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PubMed1990

The morphology of the equine iridocorneal angle: a light and scanning electron microscopic study.

The present investigation of 20 equine eyes shows that the iridocorneal angle of the horse is characterised by a very distinct pectinate ligament and a large ciliary cleft. The pectinate ligament consists of long and broad pigmented trabeculae which form a firm, flat and dense network that encircles the eye. On meridional sections, the ciliary cleft is visible as a wide triangular space comprising the trabecular meshwork which consists of two parts. The inner part is the larger and forms a three-dimensional network of large pigmented trabeculae with very wide intertrabecular spaces. The outer part occupies a much smaller area and fills the posterior angle of the ciliary cleft. It is a compact annular network consisting of small non-pigmented circularly orientated trabeculae. They enclose very narrow spaces which contain glycosaminoglycans. External to the outer network lies the angular aqueous plexus, which is rudimentary. This discontinuous plexus runs circularly and is composed of small slit-like vessels. The intrascleral venous plexus is also very weakly developed, whereas the internal collector channels and the episcleral venous plexus are clearly visible. The large ciliary cleft is supported by the strong trabeculae of both the pectinate ligament and the inner part of the trabecular meshwork, making collapse of the ciliary cleft practically impossible. This morphology of the equine iridocorneal angle helps to explain the rarity of glaucoma in the horse.

Animals↗
PubMed1976

Effects of paracentesis on the blood-aqueous barrier: a light and electron microscopic study on cynomolgus monkey.

The effects of paracentesis on the blood-aqueous barrier of cynomolgus monekeys were studied by light and electron microscopy. The following regions of the eye were examined: ciliary body, iris, Schlemm's canal, juxtacanalicular connective tissue, and trabecular meshwork. Prominent structural alterations were seen in the ciliary epithelium at the anterior portion of the pars plicata, but the epithelium at the posterior portion of the pars plicata and at the pars plana appeared less disrupted. Plasma proteins which crossed the capillary endothelium accumulated in the stroma, and appeared in the posterior chamber through the enlarged extracellular spaces of the ciliary epithelium. The plasma proteins in the ciliary stroma of the anterior portion of the pars plicata moved to the stroma of the iris root; whereas in the iris the capillary endothelium provide an impermeable barrier to proteins. Following paracentesis, the lumen of Schlemm's canal was invaded by blood, and through newly formed gaps in the endothelial lining of the inner wall of the canal, the plasma proteins and red blood cells rapidly diffused into the juxtacanalicular connective tissue, trabecular meshwork, and anterior chamber. On the basis of the present experiments, the protein of the aqueous humor can be considered as originating from both the anterior portion of the pars plicata and the inner wall of Schlemm's canal.

Animals↗
PubMed2001

Familial occurrence of pigment dispersion syndrome.

BACKGROUND: Pigment dispersion syndrome affects up to 4% of the white population. It is characterized by the presence of transillumination defects, Krukenberg's spindle and dense trabecular meshwork pigmentation. Open-angle glaucoma will develop in as many as 50% of affected patients. In this study we describe the familial occurrence of pigment dispersion syndrome in six North American pedigrees and the phenotypic characteristics with respect to pigment dispersion syndrome and glaucoma. METHODS: Probands with pigment dispersion syndrome were identified in glaucoma clinics at university eye centres in Ottawa and Durham, NC. Families with two or more affected members were evaluated. All willing members in each family underwent a thorough clinical examination and were classified as affected with pigment dispersion syndrome, suspect or unaffected. The previous medical records were reviewed to obtain the past medical and ocular history, including risk factors for glaucoma. RESULTS: All six families are white. Three families show at least two generations of affected members. Of the 43 subjects examined 58% were women. All 14 affected members showed moderate to heavy trabecular meshwork pigmentation and either Krukenberg's spindle or transillumination defects. The affected members were also considerably more myopic (mean spherical equivalent for the right eye -4.72 dioptres) than the suspect group or the unaffected group (mean spherical equivalent -0.79 D and +1.19 D respectively) (p < or = 0.001), and the intraocular pressure was higher for the affected than the unaffected group (mean for the right eye 20 mm Hg vs. 16 mm Hg) (p = 0.004). Half of those affected also had open-angle glaucoma. INTERPRETATION: We have identified and phenotypically characterized six North American families with autosomal dominant pigment dispersion syndrome. Our ultimate goal is to identify the gene(s) that causes this disorder in order to clarify its molecular etiology and pathophysiology. This may give rise to a molecular classification of the disease as well as provide the foundation for genetic testing and new treatment approaches.

