GLIS1 regulates trabecular meshwork function and intraocular pressure and is associated with glaucoma in humans

Chronically elevated intraocular pressure (IOP) is the major risk factor of primary open-angle glaucoma, a leading cause of blindness. Dysfunction of the trabecular meshwork (TM), which controls the outflow of aqueous humor (AqH) from the anterior chamber, is the major cause of elevated IOP. Here, we demonstrate that mice deficient in the Krüppel-like zinc finger transcriptional factor GLI-similar-1 (GLIS1) develop chronically elevated IOP. Magnetic resonance imaging and histopathological analysis reveal that deficiency in GLIS1 expression induces progressive degeneration of the TM, leading to inefficient AqH drainage from the anterior chamber and elevated IOP. Transcriptome and cistrome analyses identified several glaucoma- and extracellular matrix-associated genes as direct transcriptional targets of GLIS1. We also identified a significant association between GLIS1 variant rs941125 and glaucoma in humans (P = 4.73 × 10-6), further supporting a role for GLIS1 into glaucoma etiology. Our study identifies GLIS1 as a critical regulator of TM function and maintenance, AqH dynamics, and IOP.

Changes of trabecular meshwork pigmentation in patients with pigment dispersion syndrome: A 15-year study

To report the changes of trabecular meshwork (TM) pigmentation and clinical outcomes of patients with pigment dispersion syndrome (PDS) after resolution of reverse pupillary block.Twenty one eyes of 11 PDS patients were followed up periodically for 15 years after resolution of reverse pupillary block with either Nd: YAG laser peripheral iridotomy (LPI) or trabeculectomy. Visual acuity (VA), best-corrected visual acuity (BCVA), slit lamp examination, intraocular pressure (IOP), Humphrey visual field analysis (VFA), gonioscopy and stereoscopic funduscopy were performed on admission and every 6 months postoperatively. TM pigmentation was quantitatively evaluated and graded every 5 years after the treatment, in which the circumference of anterior chamber angle was divided into 4 quadrants: superior, inferior, nasal and temporal. Postoperative IOP, VA, BCVA, VFA, TM pigmentation and adjunctive anti-glaucoma medications were main outcome measurements and compared with baseline.Eleven patients (9 males, 2 females) were identified as PDS according to the diagnostic criteria, with average age of 38.25 ± 6.93 years (range, 31-55 years) at initial diagnosis. The mean IOP level was 33.1 ± 9.8 mmHg (range, 22-56 mmHg) at diagnosis. Ten PDS eyes received LPI, and the other eleven eyes underwent uneventful trabeculectomy. The median TM pigmentation score of the 21 PDS eyes was 16 (interquartile range [IQR], 15-16) on admission, which changed to 14 (IQR, 13-15), 13 (IQR, 12-14), 12(IQR, 10.5-12) at 5-, 10-, 15-year follow-up visits respectively. The decrease rate of TM pigmentation was 37% in inferior quadrant, while in nasal, temporal, and superior quadrant the reduction rate was 28%, 23%, and 18%, respectively, at the last follow-up visit. Majority of these enrolled eyes (19/21) had stable VA and BCVA with average endpoint IOP of 15.1 ± 3.4 mmHg.TM pigmentation in PDS patients attenuates with time after reverse pupillary block was resolved, in which the inferior quadrant seems faster than the other quadrants.

Crosstalk between MicroRNA and Oxidative Stress in Primary Open-Angle Glaucoma

Reactive oxygen species (ROS) plays a key role in the pathogenesis of primary open-angle glaucoma (POAG), a chronic neurodegenerative disease that damages the trabecular meshwork (TM) cells, inducing apoptosis of the retinal ganglion cells (RGC), deteriorating the optic nerve head, and leading to blindness. Aqueous humor (AH) outflow resistance and intraocular pressure (IOP) elevation contribute to disease progression. Nevertheless, despite the existence of pharmacological and surgical treatments, there is room for the development of additional treatment approaches. The following review is aimed at investigating the role of different microRNAs (miRNAs) in the expression of genes and proteins involved in the regulation of inflammatory and degenerative processes, focusing on the delicate balance of synthesis and deposition of extracellular matrix (ECM) regulated by chronic oxidative stress in POAG related tissues. The neutralizing activity of a couple of miRNAs was described, suggesting effective downregulation of pro-inflammatory and pro-fibrotic signaling pathways, including nuclear factor kappa-light-chain-enhancer of activated B cells (NF-kB), transforming growth factor-beta 2 (TGF-β2), Wnt/β-Catenin, and PI3K/AKT. In addition, with regards to the elevated IOP in many POAG patients due to increased outflow resistance, Collagen type I degradation was stimulated by some miRNAs and prevented ECM deposition in TM cells. Mitochondrial dysfunction as a consequence of oxidative stress was suppressed following exposure to different miRNAs. In contrast, increased oxidative damage by inhibiting the mTOR signaling pathway was described as part of the action of selected miRNAs. Summarizing, specific miRNAs may be promising therapeutic targets for lowering or preventing oxidative stress injury in POAG patients.

Generation of a Matrix Gla (Mgp) floxed mouse, followed by conditional knockout, uncovers a new Mgp function in the eye

The ability to ablate a gene in a given tissue by generating a conditional knockout (cKO) is crucial for determining its function in the targeted tissue. Such tissue-specific ablation is even more critical when the gene's conventional knockout (KO) is lethal, which precludes studying the consequences of its deletion in other tissues. Therefore, here we describe a successful strategy that generated a Matrix Gla floxed mouse (Mgp.floxed) by the CRISPR/Cas9 system, that subsequently allowed the generation of cKOs by local viral delivery of the Cre-recombinase enzyme. MGP is a well-established inhibitor of calcification gene, highly expressed in arteries' smooth muscle cells and chondrocytes. MGP is also one of the most abundant genes in the trabecular meshwork, the eye tissue responsible for maintenance of intraocular pressure (IOP) and development of Glaucoma. Our strategy entailed one-step injection of two gRNAs, Cas9 protein and a long-single-stranded-circular DNA donor vector (lsscDNA, 6.7 kb) containing two loxP sites in cis and 900-700 bp 5'/3' homology arms. Ocular intracameral injection of Mgp.floxed mice with a Cre-adenovirus, led to an Mgp.TMcKO mouse which developed elevated IOP. Our study discovered a new role for the Mgp gene as a keeper of physiological IOP in the eye.

