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PubMed1992

Localization of smooth muscle and nonmuscle actin isoforms in the human aqueous outflow pathway.

alpha-Smooth muscle actin is the isoform of actin restricted to vascular smooth muscle, pericytes, myofibroblasts and, certain other cells that are of myoid origin. We investigated the distribution of alpha-smooth muscle actin and nonmuscle specific filamentous actin in the human aqueous outflow system by immunohistochemical methods. Filamentous actin was observed in all cellular constituents of the outflow pathway, while distribution of alpha-smooth muscle actin was restricted to the ciliary muscle, to specific cells throughout the trabecular meshwork, and to cells adjacent to the outer wall and the collector channels. The ciliary muscle extended deep into the corneoscleral meshwork, far anterior to the scleral spur. These findings agree with our previous study localizing the distribution of smooth muscle myosin in the human aqueous outflow pathway. Although functionality of the immunoreactive cells needs to be demonstrated, our data show that a potentially contractile apparatus exists in a subpopulation of trabecular meshwork cells and in certain cells of the more distal components of the outflow system.

Actins↗
PubMed1990

[Iris nevus (Cogan-Reese) syndrome--clinicopathological correlations].

Clinicopathological correlations of iris nevus (Cogan-Reese) syndrome were studied by light and electron microscopy, using tissues obtained surgically by trabeculectomy and peripheral iridectomy. The patient was a 52-year-old female, who had a typical appearance of the disease with nodular iris nevi, distorted pupil, ectropion uveae, peripheral anterior synechia, and intractable glaucoma. The histopathological studies of the specimen revealed abnormal corneal endothelialization and basal lamina formation continuously covering the peripheral cornea, trabecular meshwork, and anterior iris surface. Lymphocyte infiltration was found in the layer of the endothelialization and in the anterior iris stroma. The nodular iris nevi were found to consist of mainly integration of degenerated iris melanocytes and clump cells of Koganei. Neovascularization associated with infiltration of lymphocytes and macrophages was also observed in the trabecular meshwork. The present study suggests that the disease might occur by chronic inflammation primarily as corneal endothelitis and iritis.

Endothelium, Corneal↗
PubMed1983

Immediate intraocular pressure response to argon laser trabeculoplasty.

We conducted a randomized, double-masked study of 40 patients with open-angle glaucoma to ascertain the immediate intraocular pressure response after treatment of either one half (180 degrees) or the entire (360 degrees) trabecular meshwork by argon laser trabeculoplasty. We found a statistically significant difference in the magnitude of intraocular pressure changes between the two groups (P less than .02), with those patients receiving fewer burns having a smaller increase. Substantial increases in intraocular pressure were observed in five of the 20 patients in whom the entire trabecular meshwork was treated. One of these patients had marked loss of visual field within 24 hours.

Adult↗
PubMed1981

Scanning and transmission electron microscopic studies of two cases of pigment dispersion syndrome.

We examined four eyes obtained post mortem from two patients who had increased intraocular pressure, normal visual fields, and pigment dispersion syndrome. Gross examination, light microscopy, scanning electron microscopy, and transmission electron microscopy disclosed elongated regions on the posterior iris surface of all the eyes. The cell membrane of the iris pigment epithelium was disrupted and there was extrusion of pigment granules at these locations. These areas of iris had a radial distribution (paralleling the course of the packets of zonular fibers) and corresponded to the peripheral iris transillumination defects. Pigment was dispersed in the anterior segment and on the pars plana. In the trabecular meshwork the pigment was free, within macrophages, and within endothelial cells. We observed giant vacuoles in the endothelium of Schlemm's canal. These findings suggested that friction between the zonular fibers and peripheral iris led to focal disruption of iris pigment epithelium and release of pigment granules. The increased pigment within the trabecular meshwork and Schlemm's canal may indicate that the glaucoma sometimes associated with pigment dispersion is caused by pigmentary obstruction, although congenital imperfections of the outflow channels may also be a factor

Aged↗
PubMed2000

Schlemm's canal becomes smaller after successful filtration surgery.

