| The most important risk for glaucoma is abnormal intraocular pressure (IOP) fluctuation and elevated IOP. The greater the IOP fluctuation, the faster the visual defect progressing. Reducing IOP is the main and precise treatment for glaucoma. After being secreted by the ciliary body, aqueous humor arrives in anterior chamber, then through trabecular meshwork (TM) draining into Schlemm's canal (SC), and then next to the collector channels and the intrascleral plexus, entering the episcleral veins which finally back to the blood circulation to maintain a dynamic balance. To maintain IOP within the normal physiological range of 10-21mmHg, the aqueous humor outflow rate must equal the aqueous humor production rate. The inner wall of SC and juxtacanalicular tissue were supposed to be the major part of aqueous outflow resistance. Abnormal aqueous humor outflow pathway resistance can result in excess aqueous humor and elevated IOP, which was a key factor in the pathogenesis of POAG.With the progress of minimally invasive surgical techniques, SC plays an important role in the surgical procedures. In recent years, canaloplasty can reduce IOP effectively. Wang et al have found that the reduction of postoperative IOP relied on the expansion of the canal. We have also observed that POAG eyes with blood reflux into SC showed a good IOP reduction after Selective Laser Trabeculoplasty (SLT) and blood reflux quadrants negatively correlated with post SLT IOP. A lack of blood reflux into SC indicated complete canal collapse. This interesting phenomenon showed that SC was strongly associated with IOP. Therefore, understanding the function of SC and TM in vivo is particularly important in treatment of glaucoma.In addition, aerobic exercise leads to the reduction of intraocular pressure, but the mechanism is unclear. Exercise also causes to sympathetic nervous activation. The hypothalamus-autonomic nervous-aqueous outflow pathway may be involved in aqueous humor circulation. But for now we have no idea if the decrease of IOP after physical exercise is associated with the status of SC and TM, and if the status of SC and TM is under the control of sympathetic nerve.Early conclusions about SC and the TM were made in vitro, not in vivo, studies than examined ocular structures using micro-CT, light microscopy, or electron microscopy. Advancements in medical imaging such as optical coherence tomography and 80-MHz ultrasound biomicroscopy make it convenient and possible to study SC and the TM in vivo.The purpose of the current study is to evaluate and compare SC and TM parameters in normal individuals and in patients with POAG using 80-MHz ultrasound biomicroscopy. Additionaly, to investigate the effects of exercise on SC and TM morphology and the mechanism of intraocular pressure reduction when exercise.Part1Schlemm's canal Measurements by 80-MHz UBM in Normal Subjects and POAG patientsPurpose(1) To compare the percentage of sections with an observable Schlemm's canal of normal subjects and POAG patients.(2) To compare the Schlemm's canal meridional diameter and coronal diameter of normal subjects and POAG patients.(3) To discuss the relationship between the Schlemm's canal diameter and intraocular pressure (IOP) in POAG patients.Methods(1) Forty-four POAG patients and 42 age-and gender-matched normal subjects were enrolled. All participants underwent 80-MHz UBM examination. Imaging of Schlemm's canal was conducted by the same experienced technician. Each eye had measurements taken at the 12,3,6 and 9 o'clock positions.(2) The Chi-square test was used for comparing the differences of percentage of sections with an observable Schlemm's canal between two groups. The Mann-Whitney U test and the Kruskal-Walk's H test were used for comparing the differences of IOP, Schlemm's canal diameter between two groups and four sections.(3) Nonparametric Spearman correlation analyses were performed to statistically examine the relationships between IOP and Schlemm's canal parameters.Results(1) The Schlemm's canal was observable significantly less often in eyes with POAG (53.1%) than in normal eyes (80.3%,?= 53.261, p< 0.001). Eyes with POAG and elevated IOP had an observable SC in 50.5% of sections and eyes with POAG and normal IOP had an observable SC in 56.6% of sections, a slight difference that was not statistically significant (x= 1.159, p= 0.282). However, both values were significantly lower than in normal eyes (x= 35.389,21.213, both p< 0.001).(2) Patients with POAG had a significantly smaller Schlemm's canal meridional diameter (233.0±34.5 ?m vs.195.6±31.3?m, p< 0.001), Schlemm's coronal diameter (44.5± 12.6 ?m vs.35.7±8.0 ?m, P< 0.001) than normal individuals. The POAG patients with elevated IOP had a smaller Schlemm's canal coronal diameter (32.6±4.9?m) than POAG subjects with normal IOP (39.5±9.3 ?m, p< 0.001). But not of Schlemm'scanal meridional diameter (192.2±31.8?m [elevated IOP] vs.199.7±30.3?m [normal IOP], p= 0.242).(3) Schlemm's canal coronal diameter (r=-0.623, p< 0.001) was significantly and negatively correlated with IOP in the POAG group. However, Schlemm's canal meridional diameter and IOP were not significantly correlated (r=-0.160, p= 0.156).Conclusions(1) Schlemm's canal can be accurate defined and measured by 80-MHz UBM in normal subjects and POAG patients.