Is Schlemm canal surgery suitable for primary angle-closure glaucoma? / 中华实验眼科杂志

Primary angle-closure glaucoma (PACG) is a common subtype of glaucoma and one of the leading causes of blindness in Asia.Trabeculectomy has been recognized as an effective filtering surgery for PACG and is widely used in clinical practice, but its high risk of postoperative complications, especially bleb scarring over time can not be ignored.Nowadays, non-bleb-based minimally invasive glaucoma surgeries (MIGS) have attracted much attention.Surgeries opening, restoring, or expanding Schlemm canal to reconstruct aqueous humor outflow pathway is one of the MIGS and able to achieve moderate intraocular pressure (IOP) reduction, which has been widely used in the treatment of primary open-angle glaucoma (POAG) for a long time.However, based on the pathogenesis of PACG and its similar pathological changes in Schlemm canal to POAG, some retrospective studies and prospective single-arm studies discovered that Schlemm canal surgery combined with phacoemulsification and/or goniosynechialysis appears to lower IOP well and safe in PACG eyes in recent years.Whether Schlemm canal surgery is also suitable or effective for PACG is getting some attention and is still controversial up to now, mostly due to some differences in pathogenesis between PACG and POAG, it is necessary to perform randomized controlled trials to confirm the efficacy of Schlemm canal surgery for PACG and upgrade the therapeutic strategy of PACG.

Advances in biometrics of the morphology of Schlemm canal / 中华实验眼科杂志

Schlemm canal is an important part of the aqueous humor outflow pathway and a circular canal around the angle of anterior chamber.Its inner wall was separated by a layer of endothelial cells with trabecular meshwork, and its outer wall was drained by 25-30 collector channels.At present, it is considered that Schlemm canal is the main part of resistance to aqueous humor outflow and plays a vital role in the regulation of intraocular pressure.The collapse of Schlemm canal will cause the increase of intraocular pressure, which will lead to the damage of fundus oculi and the occurrence of glaucoma.With the development of minimally invasive glaucoma surgeries, Schlemm canal has become a significant part in anti-glaucoma surgery.Therefore, the morphological observation of Schlemm canal is particularly important.With the development of imaging technology, mainly ultrasound biomicroscope and optical coherence tomography, the study on the morphology of Schlemm canal has developed from the initial histological study of isolated eye by light microscope and electron microscope in vitro to the imaging observation in vivo.In this review, the morphology and physiological function of Schlemm canal in aqueous humor outflow pathway and the biometrics of its morphology were described.

Association between the function of Schlemm canal and outcome following selective laser trabeculoplasty for primary open-angle glaucoma / 中华实验眼科杂志

Objective:To investigate the relationship between the function of Schlemm canal and the efficacy of selective laser trabeculoplasty (SLT) in patients with primary open-angle glaucoma (POAG).Methods:An observational case series study was conducted.Seventeen POAG patients (25 eyes), including 12 males (18 eyes) and 5 females (7 eyes), were enrolled in Tongji Hospital, Tongji Medical College, Huazhong University of Science and Technology from March to December, 2017.The three-mirror contact lens was adopted to observe the presence of blood reflux in Schlemm canal before aerobic exercise, and positive referred to that blood reflux was observed in any region of Schlemm canal, and negative was defined as that no blood reflux was observed in Schlemm canal.The intraocular pressure (IOP) and blood pressure of subjects were measured before and after exercise test by the non-contact tonometer and automatic blood pressure monitor respectively.Positive referred to the IOP reduction ≥4.6 mmHg (1 mmHg=0.133 kPa) and negative was defined as the IOP reduction <4.6 mmHg.Optical coherence tomography (OCT) was used to observe whether Schlemm canal was dilated or not and the dilated area before and after exercise test.Positive referred to the opening clock position of Schlemm canal was larger and/or the Schlemm canal was dilated at one or more clock position.The subjects presenting positive in above three indicators were classified as the positive Schlemm canal function group (8 eyes). The subjects presenting positive in above one or two indicators were classified as the mixed Schlemm canal function group (11 eyes). The subjects presenting negative in above three indicators were classified as the negative Schlemm canal function group (6 eyes). All subjects received SLT treatment.The IOP was examined at postoperative 1 week, 2 weeks and 1 month.The IOP, IOP reduction and rate of IOP reduction were compared among the three groups at various time points.This study adhered to the Declaration of Helsinki.The study protocol was approved by an Ethics Committee of Tongji Hospital, Tongji Medical College, Huazhong University of Science and Technology (No.TJ-IRB20160306). Written informed consent was obtained from each subject.Results:The preoperative IOP and postoperative 1-week, 2-week and 1-month IOP were (20.33±9.22), (17.10±2.98), (19.00±3.94) and (19.33±4.32) mmHg of negative Schlemm canal function group, (25.75±9.03), (20.00±7.60), (19.18±4.46) and (18.00±3.63) mmHg of mixed Schlemm canal function group and (22.28±4.78), (18.75±8.53), (15.50±4.98) and (14.38±3.24) mmHg of positive Schlemm canal function group, respectively.There was no statistical significance in the IOP value among the three groups ( Fgroup=1.028, P=0.374). The difference in IOP before and after surgery was statistically significant ( Ftime=6.751, P=0.002). Compared with preoperative IOP, the postoperative 1-week IOP of the negative Schlemm canal function group, the postoperative 1-week, 2-week and 1-month IOP of the mixed Schlemm canal function group, and the postoperative 2-week and 1-month IOP of positive Schlemm canal function group were significantly decreased (all at P<0.05). There was no significant difference in IOP reduction or the rate of IOP reduction among the three groups after operation ( Fgroup=0.952, P=0.401; Ftime=0.828, P=0.402; Fgroup=1.840, P=0.182; Ftime=0.419, P=0.660). Conclusions:POAG patients with better function of Schlemm canal have a better IOP-lowering efficacy after SLT treatment.Blood reflux in Schlemm canal before exercise, reduced IOP and dilated Schlemm canal after exercise can be considered as indicators to evaluate Schlemm canal function.