A novel patient-oriented numerical procedure for glaucoma drainage devices

The present work analyses the performance of four glaucoma drainage devices, by means of a novel patient-oriented numerical procedure. The procedure is based on the three-dimensional geometry reconstruction from the stacks of tomographic images of a human eye, at different angles, on meshing and on thermo-fluid dynamics modelling activities, carried out on the reconstructed computational domain. The current three-dimensional eye model considers anterior chamber (AC), trabecular meshwork, Schlemm's canal, and collector channels, making use of generalised porous medium approach for modelling ocular porous tissue and cavities. The intraocular pressure (IOP) management inside AC of human eye is analysed, by comparing the results obtained for four drainage devices implanted in a human eye for glaucoma treatment, ie, ExPRESS shunt, iStent inject, SOLX gold micro shunt, and the novel silicon shunt device. The numerical results allow predicting the effects of the installation of these implants on human eyes, in terms of IOP decrease, aqueous humour velocity, pressure, friction coefficient, and local Nusselt number, pointing out the clear distinction between pre-operative and post-operative eye conditions for different glaucoma surgical techniques.

Quantification of Pulse-Dependent Trabecular Meshwork Motion in Normal Humans Using Phase-Sensitive OCT

Purpose

The purpose of this study was to characterize the pulsatile motion of trabecular meshwork (TM) in normal subjects and demonstrate its changes in accommodation with phase-sensitive optical coherence tomography (PhS-OCT).

Methods

A new PhS-OCT laboratory prototype was designed to measure pulsatile TM motion in 13 healthy humans. Two sets of images were captured in 10 subjects, first with best corrective refraction and the other with an additional 3.0 diopters of accommodation. In each image, both maximum velocity (MV) and cumulative displacement (CD) in two selected regions of TM, the internal (IMV and ICD) and external (EMV and ECD) region, were measured.

Results

For all parameters the intraclass correlation coefficient was >0.75. Neither MV nor CD was significantly different between eyes in individual subjects (PIMV = 0.967, PEMV = 0.391, PICD = 0.603, PECD = 0.482). In 26 eyes, with best corrective refraction, the EMV was higher than the IMV (23.9 ± 9.8 vs. 18.9 ± 8.08 μm/s; P = 0.0001), as was the ECD compared with the ICD (0.340 ±0.125 vs. 0.264 ± 0.111 μm; P = 0.000004). With accommodation, MV and CD significantly increased (PIMV = 0.0003, PEMV = 0.0003, PICD = 0.019, and PECD = 0.007), whereas MV and CD in the external region were still larger than those in the internal area (PEMV vs. IMV = 0.009, PECD vs. ICD = 0.023).

Conclusions

This study demonstrates the differences in TM motion between the internal and external regions of TM and displays its change with accommodation. The findings and good reproducibility suggest PhS-OCT helps to understand TM function in regulation of IOP, and, with further refinements, it may be useful in clinical management of glaucoma.

Age-related posterior ciliary muscle restriction - A link between trabecular meshwork and optic nerve head pathophysiology

The ciliary muscle plays a major role in controlling both accommodation and outflow facility in primates. The ciliary muscle and the choroid functionally form an elastic network that extends from the trabecular meshwork all the way to the back of the eye and ultimately attaches to the elastic fiber ring that surrounds the optic nerve and to the lamina cribrosa through which the nerve passes. The ciliary muscle governs the accommodative movement of the elastic network. With age ciliary muscle mobility is restricted by progressively inelastic posterior attachments and the posterior restriction makes the contraction progressively isometric; placing increased tension on the optic nerve region. In addition, outflow facility also declines with age and limbal corneoscleral contour bows inward. Age-related loss in muscle movement and altered limbal corneoscleral contour could both compromise the basal function of the trabecular meshwork. Further, recent studies in non-human primates show that the central vitreous moves posteriorly all the way back to the optic nerve region, suggesting a fluid current and a pressure gradient toward the optic nerve. Thus, there may be pressure and tension spikes on the optic nerve region during accommodation and these pressure and tension spikes may increase with age. This constellation of events could be relevant to glaucomatous optic neuropathy. In summary, our hypothesis is that glaucoma and presbyopia may be literally linked to each other, via the choroid, and that damage to the optic nerve may be inflicted by accommodative intraocular pressure and choroidal tension "spikes", which may increase with age.

Aqueous outflow facility after phacoemulsification with or without goniosynechialysis in primary angle closure: a randomised controlled study

BACKGROUND

Goniosynechialysis (GSL) to remove peripheral anterior synechiae (PAS) alongside standard cataract surgery has potential theoretical advantages, Published randomised trials, however, have not shown conclusive functional benefits and aqueous outflow changes following GSL are unknown. This study aimed to compare electronic Shiøtz tonographic aqueous outflow facility (TOF) following phacoemulsification with or without GSL in patients with primary angle closure (PAC) and PAC glaucoma. Secondary outcomes were changes in intraocular pressure (IOP) and use of glaucoma medications.

METHODS

Prospective randomised pilot study of 26 patients on glaucoma medication, with ≥90° PAS and significant lens opacity. Patients were randomised 1:1 to receive phacoemulsification with intraocular lens (IOL) implantation only (phaco) or phacoemulsification with IOL plus GSL (phaco-GSL).

RESULTS

Fourteen patients were randomised to phaco-GSL and 12 to phaco alone. TOF increased with phaco-GSL from 0.099±0.07 μL/min/mm Hg to 0.194±0.07, μL/min/mm Hg, p=0.0006, while the phaco group showed no significant change. IOP reduced in both groups, but reduced significantly more following phaco-GSL (46.0%) compared with phaco alone (27.6%, p=0.04). Medication use and extent of PAS only reduced with phaco-GSL, from 0.923±0.86 to 0.384±0.18 medications, p=0.0279, and from 249.2±83.4 to 110.8±53.9° PAS, 6 months postoperatively. No serious adverse events occurred in either group.

CONCLUSIONS

Eyes randomised to both surgical groups had similar and good outcomes at 6 months in this pilot study. However, only eyes undergoing GSL combined with standard phacoemulsification had significantly increased TOF, reduced glaucoma medication dependence and PAS postoperatively. GSL should therefore be considered in such patients.

TRIAL REGISTRATION NUMBER

NCT00719290, Results.

