***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 
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    ***EXAMPLES*** 
    Input: Background This study was performed to compare levels of serum homocysteine ( Hcy ) , vitamin B12 and folic acid in patients with primary open-angle glaucoma ( POAG ) , pseudoexfoliative glaucoma ( PEXG ) , normotensive glaucoma ( NTG ) and healthy controls . Methods Twentyfive patients with POAG , 24 with PEXG , and 18 with NTG , along with 19 control healthy subjects were included this prospect i ve study . Levels of serum Hcy  were measured using immunoassay , and those of  serum vitamin B12 and folic acid were measured using competitive chemiluminescent enzyme immunoassay . Results The mean Hcy concentration in the PEXG group was significantly higher ( P < 0.001 ) as compared to the other groups . There were no significant differences with respect to the mean Hcy concentrations among other groups ( P > 0.05 ) . There were no statistical differences in serum vitamin B12 levels among POAG , PEXG , NTG and control subjects ( P > 0.05).The mean serum folic acid level was significantly lower in the subjects with PEXG ( P < 0.009 ) . However , the mean folic acid concentrations among the other groups did not differ significantly ( P > 0.05 ) . Conclusion Elevated levels of Hcy in PEXG may explain the role of endothelial dysfunction among patients with PEXG IMPORTANCE Nitric oxide signaling alterations in outflow facility and retinal blood flow autoregulation are implicated in primary open-angle glaucoma ( POAG ) . Nitric oxide donation has emerged as a POAG therapeutic target . An exogenous source of nitric oxide is dietary nitrates . OBJECTIVE To evaluate the association between dietary nitrate intake , derived mainly from green leafy vegetables , and POAG . DESIGN , SETTING , AND PARTICIPANTS We followed up participants biennially in the prospect i ve cohorts of the Nurses ' Health Study ( 63 893 women ; 1984 - 2012 ) and the Health Professionals Follow-up Study ( 41 094 men ; 1986 - 2012 ) at each 2-year risk period . Eligible participants were 40 years or older , were free of POAG , and reported eye examinations . EXPOSURES The primary exposure was dietary nitrate intake . Information on diet and potential confounders was up date d with vali date d question naires . MAIN OUTCOMES AND MEASURES The main outcome was the incidence of POAG and POAG subtypes ;  1483 cases were confirmed with medical records and classified into subtypes defined by intraocular pressure ( IOP ) ( ≥22 or < 22 mm Hg ) or by visual field ( VF ) loss pattern at diagnosis ( peripheral loss only or early para central loss ) . Cohort-specific and pooled multivariable rate ratios ( MVRRs ) and 95 % CIs were estimated . RESULTS During 1 678 713 person-years of follow-up , 1483 incident cases of POAG were identified . The mean ( SD ) age for the 1483 cases was 66.8 ( 8.3 ) . Compared with the lowest quintile of dietary nitrate intake ( quintile 1 : approximately 80 mg/d ) , the pooled MVRR for the highest quintile ( quintile 5 : approximately 240 mg/d ) was 0.79 ( 95 % CI , 0.66 - 0.93 ; P for trend = .02 ) . The dose response was stronger ( P for heterogeneity = .01 ) for POAG with early para central VF loss ( 433 cases ; quintile 5 vs quintile 1 MVRR = 0.56 ; 95 % CI , 0.40 - 0.79 ; P for trend < .001 ) than for POAG with peripheral VF loss only ( 835 cases ; quintile 5 vs quintile 1 MVRR = 0.85 ; 95 % CI , 0.68 - 1.06 ; P for trend = .50 ) . The association did not differ ( P for heterogeneity = .75 ) by POAG subtypes defined by IOP ( 997 case patients with IOP ≥22 mm Hg : quintile 5 vs quintile 1 MVRR = 0.82 ; 95 % CI , 0.67 - 1.01 ; P for trend = .11 ; 486 case patients with IOP < 22 mm Hg : quintile 5 vs quintile 1 MVRR = 0.71 ; 95 % CI , 0.53 - 0.96 ; P for trend = .12 ) . Green leafy vegetables accounted for 56.7 % of