***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: PURPOSE To assess the short-term effect of laser peripheral iridotomy ( LPI ) on anterior segment anatomy in angle-closure suspects using ultrasound biomicroscopy ( UBM ) . DESIGN Prospect i ve intervention study . PARTICIPANTS Persons identified as angle-closure suspects aged 50 - 79 years from a population -based survey in Guangzhou , China . INTERVENTION Laser peripheral iridotomy was performed on 1 r and omly selected eye .  Ultrasound biomicroscopy examination was carried out before and 2 weeks after the intervention . MAIN OUTCOME MEASURES Proportion of eyes with iridotrabecular contact ( ITC ) , as well as changes in UBM parameters including angle opening distance ( AOD ) , iris thickness ( IT ) , iris curvature , iris ciliary process distance , trabecular-ciliary process distance ( TCPD ) , and scleral spur to iris insertion distance ( SS-IR ) . RESULTS A total of 72 of 101 eligible subjects participated in the study . The proportion of people with UBM-identified ITC in > or = 1 quadrant dropped from 95 % ( 68/72 ) before to 59 % ( 42/72 ) after LPI . After LPI , the mean AOD at 250 microns increased from 0.064 mm ( st and ard deviation [ SD ] , 0.052 ) to 0.085 ( 0.052 ) mm ( P<0.001 ) ; angle recess area increased from 0.040 ( 0.030 ) to 0.070 ( 0.036 ) mm2 ( P<0.0001 ) ; TCPD increased from 0.537 to 0.561 mm ( P = 0.001 ) ; IT at 750 microns increased from 0.440 to 0.459 mm ( P = 0.094 ) , and IT at 1000 microns increased from 0.471 to 0.488 mm ( P = 0.0001 ) . Eyes whose angles remained closed after LPI ( pigmented trabecular meshwork not visible in > or =3 quadrants ) tended to have shallower AOD both at 250 ( 0.071 vs. 0.049 mm ; P = 0.09 ) and 500 microns ( 0.108 vs. 0.052 mm ; P = 0.001 ) , a thicker iris ( IT at 750 microns , 0.447 vs. 0.415 mm ; P = 0.041 ) , a more anterior positioned ciliary body ( TCPD , 0.514 vs. 0.562 mm ; P = 0.03 ) , and a statistically nonsignificant more anterior iris insertion ( SS-IR : 0.085 vs. 0.125 mm ; P = 0.061 ) , before LPI . CONCLUSIONS Laser peripheral iridotomy results in a significant increase in the angle width in Chinese people with narrow angles . However , some iridotrabecular contact was found in 59 % of eyes with a patent iridotomy . This was associated with smaller anterior chamber angle dimensions and a thicker iris , both of which may play a causative role in maintaining angle closure after LPI AIM To compare visual acuity and intraocular pressure outcomes 3 years after treatment of acute angle closure glaucoma ( AACG ) by operative peripheral iridectomy ( PI ) or Nd : YAG laser iridotomy ( YAG PI ) . METHODS A prospect i ve study of consecutive patients presenting to one ophthalmology department with uniocular AACG during a 2 year period . Following informed consent patients were r and omised to bilateral PI or bilateral YAG PI . Three years after treatment the mean Snellen visual acuity converted to logMAR scores of the two groups was compared using the unpaired Student ’s ttest . The number of patients with normal intraocular pressure with no further treatment in each group was compared using the χ2test with Yates ’s correction . RESULTS 21 patients underwent bilateral PI and 27 bilateral YAG PI . Three years after treatment visual acuity was 0.30 ( SD 0.28 ) log MAR units for PI eyes and 0.57 ( 0.67 ) logMAR units for YAG PI eyes ( p=0.08 , NS ) . 