Glaucoma Surgery Calculator: Limited Additive Effect of Phacoemulsification on Intraocular Pressure in Ab Interno Trabeculectomy

Purpose

To compare intraocular pressure (IOP) reduction and to develop a predictive surgery calculator based on the results between trabectome-mediated ab interno trabeculectomy in pseudophakic patients versus phacoemulsification combined with trabectome-mediated ab interno trabeculectomy in phakic patients.

Methods

This observational surgical cohort study analyzed pseudophakic patients who received trabectome-mediated ab interno trabeculectomy (AIT) or phacoemulsification combined with AIT (phaco-AIT). Follow up for less than 12 months or neovascular glaucoma led to exclusion. Missing data was imputed by generating 5 similar but non-identical datasets. Groups were matched using Coarsened Exact Matching based on age, gender, type of glaucoma, race, preoperative number of glaucoma medications and baseline intraocular pressure (IOP). Linear regression was used to examine the outcome measures consisting of IOP and medications.

Results

Of 949 cases, 587 were included consisting of 235 AIT and 352 phaco-AIT. Baseline IOP between groups was statistically significant (p≤0.01) in linear regression models and was minimized after Coarsened Exact Matching. An increment of 1 mmHg in baseline IOP was associated with a 0.73±0.03 mmHg IOP reduction. Phaco-AIT had an IOP reduction that was only 0.73±0.32 mmHg greater than that of AIT. The resulting calculator to determine IOP reduction consisted of the formula -13.54+0.73 × (phacoemulsification yes:1, no:0) + 0.73 × (baseline IOP) + 0.59 × (secondary open angle glaucoma yes:1, no:0) + 0.03 × (age) + 0.09 × (medications).

Conclusions

This predictive calculator for minimally invasive glaucoma surgery can assist clinical decision making. Only a small additional IOP reduction was observed when phacoemulsification was added to AIT. Patients with a higher baseline IOP had a greater IOP reduction.

New insights into pathophysiological mechanisms regulating conventional aqueous humor outflow

The aim of the article was to overview the pathophysiology of the conventional outflow pathway, trabecular meshwork, and intraocular pressure and to discuss the options of future glaucoma treatment directed to improvement in aqueous outflow. The literature search in the Medline, Embase, and Cochrane databases from April to May 2012 was performed; a total of 47 articles analyzed. The diminished conventional pathway may be altered by several pathophysiological mechanisms like TM obstruction caused by transforming growth factor-β2, clastic nondeformable cells, macrophages leaking from hypermature cataract, iris pigment, lens capsular fragments after YAG-laser posterior capsulotomy, proteins and their subfragments. It is known that trabecular meshwork contraction reduces outflow, and the actomyosin system is directly linked to this mechanism. New glaucoma drugs are still under investigation, but it is already proven that agents such as latranculin-B are effective in improving aqueous drainage. Selective Rho-associated coiled coilforming protein kinase inhibitors have been shown to cause a significant improvement in outflow facility and may become a new option for glaucoma treatment. Caldesmon negatively regulates actin-myosin interactions and thus increases outflow. Stem cells may replace missing or nonfunctional trabecular meshwork cells and hopefully will bring a new treatment solution. Pathophysiological mechanisms regulating conventional aqueous humor outflow are still not fully understood and require further investigations. Future treatment decisions should be directed to a specific mechanism regulating an elevation in intraocular pressure.

CXCR3 antagonism of SDF-1(5-67) restores trabecular function and prevents retinal neurodegeneration in a rat model of ocular hypertension

Glaucoma, the most common cause of irreversible blindness, is a neuropathy commonly initiated by pathological ocular hypertension due to unknown mechanisms of trabecular meshwork degeneration. Current antiglaucoma therapy does not target the causal trabecular pathology, which may explain why treatment failure is often observed. Here we show that the chemokine CXCL12, its truncated form SDF-1(5-67), and the receptors CXCR4 and CXCR3 are expressed in human glaucomatous trabecular tissue and a human trabecular cell line. SDF-1(5-67) is produced under the control of matrix metallo-proteinases, TNF-α, and TGF-β2, factors known to be involved in glaucoma. CXCL12 protects in vitro trabecular cells from apoptotic death via CXCR4 whereas SDF-1(5-67) induces apoptosis through CXCR3 and caspase activation. Ocular administration of SDF-1(5-67) in the rat increases intraocular pressure. In contrast, administration of a selective CXCR3 antagonist in a rat model of ocular hypertension decreases intraocular pressure, prevents retinal neurodegeneration, and preserves visual function. The protective effect of CXCR3 antagonism is related to restoration of the trabecular function. These data demonstrate that proteolytic cleavage of CXCL12 is involved in trabecular pathophysiology, and that local administration of a selective CXCR3 antagonist may be a beneficial therapeutic strategy for treating ocular hypertension and subsequent retinal degeneration.

[The progress of aqueous humor outflow pathway in open-angle glaucoma]

Primary open angle glaucoma (POAG) is defined as an optic neuropathy characterized by loss of optic nerve axons and retinal ganglion cells. Increase of intraocular pressure (IOP) is a major risk factor for POAG, which is partially due to an abnormally high aqueous humor outflow resistance in trabecular meshwork (TM). Trabecular outflow pathway is a key element in drainage of aqueous humor. Malfunction of TM in POAG is associated with over expression of inflammatory markers, cellular senescence, oxidative stress, and decrease of cellularity. The biological changes of TM cell and extracellular matrix compromise trabecular pathway drainage resulting in an increased IOP. This article reviewed the progression in research on aqueous humor outflow pathway emphasizing the alteration of trabecular pathway.

Trabecular meshwork gene expression after selective laser trabeculoplasty

BACKGROUND

Trabecular meshwork and Schlemm's canal are the tissues appointed to modulate the aqueous humour outflow from the anterior chamber. The impairment of their functions drives to an intraocular pressure increase. The selective laser trabeculoplasty is a laser therapy of the trabecular meshwork able to decrease intraocular pressure. The exact response mechanism to this treatment has not been clearly delineated yet. The herein presented study is aimed at studying the gene expression changes induced in trabecular meshwork cells by selective laser trabeculoplasty (SLT) in order to better understand the mechanisms subtending its efficacy.

