Association Between Primary Angle-closure Glaucoma And Peripheral Iris Thickness

Purpose: Glaucoma is a complex optic neuropathy,it is associated withintraocular pressure.People who suffers from glaucoma would always losevisual acuity without any symptom.And finally glaucoma is characterized byprogressive loss of retinal ganglion cells and optic nerve axons, andaccompanied by loss of visual field sensitivity.At present,it is accepted todivide glaucoma into primary open-angle glaucoma （POAG）and primaryangle-closure glaucoma（PACG）by the angle.A previous report showed thatprimary angle-closure glaucoma has higher incidence of damage to visualacuity and blindness than primary open-angle glaucoma.It is about two tothree times.Currently, primary angle-closure glaucoma is the major cause forblindness in China.Foster and Johnson found that PACG resulted in about91％total blindness in China.Previously reported anatomical risk factors for angle closure include ashallow central anterior chamber depth （ACD）, a thick len,short cornea radiusand axial length.But the pathogenetic mechanism of primary angle-closureglaucoma is not fully explained by all of the above. Characteristics of the irishave not been extensively studied as potential risk factors for angle closure,although many studies suggested that the iris plays a key role in itspathogenesis.A recent study indicated quantitative iris parameters, such as iriscurvature and thickness, were independently associated with narrow angles ina community-based sample of participants aged50years or older. B-S Wanget al compared iris parameters between eyes with primary angle-closureglaucoma and normal eyes in population-based study.All patients with PACGhad previously undergone laser peripheral iridotomy（LPI）.And the studyshowed that iris parameters are associated with primary angle-closureglaucoma especially peripheral iris thickness.Our study is to measure peripheral iris thickness(IT₅₀₀) and trabecular-iris angle（TIA） of primaryangle-closure glaucoma by ultrasound biomicroscopy（UBM）.The aim is toinvestigate the relationship between peripheral iris thickness and primaryangle-closure glaucoma.Methods: Study participants were recruited from the department ofophthalmology in the second hospital of Hebei Medical University.Wedivided them into four group:primary angle-closure,fellow eyes of acuteprimary angle-closure, chronic angle-closure glaucoma and normalparticipants as control. Ultrasound biomicroscopy was performed on allparticipants under unified conditions.We used proparacaine hydrochloride eyedrops for surface anesthesia on supine position about two times.And we chosesuitable eye cups for examination.Participants were told to stare right abovefirst in order to exam cornea and anterior chamber,and then stareupward,downward,left,right.We accessed the results.Antibiotic eye dropsshould be uesd at last.We measured pupilary distance in all participants.At thesame time,we recorded peripheral iris thickness and trabecular-iris angle atposition of12:00,3:00,6:00,9:00. All analyses were performed with SPSS13.0software, IT₅₀₀and TIA between the four groups were compared by theanalysis of variance,the pearson correlation and spearman correlation wereapplied to analyse the association of IT₅₀₀and TIA.Results:A total of150angle closure patients in3groups and50normalparticipants were studied.Gender,ages,ratio of OD/OS and pupilary distancewere compared by the analysis of variance and the χ2test between groups.Andthere was no statistical differences among four groups.The analysis ofvariance was applied compare peripheral iris thickness and trabecular-irisangle between groups.Compared to peripheral iris thickness of normalparticipants（0.46±0.36）,p values of primary angle closure（0.52±0.12）,acuteprimary angle-closure（0.50±0.78） and chronic angle-closureglaucoma（0.54±0.19） were <0.001,0.005and <0.001.There were statisticallysignificant differences.So peripheral iris thickness of angle closure patientswas thicker than normal participants.Also peripheral iris thickness of primary angle closure was thicker than that of acute primary angle-closure,and thinnerthan that of chronic angle-closure glaucoma.Compared to trabecular-iris angleof normal participants（33.82±7.36）,p values of primary angleclosure（26.78±6.87）,acute primary angle-closure（21.21±9.08） and chronicangle-closure glaucoma（19.57±9.62） were all less than0.001.There werestatistically significant differences.So trabecular-iris angle of angle closurepatients was less than normal participants.Also trabecular-iris angle ofprimary angle closure was more than that of acute primary angle-closure andchronic angle-closure glaucoma.Correlation analysis was used to analyse theassociation between peripheral iris thickness and trabecular-iris angle of allparticipants.Result came that the coefficient of Spearman association was-0.252,and p value was less than0.001.So there was statistically significantdifference.It represented that negative correlation existed between peripheraliris thickness and trabecular-iris angle.When peripheral iris thicknessincreased, trabecular-iris angle decreased.But when we analysed thecorrelation between peripheral iris thickness and trabecular-iris angle withingroups,there were no statistically significant differences.Conclusions:Peripheral iris thickness of eyes with primary angle-closure ismore thicker than that of normal eyes.Increased peripheral iris thickness playsan important role in angle closure pathogenesis.It may supply a new theory forpathogenetic mechanism and treatment of primary angle-closure glaucoma.But further study should be done to research whether peripheral iris thicknesschanges following the disease of glaucoma.There is some correlation betweenperipheral iris thickness and trabecular-iris angle.