nitrate intake variation . Compared with consuming 0.31 servings per day , the MVRR for consuming 1.45 or more servings per day was 0.82 for all POAG ( 95 % CI , 0.69 - 0.97 ; P for trend = .02 ) and 0.52 for POAG with para central VF loss ( 95 % CI , 0.29 - 0.96 ; P for trend < .001 ) . CONCLUSIONS AND RELEVANCE Higher dietary nitrate and green leafy vegetable intake was associated with a lower POAG risk , particularly POAG with early para central VF loss at diagnosis Objective : To compare the levels of plasma homocysteine ( Hcy ) , vitamin B6 ( vit-B6 ) , serum vitamin B12 ( vit-B12 ) , and folate in healthy individuals and in patients with normal tension glaucoma ( NTG ) , pseudoexfoliative glaucoma ( PXG ) , or primary open-angle glaucoma ( POAG ) . Study design : A prospect i ve controlled trial . Participants and methods : Forty healthy subjects , 48 patients with NTG , 38 patients with PXG , and 34 patients with POAG were included in the study . Those who used vitamin supplements or medications affecting Hcy and vitamin levels were excluded from the study . The levels of Hcy and vit-B6 were measured by High Performance Liquid Chromatography ( HPLC ) . The levels of serum vit-B12 and folic acid were measured by competitive chemiluminescent enzyme immunoassay ( CEI ) . One-way analysis if variance ( ANOVA ) , analysis of covariance ( ANCOVA ) , and the Tukey honestly significant difference test were used for statistical analysis . Results : The mean Hcy level of the PXG group was 15.46 ± 9.27 μmol/L which was significantly higher ( P = 0.03 ) than that of the control group . There were no statistical differences in serum vit-B12 and folate levels among control subjects and NTG , PXG and POAG groups ( P > 0.05 ) . It was found that the mean plasma vit-B6 level was significantly higher in subjects with NTG ( P = 0.03 ) and POAG ( P = 0.025 ) versus controls . Mean vit-B6 levels in NTG and POAG were 30.50 ± 11.29 μg/L and 30 ± 12.15 μg/L , respectively . Conclusions : The plasma level of Hcy was found to be increased only in PXG patients and the plasma levels of vit-B6 were found to increase in the NTG and POAG sample groups . Using homocysteine and vit-B6 levels as the determinants of hyperhomocysteinemia still needs further research Open-angle  glaucoma ( OAG ) is the commonest cause of irreversible blindness worldwide . Apart from an increased intraocular pressure ( IOP ) , oxidative stress and an impaired ocular blood flow are supposed to contribute to OAG . The aim of this study was to determine whether the dietary intake of nutrients that either have anti-oxidative properties ( carotenoids , vitamins , and flavonoids ) or influence the blood flow ( omega fatty acids and magnesium ) is associated with incident OAG . We investigated this in a prospect i ve population -based cohort , the Rotterdam Study . A total of 3502 participants aged 55 years and older for whom dietary data at baseline and ophthalmic data at baseline and follow-up were available and who did not have OAG at baseline were included . The ophthalmic examinations comprised measurements of the IOP and perimetry ; dietary intake of nutrients  was assessed by vali date d question naires and adjusted for energy intake . Cox proportional hazard regression analysis was applied to calculate hazard ratios of associations between the baseline intake of nutrients and incident OAG , adjusted for age , gender , IOP , IOP-lowering treatment , and body mass index . During an average follow-up of 9.7 years , 91 participants ( 2.6 % ) developed OAG . The hazard ratio for retinol equivalents ( highest versus lowest tertile ) was 0.45 ( 95 % confidence interval 0.23–0.90 ) , for vitamin B1 0.50 ( 0.25–0.98 ) , and for magnesium 2.25 ( 1.16–4.38 ) . The effects were stronger after the exclusion of participants taking supplements . Hence , a low intake of retinol equivalents and vitamin B1 ( in line with hypothesis ) and a high intake of magnesium ( less unambiguous to interpret ) appear to be associated with an increased risk of OAG The relation between dietary antioxidant intake and  primary open-angle glaucoma risk  was examined in participants aged over 40 years in the Nurses ' Health Study ( n = 76,200 ) and the Health Professionals Follow-up Study ( n = 40,284 ) . They were followed biennially from 1980 and 1986 , respectively , to 1996 , during periods when they received an eye examination .  