Evaluation The Value Of Pentacam Segment Analysis System In The Measure Of Eye Anterior Segment In Primary Angle Closure

Background：Glaucoma is an eye disease that intermittent or persistent elevations inintraocular pressure due to some causes, the different pathogenesis with different clinicalsymptoms. Primary angle-closure glaucoma (PACG) is a kind of glaucoma with peripheraliris mechanical blockage of anterior chamber angle, resulting in the obstruction of aqueoushumor drainage of intraocular pressure, while absence of other factors in the case of the eye.PACG has a narrow anterior chamber angle, iris liablely contact with the surroundingtrabecular meshwork and other anatomical features, and sustained high intraocular pressureleading to irreversible damage of various parts of the eye and visual function, resulting indecreased visual acuity and visual field narrowing. Researchers have estimated that1.7million people in China are bilaterally blind from glaucoma and that91%of glaucomablindness is attributable to primary angle closure. Without proper treatment in time, acutePACG will lead to irreversible blindness. An epidemiology study showed that almost22%primary angle closure suspect (PACS) may develop into primary angle closure (PAC), and28.5%PAC may develop to PACG without treatment in5years. Primary angle-closureglaucoma is expected to account for nearly50%of bilateral glaucoma blindness by2020.PACG patients often have anterior segment structures as shallow anterior chamber,lens thickness, position forward, short axial length, small eyes, etc. The anterior segmentparameters include: Central Corneal Thickness (CCT)、Keratometric、Central AnteriorChamber Depth(CACD)、Anterior Chamber Angle(ACA)、Perimeter Anterior ChamberDepth(PACD)、 Anterior Chamber Volume(ACV) and so on. A major challenge todeveloping a systematic approach to screening for angle closure and adopting universalapproaches to prophylaxis remains the assessment of the ACD and ACA.The current methods to exam ACD and ACA, including slit lamp、A scan andgonioscopy, remain problematic due to the difficulty of obtaining good images of the anterior chamber. Approaches have been developed to aid in the assessment of the ACDand ACA, Ultrasound biomicroscopy (UBM), Scheimpflug photography, and opticalcoherence tomography of the anterior segment (AS-OCT) all provide some insight into theconfiguration of the nornea、anterior chamber、ACA、iris and lens images. Pentacam withhigh measurement accuracy, repeatability, providing a wide range of information, has beensuccessfully applied in clinical practice, like corneal shape analysis of refractive surgery,lens degree analysis of preoperative cataract surgery. However there is no in-depth study nthe field of glaucoma.Therefore, the present study assess the anterior segment parameters using Pentacamfor the diagnosis and monitoring of glaucoma, as a preoperative and postoperativefollow-up measurment.Objective：1. the aim of this study is to explore the difference and agreement in the measurementof anterior segment morphology between Pentacam and SL-OCT of primary angle-closure(PAC) patients and normal eyes; to compare the anterior chamber depth (ACD) of thenormal eyes and PAC patients using Pentacam, seeking for the sensitive indicators for earlyscreening and dignosis of PAC.2. to assess the longitudinal changes in anterior segment parameters after laserperipheral iridotomy（LPI）in PAC patients using Pentacam, and the effects of LPI onperipheral anterior chamber depth (PACD) were determined quantitatively.Methods：1. From2012-11to2013-4Third Millitary Medical University Daping hospital,100eyes of normal group，LPI group:58eyes of primary angle-closure patients.All diagnosticcriteria are strictly based on primary angle-closure glaucoma clinical diagnostic guidelinesin2000developed by the American Academy of Ophthalmology, and exclude subjects withsevere heart and lung disease or any previous eye surgeries. All subjects underwent acomplete ophthalmic examination, slit-lamp examination, Goldmann applanation tonometryand gonioscopy.2. Anterior segment parameters of normal and LPI group were calculated with thePentacam device and the SL-OCT, including center anterior chamber depth (CACD)、 anterior chamber volume (ACV)、anterior chamber angle (ACA)、Keratometric (KM)、Central Corneal Thickness(CCT), and Peripheral Anterior Chamber Depth (PACD) byPentacam. Results were analysed by means of the Wilcoxon signed rank test, Bland-Altmananalysis and intraclass correlation coefficient. P-values <0.01were considered statisticallysignificant.3. LPI was performed in the superior region of the iris (from10to2o’clock) bysequential argon and neodymium-yttrium-aluminum-garnet after pretreatment with2%pilocarpine instilled into the eye1hour before LPI. All subjects were evaluated at1d、1wk、1mo after LPI using Pentacam.Results：1. The difference and agreement in the measurement of anterior segment parametersbetween Pentacam and SL-OCTThere were statistically significant differences between Pentacama and SLOCTmeasurement in CACD、ACV、ACA、KM、CCT in normal group and LPI group (P <0.001).all correlation coefficients were high (normal group：r=0.888，P<0.001；r=0.933，P<0.001；r=0.957，P<0.001；r=0.782P <0.001；r=0.880P <0.001；LPI group：r=0.898，P<0.001；r=0.942，P<0.001；r=0.975，P<0.001；r=0.782P<0.001；r=0.880P<0.001). Bland-Altmananalysis showed that the two techniques had comparable results for CACD、ACV、ACA、KM、CCT.2. anterior segment parameters between normal group and PAC patientsCompared with normal group, there were significant differences in CACD、ACV andACA in PAC patients (P<0.001), and all measure values of LPI group were lower thannormal group, while no significant differences in KM and CCT. Also differences werefound in the PACD in all quadrants (anodic、bottom、bitamporal and nasal side) between thetwo groups by Pentacam (P<0.001). PACD was narrowest in up side in normal group,deepest in bitamporal side, next is bottom. PACD top of the normal group shallow,temporal deepest, followed by the bottom; PACD before LPI group compared with thecontrol group in patients undergoing superficial to the nasal most shallow, top, followedby the temporal side than the bottom of the deep.3preoperative Pentacam measurements LPI group, postoperative changes in theprevious section of the structural parameters LPI postoperative1d,1wk, the difference was not statistically significant (P>0.05)before1mo CACD measurement results with surgery; ACA, ACV, PACD (lower, upper,temporal, nasal and laser-bit) measurement results preoperative difference wasstatistically significant (P <0.01), and postoperative1wk, after1mo after1d relativedifference was statistically significant (P <0.01), but after1wk and there was no statisticaldifference1mo significance (P>0.05); postoperative1d peripheral anterior chamber depthfrom the wide to the narrow bottom, respectively, above, temporal, nasal, laser-bit (1.16±0.22mm,1.14±0.26mm,1.03±0.24mm,0.98±0.21mm,0.89±0.18), after1wk,1motrends and postoperative1d similar.Conclusions：1.Compare with the measurements of Pentacam and SLOCT, there were thestatistically significant difference, but the two methods have good consistency andrelevance, but the value is not universal, so the both of them can complement each other;2.There were no significantly with central anterior chamber depth in patients ofprimary angle closure after YAG laser iridectomy, but the anterior chamber volume,peripheral anterior chamber depth increased significantly, especially in the peripheralanterior chamber depth below, suggesting possible by increasing peripheral LPI reduceintraocular pressure chamber depth to the bottom of the temporal-based, LPI caneffectively prevent acute episodes in PAC;3. Pentacam anterior segment analysis system is currently the only checks the data toquantify the peripheral anterior chamber, the image acquisition to obtain data fast,accurate, intuitive and strong, the overall trend in the anterior chamber can be convenient,noninvasive, reproducible, may for primary angle-closure glaucoma screening providedinitial guidance.