Contractile markers distinguish structures of the mouse aqueous drainage tract.

PURPOSE: Structures of the aqueous humor drainage tract are contractile, although the tract is not entirely composed of muscle. We characterized the mouse aqueous drainage tract by immunolabeling contractile markers and determined whether profiling these markers within the tract distinguished its key structures of the trabecular meshwork (TM) and ciliary muscle (CM). METHODS: Enucleated eyes from pigmented C57BL/6 (n=8 mice) and albino BALB/c (n=6 mice) mice were processed for cryo- and formalin-fixed paraffin-embedded sectioning. Immunofluorescence labeling was performed for the following: (a) filamentous actin (using fluorescence-conjugated phalloidin), representing a global contractile marker; (b) α-smooth muscle actin (α-SMA), caldesmon, and calponin, representing classic smooth muscle epitopes; and (c) nonmuscle myosin heavy chain, representing a nonmuscle contractile protein. Tissue labeling was identified by confocal microscopy and analyzed quantitatively. Hematoxylin and eosin staining provided structural orientation. RESULTS: A small portion of the TM faced the anterior chamber; the rest extended posteriorly alongside Schlemm's canal (SC) within the inner sclera. Within the drainage tract, filamentous actin labeling was positive in TM and CM. α-SMA and caldesmon labeling was seen primarily along the CM, which extended from the anterior chamber angle to its posterior termination beyond the SC near the retina. Low intensity, patchy α-SMA and caldesmon labeling was seen in the TM. Myosin heavy chain immunoreactivity was primarily found in the TM and calponin was primarily observed in the CM. C57BL/6 and BALB/c comparison showed that pigment obscured fluorescence in the ciliary body. CONCLUSIONS: Our strategy of profiling contractile markers distinguished mouse aqueous drainage tract structures that were otherwise indistinguishable by hematoxylin and eosin staining. The mouse TM was seen as an intervening structure between SC, a part of the conventional drainage tract, and CM, a part of the unconventional drainage tract. Our findings provide important insights into the structural and functional organization of the mouse aqueous drainage tract and a basis for exploring the role of contractility in modulating aqueous outflow.

Acute ultrastructural changes of the trabecular meshwork after selective laser trabeculoplasty and low power argon laser trabeculoplasty.

BACKGROUND AND OBJECTIVES: To compare the histopathological changes in the human trabecular meshwork after low power argon laser trabeculoplasty (ALT) and selective laser trabeculoplasty (SLT) with a Q-switched, frequency-doubled, neodymium:yttrium-aluminium-garnet (Nd:YAG) laser. STUDY DESIGN/MATERIALS AND METHODS: In gonioscopically normal trabecular meshwork of three patients awaiting enucleation due to malignant melanoma of the choroid, SLT and ALT were performed 1-5 days prior to enucleation. In each eye, the lower half of trabecular meshwork received SLT, one quadrant low power (460 mW) ALT and one quadrant was left untreated. Specimens were evaluated with light and transmission electron microscopy. RESULTS: A sharp demarcation line was visible between the laser treated and untreated intact trabecular meshwork after ALT and SLT. Both lasers caused disruption of trabecular beams, but the extent of the damage was smaller after SLT. The collagen component of trabecular beams was mostly amorphous, the long-spacing collagen was scanty after ALT, but more abundant after SLT. In the intertrabecular spaces fragmented cells and tissue debris with only a few pigmented cells were observed. Some endothelial cells were desquamated, but appeared slightly better preserved after SLT than ALT. CONCLUSIONS: Our ultrastructural comparison of the morphological changes after low power ALT and SLT in patients demonstrated that both lasers caused splitting and fragmentation of the trabecular beams of the trabecular meshwork, but the extent of the damage was smaller and the preservation of long-spacing collagen better after SLT than after ALT.

Anterior chamber angle vascularization in Sturge-Weber syndrome. Report of a case.

The case of a 20-year-old woman with a left-sided facial hemangioma and a homolateral glaucoma is reported, complete with the histology of a trabeculectomy specimen. Her left eye had an episcleral hemangioma and goniodysgenetic features in the anterior chamber angle, while the intraocular pressure was measured to be 45 mmHg. The left optic disc showed a large cupping and the left visual field was constricted. The right eye had no glaucomatous changes. Histological examination of the trabeculectomy specimen by both light and electron microscopy showed multiple congenital anomalies. There was a cluster of blood vessels in the trabecular meshwork. Abnormal accumulations of fine granular extracellular matrixes were observed in both the juxtacanalicular connective tissue and around the vascular structures. The lumen of Schlemm's canal was subdivided into three or four parts with few giant vacuole structures. The endothelial cells lining the inner wall of Schlemm's canal contained a well-formed basal lamina with many villi projecting into the lumen. These findings suggest that the multiple anomalies observed in the trabecular tissue may contribute to the manifestation of glaucoma in Sturge-Weber syndrome.

Laser trabecular ablation (LTA).

As part of a pilot study for glaucoma surgery, the use of 3 infrared solid state lasers with 4 fiber optic delivery systems to ablate human trabecular meshwork was investigated. Laser trabecular ablation (LTA) was attempted with the Erbium:YAG (2.94 microns), Erbium:YSGG (2.79 microns), and Holmium:YSGG (2.1 microns) lasers. Laser energy was delivered as a single pulse (250 microseconds) by tissue fiber optic contact with low hydroxyl-fused silica (200 and 500 microns), zirconium fluoride (250 microns), or sapphire (250 microns) fiber optics. Total energy required and thermal effects decreased as laser wavelength increased. LTA was best achieved at 2.94 microns (4 mJ total energy; energy densities = 8.2-12.7 J/cm2; pulse length 250 microseconds) with average thermal damage zones of 5.3-10.3 +/- 1.3-2.4 microns (means +/- SDs) to contiguous structures. This finding has potential applications in the surgical treatment of open-angle and congenital glaucoma and may minimize failure rates seen in other types of surgery on the trabecular meshwork where disrupted trabecular meshwork is not removed.

Ultrastructural and pharmacologic studies on laser-induced glaucoma in primates and rabbits.

Sustained high intraocular pressure resulting in optic nerve cupping and loss of ganglion cells was produced in five rhesus monkeys and eight pigmented rabbits by applying argon laser energy to the trabecular meshwork. In addition, the rabbits manifested buphthalmus. Flow of carbon particles subsequently injected into the anterior chamber was obstructed at the trabecular meshwork by a wound-healing response that closed the intratrabecular spaces. Besides this sustained high intraocular pressure as a result of late scarring, an acute hypertensive response was seen in all rabbits which may correspond to the acute hypertension seen after laser trabeculoplasty in humans. The acute hypertensive response could be only partially blocked by prostaglandin inhibitors and we believe that prostaglandins are not primarily responsible for this effect. Medications known to lower intraocular pressure were systematically tested in both glaucoma models.