Dynamic changes of scleral spur length in different accommodation stimuli states.

This study aimed to evaluate the scleral spur length (SSL) in response to different accommodation stimuli states, as well as the correlation with Schlemm's canal (SC) and trabecular meshwork (TM). 74 children were recruited for this study. The 0D, - 4D, and - 8.0 D accommodation stimuli state was achieved by looking at a variable distance optotype. The ciliary muscle (CM), scleral spur (SS), SC, and TM were imaged by swept-source optical coherence tomography. The SSL (Method III) increased significantly from 221.56 ± 30.74 µm at base state to 234.99 ± 30.11 µm at - 4D accommodation stimuli state (p = 0.028) and increased to 250.09 ± 29.87 µm at - 8D accommodation stimuli state (p = 0.011). Method III had the largest areas under receiver operating characteristic (ROC) curves (0.798, 95% CI 0.721-0.875). Moreover, CM 1, SC, and trabecular meshwork length (TML) were significantly correlated with SSL (Method III) (p < 0.05). These findings suggest that the contractile ability and compliance of the SS play an important role in maintaining the morphology of the SC. Moreover, the force of accommodation regulates the SC size by increasing the length of SS.

Measuring changes in Schlemm's canal and trabecular meshwork in different accommodation states in myopia children: an observational study.

PURPOSE: The aim of the study was to evaluate changes in size of Schlemm's canal (SC) and trabecular meshwork(TM) in response to accommodation stimuli and cycloplegia states in myopia children. METHODS: In total, 34 children were enroled in this study. A -6.0 D accommodation stimulus was achieved by looking at an optotype through a mirror. Cycloplegia state was induced with 1% tropicamide. Two states were confirmed by measuring the central lens thickness (CLT), anterior chamber depth and pupil diameter. The size of SC and TM was measured using swept-source optical coherence tomography. The association between changes in SC size and CLT was analysed. RESULTS: Compared with that in the relaxation state, SC size increased significantly under -6.0 D accommodation stimuli. SC area (SCA) increased from 6371 ± 2517 µm2 to 7824 ± 2727 µm2, SC length (SCL) from 249 ± 10 µm to 295 ± 12 µm and SC width (SCW) from 27 ± 9 µm to 31 ± 8 µm. Under the cycloplegia state, SCA decreased to 5009 ± 2028 µm2; SCL to 212 ± 14 µm, and SCW to 22 ± 5 µm. Changes in SCA (r = 0.35, P = 0.0007), SCL (r = 0.251, P = 0.0172) and SCW (r = 0.253, P = 0.016) were significantly correlated with changes in CLT. TM size was not significantly altered compared to that in the relaxation state. TM length (TML) increased from 562 ± 45 µm to 587 ± 47 µm after exposure to -6.0 D accommodation stimulus. CONCLUSION: SC size enlarged in response to -6.0 D accommodation stimuli and shrunk under cycloplegia. TM length increased under the accommodation stimulus state.

Influence of the Water-Drinking Test on Intraocular Pressure, Schlemm's Canal, and Autonomic Nervous System Activity.

Purpose: To assess changes in Schlemm's canal (SC), intraocular pressure (IOP), and autonomic nervous system activity in healthy individuals after performing the water-drinking test (WDT). Methods: The SC area (SCAR), trabecular meshwork (TM) thickness, IOP, high frequency (HF) of heart rate variability (HRV), heart rate (HR), and systolic (SBP) and diastolic blood pressure (DBP) were measured in 22 young healthy participants before and after the WDT, which involved drinking a 1-liter water load in 5 minutes.The SC and TM profiles were captured using a Spectralis optical coherence tomography device (anterior segment module). HF was recorded using Kubios HRV Premium software to evaluate parasympathetic nervous system activity. Results: Compared with baseline values, IOP increased significantly (14.9 ± 2.7 mm Hg vs. 18.4 ± 3.3 mm Hg; P < 0.001), whereas HF (1587 ± 930 ms2 vs. 2193 ± 863 ms2; P < 0.001), mean SCAR (6521 ± 1360 µm2 vs. 5180 ± 1455 µm2; P < 0.001), and HR (69 ± 9.7 beats/min vs. 63 ± 8.9 beats/min; P < 0.001) values decreased significantly by 15 minutes after water-loading. Least significant difference pairwise comparison revealed significant fluctuations of all parameters (SCAR, IOP, HF, and HR) at 15 minutes and their recovery at 30-minutes post-WDT. TM thickness, SBP, and DBP post-WDT did not differ significantly. The increase in IOP (r = -0.4047; P = 0.010) and HF (r = -0.386; P = 0.014) correlated significantly with the decrease in SCAR. Conclusions: The WDT may cause parasympathetic nervous system stimulation, leading to the collapse of SC, which leads to increased IOP.