METHODOLOGY/PRINCIPAL FINDINGS

Primary human trabecular meshwork cells cultured in fibroblast medium underwent selective laser trabeculoplasty treatment. RNA was extracted from a pool of cells 30 minutes after treatment while the remaining cells were further cultured and RNA was extracted respectively 2 and 6 hours after treatment. Control cells stored in incubator in absence of SLT treatment were used as reference samples. Gene expression was evaluated by hybridization on miRNA-microarray and laser scanner analysis. Scanning electron microscopic examination was performed on 2 Trabecular meshwork samples after SLT at 4(th) and 6(th) hour from treatment. On the whole, selective laser trabeculoplasty modulates in trabecular meshwork the expression of genes involved in cell motility, intercellular connections, extracellular matrix production, protein repair, DNA repair, membrane repair, reactive oxygen species production, glutamate toxicity, antioxidant activities, and inflammation.

CONCLUSIONS/SIGNIFICANCE

SLT did not induce any phenotypic alteration in TM samples. TM is a complex tissue possessing a great variety of function pivotal for the active regulation of aqueous humour outflow from the anterior chamber. SLT is able to modulate these functions at the postgenomic molecular level without inducing damage either at molecular or phenotypic levels.

Bioinformatic and statistical analysis of the optic nerve head in a primate model of ocular hypertension

BACKGROUND

The nonhuman primate model of glaucomatous optic neuropathy most faithfully reproduces the human disease. We used high-density oligonucleotide arrays to investigate whole genome transcriptional changes occurring at the optic nerve head during primate experimental glaucoma.

RESULTS

Laser scarification of the trabecular meshwork of cynomolgus macaques produced elevated intraocular pressure that was monitored over time and led to varying degrees of damage in different samples. The macaques were examined clinically before enucleation and the myelinated optic nerves were processed post-mortem to determine the degree of neuronal loss. Global gene expression was examined in dissected optic nerve heads with Affymetrix GeneChip microarrays. We validated a subset of differentially expressed genes using qRT-PCR, immunohistochemistry, and immuno-enriched astrocytes from healthy and glaucomatous human donors. These genes have previously defined roles in axonal outgrowth, immune response, cell motility, neuroprotection, and extracellular matrix remodeling.

CONCLUSION

Our findings show that glaucoma is associated with increased expression of genes that mediate axonal outgrowth, immune response, cell motility, neuroprotection, and ECM remodeling. These studies also reveal that, as glaucoma progresses, retinal ganglion cell axons may make a regenerative attempt to restore lost nerve cell contact.

Trabectome (trabeculectomy-internal approach): additional experience and extended follow-up

PURPOSE

To report a retrospective case series of 1127 Trabectome surgical procedures, including 738 Trabectome-only and 366 Trabectome-phacoemulsification surgeries.

METHODS

Electroablation of meshwork via a temporal corneal incision. Outcomes included changes in intraocular pressure (IOP) and medication use, complications, and Kaplan-Meier success estimates.

RESULTS

For all cases, mean preoperative IOP of 23.8 +/- 7.7 mm Hg decreased by 39% to 16.5 +/- 4.0 mm Hg at 24 months (n = 50). Intraoperative reflux bleeding occurred in 77.6%. Medications decreased from 2.8 to 1.2 by 24 months. Sixty-five patients (5.8%) had IOP elevation > 10 mm Hg above baseline on day 1. Failure led to trabeculectomy in 5.9% (n = 67) and shunt installation in 1.6% (n = 18). Kaplan-Meier failure was defined across groups with at least 2 weeks follow-up as IOP > 21 mm Hg with or without medications and not reduced by 20% below baseline on 2 consecutive visits or repeat surgery. For Trabectome-only cases, mean preoperative IOP of 25.7 +/- 7.7 mm Hg was reduced by 40% to 16.6 +/- 4.0 mm Hg at 24 months (n = 46). No prolonged hypotony, choroidal effusion, choroidal hemorrhage, or infections occurred. Failure led to trabeculectomy in 8.1% (n = 60) and shunt installation in 1.9% (n = 14). Medications decreased from 2.93 to 1.2 by 24 months. For Trabectome-phacoemulsification cases, baseline IOP of 20.0 +/- 6.2 mm Hg decreased at 12 months to 15.9 +/- 3.3 mm Hg (18%) (n = 45) and medications decreased from 2.63 +/- 1.12 to 1.50 +/- 1.36. Sixteen (4.4%) of 365 had prior failed trabeculectomy, and 139 of 365 (38%) had prior laser trabeculoplasty.

CONCLUSION

Trabectome offers a minimally invasive method of improving IOP control in open-angle glaucomas.

A modified in vitro method for aqueous humor outflow studies in enucleated porcine eyes

The aim of this study was to develop and test a short-term in vitro method for aqueous humour outflow studies using enucleated porcine eyes. The method used was a modification of two methods that have previously been used: whole eyes and anterior segment cultures. The advantage of the model used in this study was that the anterior part of the eye, including the anterior and posterior chambers, remained intact as in whole enucleated eyes, but neither iridotomia nor trephination through the cornea was needed. The deepening of the anterior chamber during perfusion was avoided by regulating the "vitreal" pressure. Test compounds were administered topically or intracamerally to an anatomically normal anterior chamber. Fresh porcine eyes (n = 48) were sectioned at the equator, and the vitreous mass was carefully removed. This anterior bisection was bound around a specific plastic chamber, thus creating a closed eye. The anterior chamber was perfused at a pressure of 15 mmHg. The mean outflow rate in the nonmedicated eye group was 3.7 +/- 0.20 microL/min (mean +/- standard error of the mean), and it increased by 18% during 9 h owing to a wash-out effect. Compounds known to enhance the aqueous outflow were used for testing the validity of the preparation.

[The action of dexamethasone on trans epithelial electrical resistance and the expression of aquaporin-1 in immortalized trabecular cells]

OBJECTIVE

To study the effect of dexamethasone on trans epithelial electrical resistance (TEER) and the expression of AQP-1 in immortalized trabecular cells.

METHODS

Immortalized human trabecular cells were cultured on PET membrane in 24 wells plate. The cells were treated with Dexamethasone in concentration of 10(-7) mol/L. After the cultured cell became confluence, TEER of the cells was detected to evaluate the resistance of outflow pathway at different time points. Western blot was used to analyze the expression of AQP-1 in the trabecular cells.

RESULTS

The TEER and the expression of AQP-1 were much higher in the cells treated by Dexamethasone in comparison to control without dexamethasone exposure.

CONCLUSIONS

The TEER and expression of AQP-1 in immortalized trabecular cells can be enhanced by Dexamethasone. AQP-1 upregulation induced by Glucocorticoid may relate with the increased resistance of outflow pathway in glaucoma.