Adult↗
PubMed1998

Aqueous humor dynamics in beagle dogs with caffeine-induced ocular hypertension.

In order to investigate the possible mechanisms for caffeine-induced ocular hypertension, the intraocular pressure (IOP) and the outflow through the trabecular meshwork were measured in beagle dog eyes after dosing with intravenous caffeine (30 mg/kg) alone or in combination with the topical beta-blocker befunolol [applied as 100 microliters of a 1% (w/v) solution] which inhibits aqueous humor formation in the ciliary body. Intravenous injections of caffeine significantly increased the IOP at 0.25 and 1 hr after a single dose. The ocular hypertension recovered within 2 hr following dosing. Over time, there were no differences in the outflow between the caffeine and control groups. The instillation of befunolol lowered outflow and produced ocular hypotension. The levels of the IOP and outflow in dogs treated with caffeine and befunolol in combination were almost the same as those in dogs treated with befunolol alone. Single-dose and combination-dose studies demonstrate that intravenous caffeine increases the IOP in normal beagle dogs possibly by increasing aqueous humor formation and not by the inhibition of aqueous humor drainage through the trabecular meshwork.

Adrenergic beta-Antagonists↗
PubMed2004

[Selective laser trabeculoplasty].

The prospective clinical study of the selective laser trabeculoplasty (SLT) by means the Coherent Selecta 7000 laser (wave length 532 nm) was conducted. Totally 108.7 +/- 18.3 laser non-overlapping spots (mean energy level 1.04 +/- 0.22 mJ) along the whole circle of the trabecular meshwork in the anterior chamber angle were applied. The study included 258 eyes of 146 patients (50 of them were men) with glaucoma. The mean age of the whole group was 55.9 +/- 13.7 years. The group of unsuccessfully treated patients (30 patients, 41 eyes) in whom the intraocular pressure (IOP) elevated from 23.2 +/- 3.7 mm Hg in 4.7% (measured 493 +/- 474 days after the treatment) during the follow up, was removed from the study. In the group with good response to the SLT, 116 patients (217 eyes) were evaluated 650 +/- 405 days after treatment. Before treatment, in this group the IOP was 23.9 +/- 3.0 mm Hg, at the end of the study the IOP was lowered by 4.5 +/- 2.9 mm Hg, in total by 18.6%. IOP decrease was more pronounced in patients with higher level of IOP at the beginning. Immediately after SLT, no significant rising of the IOP level was recorded. Selective laser trabeculoplasty preserves the integrity of the trabecular meshwork of the anterior chamber angle, and is a safe and clinically effective method of treatment of different forms of glaucoma and ocular hypertension.

Adolescent↗
PubMed2006

Does the aqueous humor have a role in mitogen-activated protein kinase (MAPK) intracellular signaling in Glaucoma?

Glaucoma is a common blinding disease worldwide. Glaucoma treatment today is based on reduction of aqueous humor production or increase aqueous humor drainage. By medical manipulation, the treatment goal is to reduce the main risk factor, elevated intra ocular pressure. Here we hypothesize that the aqueous humor has a role, beside oxygen and nutrient supply, in transferring signaling to the trabecular meshwork. This signaling might be delivered from the ciliary body were the aqueous humor is produced, or from the lens or the cornea. Recently in our lab we proposed that MAPKs present in the aqueous humor are a novel signal involved in glaucoma pathology. Here we show that this pathway exists at an unexpected, extracellular media. Western blot analysis of aqueous humor from congenital glaucomatic rabbits and a rat model of induced elevated intra ocular pressure (IOP) were found to express several signaling members of the MAPK family. Although these members are usually found in an intracellular environment, they can be detected at an extracellular environment, namely the aqueous humor. These signaling proteins are found also in normal eyes. Moreover the MAPK signaling proteins are found in the active phosphorylated form and in non-active form in elevated IOP animals as well as in the control, normal IOP groups. Understanding the signaling cascade, at the aqueous humor, opens a new area for treatment of glaucoma patients. By interfering with the signaling cascade, taking place at a reachable location, the anterior chamber, we will be able to manipulate these protein effects on the trabecular meshwork.

