Computational Modeling of Fluid Flow and Intra-Ocular Pressure following Glaucoma Surgery

Background Glaucoma surgery is the most effective means for lowering intraocular pressure by providing a new route for fluid to exit the eye. This new pathway is through the sclera of the eye into sub-conjunctival tissue, where a fluid filled bleb typically forms under the conjunctiva. The long-term success of the procedure relies on the capacity of the sub-conjunctival tissue to absorb the excess fluid presented to it, without generating excessive scar tissue during tissue remodeling that will shut-down fluid flow. The role of inflammatory factors that promote scarring are well researched yet little is known regarding the impact of physical forces on the healing response. Methodology To help elucidate the interplay of physical factors controlling the distribution and absorption of aqueous humor in sub-conjunctival tissue, and tissue remodeling, we have developed a computational model of fluid production in the eye and removal via the trabecular/uveoscleral pathways and the surgical pathway. This surgical pathway is then linked to a porous media computational model of a fluid bleb positioned within the sub-conjunctival tissue. The computational analysis is centered on typical functioning bleb geometry found in a human eye following glaucoma surgery. A parametric study is conducted of changes in fluid absorption by the sub-conjunctival blood vessels, changes in hydraulic conductivity due to scarring, and changes in bleb size and shape, and eye outflow facility. Conclusions This study is motivated by the fact that some blebs are known to have ‘successful’ characteristics that are generally described by clinicians as being low, diffuse and large without the formation of a distinct sub-conjunctival encapsulation. The model predictions are shown to accord with clinical observations in a number of key ways, specifically the variation of intra-ocular pressure with bleb size and shape and the correspondence between sites of predicted maximum interstitial fluid pressure and key features observed in blebs, which gives validity to the model described here. This model should contribute to a more complete explanation of the physical processes behind successful bleb characteristics and provide a new basis for clinically grading blebs