Trabecular meshwork as a new target for the treatment of glaucoma

Glaucoma, a group of optic neuropathies, is one of the leading causes of irreversible blindness in the world. It is characterized by degeneration of the optic nerve and progressive visual field loss, often associated with elevated intraocular pressure (IOP). In primary open-angle glaucoma, the most common form of the disease, IOP occurs as a result of abnormally increased resistance to drainage of aqueous humor through the conventional outflow system, which comprises the trabecular meshwork and the Schlemm's canal. The pharmacological treatment of glaucoma has been classically aimed at lowering elevated IOP, either decreasing the production of aqueous humor or improving its outflow. Increasing knowledge of trabecular meshwork physiology shows that this tissue has unique morphologic and functional properties involved in the regulation of aqueous humor outflow. Although trabecular meshwork physiology is yet to be fully revealed, ion channels involved in cell contractility or cell volume regulation, or those capable of responding to high pressure, have been described and may be considered promising pharmacological targets for the treatment of glaucoma. The cytoskeleton architecture of the trabecular meshwork cell is thought to be an important regulator of aqueous humor outflow. Gene technology directed at discovering genes linked to the development of glaucoma or to those upregulated in response to elevated IOP is challenging research but provides an insight into future gene therapy. New tools to study trabecular meshwork physiology have recently been developed, including the use of lentivirus for gene delivery or fusion proteins with a protein transduction domain. These vectors are targeted specifically to the trabecular meshwork and are powerful techniques with broad applications for future gene therapy or as new forms of drug delivery.

Evaluation of Aqueous Outflow Facility in Patients With High Intraocular Pressure After Cataract Surgery

BACKGROUND AND OBJECTIVE

To study whether patients with a marked elevation of intraocular pressure (IOP) the day after cataract surgery may have a chronically impaired aqueous outflow.

PATIENTS AND METHODS

In 128 consecutive patients, IOP was measured both preoperatively and the day after phacoemulsification and intraocular lens implantation. In the late postoperative period, aqueous outflow facility (C-value) was measured with pneumatonography in patients (n = 7) who experienced a postoperative IOP increase of at least 20 mm Hg and in patients (n = 11) with a difference between preoperative and postoperative IOP of not more than 2 mm Hg.

RESULTS

Aqueous outflow facility was normal in both groups. Mean C-value was 0.32 +/- 0.18 microL/min/ mm Hg in the hypertensive group and 0.23 +/- 0.10 microL/ min/mm Hg in the normotensive group. The difference was not statistically significant (P = .20).

CONCLUSIONS

Patients with marked IOP elevation the day after cataract surgery do not seem to have a chronically impaired aqueous outflow facility compared with normotensive patients.

Reduction in normalized bone elasticity following long-term bisphosphonate treatment as measured by ultrasound critical angle reflectometry

Using an improved version of ultrasound critical angle reflectometry, the bone quality of cortical and trabecular bone was assessed in vivo by measuring elastic moduli (normalized for bone density) at both principal axes, referred to as the minimum and maximum normalized elasticities. The measurements were made in 30 normal premenopausal women, 30 normal postmenopausal women, 22 untreated postmenopausal women with osteoporosis, 74 postmenopausal women with osteoporosis or osteopenia on bisphosphonate treatment, and 32 patients with renal transplantation (16 women and 16 men) taking steroids. Cortical elasticity was higher than trabecular elasticity; both declined slightly and non-significantly with age in normal women. Among untreated postmenopausal women with osteoporosis, cortical maximum normalized elasticity (E(cmax)) remained within 95% prediction intervals of normal women. Among patients on bisphosphonate, E(cmax) was low in the majority of patients. E(cmax) was significantly more depressed among those taking the drug > or =3 years than <3 years (22.1% below normal premenopausal women versus 17.2%, P =0.001), and among those with incident non-spinal fractures than without (75.9 vs. 81.5%, P =0.008). E(cmax) was independent of bone mineral density at the calcaneus. Most patients with renal transplantation had low E(cmax), with a mean 20.8% below the normal premenopausal mean. Qualitatively similar findings were found with cortical minimum elasticity and with trabecular minimum and maximum elasticities. Thus, the material bone quality of cortical and trabecular bone may be impaired following bisphosphonate treatment, as in renal transplantation on steroids.

Pseudohypopyon after intravitreal triamcinolone acetonide injection for cystoid macular edema

PURPOSE

To report pseudohypopyon after intravitreal triamcinolone acetonide injection for cystoid macular edema.

DESIGN

Retrospective, noncomparative, consecutive case series.

METHODS

Records were reviewed of all patients who developed pseudohypopyon after intravitreal triamcinolone acetonide injection at Bascom Palmer Eye Institute between January 1, 2002 and February 1, 2004.

RESULTS

A total of 828 intravitreal triamcinolone acetonide injections were administered to 686 patients during the study period. A pseudohypopyon (fine white crystalline opacities in the inferior anterior chamber angle) and suspended white crystalline opacities in the aqueous humor developed after 7 of the 828 injections (0.8%); all pseudohypopyons occurred within 3 days of injection and resolved completely within 2 weeks. None of the 686 patients developed clinically suspected infectious endophthalmitis.

CONCLUSIONS

A transient pseudohypopyon may occur in the early postinjection period after intravitreal triamcinolone acetonide injection. Unless progressive intraocular inflammation occurs, close observational management is indicated.

Overexpression of myocilin in cultured human trabecular meshwork cells

The trabecular meshwork, a specialized eye tissue, is a major site for regulation of the aqueous humor outflow. Malfunctioning of the trabecular meshwork is believed to be responsible for development of glaucoma, a blinding disease. Myocilin is a gene linked to the most common form of glaucoma. Its expression is known to be upregulated by glucocorticoids in trabecular meshwork cells and the altered myocilin level may be the culprit for glaucomatous conditions such as corticosteroid-induced glaucoma. In this study, we examined the influence of myocilin overexpression on the adhesion, spreading, migration, phagocytosis, and apoptosis of human trabecular meshwork cells in culture. When the myocilin expression was increased by 3- to 4-fold, the transfectants showed a dramatic loss of actin stress fibers and focal adhesions. Cell adhesion to fibronectin and spreading were also compromised. Myocilin thus appeared to have a de-adhesive activity, similar to that reported extensively with matricellular proteins. The transfected cells in addition displayed an increased sensitivity to apoptosis. These results demonstrate that overexpression of myocilin renders trabecular meshwork cells in a de-adhesive and vulnerable state. This vulnerability may be the basis for pathologic consequences in subtypes of glaucoma.