Dietary intakes were measured repeatedly from 1980 in the Nurses ' Health Study and from 1986 in the Health Professionals Follow-up Study using vali date d food frequency question naires . The authors analyzed 474 self-reported glaucoma cases confirmed by medical chart review to have primary open-angle glaucoma with visual field loss . The authors used Cox proportional hazards models for cohort-specific multivariate analyses , and results were pooled using r and om effects models . The pooled multivariate rate ratios for primary open-angle glaucoma comparing the highest versus lowest quintile of cumulative up date d intake were 1.17 ( 95 % confidence interval ( CI ) : 0.87 , 1.58 ) for alpha-carotene , 1.10 ( 95 % CI : 0.82 , 1.48 ) for beta-carotene , 0.95 ( 95 % CI : 0.70 , 1.29 ) for beta-cryptoxanthin , 0.82 ( 95 % CI : 0.60 , 1.12 ) for lycopene , 0.92 ( 95 % CI : 0.69 , 1.24 ) for lutein/zeaxanthin , 1.05 ( 95 % CI : 0.59 , 1.89 ) for vitamin C , 0.97 ( 95 % CI : 0.62 , 1.52 ) for vitamin E , and 1.11 ( 95 % CI : 0.82 , 1.51 ) for vitamin A. In conclusion , the authors did not observe any strong associations between  antioxidant consumption  and the risk of primary open-angle glaucoma OBJECTIVE Open-angle glaucoma ( OAG ) is one of the major chronic diseases involving the optic nerve . However , little is known about the association between vitamin D and OAG . The present study was conducted to test the hypothesis that lower vitamin D status is associated with greater prevalence of OAG . DESIGN Cross-sectional study . Multivariable logistic regression was performed to examine the relationship between serum 25-hydroxyvitamin D ( 25(OH)D ) and OAG after adjusting for traditional potential confounders . OAG was defined by the criteria of the International Society for Geographical and Epidemiological Ophthalmology . SETTING The Fifth Korean National Health and Nutrition Examination Survey conducted in 2010 - 2011 . SUBJECTS Six thous and and ninety-four adult participants r and omly selected from 192 surveys in 131 locations in South Korea . RESULTS Multivariable-adjusted odds ratios of OAG across quintiles of decreasing 25(OH)D were 1.26 , 1.00 ( reference ) , 1.31 , 1.36 and 1.69 ( P for quadratic trend < 0.01 ) . The odds ratio for the lowest 25(OH)D quintile was significantly higher than that for the second quintile ( P < 0.01 ) . In addition , we discovered that the predictors for worsening of OAG , such as intraocular pressure or vertical and horizontal cup-to-disc ratios , had a significant relationship with 25(OH)D level . CONCLUSIONS There was a reverse J-shaped association between 25(OH)D levels and the risk of OAG , with significantly elevated risk at lower 25(OH)D. The findings of this research suggest that vitamin D deficiency should be considered as a potential risk factor for the development of OAG . To our knowledge , the present study is the first one that shows an association between 
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However , after addressing heterogeneity , vitamin C showed a protective effect as well .
Especially , foods high in these vitamins ( e.g. , dark green vegetables ) were protective for OAG .
CONCLUSIONS Dietary intake of vitamin A and C showed a beneficial association with OAG ; however , findings on blood levels of vitamins do not show a clear relation with OAG