(2) POAG patients have a less observable Schlemm's canal and smaller Schlemm's canal diameter, than normal subjects. The IOP correlates well with Schlemm's canal coronal diameter, but not correlates with meridional diameter.Part 2Trabecular meshwork Measurements by 80-MHz UBM in Normal Subjects and POAG patientsPurpose(1) To compare the trabecular meshwork thickness of normal subjects and POAG patients.(2) To study the relationship between the trabecular meshwork thickness and IOP in POAG patients.Methods(1) Forty-four POAG patients and 42 age- and gender-matched normal subjects were enrolled. All participants underwent 80-MHz UBM examination. Imaging of trabecular meshwork was conducted by the same experienced technician. Each eye had measurements taken at the 12,3,6 and 9 o'clock positions.(2) The Mann-Whitney U test and the Kruskal-Wallis H test were used for comparing the differences of IOP, trabecular meshwork thickness between two groups and four sections.(3) Nonparametric Spearman correlation analyses were performed to statistically examine the relationships between IOP and trabecular meshwork.Results(1) POAG patients had a significantly smaller TM thickness (103.9±11.1 ?m vs.88.3± 13.2 ?m, P< 0.001) than normal individuals. The POAG patients with elevated IOP had a smaller trabecular meshwork thickness than POAG subjects with normal IOP (81.8 ± 10.0 ?m vs.97.1±12.0 ?m, p<0.001).(2) TM thickness (r=-0.663, p<0.001) was significantly and negatively correlated with IOP in the POAG group.Conclusions(1) POAG patients have a smaller trabecular meshwork than normal subjects. The IOP correlated well with trabecular meshwork thickness.(2) Trabecular meshwork thickness may be a useful clinical measure for evaluating physiologic trabecular meshwork changes in patients with POAG.(3) Providing potential theorical basis for the gluacom treatment by changing the statu of TM (drug or surgery).Part 3Exercise Influence on Intraocular Pressure, Schlemm's canal and Trabecular meshworkPurpose(1) To observe the IOP changes in young healthy individuals before and after exercise.(2) To observe the morphological changes of Schlemm's canal and trabecular meshwork in young healthy individuals before and after exercise.(3) To explore the relationship between the change of IOP and the morphological changes of Schlemm's canal and trabecular meshwork in young healthy individualsMethods(1) Thirty young healthy individuals were recruited. Each participant exercised for 20 min by jogging. IOP, blood pressure (BP), heart rate (HR), image of Schlemm's canal and trabecular meshwork, pupil diameter were measured before and 0 min after exercise.(2) Schlemm's canal area, perimeter, trabecular meshwork thickness and pupil diameter were measured using Image J software. The unit was defined as pixel. Caculate the HRmax%, the mean arterial pressure (MAP), the mean ocular perfusion pressure (MOPP).(3) The Chi-square test was used for comparing the percentage of sections with an observable Schlemm's canal before and after exercise. The Wilcoxon test (paired samples) was used to compare Schlemm's canal area, perimeter, trabecular meshwork thickness, IOP, pupil diameter and other parameters. The Mann-Whitney U test was used to compare parameters of every quadrant and the Kruskal-Wallis H test were used to compare parameters of four quadrants in same group. Nonparametric Spearman correlation analyses were performed to statistically examine the relationships between IOP change and Schlemm's canal and trabecular meshwork parameters changes.Results(1) A significant drop in IOP (15.4±2.4 vs 11.1±2.7 mmHg p<0.001) and increase in both MOPP (40.8±5.2 vs 54.9±6.3mmHg p<0.001), MAP (84.3±8.4 vs 98.9±10.0 mmHg p<0.001) and pupil diameter, the mean diameter increased by 5.7%(p=0.001) after exercise compared to the baseline.(2) The Schlemm's canal was observable in 81.9%of sections before exercise and Schlemm's canal was observable in 90.5% of sections after exercise, a slight difference that was not statistically significant (x= 3.652, p=0.057).(3) As compared with baseline, the mean Schlemm's canal area (132.83±19.67 vs. 155.33±21.46 pixels, p< 0.001), Schlemm's canal perimeter (54.94±4.95 vs. 60.23±4.19 pixels, p< 0.001) and trabecular meshwork thickness (10.30±1.28 vs. 11.48±1.07 pixels, p< 0.001) increased after exercise.(4) The increase of Schlemm's area (r= 0.019, p= 0.923) and perimeter (r=-0.109, p= 0.573) were not significantly correlated with the reduction of IOP, the increase of trabecular meshwork thickness (r=-0.088, p= 0.651) also was not significantly correlated with the drop of IOPConclusions(1) A decrease in IOP as well as expansion in the trabecular meshwork and Schlemm's canal are observed after aerobic exercise. Trabecular meshwork and Schlemm's canal expansion may be one of the reasons for the reduction in IOP. Sympathetic nerve activity after exercise may participate in Schlemm's canal and trabecular meshwork opening and closing state.(2) Schlemm's canal and trabecular meshwork may have automatic regulation function and their expansion and collapse may not be completely depended on the IOP. |
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