Proteasome inhibition by chronic oxidative stress in human trabecular meshwork cells

The pathophysiologic mechanisms leading to the malfunction of the trabecular meshwork (TM)-Schlemm's canal (SC) outflow pathway in glaucoma are still unclear. We hypothesize that chronic oxidative stress may contribute to the malfunction of the outflow pathway by impairing the intracellular proteasome system of the cells, decreasing the ability of the tissue to modulate outflow resistance. To study the effects of chronic oxidative stress on proteasome function, primary cultures of human TM cells were incubated under 40% oxygen and proteasome activity was analyzed by measuring the accumulation of enhanced green fluorescent protein fused to a PEST motif. Changes in proteasome content, cellular senescence, and cell viability were also monitored. After 10 days of exposure to chronic oxidative stress, TM cells showed a marked decline in proteasome activity that was associated with premature senescence and decreased cell viability. These results suggest that proteasome failure may be involved in glaucoma pathophysiology.

Loss of heterozygosity in patients with pseudoexfoliation syndrome

PURPOSE

The purpose of the study was to evaluate the possible occurrence of loss of heterozygosity (LOH) in the anterior capsule, lens nucleus, iris, and trabeculum samples taken from patients with pseudoexfoliation syndrome (PEX). Loss of heterozygosity in a microsatellite marker locus indicates that the neighboring gene may be inactivated. Previous attempts to find a gene defect that might be responsible for pseudoexfoliation glaucoma have been unsuccessful.

METHODS

Specimens of the anterior capsule, the lens nucleus, the iris, the trabeculum, and reference blood samples were collected from 19 PEX patients. Fluorescent multiplex PCR was used to amplify the microsatellite markers located on chromosomes 2, 4, 7, 12, 18, 19, and 21.

RESULTS

LOH was found in 58% of the iris specimens and 50% of the anterior capsule specimens collected from PEX patients. The highest incidence of LOH was observed at the marker D7S820.

CONCLUSIONS

It is possible, that genetic factors may be involved in the etiology and pathogenesis of PEX.

Tonography demonstrates reduced facility of outflow of aqueous humor in myocilin mutation carriers

PURPOSE

To demonstrate the effect in vivo of the myocilin gene mutation Thr377Met on outflow facility of aqueous humor, as measured by tonography.

MATERIALS AND METHODS

Forty-two members of a pedigree known to carry the Thr377Met mutation were examined for glaucoma, evaluated with tonography, and screened for myocilin mutations. Tonography was used to calculate the coefficient of aqueous outflow facility (C), as well as the ratio of the resting intraocular pressure to C (P(0)/C). Subjects were reexamined for glaucoma 5 years after tonography.

RESULTS

Seven subjects were excluded because of previous treatment known to alter facility of aqueous outflow. The mean outflow facility of the eyes of the 12 subjects carrying the Thr377Met mutation was significantly reduced compared with the 23 non-carriers' eyes using both C (P<0.001) and P(0)/C (P<0.001). Reduced outflow facility was also demonstrated in those mutation carriers who were not yet expressing clinical signs of glaucoma or ocular hypertension when measured using C (P = 0.015) and P(0)/C (P = 0.001). After 5 years, progression towards glaucoma had occurred in 5 of the myocilin mutation-carriers, 2 of whom showed bilateral progression; 3 carriers remained completely normal. Four subjects had bilateral glaucoma at the outset and remained unchanged. The carriers' eyes that progressed towards glaucoma had reduced outflow facility compared with those that remained normal, although the difference was not statistically significant.

CONCLUSIONS

Carriers of the myocilin Thr377Met mutation have reduced outflow facility, which may be detected prior to developing glaucoma. Tonography was not seen to be clinically useful in predicting progression towards glaucoma.

Myocilin and glaucoma: A TIGR by the tail?

In 1997, Stone and 14 colleagues from 7 laboratories reported the identification of a gene (TIGR) associated with juvenile open-angle glaucoma (JOAG). Screening of adults with primary open-angle glaucoma (POAG) revealed that about 4% also carried a mutation of the coding region of this gene. The mutations were found through genetic linkage analysis of families with JOAG. Juvenile open-angle glaucoma was a logical starting point in the search for genetic causes of open-angle glaucoma: it shows a strong autosomal-dominant inheritance pattern, occurs at an early age, demonstrates obvious phenotypic signs (dramatic elevation of intraocular pressure and subsequent optic nerve damage), and is likely to be found in multiple generations as parents of affected children are still living. These factors, however, also serve to distinguish it from adult-onset POAG, which generally has a lower intraocular pressure and a less severe course. The discovery of the actual gene represented a true advance over previous studies that had mapped the gene to a segment of a chromosome but did not identify the specific gene. How the mutant gene causes glaucoma is unknown and is the subject of intense research. To date, 26 mutations in the TIGR gene sequence (the term TIGR has been replaced by the term myocilin, abbreviated MYOC) have been described, all associated with either JOAG or adult-onset POAG. A correlation between specific mutations in MYOC and the clinical course of glaucoma has been found. Not all cases of JOAG or POAG have mutations in the MYOC gene, however, indicating that more discoveries of other genes are yet to come. Arch Ophthalmol. 2000;118:974-978

Ocular blood flow in experimental glaucoma: a study in cynomolgus monkeys

Experimental glaucoma was induced in 1 eye of 6 cynomolgus monkeys by laser treatment of the trabecular meshwork. In 5 of the 6 monkeys the increased intraocular pressure (IOP) caused marked glaucomatous damage in the experimental eye. Ocular blood flow was determined with labeled microspheres 4 years after the laser treatment. IOP was regulated with an external reservoir. With the same perfusion pressure in both eyes no statistically significant difference was observed between the 2 eyes for total ocular blood flow or for blood flow through any of the ocular tissues. Total ocular blood flow was 343.5 +/- 61.4 mg/min (mean +/- SEM) in the control eye and 385.3 +/- 107.7 mg/min in the experimental eye.

Ciliary body ablation: where are we and how did we get here?