Choosing the schlemm's canal surgeries correctly based on the recognition of the aqueous humor outflow resistance / 中华实验眼科杂志

The surgery related to the schlemm's canal is characterized by draining aqueous homur from natural pathway.It is widely accepted by ophthalmologists due to less complications and no need for concern about the scar formation.But we should understand these emerging and evolving technologies rationally.In the article,some topics were discussed,including the relationship between schlemm's canal and glaucoma,evolution,principle and effect of these surgeries,some dilemma problems and the expectations for the future.We hope it would help the ophthalmologist to understand this type of surgeries.

Influencia de la Posición de los Canales Colectores en la Presión Intraocular / Influence of the Collector Channels on the Intraocular Pressure

RESUMEN: El objetivo del presente trabajo es determinar la influencia que tiene la posición de los canales colectores en la presión intraocular y su contribución en el desarrollo del glaucoma. Para realizar el análisis se llevaron acabo simulaciones numéricas utilizando el método de elemento finito para dos casos de estudio. El primer caso es un modelo simplificado de sección rectangular que simula el flujo entre dos canales colectores; el segundo modelo describe el flujo en todo el canal de Schlemm (CS), considerando que es un aro rígido de espesor constante, con cuatro distribuciones de los canales colectores. Se obtuvieron los perfiles de presión y velocidad en los dos casos. En el caso simplificado se tienen diferencias de 10 P a entre las presiones medias. El segundo modelo muestra que el arreglo simétrico tiene una distribución de presiones constante mientras que los casos asimétricos presentan variaciones de 2 P a. Los resultados confirman que la posición de los canales colectores tiene influencia en la presión intraocular. Este estudio da lugar a realizar un análisis en estado transitorio, considerando las propiedades elásticas del CS así como las variaciones de diámetro de los canales colectores.

ABSTRACT: The aim of the present study is to determine the influence of the position of the collecting channels on intraocular pressure and its contribution to the development of glaucoma. Numerical simulations were performed using the finite element method for two case studies. The first case is a simplified model of rectangular section that simulates the flow between two collecting channels. The second model describes flow throughout the Schlemm channel (CS), considering that it is a rigid ring of constant thickness, with four distributions of the collector channels. The pressure and velocity profiles are shown for both cases. In the simplified case, there are differences of 10 P a between the average pressures. The second model shows that the symmetric arrangement has a constant pressure distribution while the asymmetric cases have variations of 2 P a. The results confirm that the position of the collecting channels influences the intraocular pressure. This study shows that a transient analysis is needed to understand the whole process, considering the elastic properties of the CS as well as the variations of diameter of the collecting channels.