Aqueous Humor↗
PubMed2000

[Use of YAG-Selecta laser and argon laser in the treatment of open angle glaucoma].

INTRODUCTION: The falling success rate of ALT (Argon Laser Trabeculoplasty) has raised the interest in some new laser techniques, such as q-switched Nd:YAG laser trabeculoplasty (Coherent Selecta 7000). The "selective" laser trabeculoplasty destroys melanosomes of pigmented trabecular meshwork cells, sparing adjacent non-pigmented cells and tissues. AIM: Our goal was to establish the IOP lowering effect of selective laser trabeculoplasty (SLT--Selecta Laser Trabeculoplasty) in comparison with ALT. MATERIAL AND METHODS: We have examined 27 patients (10 men, 17 women) aged 35-82, with open angle glaucoma and visual field deterioration despite maximal tolerated topical therapy (21 patients--POAG, 3--NPG, 1--pigmentary glaucoma, 1--pseudoexfoliative glaucoma, 1--juvenile glaucoma). One eye of each patient was randomly chosen for SLT, the other eye underwent ALT. In each method 50 burns were applied in 180 degrees angle with power settings of 600-1000 mW for ALT and energy settings of 0.5-1.4 mJ for SLT. The IOP was measured 1 hour before laser treatment and 1, 2, 24 hours and 3 months after treatment. RESULTS: The mean initial IOP in eyes selected for SLT was significantly higher (21.26 +/- 4.82 mm Hg) than in eyes selected for ALT (20.26 +/- 4.01 mm Hg), t-test: p = 0.037. However, there was no statistically significant difference in the IOP lowering effect between eyes treated with SLT and eyes treated with ALT. The mean IOP drop from the pre-treatment values was -2.85 +/- 4.62 mm Hg after SLT and -2.63 +/- 3.60 mm Hg after ALT (t-test, p = 0.84). All values: 2, 24-hours and 3 months after treatment were significantly lower than pre-treatment values in both groups (t-test, p < 0.03). Only in the 1st hour after SLT the IOP drop was not significant. There was a significant correlation between the amount of pigment on the trabecular meshwork and the IOP fall (U Mann-Whitney test). In SLT group 6 patients (21%) developed mild iritis during 1st day after laser treatment, which disappeared after fluorometholon drop therapy. CONCLUSION: Both methods--SLT and ALT--have equivalent IOP lowering effect in short time observation (3 months). Due to entirely novel mode of Selecta laser action, long term results may show significant differences.

Adult↗
PubMed2001

Ring melanoma of the anterior chamber angle: a report of fourteen cases.

