significantly lower in group F. These 2 factors were also significantly lower in the 3 groups that received diclofenac instead of fluorometholone , with no difference among these groups . The intraocular pressure decline was significant in groups that received timolol compared with groups that received PV or NPV . CONCLUSIONS Timolol and its preservative , benzalkonium chloride , cause disruption of the blood-aqueous barrier in early postoperative pseudophakia and increased incidence of angiographic CME . The concurrent administration of nonsteroidal anti-inflammatory drug such as diclofenac prevents these adverse effects without interfering with the drop in intraocular pressure caused by timolol . The addition of benzalkonium chloride to timolol contributes considerably to these adverse effects . CLINICAL RELEVANCE The present results suggest the cause of similar complications produced by other antiglaucoma eyedrops containing similar preservatives Background / aims : Several studies have reported that sodium hyaluronate is able to improve both symptoms and signs in patients with dry eye but none have demonstrated an improvement of conjunctival epithelial cell abnormalities of the ocular surface . The aim of this study was to explore the effect of sodium hyaluronate-containing eye drops on the ocular surface of patients with dry eye during long term treatment 
    Output:
    
No statistically significant difference was observed between the two groups , and no side effects were attributed to the interventions .
Evidence proving that preservative-free artificial tears are more effective than preserved artificial tears is lacking