Physiological mechanisms of prostaglandin analogues on lowing intraocular pressure / 国际眼科杂志(Guoji Yanke Zazhi)

@#Pathological elevation of intraocular pressure(IOP)is the most prevalent risk factor in the development and progress of glaucoma. Up to date, all treatments for glaucoma are aimed to lower IOP through surgeries and drugs. Prostaglandin analogues are the first-line IOP-lowing drugs for glaucoma due to their ability to reduce IOP. Enough evidences have suggested that they increase aqueous humor outflow through uveoscleral pathway. More recently, people found that bimatoprost was able to increase aqueous humor outflow through trabecular meshwork-Schlemm's canal pathway. Nowadays, a large number of studies are performed to study the mechanism of prostaglandin analogues on lowing intraocular pressure.

Detection of lymphatic biomarker D2-40 in human trabecular meshwork / 中华实验眼科杂志

Background The pathological basis of human primary open angle glaucoma mainly is the degeneration of trabecular meshwork and Schlemm canal.As the outflow pathway of aqueous humor, the tissue origin and characteristics of trabecular meshwork remain less clear.Studying the characteristics of trabecular meshwork may contribute a new thought to the treatment of primary open angle glaucoma.Objective This study was to explore the histological property of trabecular meshwork by detecting the expression of D2-40, a lymphatic biomarker,and CD31,CD34 and smooth muscle actin (SMA), some vascular endothelial biomarkers.Methods Twenty specimens of adult eyeballs were collected from Zhongshan Ophthalmic Center of Sun Yat-sen University,including l0 eyeballs from accident death donors,3 enucleated eyeballs due to posterior segment of choroidal malignant melanoma and 7 orbital exenterated eyeballs.The series ocular meridian sections with the thickness of 4 μm were prepared for the haematoxylin-eosin staining.Immunohistochemistry was employed to detect the expression of D2-40,CD31 ,CD34 and SMA in trabecular meshwork and Schlemm canal.Results Intact structure of chamber angle was observed under the optical microscope by haematoxylin-eosin staining.Human trabecular meshwork tissue was presented with meshlike structure,while Schlemm canal showed the lumen structure.No abnormal substance and periphery synechia were found.D2-40 was strongly expressed in the trabecular meshwork endothelial cells with staining score for 3 points, but CD31, CD34 and SMA were negatively expressed.In contrast, CD31, CD34 and SMA rather than D2-40 were positively expressed in the Schlemm canal.In addition, CD31 and CD34 were also positively expressed in the vascular endothelial cells around the trabecular meshwork.Conclusions The trabecular meshwork expresses lymphatic biomarker rather than vascular biomarkers.This result indicates that trabecular meshwork of human eyes is lymphatic vessel-like tissue.

Qualitative changes in fetal trabecular meshwork fibers at the human iridocorneal angle / 대한해부학회지

We examined a series of changes that occur in the trabecular meshwork fibers of human eyes during fetal development at 12-30 weeks of gestation. At 12 and 15 weeks, the uveal meshwork was stained black with silver impregnation (indicating the predominance of collagen types III and IV) in the endomysium of the ciliary muscle. At 20 weeks, in combination with Schlemm's canal, a dense fibrous tissue mass corresponding to the trabecular meshwork anlage appeared and was colored black. The anlage was continuous with the corneal endothelium rather than with the ciliary muscle. Until 25 weeks, the trabecular meshwork was identifiable as fragmented fiber bundles that stained red-black, suggesting a mixture of collagen types I, III, and IV. At 30 weeks, half of the ciliary muscle fibers were inserted into the scleral spur and not into the meshwork. Therefore, any contribution of ciliary muscle contraction to the differentiation of the trabecular meshwork would appear to be limited. We hypothesize that an uneven distribution of mechanical stresses in the area of the cornea-sclera junction causes a tear thereby creating Schlemm's canal and is accompanied by a change in the collagen fiber types comprising the meshwork.

New glaucoma surgeries in and around Schlemm's canal / 眼科

Filtration surgeries,especially trabeculectomy,are the most common surgeries for glaucoma.Although trabeculectomy has excellent efficacy for reducing intraocular pressure(IOP),glaucoma filtering blebs have been frequently associated with various postoperative complications including filtering bleb failure and ocular surface dysfunctions.Surgical treatments of the natural aqueous outflow system,in and around Schlemm's canal,to restore normal function without penetration of the intraocular space has been considerable interest in recent years as glaucoma surgeons continue their quest for a procedure that reduces IOP without the risk related with filtering bleb.As a result,more blebless glaucoma surgeries have developed gradually in the past years.