Light and electron microscopy of Sondermann's channels in the human trabecular meshwork

Differences in outflow channels between two eyes of unilateral primary congenital glaucoma

PURPOSE

Primary congenital glaucoma (PCG) occurs in only one eye in some patients. We aimed to characterize anatomical features of the angle and Schlemm's canal (SC) in vivo among fellow eyes of patients with unilateral primary congenital glaucoma.

METHODS

Both eyes of 33 children with unilateral PCG and 30 healthy, age-matched children, old enough to co-operate were analysed using high-resolution anterior segment spectral domain (SD) OCT. Subgroup analysis was done for the presence/absence of angle dysgenesis as defined by the presence of abnormal tissue/hyper-reflective membrane within angle recess and/or the absence of SC. Other anatomical landmarks differentiating the fellow eyes from eyes with glaucoma were also evaluated and compared with healthy subjects.

RESULTS

The presence of abnormal tissue at the angle and/or a hyper-reflective membranous structure covering the meshwork was seen in all affected PCG eyes (100%) and in 21 (63%) unaffected fellow eyes; p = 0.001. The SC could be seen in 8 (24%) affected in comparison with 29 (88%) fellow unaffected eyes; p = 0.001. The ASOCT scans of 54 (90%) healthy eyes and 3 (9%) fellow PCG eyes revealed a direct communication of anterior portion of the SC with the anterior chamber. Among the fellow eyes, a communication of the supraciliary space with anterior chamber could be discerned in 26 eyes (79%).

CONCLUSIONS

Despite angle dysgenesis, outflow channels such as the uveoscleral or a direct communication of SC with the anterior chamber play a role in preventing the development of glaucoma in fellow eyes of unilateral PCG.

Aqueous outflow in the beagle. II. Postnatal morphologic development of the iridocorneal angle: corneoscleral trabecular meshwork and angular aqueous plexus

The morphology and postnatal ontogeny of the major pathway for aqueous outflow in the canine eye has been examined. Normal canine chamber angles of the Beagle at one day, one through ten weeks, three, four and six months, and one and two years of age were used. Angle tissue was prepared and examined by standard techniques for light and electron microscopy. At birth the corneoscleral trabecular meshwork largely consisted of spongy mesenchyme. By the end of the first month the corneoscleral trabecular meshwork developed into a series of longitudinally oriented sheets anteriorly covered by the peripheral extremity of the corneal endothelium. The angular aqueous plexus (trabecular veins), which was formed at birth, was continually separated from the corneoscleral meshwork by an endothelial lining. Transcellular channels interconnected the trabecular veins and the corneoscleral trabecular meshwork. The corneoscleral trabecular meshwork and angular aqueous plexus in the canine angle are similar topographically, structurally and ultrastructurally to that described in other nonprimate and primate angles.

Pressure-induced changes in the ultrastructure of the endothelium lining Schlemm's canal

In a transmission electron microscopic investigation of the endothelium lining Schlemm's canal subjected to graded levels of intraocular pressure (0 to 50 mm Hg for one hour), there was an increase in the number of vacuolar structures with the increase in pressure (range, 8 to 30 mm Hg). At 0 mm Hg, giant vacuoles were absent, while at 50 mm Hg their numbers were less than at 22 and 30 mm Hg. Vacuoles were invaginations either from the meshwork or from the canal surface of the endothelium. A few were transcellular channels that possibly served as a pressure-sensitive outflow system. In addition, the numbers of nonvacuolar transcellular channels and minipores increased with an increase in pressure while the numbers of pinocytotic and micropinocytotic vesicles decreased. The changes were not accompanied by alterations in organelles associated either with protein or energy production. At 50 mm Hg, breaches in the endothelium lining the trabecular wall were obvious and aqueous outflow was considered to be by nonphysiologic routes.