15 ( 70.4 % ) PI eyes and 19 ( 71.8 % ) YAG PI eyes had an intraocular pressure less than 21 mm Hg with no further treatment ( NS ) . CONCLUSIONS There was no significant difference in visual acuity or intraocular pressure control 3 years after treatment of AACG with PI or YAG PI PURPOSE Novel anterior segment optical coherence tomography ( ASOCT ) parameters associated with angle closure include anterior chamber area ( ACA ) , anterior chamber volume ( ACV ) , anterior chamber width ( ACW ) , lens vault ( LV ) , iris thickness ( IT ) , iris area ( I-area ) , and iris curvature ( I-curv ) . We aim ed to investigate changes in these parameters after laser peripheral iridotomy ( LPI ) in a cohort of primary angle-closure suspects ( PACS ) . DESIGN Prospect i ve observational study . PARTICIPANTS AND CONTROLS A total of 176 PACS aged ≥ 50 years who underwent LPI in 1 eye . METHODS We analyzed ASOCT images ( Visante , Carl Zeiss Meditec , Dublin , CA ) from all subjects using customized software before and 1 week after LPI . Multivariate linear regression analysis was performed for predictors of percentage change in mean angle opening distance ( AOD750 ) . MAIN OUTCOME MEASURES Change in ASOCT parameters after LPI . RESULTS The mean age of participants was 63 ± 7.3 years . The majority of subjects were Chinese ( 95.5 % ) and women ( 76.7 % ) . Mean angle width ( modified Shaffer grade ) changed from 0.68 ± 0.54 at baseline to 1.76±0.69 after LPI ( P<0.001 ) with a corresponding increase in mean AOD500 ( 0.12 vs. 0.19 mm , P<0.001 ) , trabecular iris surface area ( TISA500 , 0.06 vs. 0.08 mm(2 ) , P<0.001 ) , and angle recess area ( ARA , 0.13 vs. 0.17 mm(2 ) , P<0.001 ) . Mean ACA ( 15.0 vs. 16.0 mm(2 ) , P<0.001 ) and ACV ( 91.6 vs. 103.0 mm(3 ) , P<0.001 ) increased significantly after LPI , but there was no change in ACW , anterior chamber depth ( ACD ) , or LV . Mean I-curv was reduced ( 0.375 vs. 0.18 mm , P<0.001 ) after LPI , but there was no significant change in IT or I-area . After multivariate analysis , mean LV ( β = 0.286 , P = 0.001 ) , mean IT at 2000 μm ( IT2000 , β = 0.172 , P = 0.034 ) , and intraocular pressure ( β = 0.159 , P = 0.042 ) at baseline were found to be associated with ΔAOD750 . CONCLUSIONS This study confirms that LPI results in a significant increase in the angle width in PACS . The ACA and ACV increased after LPI , but there was no change in ACD , ACW , LV , IT , or I-area . The increase in ACA/ACV was mainly due to decreased I-curv after LPI PURPOSE To determine the prevalence of plateau iris in a cohort of primary angle closure suspects ( PACSs ) using ultrasound biomicroscopy ( UBM ) . DESIGN Cross-sectional observational study . PARTICIPANTS Subjects over the age of 50 years diagnosed as PACSs . INTERVENTION Subjects were r and omized to undergo laser peripheral iridotomy ( LPI ) in one eye . Ultrasound biomicroscopy was performed before and a week after LPI . MAIN OUTCOME MEASURES  Ultrasound biomicroscopy images were qualitatively assessed using st and ardized criteria . Plateau iris was defined in a quadrant by the presence of an anteriorly directed ciliary body , an absent ciliary sulcus , a steep iris root from its point of insertion followed by a downward angulation from the corneoscleral wall , presence of a central flat iris plane , and irido-angle contact . At least 2 quadrants had to fulfil the above criteria for an eye to be defined as plateau iris . RESULTS Two hundred five subjects were enrolled ; UBM images of 167 subjects were available for analysis . Plateau iris was found in 54 of 167 ( 32.3 % ) PACS eyes after LPI . Quadrantwise analysis showed that 44 of 167 ( 26.3 % ) eyes had plateau iris in 1 quadrant , 36 ( 21.5 % ) in 2 quadrants , 16 ( 9.5 % ) in 3 quadrants , and 2 ( 1.2 % ) in all 4 quadrants . Plateau iris was most commonly observed in the superior and inferior quadrants . CONCLUSIONS Using st and ardized UBM criteria , plateau iris was found in about a third of PACS eyes after LPI . Prospect i ve longitudinal studies are required to determine the clinical significance of this finding for the management of PACSs Purpose : To summarize the design and methodology of a large-scale trial in southern China , the Zhongshan Angle Closure Prevention ( ZAP ) trial . This trial will determine if laser iridotomy ( LI ) is superior to no treatment for managing Chinese people who are Primary Angle Closure Suspects ( PACS ) . In this trial , PACS was defined as having 6 or more clock hours of angle circumference in which the pigmented trabecular meshwork was not visible under static gonioscopy in both eyes without elevated intraocular pressure , peripheral anterior synechiae or glaucomatous neuropathy . Methods : Subjects were recruited from an urban district in Guangzhou . The target sample size was 870 . Persons 50 years of age and older with 20/40 or better vision in both eyes identified as having 6 or more clock hours of angle circumference in which the pigmented trabecular meshwork was not visible under static gonioscopy in both eyes were enrolled . Each subject was r and omized to undergo LI in one eye with the fellow eye left untreated . Follow up is planned for a minimum period of 3 years . Baseline examination included tonometry , limbal chamber depth grading , gonioscopy , fundus photography , anterior segment coherence tomography , ultrasound A scan , ultrasound biomicroscopy , specular microscopy and dark room provocative testing . Endpoints for the study include developing elevated intraocular pressure , peripheral anterior synechiae or experiencing acute primary angle closure . Conclusion : The ZAP trial will determine if LI is safe and effective at preventing pathological angle closure in asymptomatic eyes with narrow angle configurations on gonioscopy . It will also provide data on what happens to untreated eyes in PACSs . Data collected at baseline will also help identify those at high risk for developing primary angle closure and primary angle closure glaucoma Aims To determine if screening with an ultrasound A-scan and prophylactic treatment of primary angle closure ( PAC ) with laser peripheral iridotomy ( LPI ) can reduce the incidence of primary angle closure glaucoma ( PACG ) in Mongolia . Methods A single-masked r and omised controlled trial was initiated in 1999 . 4725 volunteer Mongolian participants ≥50 years old from the capital Ulaanbaatar or the rural province of Bayankhongor were recruited , of which 128 were excluded with glaucoma . 4597 were r and omly allocated to the control , no-screening arm or screening with ultrasound central anterior chamber depth ( cACD ) , with the cut-off set at < 2.53 mm . 685 screen-positive participants were examined and angle closure was identified by gonioscopy in 160 , of which 156 were treated with prophylactic LPI . Primary outcome of incident PACG was determined using both structural and functional evidence from objective grading of paired disc photographs from baseline and follow-up , objective grading of follow-up visual fields and clinical examination . Results Six years later , 801 ( 17.42 % ) participants were known to have died , and a further 2047 ( 53.92 % ) were traced and underwent full ophthalmic examination . In an intention to treat analysis using available data , PACG was diagnosed in 33 participants ( 1.61 % , 95 % CI 1.11 % to 2.25 % ) , of which 19 were in the screened group and 14 in the non-screened group ( OR 1.29 , 95 % CI 0.65 to 2.60 , p=0.47 ) , indicating no difference between groups . Conclusions We were not able to identify a reduction in the 6 year incidence of PACG after screening with cACD < 2.53 mm and prophylactic treatment of PAC PURPOSE To assess the immediate effect of laser peripheral ir 
    Output:
    
At present , we can not draw reliable conclusions based on r and omized controlled trials as to whether iridotomy slows progression of visual field loss at one year compared to no iridotomy .
Full publication of the results from the studies may clarify the benefits of iridotomy