PURPOSE: Ring melanoma of the anterior chamber angle is a rare variant of uveal melanoma that manifests as circumferential, flat tumor growth predominantly confined to the trabecular meshwork and other anterior chamber angle structures. We report the clinical and histopathological features, management, and prognosis of ring melanoma of anterior chamber angle. METHODS: A retrospective review of clinical features, management, histopathologic features, and prognosis was performed. Of 8800 patients with uveal melanoma examined on the Oncology Service at Wills Eye Hospital over a 25-year period, only 14 patients (0.2%; 14 eyes) were classified clinically as ring melanoma of the anterior chamber angle. In no case was there appreciable involvement of the iris or ciliary body on clinical examination. RESULTS: The patients were followed elsewhere for a mean of 8 months before intraocular malignancy was suspected. Upon referral to the Oncology Service, the intraocular pressure was greater than 22 mm Hg in the affected eye in all patients (mean, 36 mm Hg; median, 35 mm Hg; range, 24 to 48 mm Hg), and all patients were using at least two glaucoma medications. The melanoma infiltrated the anterior chamber angle for a mean of 10 clock hours (range, 8 to 12 clock hours). Tumor management consisted of enucleation in 13 cases and plaque radiotherapy in one case. Histopathologic examination revealed epithelioid cell type melanoma in one case, mixed cell type in nine, and spindle cell type in four. Of the 13 patients who underwent enucleation, tumor cells were found within the Schlemm canal in all cases. Five cases displayed invasion of the intrascleral canals, and three showed episcleral invasion. With the exception of two recent cases, 12 patients were followed for a mean of 64 months (median, 47 months; range, 23 to 225 months). Distant metastasis to the liver was detected in three of 12 patients (25%) after a mean follow-up of 78 months (median, 70; range, 37 to 128 months). CONCLUSIONS: Ring melanoma of the trabecular meshwork and angle structures is a rare variant of diffuse uveal melanoma. It often masquerades as unilateral glaucoma and can be difficult to recognize clinically unless careful comparative gonioscopy is performed. Despite the relatively small tumor volume, life prognosis is guarded with distant metastasis in 25% at mean 6 years follow-up.

Adult↗
PubMed1978

Laser iridotomy and trabeculotomy in monkeys. A morphological study.

We performed laser iridotomy and trabeculotomy on Rhesus and Cynomologous monkeys with a Britt Model 152 repetitively pulsed argon laser. The total energy delivered varied from 2 to 6 joules. The easiest sites for laser iridotomy were at 3 and 9 o'clock. The iridotomy remained open for at least 2 months. Scanning electron microscopy confirmed that no damage occurred to the lens. After laser burns to the trabecular meshwork light microscopy showed anterior synechiae, corneal endothelial swelling and trabecular coagulation. Scanning electron microscopy showed that only a few holes were made in the trabecular tissue, even after a massive dose; some of them appeared to lead directly to the canal of Schlemm. We feel that although this machine can be used successfully to perform iridotomy in humans, it cannot replace the current surgical procedures in glaucoma.

Animals↗
PubMed1981

Exfoliation glaucoma: a quantitative perfusion and ultrastructural study.

The aqueous outflow systems of both eyes from a patient with well documented exfoliation syndrome were studied postmortem by quantitative perfusion and scanning and transmission electron microscopy. This provided a rare opportunity to correlate clinical and postmortem findings. the right eye was phakic with early glaucoma. The left eye was aphakic with moderately severe glaucoma prior to the cataract surgery. The eyes were fixed at a perfusion pressure of 25 mm Hg. In both eyes the spaces of the corneoscleral trabecular meshwork were open and mostly free of exfoliation material. The trabecular cells appeared normal and contained no exfoliation material. Failure to take up exfoliation material contrasts with the known tendency of these cells to take up pigment and other particles. The main pathology involved destruction of Schlemm's canal and accumulation of exfoliation material in the juxtacanalicular region of both eyes. The changes in Schlemm's canal and the juxtacanalicular region appeared sufficient to account for increase in resistance to aqueous outflow.

Aged↗
PubMed1977

[Some aspects of congenital glaucoma (author's transl)].

The following paper on certain aspects of congenital glaucoma was read at a meeting for advanced medical education. Particular emphasis was placed on a review of the theories and concepts dealing with pathogenetic factors of congenital glaucoma. Two main concepts appeared to be most prominent in past and current literature: 1. The concept of a membrane obstructing the chamber angle, 2. underdevelopment or malformation of all or some structure of the chamber angle region. In order to clarify the above mentioned concepts, three stages of development of normal human chamber angles were demonstrated by light and electronmicroscopy. Aspects of surgical treatment of congenital glaucoma were discussed. Light and electronmicroscopic findings in some trabeculectomy specimens were shown. In eyes which underwent repeated surgery, marked scar tissue was seen in the area of trabecular meshwork, thus obliterating aqueous pathways. In those cases, an excision of trabecular tissue (trabeculectomy) was recommended rather than destruction of remaining trabecular tissue (trabeculotomy).