Direct matrix metalloproteinase enhancement of transscleral permeability

PURPOSE. Previous studies have shown that increased transscleral permeability after exposure to certain prostaglandins is associated with increased intrascleral matrix metalloproteinases (MMPs). The present study was undertaken to determine whether these MMPs could directly alter transscleral permeability. METHODS. Freshly enucleated mouse eyes were incubated with human MMP-1, -2, and -14 for 4 hours at 37°C. The eyes then were incubated with 10 or 70 kDa dextran-tetramethylrhodamine-lysine for 16 to 32 minutes at 37°C. Two methods of analysis were used. In the first, quickly isolated retinas were homogenized and centrifuged. Fluorescence in the supernatants was determined by microspectrofluorimetry. In the second, the eyes were fixed in 4% paraformaldehyde, and frozen sections were prepared. After the identity of the sections was masked, the intensity of fluorescence in anterior, middle, and posterior regions of the outer retina and inner retina was scored with a 7-point grading scheme. RESULTS. The concentration of 10-kDa fluorescent dextran was 5.14 Ϯ 1.61 g/mL (mean Ϯ SD, n ϭ 33) in the control retinal supernatants, and 6.37 Ϯ 2.67 g/mL (n ϭ 40) in the retinal supernatants from the MMP-treated eyes. This increase was statistically significant (P Ͻ 0.02, t-test). The structural organization of the retina and other ocular tissues was maintained in all experimental conditions. Histologic scoring of fluorescence found significantly increased dextran in the outer retina of eyes treated with MMPs for 32 minutes (the score of control eyes was 2.5 Ϯ 0.4 and of MMP-treated eyes was 3.5 Ϯ 0.1, mean Ϯ SD; P ϭ 0.02, n ϭ 3). Analysis by region found greater scores in the third of the retina nearest to the optic nerve head. CONCLUSIONS. These results show that MMP-1, -2, and -14 can directly increase transscleral permeability and support the view that the increased MMP-1 and -2 observed after topical PG treatment could contribute to increased uveoscleral outflow. (Invest Ophthalmol Vis Sci. 2007;48:752-755 of certain matrix metalloproteinases (MMPs), neutral proteases that can specifically initiate cleavage of extracellular matrix components. METHODS MMP Incubation The procedures were conducted in accordance with the ARVO Statement for the Use of Animals in Ophthalmic and Vision Research. Adult Swiss white mice weighing 28 to 35 g were anesthetized by intraperitoneal injection of ketamine hydrochloride (100 mg/kg) and xylazine hydrochloride (9 mg/kg), and the eyes were quickly harvested. Control eyes were incubated in Hanks'-buffered saline with calcium, magnesium, and glucose (Invitrogen-Gibco, San Diego, CA) and supplemented with 10 M zinc chloride. These incubations were run for 4 hours at 37°C in a shaking water bath with gentle agitation. The incubation medium for the experimental eyes also contained 1 g/mL each of purified human proMMP-1 and activated MMP-2 and -14 catalytic domain (EMB/Calbiochem, San Diego, CA). After these incubations were complete, the eyes were transferred to Hanks'-buffered saline containing 2.5 g /mL 10-or 70-kDa dextran conjugated to tetramethylrhodamine (TMRD) and to lysine (Invitrogen-Molecular Probes, Eugene, OR) and then incubated at 37°C for 4 to 64 minutes. Transscleral permeability of these dextrans has been studied previously. Spectrophotometric Analysis of Permeability After incubation in 2.5 mg/mL TMRD conjugated to 10-kDa dextran (10 kDa-TMRD) for 30 minutes, the retinas were isolated and homogenized on ice with 60 L of PBS using a ground-glass homogenizer. The homogenate was then centrifuged at 14,000g for 10 minutes. Fluorescence in 2-L samples of supernatant was measured directly using a microspectrofluorimeter (ND-3300; Nanodrop Technologies, Wilmington, DE). Calibration of the measurements was achieved by measuring fluorescence in serial dilutions of 10 kDa-TMRD standards. Histologic Assessment of Permeability The isolated eyes were incubated in 2.5 mg/mL TMRD conjugated to 70-kDa dextran (70 kDa-TMRD) for 4, 8, 16, 32, or 64 minutes, quickly rinsed in plain Hanks'-buffered saline, and then transferred to 4% formaldehyde (freshly prepared from paraformaldehyde in 0.1 M phosphate buffer, pH 7.4) at 4°C for 4 hours. This step chemically crosslinked the lysine groups on the fluorescent 70 kDa-TMRD to lysine residues within the tissue proteins and thus prevented any further diffusion of the dextran during subsequent tissue processing. The eyes were placed sequentially in 10% sucrose in phosphate-buffered saline From the Hamilto

Six-month Longitudinal Comparison of a Portable Tablet Perimeter With the Humphrey Field Analyzer.

PURPOSE: To establish the medium-term repeatability of the iPad perimetry app Melbourne Rapid Fields (MRF) compared to Humphrey Field Analyzer (HFA) 24-2 SITA-standard and SITA-fast programs. DESIGN: Multicenter longitudinal observational clinical study. METHODS: Sixty patients (stable glaucoma/ocular hypertension/glaucoma suspects) were recruited into a 6-month longitudinal clinical study with visits planned at baseline and at 2, 4, and 6 months. At each visit patients undertook visual field assessment using the MRF perimetry application and either HFA SITA-fast (n = 21) or SITA-standard (n = 39). The primary outcome measure was the association and repeatability of mean deviation (MD) for the MRF and HFA tests. Secondary measures were the point-wise threshold and repeatability for each test, as well as test time. RESULTS: MRF was similar to SITA-fast in speed and significantly faster than SITA-standard (MRF 4.6 ± 0.1 minutes vs SITA-fast 4.3 ± 0.2 minutes vs SITA-standard 6.2 ± 0.1 minutes, P < .001). Intraclass correlation coefficients (ICC) between MRF and SITA-fast for MD at the 4 visits ranged from 0.71 to 0.88. ICC values between MRF and SITA-standard for MD ranged from 0.81 to 0.90. Repeatability of MRF MD outcomes was excellent, with ICC for baseline and the 6-month visit being 0.98 (95% confidence interval: 0.96-0.99). In comparison, ICC at 6-month retest for SITA-fast was 0.95 and SITA-standard 0.93. Fewer points changed with the MRF, although for those that did, the MRF gave greater point-wise variability than did the SITA tests. CONCLUSIONS: MRF correlated strongly with HFA across 4 visits over a 6-month period, and has good test-retest reliability. MRF is suitable for monitoring visual fields in settings where conventional perimetry is not readily accessible.Funding/Support: Cambridge Eye Trust Jukes Glaucoma Research Fund Glance Optical Pty. Ltd

Nicotinamide provides neuroprotection in glaucoma by protecting against mitochondrial and metabolic dysfunction.