OBJECTIVE: To determine whether filtration surgery causes secondary changes in the trabecular meshwork and Schlemm's canal. Successful filtration surgery allows most aqueous outflow to enter the filtration bleb, bypassing the meshwork and canal, and may result in underperfusion of these structures. METHODS: Eyes with primary open-angle glaucoma (POAG) that had undergone filtration surgery were studied and compared with eyes with POAG that had not undergone surgery. In addition, normal eyes and eyes with pseudoexfoliative glaucoma were studied for comparison. The trabecular meshwork and Schlemm's canal were examined by light and electron microscopy. RESULTS: Schlemm's canal was significantly smaller in eyes with POAG after filtration surgery than in normal eyes (canal width, 178 +/- 71 microm vs 276 +/- 52 microm; P<.001) or in eyes with medically treated POAG of similar clinical severity (261 +/- 60 microm, P =. 03). The decrease in canal size seemed to be related to the success of the filtration procedure, since eyes with blebs and low pressures had the smallest canals. Eyes with medically treated POAG at earlier clinical stages of glaucoma did not have a significant decrease in canal size when compared with normal eyes. Eyes with advanced pseudoexfoliative glaucoma had canal widths 20% smaller than those in normal eyes (P =.08). CONCLUSIONS: Filtration surgery was associated with a decrease in the size of Schlemm's canal, most likely due to underperfusion of the meshwork. A significant decrease in canal size is otherwise not a finding in POAG. In contrast, the canal tended to become smaller in advanced cases of pseudoexfoliative glaucoma. CLINICAL RELEVANCE: The decrease in size of Schlemm's canal after successful filtration surgery could make glaucoma more difficult to control if the filter ultimately fails. Arch Ophthalmol. 2000;118:1251-1256

Aged↗
PubMed1985

Aqueous outflow in the beagle: unconventional outflow, using different-sized microspheres.

Normal drainage of aqueous humor from the anterior chamber of the canine eye occurred through the angular aqueous plexus and uveoscleral route. In order to understand more clearly, uveoscleral outflow with regard to larger sized tracer particles and the possible influence that varying intraocular pressure (IOP) may have on them, microspheres of 3 sizes, 0.5, 1.0, and 3.0 micron, were perfused at 3 different IOP (20, 50, and 75 mm of Hg) for 3 different times (30, 60, and 90 minutes). Presence of spheres was detected by light microscopy and scanning electron microscopy, and verified by transmission electron microscopy. By 30 minutes of perfusion, all 3 sphere sizes thoroughly infiltrated the anterior uveal trabecular meshwork. At normotensive pressure (20 mm of Hg), spheres of each size penetrated the outer anterior extension of the ciliary musculature and entered the supraciliary space. Only 0.5- and 1.0-micron spheres moved posteriorly into the suprachoridal space. At hypertensive pressures, movement of the tracer particles increased markedly toward the posterior uveal trabecular meshwork. However, 3.0- and 1.0-microns spheres did not enter the supraciliary space and suprachoroidal space, respectively. Spheres also entered the iris, mostly at its root. They remained comparably sparse at different perfusion times and IOP. The present study supported evidence for uveoscleral outflow (vs uveovortex) in the dog and indicated that passage of materials through this pathway may be influenced by IOP when these substances are within a critical size range.

Animals↗
PubMed1986

An in-vitro morphological study of Q-switched neodymium/YAG laser trabeculotomy.

Laser trabeculotomies produced by directing a pulsed neodymium/YAG laser beam at specimens of human anterior chamber angle obtained post mortem or after enucleation were studied by light microscopy and by scanning and transmission electron microscopy to assess the dimensions of the openings created in the trabecular meshwork, their penetrance to the canal of Schlemm, and the extent or absence of laser induced cellular damage in immediately adjacent tissue. A pulse duration of 40-50 ns at energy levels of around 30 mJ was used and the laser cavity carefully tuned to give a Gaussian spatial mode pattern. Openings in the trabecular meshwork typically of 100 microns in diameter and penetrating through to the canal of Schlemm could be regularly created with only minimal damage to adjacent tissue as judged by transmission electron microscopy. The information so gained may be useful in determining the parameters required for successful laser trabeculotomy as a treatment for primary open-angle glaucoma.

Aged↗
PubMed1999

Hydraulic pressure stimulates adenosine 3',5'-cyclic monophosphate accumulation in endothelial cells from Schlemm's canal.

