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The microfibril hypothesis of glaucoma: implications for treatment of elevated intraocular pressure.

ABSTRACT: Microfibrils are macromolecular aggregates located in the extracellular matrix of both elastic and nonelastic tissues that have essential functions in formation of elastic fibers and control of signaling through the transforming growth factor beta (TGF?) family of cytokines. Elevation of systemic TGF? and chronic activation of TGF? signal transduction are associated with diseases caused by mutations in microfibril-associated genes, including FBN1. A role for microfibrils in glaucoma is suggested by identification of risk alleles in LOXL1 for exfoliation glaucoma and mutations in LTBP2 for primary congenital glaucoma, both of which are microfibril-associated genes. Recent identification of a mutation in another microfibril-associated gene, ADAMTS10, in a dog model of primary open-angle glaucoma led us to form the microfibril hypothesis of glaucoma, which in general states that defective microfibrils may be an underlying cause of glaucoma. Microfibril defects could contribute to glaucoma through alterations in biomechanical properties of tissue and/or through effects on signaling through TGF?, which is well established to be elevated in the aqueous humor of glaucoma patients. Recent work has shown that diseases caused by microfibril defects are associated with increased concentrations of TGF? protein and chronic activation of TGF?-mediated signal transduction. In analogy with other microfibril-related diseases, defective microfibrils could provide a mechanism for the elevation of TGF?2 in glaucomatous aqueous humor. If glaucoma shares mechanisms with other diseases caused by defective microfibrils, such as Marfan syndrome, therapeutic interventions to inhibit chronic activation of TGF? signaling used in those diseases may be applied to glaucoma.

SUBMITTER: Kuchtey J

PROVIDER: S-EPMC3991966 | biostudies-literature | 2014 Mar-Apr

REPOSITORIES: biostudies-literature

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The microfibril hypothesis of glaucoma: implications for treatment of elevated intraocular pressure.

Kuchtey John J Kuchtey Rachel W RW

Journal of ocular pharmacology and therapeutics : the official journal of the Association for Ocular Pharmacology and Therapeutics 20140212 2-3

Microfibrils are macromolecular aggregates located in the extracellular matrix of both elastic and nonelastic tissues that have essential functions in formation of elastic fibers and control of signaling through the transforming growth factor beta (TGFβ) family of cytokines. Elevation of systemic TGFβ and chronic activation of TGFβ signal transduction are associated with diseases caused by mutations in microfibril-associated genes, including FBN1. A role for microfibrils in glaucoma is suggested ...[more]

PMID: 24521159

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Project description:ObjectiveTo report the 2-year incidence of raised intraocular pressure (IOP) and glaucomatous optic nerve damage in patients with uveitis randomized to either fluocinolone acetonide (FA) implants or systemic therapy. Secondarily, we sought to explore patient and eye characteristics associated with IOP elevation or nerve damage.DesignA randomized, partially masked trial in which patients were randomized to either FA implants or systemic therapy.ParticipantsPatients aged ? 13 years with noninfectious intermediate, posterior, or panuveitis active within the prior 60 days for which systemic corticosteroids were indicated were eligible.MethodsVisual fields were obtained at baseline and every 12 months using the Humphrey 24-2 Swedish interactive threshold algorithm (SITA) fast protocol. Stereoscopic optic nerve photos were taken at baseline and at 3-, 6-, 12-, and 24-month follow-up visits. Masked examiners measured IOP at every study visit.Main outcome measuresGlaucoma was diagnosed based on an increase in optic nerve cup-to-disc ratio with visual field worsening or increased cup-to-disc ratio alone, for cases where visual field change was not evaluable, because of missing data or severe visual field loss at baseline.ResultsMost patients were treated as assigned; among those evaluated for glaucoma, 97% and 10% of patients assigned to implant and systemic treatment, respectively, received implants. More patients (65%) assigned to implants experienced an IOP elevation of ? 10 mmHg versus 24% assigned to systemic treatment (P<0.001). Similarly, 69% of patients assigned to the implant required IOP-lowering therapy versus 26% in the systemic group (P<0.001). Glaucomatous optic nerve damage developed in 23% versus 6% (P<0.001) of implant and systemic patients, respectively. In addition to treatment assignment, black race, use of IOP-lowering medications, and uveitis activity at baseline were associated with incident glaucoma (P<0.05).ConclusionsImplant-assigned eyes had about a 4-fold risk of developing IOP elevation of ? 10 mmHg and incident glaucomatous optic neuropathy over the first 2 years compared with those assigned to systemic therapy. Central visual acuity was unaffected. Aggressive IOP monitoring with early treatment (often including early filtration surgery) is needed to avoid glaucoma when vision-threatening inflammation requires implant therapy.Financial disclosure(s)Proprietary or commercial disclosure may be found after the references.