Nicotinamide adenine dinucleotide (NAD) is a REDOX cofactor and metabolite essential for neuronal survival. Glaucoma is a common neurodegenerative disease in which neuronal levels of NAD decline. We assess the effects of nicotinamide (a precursor to NAD) on retinal ganglion cells (the affected neuron in glaucoma) in normal physiological conditions and across a range of glaucoma relevant insults including mitochondrial stress and axon degenerative insults. We demonstrate retinal ganglion cell somal, axonal, and dendritic neuroprotection by nicotinamide in rodent models which represent isolated ocular hypertensive, axon degenerative, and mitochondrial degenerative insults. We performed metabolomics enriched for small molecular weight metabolites for the retina, optic nerve, and superior colliculus which demonstrates that ocular hypertension induces widespread metabolic disruption, including consistent changes to α-ketoglutaric acid, creatine/creatinine, homocysteine, and glycerophosphocholine. This metabolic disruption is prevented by nicotinamide. Nicotinamide provides further neuroprotective effects by increasing oxidative phosphorylation, buffering and preventing metabolic stress, and increasing mitochondrial size and motility whilst simultaneously dampening action potential firing frequency. These data support continued determination of the utility of long-term nicotinamide treatment as a neuroprotective therapy for human glaucoma

Highlights from the 2019 International Myopia Summit on 'controversies in myopia'.

Myopia is an emerging public health issue with potentially significant economic and social impact, especially in East Asia. However, many uncertainties about myopia and its clinical management remain. The International Myopia Summit workgroup was convened by the Singapore Eye Research Institute, the WHO Regional Office for the Western Pacific and the International Agency for the Prevention of Blindness in 2019. The aim of this workgroup was to summarise available evidence, identify gaps or unmet needs and provide consensus on future directions for clinical research in myopia. In this review, among the many 'controversies in myopia' discussed, we highlight three main areas of consensus. First, development of interventions for the prevention of axial elongation and pathologic myopia is needed, which may require a multifaceted approach targeting the Bruch's membrane, choroid and/or sclera. Second, clinical myopia management requires co-operation between optometrists and ophthalmologists to provide patients with holistic care and a tailored approach that balances risks and benefits of treatment by using optical and pharmacological interventions. Third, current diagnostic technologies to detect myopic complications may be improved through collaboration between clinicians, researchers and industry. There is an unmet need to develop new imaging modalities for both structural and functional analyses and to establish normative databases for myopic eyes. In conclusion, the workgroup's call to action advocated for a paradigm shift towards a collaborative approach in the holistic clinical management of myopia

Non-invasive in vivo hyperspectral imaging of the retina for potential biomarker use in Alzheimer's disease

Studies of rodent models of Alzheimer's disease (AD) and of human tissues suggest that the retinal changes that occur in AD, including the accumulation of amyloid beta (Abeta), may serve as surrogate markers of brain Abeta levels. As Abeta has a wavelength-dependent effect on light scatter, we investigate the potential for in vivo retinal hyperspectral imaging to serve as a biomarker of brain Abeta. Significant differences in the retinal reflectance spectra are found between individuals with high Abeta burden on brain PET imaging and mild cognitive impairment (n = 15), and age-matched PET-negative controls (n = 20). Retinal imaging scores are correlated with brain Abeta loads. The findings are validated in an independent cohort, using a second hyperspectral camera. A similar spectral difference is found between control and 5xFAD transgenic mice that accumulate Abeta in the brain and retina. These findings indicate that retinal hyperspectral imaging may predict brain Abeta load

Clinical audit examining the impact of benzalkonium chloride-free anti-glaucoma medications on patients with symptoms of ocular surface disease