Management of intraocular pressure remains the cornerstone of glaucoma treatment. Related medical and surgical practices involve increasing aqueous outflow or decreasing aqueous production. Filtration procedures that increase aqueous outflow are the first-line surgical defense in glaucoma. However, some cases of glaucoma are resistant to such treatment. In these cases, ciliary body ablation by various methods has had substantial success. Surgical manipulation of aqueous production has been used in glaucoma management since the turn of the century. Techniques have progressed markedly as technology has produced more discrete therapies designed to decrease aqueous production by destroying ciliary body epithelium. Over the past 90 years success has been achieved with a wide range of techniques, from surgical disinsertion of the ciliary body to recent laser and ultrasound techniques. With the development of more precise contact lasers and endoscopic visualization, side effects have been reduced and clinical success rates increased.

Effects of Er:YAG laser trabecular ablation on outflow facility in cadaver porcine eyes

BACKGROUND

Mid-infrared laser technology opens new perspectives in experimental glaucoma surgery. The aim of this study was to establish the effectiveness of Er:YAG laser photoablation of the trabecular meshwork in increasing outflow facility in cadaver porcine eyes.

METHODS

Eye cups of 20 freshly enucleated cadaver porcine eyes were fixed in an anterior segment perfusion system, measuring outflow facility under constant pressure conditions (7-13 mmHg) over a period of 45 min. Trabecular ablation was performed using a pulsed Er:YAG (2.94 microns) laser. Radiation was delivered in a single 4-mJ pulse of 200 microseconds duration by means of an articulated zirconium fluoride optical fibre and a 320-microns quartz-fibre tip.

RESULTS

Er:YAG laser treatment yielded reproducible ablation areas confined to the trabecular meshwork, with a diameter corresponding to that of the fibre tip. Collateral thermal damage extended up to a depth of 30 microns. Outflow facility measurements revealed an increase (mean +/- SD) from 0.128 +/- 0.041 microliter min-1 mmHg-1 in control eyes (n = 11) to 0.308 +/- 0.093 microliter min-1 mmHg-1 in treated ones (n = 9).

CONCLUSION

Application of the photoablative Er:YAG laser technique in non-fistulating trabecular surgery produces patent trabecular perforation with minimal collateral tissue damage and effects a significant reduction (79%) in outflow resistance.

Latanoprost as a new horizon in the medical management of glaucoma

Latanoprost is a new prostaglandin F2 alpha analogue specifically developed for the treatment of glaucoma. Latanoprost is a selective FP receptor agonist, with a primary mode of action of increased uveoscleral outflow of aqueous humor. A dose of 50 micrograms/mL (0.005%) once daily has been found optimal in clinical trials. Latanoprost reduces the nocturnal intraocular pressure in addition to the diurnal, and has been shown to be additive to other glaucoma medication. In long-term phase III clinical trials, latanoprost 0.005% once daily has been proven to be at least as effective as timolol 0.5% twice a day. The main side effect of latanoprost is increased iridial pigmentation, which is relatively frequent in patients with mixed color of the iris. This unique side effect is based on the ability of prostaglandins to stimulate melanin formation in melanocytes. The advantages of latanoprost compared with other glaucoma medication comprise different mode of action, good intraocular pressure-reducing effect, once-daily dosing, and absence of systemic side effects. The long-term consequences of increased iridial pigmentation need to be further studied.

[The efficacy of a microtrabecular prosthesis in the surgery of refractory glaucomas]

A new model of intermediate artificial drainage system (called microtrabeculoprosthesis--MTP) in the surgery of refractory glaucoma is suggested. The prospective study includes 37 operated cases followed up for an average interval of 18.2 months (ranges 11 and 72 months). Surgery is not difficult, and MTP is very well tolerated. A relief of elevated intraocular pressure (IOP < or = 20 mm Hg) was obtained in 73% of the cases (with or without additional antiglaucoma drugs); the irritative phenomena have disappeared in preterminal and absolute glaucoma; the overall therapeutic success rate was 86.5%. The results obtained with MTP are definitely superior to those by conventional surgery but inferior to modern posterior artificial drainage systems (with ameliorative techniques); the rate of postoperative complications is small, and their severity is minimal. In the absence of modern posterior artificial drainage systems. MTP is an efficient solution for the treatment of refractory glaucoma.

Zonular function: a new hypothesis with clinical implications

A new hypothesis about zonular function is presented that has implications in regard to the cause and treatment of ocular hypertension and open-angle glaucoma. This hypothesis is based on the concept that the lens is under constant tension. The anterior and posterior zonules serve a different function than do the equatorial zonules. The anterior and posterior zonules are passive in terms of structural support of the lens; the equatorial zonules are the active components during accommodation.

[Behavior of the intraocular pressure after blunt eye injuries]

Elevation of intraocular pressure is often seen immediately after blunt trauma of the eye, but it can occur even years after the primary impact. A retrospective study was performed in 144 patients with contusion to the eye. After a mean observation period of 6.1 years, a significant rise in intraocular pressure was found in the engaged eye (P < 0.05). In more than 8% of the patients the level of intraocular pressure exceeded 22 mmHg, but only 3 cases developed a glaucomatous visual field and optic nerve head changes. Thus, the risk of secondary glaucoma after contusion of the eye is low.

Immunohistochemical monitoring of the effect of a synthetic fibronectin-like peptide (Arg-Gly-Asp) on the age-related changes in the isolated human corneoscleral tissue of glaucomatous eyes

Fibronectin, an adhesion glycoprotein has been detected and localized in samples of the trabecular meshwork from eight normotensive and 30 glaucomatous human eyes of various ages by means of the indirect immunoperoxidase staining technique. Fibronectin concentration in the trabecular meshwork tissue was evaluated by morphometric analysis. Deposits of the adhesion glycoprotein fibronectin were shown to be spread in the ocular drainage outflow system from patients along with progressive primary open-angle glaucoma (POAG). The fibronectin level quantitatively evaluated in serial cross-sections of trabecular meshwork, appeared to be increased during ageing and more rapidly in the event of POAG development. The active amino acid sequence in fibronectin is an arginine-glycine-aspartic acid tripeptide (Arg-Gly-Asp) and it was shown that the synthetic Arg-Gly-Asp peptide specifically inhibited the adhesive function of fibronectin in trabecular meshwork samples when incubated for 30 min at a concentration of 1-2 mg/ml. The peptide concentration necessary for a 50% decrease of the maximal fibronectin level in the trabecular meshwork specimen derived from patients with moderately advanced POAG stage, was about 1 mg/ml. Immunohistochemical staining exhibited a fainter fibronectin staining in trabecular tissues including the external trabecular layers and subendothelial region of Schlemm's canal, in samples incubated with the synthetic peptide compared with the same tissue explants before peptide treatment. It may be concluded that the adhesion control system is likely to play an important role in development and maintenance of tissue architecture and specialization of the normal human trabecular meshwork.