Effect of age on the morphologies of the human Schlemm's canal and trabecular meshwork measured with swept­source optical coherence tomography.

PURPOSE: We aimed to measure the sizes of Schlemm's canal (SC) and the trabecular meshwork (TM) in healthy individuals and to evaluate variations with age from childhood to old age by using swept-source optical coherence tomography (OCT). METHODS: Anterior chamber angle imaging of the superior, inferior, nasal, and temporal regions of the right and left eyes was performed with swept-source OCT. The diameter and area of SC and TM width and thickness were measured manually from OCT images. RESULTS: A total of 114 healthy individuals were enrolled and included 48 male subjects and 66 female subjects; their ages ranged from 7 to 83 years. Both the SC diameter and area in the four quadrants decreased significantly with aging (P < 0.001) and were wider in the nasal and temporal quadrants compared with the superior and inferior quadrants. Changes in SC size showed significant positive correlations with axial length (AL) and anterior chamber depth (P < 0.001). There was a significant positive association between age and TM thickness in the nasal and temporal quadrants (P < 0.05). The inferior quadrant TM width was the widest among the quadrants. The superior quadrant TM thickness was the thinnest among the quadrants. Changes in TM thickness in the nasal and temporal quadrants showed a significant negative correlation with AL (P < 0.05). There was no statistically significant correlation in SC and TM parameters with central corneal thickness, intraocular pressure, sex, or right or left eye (P > 0.05). CONCLUSIONS: With aging, the SC diameter and area became smaller, TM thickness increased, and TM width seemed to remain constant. Measurements of the sizes of SC and the TM with swept-source OCT could assist in clinical assessments and treatment planning for glaucoma.

Schlemm's canal and trabecular meshwork morphology in high myopia.

PURPOSE: Myopes have a higher risk for open-angle glaucoma; however, the reason is not clear. This study aims to explore the morphologic alterations of Schlemm's canal and trabecular meshwork size in highly myopic eyes. METHODS: Forty myopic eyes from 40 patients with high myopia and 40 control eyes from 40 subjects with low myopia, emmetropia or low hyperopia were enrolled. Optical coherence tomography (OCT) was used to image Schlemm's canal and trabecular meshwork size. The correlations between the morphological alterations of Schlemm's canal and trabecular meshwork, spherical equivalent refractive error, axial length, and intraocular pressure were analysed. RESULTS: Subjects with high myopia had a significantly larger Schlemm's canal diameter in the nasal (188.1 ± 85.6 µm vs 127.4 ± 46.7 µm, P < 0.001), temporal (200.1 ± 7.2 µm vs 147.6 ± 68.1 µm, P = 0.001) quadrants and average value (173.1 ± 48.1 µm vs 137.3 ± 39.6 µm, P = 0.001), and larger Schlemm's canal area in the nasal (7333.2 ± 3877.7 µm2 vs 3833.2 ± 2094.7 µm2 , P < 0.001), temporal (7274.8 ± 3247.4 µm2 vs 4631.1 ± 2431.9 µm2 , P < 0.001) inferior (5512 ± 2504.9 µm2 vs 3922.6 ± 1935.6 µm2 , P = 0.003) quadrants and average value(6165.4 ± 2080.5 µm2 vs 4044.4 ± 1581.1 µm2 , P < 0.001). In the high myopia group, trabecular meshwork thickness of the nasal and temporal quadrants was significantly smaller (108.8 ± 31.6 µm vs 126 ± 42.2 µm, P = 0.045; 100.5 ± 15.4 µm vs 118.4 ± 26.8 µm, P = 0.001, respectively) compared with the control group, as well as the average value (106.4 ± 16.5 µm vs 120.9 ± 23.5 µm, P = 0.002). In the high myopia group, Schlemm's canal and trabecular meshwork size were not correlated with spherical equivalent refractive error and axial length (P > 0.05), while Schlemm's canal area showed a significant negative correlation with intraocular pressure (r = -0.33, P = 0.039). CONCLUSIONS: This study reports for the first time that eyes with high myopia have a larger Schlemm's canal diameter and area, as well as decreased trabecular meshwork thickness, which may help to understand the close association between high myopia and open-angle glaucoma. Schlemm's canal and trabecular meshwork analysis by OCT images may help to characterise the underlying pathophysiological mechanisms involved in high myopia.