PURPOSE: Fluid flow across various endothelia results in a variety of intracellular and extracellular adaptations. In the living eye, aqueous humor flows across the surface of endothelial cells on trabecular meshwork (TM) beams and in the juxtacanalicular tissue and through or between a continuous monolayer of endothelial cells that line Schlemm's canal (SC). This study was undertaken to test the hypothesis that fluid flow induces biochemical changes in the endothelial cells of the outflow pathway that may modify outflow resistance. METHODS: Trabecular meshwork and SC cells isolated from the outflow pathway of human cadaveric eyes were seeded onto porous filters, placed in Ussing-type chambers, and subjected to fluid flow driven by a pressure head of 15 mm Hg on their apical surface. Cell lysates were prepared and analyzed for adenosine 3',5'-cyclic monophosphate (cAMP) accumulation. Barrier function of cell monolayers was examined using transendothelial electrical resistance measurements. RESULTS: Three different SC cell strains in 14 independent experiments responded with at least a threefold increase in cAMP that was both time and pressure dependent. Conversely, flow-treated TM cells failed to respond in six independent experiments in which five different TM cell strains were used. Electrical resistance across cell monolayers positively correlated with cAMP accumulation and was calcium sensitive. CONCLUSIONS: cAMP signaling is affected by pressure differentials across SC cell monolayers and provides evidence for the participation of SC cells in the regulation of aqueous outflow.

Anterior Eye Segment↗
PubMed1985

In vitro studies with a pulsed neodymium/YAG laser.

The relationships between the destructive effects of Q-switched Nd/YAG laser pulses and a number of experimental parameters were studied for various target materials including in particular excised, fixed samples of human trabecular meshwork. The laser parameters altered were the pulse energy, the convergence angle of the focused beam, and the position of the focus of the beam relative to the target's axial position. The main finding was that it was possible to make deep holes, of a diameter less than 100 micron, in virtually transparent samples of trabecular meshwork with a laser delivery system of 6 degrees convergence and pulse energies of 14 mJ or more. The relevance of this and the other experimental results to the development of a reliable system for performing internal trabeculotomies for the treatment of open-angle glaucoma is presented.

Cornea↗
PubMed2000

Variability of dissection depth in deep sclerectomy: morphological analysis of the deep scleral flap.

BACKGROUND: Deep sclerectomy and similar procedures including a deroofing of Schlemm's canal are meeting with increasing interest owing to the limited risk profile of non-perforating glaucoma surgery. The aim of our study was to investigate how often the outer wall of Schlemm's canal or parts of the trabecular meshwork were incorporated in the excised tissue on deep scleral flap dissection by an experienced glaucoma surgeon. METHODS: The excised deep scleral flap was prepared for light microscopy after performing deep sclerectomy in 7 children and 22 adult patients suffering from glaucoma. Meridional serial sections were checked for the presence of fragments of trabecular beams and collector channels and parts of the endothelial wall of Schlemm's canal. Morphology was compared with the intraoperative appearance of the operated tissue. RESULTS: In 15 patients (52%) the deep scleral flap contained at least some tissue from the outer wall of Schlemm's canal; in 5 of these 15 patients noticeable remnants of the juxtacanalicular trabecular meshwork were also found, although only in one patient was this obvious during surgery. In 14 patients (48%) no evidence of the deroofing of Schlemm's canal was found within the excised deep scleral flap, although intraoperatively the dissection seemed to have been too superficial in only 5 patients. CONCLUSION: Even when performed by an experienced glaucoma surgeon, deep sclerectomy produces biopsy material of remarkable morphological variability that does not always correspond to the intraoperative appearance of the site of operation. More than in conventional trabeculectomy this variability may be of importance for the outcome of surgery.

Adult↗
PubMed2000

Ocular sequelae of pneumatic drills.

PURPOSE: To determine the ocular sequelae of rock-drilling. METHODS: Nineteen rock-drillers and 20 age-, sex- and race-matched control subjects underwent ocular examination in a prospective manner. RESULTS: Subepithelial corneal opacities were found in 12 drillers (63%) and none of the controls; pigmented trabecular meshwork was noted in 13 drillers (68%) and 1 control (5%); low-tension glaucoma was diagnosed in 1 driller (5%); vitreous liquefaction was present in 17 of 17 drillers (100%) examined by a retina specialist and 9 of 20 controls (45%). CONCLUSIONS: The sequelae of drilling include corneal scars from projectile pieces of drilled stone as well as vibration-induced pigment deposition in the trabecular meshwork and vitreous liquefaction. Wearing of safety glasses is recommended.

Adult↗
PubMed1991

Normal anatomy of the aqueous humour outflow system in the domestic pig eye.