Argon laser trabeculoplasty: a review

A review of argon laser trabeculoplasty (ALT) indicates that it appears to be a viable tool in the treatment of many forms of open angle glaucoma. It effectively lowers intraocular pressure with few relative risks to the patient. Unfortunately, its pressure-lowering effects diminish with time. The primary risks of ALT are a transient rise in IOP (20 percent incidence) and the development of peripheral anterior synechia (20-46 percent incidence). The Glaucoma Laser Trial (GLT), a multi-institutional study, is currently evaluating the long-term effect of ALT.

Laser trabeculostimulation in open-angle glaucoma: a new trial. Part I

We describe herein a new trial to stimulate trabecular meshwork tissue and thereby increase outflow facility. The efficacy of our laser trabeculostimulation (LTS) was compared with that of conventional laser trabeculoplasty (LTP), since LTP causes shrinkage and cicatrization of the meshwork tissue, thus limiting the reduction of postoperative intraocular pressure (IOP). The mean preoperative IOP of 40 eyes was 24.9 +/- 6.8 mm Hg (mean +/- SD). LTS was applied with a 50-microns spot, a power setting of 50 mW and an exposure time of 1 s. With LTS, the IOP decreased but then increased afterward. Results indicate that low power (50 mW) is effective if used for a longer duration. Our LTS can be applied repeatedly and used in addition to conventional LTP. Although our LTS was less effective than LTP, the trial may lead to the development of another useful treatment modality.

Obstruction of the trabecular meshwork by retinal rod outer segments

Rod outer segments (ROS) have been described in the anterior chamber of patients with the Schwartz syndrome (retinal detachment, uveitis, and glaucoma). The effect of ROS on aqueous outflow was studied by intracameral injection of ROS in human eye bank eyes and in vivo in the cat. Injection of 10(8) ROS in eye bank eyes (n = 8) caused a 19.7% decrease in outflow facility. This was significantly different than in control eyes (n = 8), where the outflow facility decreased 5.2%. Injection of intracameral ROS in the cat resulted in a rise in intraocular pressure (IOP) from a baseline of 19.7 +/- 1.3 mm Hg to a peak of 30.0 +/- 0.7 mm Hg at 24 hours. By 48 hours, IOP returned to baseline. Control injection did not cause a change in IOP. Electron microscopy of the cat trabecular meshwork revealed occlusion of the intratrabecular spaces by ROS with little evidence of inflammatory activity.

[Cofactorial glaucoma--causes]

The various types of glaucoma may be classified more accurately by studying the structure and physiology of the trabecular meshwork. Seen in this light, the development of glaucoma is linked to "extrinsic" and "intrinsic" factors. The intrinsic factors represent the predisposition to glaucoma; the secondary factors intervene in a secondary phase, creating a resistance to aqueous humor outflow. In so-called primary glaucoma the predisposition plays a decisive role, while the extrinsic factors are not so important. In cofactorial glaucoma the predisposition is only of slight significance, while the extrinsic factors are extremely important. In true secondary glaucoma predisposition plays a minimal role, while the extrinsic factors are all the more important. In correlated glaucomas the predisposition may be extremely relevant, but the extrinsic factors which represent the key causes are still unknown. Several types of glaucoma are described as examples.

Pathophysiology of laser trabeculoplasty

The precise effect of argon laser trabeculoplasty on the trabecular meshwork is only partially understood. Its intraocular pressure lowering effect through enhancement of aqueous outflow is well documented. Clinically, this effect seems non-specific for laser characteristics, including wave form, wave length, burn location, clock hours treated, and even to some degree, laser power. The response is delayed in onset, diminishes over time, and in some cases can be renewed with retreatment. Laser photocoagulation of the trabecular meshwork focally destroys, but diffusely stimulates trabecular meshwork cells. Shape alterations in the trabecular meshwork after laser are likely to contribute to outflow enhancement only at very high levels of intraocular pressure. More likely, cellular stimulation activates a molecular biologic chain of events, perhaps within the trabecular extracellular matrix, that permits improved facility of aqueous outflow.

Alteration of trabecular aqueous flow after cataract extraction

Two human eyes that had undergone intracapsular cataract extraction were perfused with cationized ferritin. In both eyes segmental areas of trabecular meshwork collapse were demonstrated superiorly, adjacent to the cataract incision. Electron-microscopic study of these regions disclosed no labeling of the trabecular beams and trabecular spaces, suggesting impermeability to aqueous flow. In other regions, a diffuse labeling with cationized ferritin was demonstrated throughout the trabecular spaces, indicating aqueous flowthrough. Use of corneoscleral sutures may cause trabecular collapse and impermeability. When the collapse is extensive, subsequent increase in intraocular pressure may follow.

Pigmentary dispersion glaucoma secondary to posterior chamber intra-ocular lenses

Thirteen cases of pigmentary dispersion glaucoma are presented. These had in common heavy pigment granule deposition in the trabecular meshwork in the operated eye alone, a history of posterior chamber intra-ocular lens implantation, and mild to marked iris pigment atrophy in areas contingent with or adjacent to the lens. High intra-ocular pressures were usually transient and easily controlled. One, however, eventually required trabeculoplasty.

Corticosteroid glaucoma

Topical instillations of parabulbar injections of corticosteroids produce an increase of insoluble polymerized acid mucopolysaccharides. These glycosaminoglycans close the intratrabecular meshes by increasing the thickness of the trabeculae. Perfusion with hyaluronidase, which depolymerizes the mucopolysaccharides, diminishes the diameter of the trabeculae, the more so that after the suppression of the corticosteroid treatment the lysosomal membranes become more permeable for the acid hydrolases.

Why is intraocular pressure elevated in chronic simple glaucoma? Anatomical considerations

Ultrastructural analysis of 400 trabeculectomy specimens of glaucomatous eye revealed three types of extracellular deposits within the cribriform layer of the trabecular meshwork. One of these derives from the sheath of the subendothelial elastic-like fibres. Tissue culture and ultrahistochemical studies led to the assumption that these deposits contain glycoproteins, probably secreted by the cribriform layer cells.