Cornea↗
PubMed1981

Congenital glaucoma associated with a chromosomal defect. A histologic study.

A pair of eyes with congenital glaucoma, one treated by goniotomy, was examined by light and electron microscopy. Examination of the drainage angles afforded the opportunity to compare anatomic changes in the treated eye with the surgically unaltered tissue of the fellow eye. The congenital glaucoma appeared to arise from compression of the trabecular meshwork and closure of the intertrabecular and transtrabecular spaces by a discontinuous "membrane" consisting of ectopic trabecular pillars that bridged the drainage angle from the iris root to the normally positioned uveal meshwork. Cleavage of trabecular pillars during goniotomy and conversion of angle architecture to that of a nonglaucomatous neonatal eye suggest that aberrant or ectopic trabecular pillars acted mechanically in maintaining angle compression. The uveal and corneoscleral meshwork and Schlemm's canal are present and appear normal.

Anterior Chamber↗
PubMed1989

Human fetal iridocorneal angle: a light and scanning electron microscopic study.

The iridocorneal angle and inner layers of the trabecular meshwork in human fetal eyes were studied by scanning electron microscopy. Tissue from 32 eyes of 17 fetuses with a gestational age from 12 to 22 weeks were investigated in order to determine the morphological changes in the cellular lining of the anterior chamber angle recess during development. The findings indicate that, although hexagonal corneal endothelial profiles extend almost to the angle apex in a few of the younger eyes examined (12-14 weeks), the lining is always perforated by a few discrete intercellular gaps (2-6 microns diameter). As development progresses it becomes clearer that the maturing meshwork is lined by uveal trabecular endothelial cells which are morphologically distinguishable from corneal endothelium. The frequency and size of the gaps between the inner uveal trabecular endothelial cells increase and are well developed by 18-20 weeks, clearly providing a route of communication between the fetal anterior chamber and the developing intercellular spaces in the primitive trabecular tissue. The implications of these observations on the 'Barkan's membrane' theory of congenital glaucoma are discussed.

Cornea↗
PubMed1980

Effects of intracameral Na2EDTA and EGTA on aqueous outflow routes in the monkey eye.

Intracameral perfusion with 4 to 6 mM Na2EDTA or 4 mM EGTA for 40 to 80 min caused a very large increase in gross outflow facility. This effect was partly reversible when followed by perfusion with mock aqueous humor. Eyes perfused with Na2EDTA were studied morphologically. In the trabecular meshwork the cells separated due to a splitting of the cell junctions. A distention of the cribriform meshwork, a wash-out of extracellular material , and a disintegration of the denuded trabecular cores were also noticed. The inner wall of Schlemm's canal protruded in a "balloonlike" manner into the lumen of the canal and showed frank ruptures, especially after prolonged perfusion times. The conventional outflow pathways beyond Schlemm's canal showed no abnormalities. In the uveoscleral outflow routes the anterior and middle part of the ciliary muscle demonstrated very wide intermuscular clefts and many degenerated muscle fibers. The posterior third of the muscle was normal. So were the ciliary epithelium, the choroid, and the retina. The pupillary sphincter also showed degeneration. The corneal endothelial cells separated, starting at the apical junctional complex.

Animals↗
PubMed1989

Scleral spur and ciliary muscle in man and monkey.

The development of the human scleral spur and the role of the scleral spur in human and monkey eyes were studied by measuring the height of the scleral spur, the thickness of the uveal meshwork and the thickness of the longitudinal ciliary muscle. In an attempt to study how the tension of the ciliary muscle is transmitted to the inner wall of the Schlemm's canal, interconnections within the trabecular meshwork were also studied. The results indicate that after 40 weeks of gestation there is little or no further change with aging in the height of the scleral spur but there is a change in shape. The scleral spur is much less developed in monkey eyes than in human eyes. The corneoscleral meshwork predominates over the uveal meshwork in most human eyes while in monkey eyes the situation is the opposite. In man the thickness of the meridional part of the ciliary muscle attached to the scleral spur varies greatly in eyes with a well developed scleral spur. Interconnecting trabecular beams composed of elastic-like fiber were observed in the uveal and corneoscleral meshwork, as well as in the juxtacanalicular meshwork, extending to the cells of the inner wall of the Schlemm's canal. These findings and the dense structure of the scleral spur suggest that in monkey eyes, and at least in some human eyes, contraction of the ciliary muscle causes unfolding of the trabecular meshwork, not so much through the movement of the scleral spur as by movement of the interconnecting trabecular beams and fibers. One important role of the scleral spur is probably to keep the corneoscleral meshwork open when the ciliary muscle relaxes, and another is to enable inward-forward movement of the circular part of the ciliary muscle by pulling the posterior tip of the ciliary muscle anteriorly when the ciliary muscle contracts. A rigid scleral spur is an advantage for these two functions.