The normal functional anatomy of the aqueous humour outflow pathways in the domestic pig is poorly documented in the literature despite its being readily available and of a similar size to the human eye. Anterior segment tissue from 12 pig eyes was appropriately fixed and investigated by light microscopy, and scanning and transmission electron microscopy. The configuration of the iridocorneal angle tissues is similar to other nonprimate mammals in several respects, i.e. it possesses a deep ciliary cleft crossed by stout pectinate ligaments and delicate uveal cords, poorly developed ciliary musculature, and an angular aqueous plexus. However, there were some noteworthy features which may make it a suitable model for specific types of glaucoma related research. These features include a shallow scleral sulcus which contains a wedge-shaped mass of corneoscleral tissue comparable in size to the human trabecular meshwork. This tissue was more trabecular than 'reticular' in arrangement, the latter being the more common in nonprimate mammalian species. The relevance of the present findings to the use and limitations of the porcine eye as a model of the human aqueous outflow pathways is discussed.

Animals↗
PubMed1985

Q-switched neodymium-YAG laser angle surgery in open-angle glaucoma.

In a short-term pilot study, we evaluated Q-switched neodymium-YAG laser angle surgery in 25 eyes from 22 patients with medically uncontrolled open-angle glaucoma. All eyes had unacceptable intraocular pressures (IOPs), despite maximum tolerated medical therapy, argon laser trabeculoplasty, and prior intraocular filtration surgery (eight eyes). Using a pulse energy of 10 millijoules, ten spots were placed approximately 4 degrees apart in the mid-trabecular meshwork using an Nd-YAG laser (Coherent 9900). The mean preoperative and final postoperative IOPs were 30 +/- 6 mm Hg and 21 +/- 8 mm Hg, respectively. The mean follow-up time was five (+/- 3) months (range, two to 14 months). The final postoperative IOP was less than 22 mm Hg in 17 eyes (68%). Holes within the trabecular meshwork were visible in 14 eyes, and laser therapy was associated with the liberation of debris into the anterior chamber in all eyes. Complications included transient postoperative IOP elevation (eight eyes), angle bleeding (six eyes), and posterior displacement of the iris root (four eyes).

Adolescent↗
PubMed2001

Comparison of the morphologic changes after selective laser trabeculoplasty and argon laser trabeculoplasty in human eye bank eyes.

OBJECTIVE: To compare the histopathologic changes in the human trabecular meshwork (TM) after argon laser trabeculoplasty (ALT) and selective laser trabeculoplasty (SLT) with a Q-switched, frequency-doubled, neodymium:yttrium-aluminum-garnet laser. DESIGN: Human "in vitro" experimental study. TISSUE AND CONTROLS: Eight human autopsy eyes were obtained within 18 hours of death from persons aged 71 to 78 years. METHODS: The anterior segment of autopsy eyes was isolated, and one half of each trabecular meshwork underwent SLT and the other half ALT. Specimens were evaluated with scanning and transmission electron microscopy. MAIN OUTCOME MEASURES: Structural changes in the TM were detected by scanning electron microscopy, and cellular or intracellular changes were seen with transmission electron microscopy. RESULTS: Evaluation of the TM after ALT revealed crater formation in the uveal meshwork at the junction of the pigmented and nonpigmented TM. Coagulative damage was evident at the base and along the edge of craters, with disruption of the collagen beams, fibrinous exudate, lysis of endothelial cells, and nuclear and cytoplasmic debris. Evaluation of the TM after SLT revealed no evidence of coagulative damage or disruption of the corneoscleral or uveal trabecular beam structure. Minimal evidence of mechanical damage was present after SLT, and the only ultrastructural evidence of laser tissue interaction was cracking of intracytoplasmic pigment granules and disruption of trabecular endothelial cells. CONCLUSIONS: SLT applied "in vitro" to the TM of human eye bank eyes seemed to cause no coagulative damage and less structural damage to the human TM when compared with ALT and, therefore, may be a safer and more repeatable procedure.

Aged↗
PubMed1999

Effects of ethacrynic acid on intraocular pressure of anesthetized rats.