Project description:ImportanceThe ability of patients to measure their own intraocular pressure (IOP) would allow more frequent measurements and better appreciation of peak IOP and IOP fluctuation.ObjectiveTo examine whether patients with glaucoma can perform self-tonometry using a rebound tonometer and examine patient acceptability.Design, setting, and participantsAn observational study in which IOP was assessed using Goldmann applanation tonometry and a rebound tonometer. Consecutive patients were provided with a patient information sheet and those consenting to take part in the study received standardized self-tonometry training and were then instructed to measure their own IOP under observation. This study was conducted at a glaucoma clinic at a university hospital from March 1, 2016, to December 30, 2016, and included both eyes of 100 patients with glaucoma or ocular hypertension.Main outcomes and measuresThe percentage of patients who could successfully perform self-tonometry. Complete success was defined by a good technique and an IOP reading within 5 mm Hg of that obtained by a clinician using the same device. A 3-item questionnaire was used to examine perceptions of self-tonometry among patients.ResultsAmong the 100 patients, the mean (SD) age was 67.5 (10.9) years (53% female). A total 73 of 100 patients (73%) met the complete success criteria. An additional 6 patients could use the device but had IOP readings greater than 5 mm Hg different from those obtained by the clinician. On average, IOP by the rebound tonometer was 2.66 mm Hg lower than Goldmann applanation tonometry (95% limits of agreement, -3.48 to 8.80 mm Hg). The IOPs with the rebound tonometer were similar whether obtained by self-tonometry or investigator, with excellent reproducibility with an intraclass correlation coefficient of 0.903 (95% CI, 0.867-0.928). A total of 56 of 79 successful or partially successful patients (71%) felt self-tonometry was easy, with 73 of 79 (92%) reporting self-tonometry to be comfortable, and a similar number happy to perform self-tonometry in the future.Conclusions and relevanceMost patients could perform self-tonometry and the method was acceptable to patients. Self-tonometry has the potential to improve patient engagement, while also providing a more complete picture of IOP changes over time.

Project description:Glaucoma is a group of eye conditions that damage the optic nerve, the health of which is vital for vision. The key risk factor for the development and progression of this disease is increased intraocular pressure (IOP). Implantable glaucoma drainage devices have been developed to divert aqueous humor from the glaucomatous eye as a means of reducing IOP. The artificial drainage pathway created by these devices drives the fluid into a filtering bleb. The long-term success of filtration surgery is dictated by the proper functioning of the bleb and overlying Tenon's and conjunctival tissue. To better understand the influence of the health condition of these tissues on IOP, we have developed a mathematical model of fluid production in the eye, its removal from the anterior chamber by a particular glaucoma implant-the PRESERFLO® MicroShunt-, drainage into the bleb and absorption by the subconjunctival vasculature. The mathematical model was numerically solved by commercial FEM package COMSOL. Our numerical results of IOP for different postoperative conditions are consistent with the available evidence on IOP outcomes after the implantation of this device. To obtain insight into the adjustments in the implant's hydrodynamic resistance that are required for IOP control when hypotony or bleb scarring due to tissue fibrosis take place, we have simulated the flow through a microshunt with an adjustable lumen diameter. Our findings show that increasing the hydrodynamic resistance of the microshunt by reducing the lumen diameter, can effectively help to prevent hypotony. However, decreasing the hydrodynamic resistance of the implant will not sufficiently decrease the IOP to acceptable levels when the bleb is encapsulated due to tissue fibrosis. Therefore, to effectively reduce IOP, the adjustable glaucoma implant should be combined with a means of reducing fibrosis. The results reported herein may provide guidelines to support the design of future glaucoma implants with adjustable hydrodynamic resistances.

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The microfibril hypothesis of glaucoma: implications for treatment of elevated intraocular pressure.

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The microfibril hypothesis of glaucoma: implications for treatment of elevated intraocular pressure.

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