Adult↗
PubMed1986

Age-related changes in the human outflow apparatus.

Tissue from 53 human eyes was used for qualitative and quantitative morphological study (light microscopy and electron microscopy) of age-related changes in the human outflow apparatus. The specimen source was surgical procedures. Qualitative observations showed that the general configuration of the trabecular meshwork changed gradually with age, from a long wedge shape to a shorter, more rhomboidal form. The scleral spur became more prominent, the uveal meshwork more compact, and localized canal closure increased in incidence. Intercellular cytoplasmic processes between neighboring trabecular endothelial cells were less evident and areas of trabecular denudation were frequently observed in older eyes. Quantitative light microscopic studies showed a progressive thickening of the trabeculae, and the numbers of giant vacuoles in the lining endothelium of Schlemm's canal decreasing significantly with age. Morphometric analysis of the cribriform layer (transmission electron microscopy) showed that there was a change in the character of the extracellular materials with an increase in the deposition of electron dense plaques and a decrease in the ground substances from the fifth decade onwards.

Adolescent↗
PubMed1992

Factors influencing in vivo trabecular cell replication as determined by 3H-thymidine labelling; an autoradiographic study in cats.

Because trabecular cell loss is thought to play a role in the pathogenesis of some forms of glaucoma, identification of factors which influence trabecular cell division may provide some insight into the mechanisms and potential treatment of this disease. We studied several commonly encountered clinical situations which may affect the trabecular meshwork: phagocytosis of debris, hyphema, and argon laser trabeculoplasty. The effect of these factors on trabecular cell division was determined using 3H-thymidine autoradiography. Laser trabeculoplasty induced a 307% increase in 3H-thymidine labelling of trabecular cells while phagocytosis and hyphema had no effect on cell labelling. In addition, subgroups of eyes with a loss of trabecular cells or with inflammation did not have increased labelling. Thus laser trabeculoplasty, known to increase outflow facility, was associated with increased trabecular cell labelling while factors often associated with decreased outflow facility and glaucoma were not.

Animals↗
PubMed1982

Distribution of glycosaminoglycans in the aqueous outflow system of the cat.

Although glycosaminoglycans (GAGs) have been postulated to play a role in the regulation of intraocular pressure, structural localization of specific varieties of GAGs in the outflow system is necessary before their precise role can be determined. In this study, the outflow system of the cat was stained with ruthenium red to identify GAGs with the electron microscope. The composition of the ruthenium red-stainable material was determined by predigestion of tissues with testicular hyaluronidase, neuraminidase, or papain. Testicular hyaluronidase-sensitive GAGs were located on the surfaces of the endothelial cells in the trabecular meshwork and aqueous plexus, within their basal laminae, and in the amorphous tissue of the trabecular beams and tissue adjacent to the aqueous plexus. Collagen and elastic fibers throughout the outflow system were also associated with ruthenium red-stainable material that was resistant to testicular hyaluronidase. Connective tissue GAGs, but not endothelial cell-associated GAGs, were demonstrated to be complexed to protein, since they were disrupted by papain treatment. Neuraminidase-sensitive material (sialoglycoprotein) was identified only on the lumenal surface of the endothelial cells of the aqueous plexus. The complex distribution of GAGs and order polyanions in the outflow system of the cat suggests that the these macromolecules may serve more than one function.

Animals↗