Ethacrynic acid (ECA) lowers intraocular pressure (i.o.p.) by an effect usually ascribed to increased drainage of aqueous humor by the trabecular meshwork. Here, we describe the effects of a continuous 2-hr intracameral infusion of balanced salt solution (BSS), with or without 2 mM ECA (sodium salt), on IOP of pentobarbital anesthetized rats. The infusion was divided into a constant (0.05 microliter/min) and a periodic (0.25 microliter/min) component that cycled 4 min on then 4 min off. This permitted the calculation of dynamic changes in resistive (trabecular and uveoslceral drainage) and nonresistive (aqueous synthesis, episcleral venous pressure) components of IOP by fitting a second-order transfer function to the responses. ECA markedly blunted the BSS-induced rise in IOP (P < 0.01). The rise in resistive mechanisms (ocular impedance) was transiently blunted by ECA (P < 0.05) during the third and fourth 8-min cycles, and nonresistive mechanisms were reduced by ECA from cycles 3-10 (P < 0.05). Then, at the end of the infusion, the control and ECA dynamic values were similar (P < 0.05), although IOP of ECA-treated rats was still slightly reduced (P < 0.05). The most likely explanation is a summation of small changes in both resistive and nonresistive components of IOP dynamics. Systemic blood pressure was unchanged within either group. The well-known effects of ECA on the trabecular meshwork, alone, are insufficient to explain the dynamic changes in IOP observed in this model.

Anesthesia↗
PubMed1982

Effect of delta 9-tetrahydrocannabinol on monoamine oxidase activity in bovine eye tissues, in vitro.

An investigation was undertaken to analyze the effects of delta 9-tetrahydrocannabinol (THC) on monoamine oxidase (MAO) activity from calf ocular tissues. Ciliary processes, retina, trabecular meshwork, choroid, and iris all demonstrated significant MAO activity in decreasing order of magnitude. THC in concentrations from 10(-8)M to 10(-12)M stimulated MAO activity in extracts from all five tissues, except for iris at 10(-8)M. Maximum stimulation of MAO activity occurred at the 1 x 10(-12)M level for all tissues. Retina, followed next by trabecular meshwork and then ciliary processes, exhibited the largest increase in MAO activity at 10(-12)M THC. This latter effect could possibly by related to the influence of THC on intraocular pressure.

Animals↗
PubMed1990

[A brief review of outflow facility from the viewpoint of metabolic inhibitors].

Aqueous humor is generally considered to flow through the trabecular meshwork without requiring pumping energy from this tissue. Previous studies of the influence of metabolic inhibitors were done mostly at room temperature and usually showed no effect. However, we found that, when tested at 35-36 degrees C, F- reduced the facility of outflow of enucleated bovine eyes. Furthermore, F- did not significantly change the tone of the isolated bovine ciliary muscle, thus the mechanical opening of the trabecular meshwork "pore" could be eliminated. The author made a brief review in this article that outflow facility might happen to be altered by changes in cellular activity involving metabolic processes in the aqueous drainage system.

Animals↗
PubMed1997

Transient loss of alphaB-crystallin: an early cellular response to mechanical stretch.

Human trabecular meshwork (HTM) is distended and stretched with increases in intraocular pressure. During this stretching, there is a rearrangement of actin filaments. The HTM cells express alpha B-crystallin, a small heat shock protein that may have a role in the stabilization and regulation of the cytoskeleton in mammalian cells. The levels of alpha B-crystallin were examined in trabecular meshwork cells after mechanical stretch. Human TM primary cell cultures, plated onto silicone sheets, were subjected to a single 10% linear stretch and samples were prepared at various times after stretch for immunoblotting or Northern blotting. Immunoblots of total protein extracts with antibody specific for alpha B-crystallin detected a 26% decrease of cellular alpha B-crystallin levels within 2 minutes. After 1 hour alpha B-crystallin levels had decreased 90% compared to control cells. The levels of alpha B-crystallin began to recover in cells stretched for 2 hours and returned to initial levels by 24 hours. Northern blots probed with alpha B-crystallin exon III cDNA detected a transcript of 0.65 kb in human TM cells and the levels of the alpha B mRNA remained constant during alpha B-crystallin protein decrease. Later, levels of the 0.65 kb transcript of alpha B-crystallin increased during the cellular recovery. These results suggest that decreased levels of alpha B-crystallin after mechanical stretch were probably not due to transcriptional changes but rather to increased degradation of alpha B-crystallin protein. An increase in mRNA levels may play a role in the recovery of alpha B-crystallin during reorganization of the cytoskeleton and attachment to the substratum. These data raise the possibility of a specific proteolysis of alpha B-crystallin protein in cells after a physiological challenge.

Blotting, Northern↗