Background: Ocular surface disease (OSD) is relatively common in glaucoma patients. OSD symptoms could be linked to prolonged exposure to preservatives in anti-glaucoma medications, especially benzalkonium chloride (BAK). The OBSERVE clinical audit was designed to track the impact of intraocular pressure lowering medications in patients with evidence of OSD to test the hypothesis that BAK-free anti-glaucoma preparations offer clinical advantages over BAK-containing products. Design: Prospective clinical audit from March 2012 to April 2013, open to ophthalmologists practising in Australia. Participants: There were 375 patients enrolled, with a completion rate of 64%. The cohort was predominantly female (68%) with an average age of 71 years. Methods: Patients were screened for inclusion during a routine consultation. If eligible, they were enrolled. At the ophthalmologist's discretion, some patients were switched to BAK-free anti-glaucoma products. Data were collected via an online survey completed by the ophthalmologist during three appointments over a 16- to 30-week period for all patients. Main Outcome Measures: Intraocular pressure, tear-film breakup time, McMonnies Dry Eye Questionnaire score and reported lubricant use. Results: Patients who switched to BAK-free preparations reported a significant fall in the use of lubricants (P = <0.001). Patients in both groups experienced a significant improvement in McMonnies Dry Eye Questionnaire score (P = <0.0001). The percentage of patients with low tear-film breakup time decreased significantly in both groups (P = 0.0001). There was no significant change in intraocular pressure from pre-study levels for either group (P = 0.105). Conclusions: BAK-free anti-glaucoma preparations were associated with a change in lubricant use, suggesting reduction in some OSD symptoms, but more research is needed.7 page(s

Effect of latanoprost on outflow facility in the mouse. Invest Ophthalmol Vis Sci.

PURPOSE. To assess the early effect of latanoprost on outflow facility and aqueous humor dynamics in the mouse. METHODS. Aqueous humor dynamics in NIH Swiss White mice were assessed with an injection and aspiration system, using fine glass microneedles. A single 200-ng (4 L) dose of latanoprost was applied to one eye 2 hours before measurement. The fellow eye served as a control. Intraocular pressure (IOP) was measured by using an established microneedle procedure. Outflow facility (C) was determined by constant-pressure perfusion measurements obtained at two different IOPs. Aqueous humor flow (Fa) was determined by a dilution method using rhodamine-dextran. Conventional and uveoscleral outflow (Fc and Fu) were calculated by the Goldmann equation. RESULTS. Average IOP, Fa, and C of control eyes were 15.7 Ϯ 1.0 mm Hg, 0.144 Ϯ 0.04 L/min (mean Ϯ SD, n ϭ 8), and 0.0053 Ϯ 0.0014 L/min per mm Hg (n ϭ 21), respectively. Average IOP, Fa, and C of treated eyes were 14.0 Ϯ 0.8 mm Hg, 0.138 Ϯ 0.04 L/min (n ϭ 8 for each), and 0.0074 Ϯ 0.0016 L/min per mm Hg (n ϭ 21), respectively. The differences between treated and control eyes were significant for IOP and total outflow facility only. CONCLUSIONS. These data indicate that the early hypotensive effect of latanoprost in the mouse eye is associated with a significant increase in total outflow facility. Alterations in the aqueous dynamics induced by latanoprost can be measured reproducibly in the mouse and may provide a useful model for further determining the mechanism by which latanoprost reduces IOP and alters outflow facility. (Invest Ophthalmol Vis Sci

Interferon-␣ and Interferon-␥ Sensitize Human Tenon Fibroblasts to Mitomycin-C

PURPOSE. To investigate the effect of interferon (IFN)-␣ and IFN-␥ pretreatment on mitomycin C (MMC)-induced cell death in human Tenon fibroblasts (HTFs) and the mechanisms by which IFN-␣ and IFN-␥ modulate the susceptibility of HTFs to MMC. METHODS. HTFs were pretreated with IFN-␣ and IFN-␥ for 48 hours before 5-minute application of 0.4 mg/mL MMC. Cell death after 48 hours was determined by Annexin V/propidium iodide (PI) staining and lactate dehydrogenase (LDH) release assay. Fas, Fas-ligand, and Bcl-2 expression were determined by flow cytometry. Fas associated death domain (FADD), Bax, cytochrome c, and caspase expression were determined by Western blot analysis and immunofluorescence staining. RESULTS. MMC treatment increased cell death and upregulated Fas and FADD expression, but had no effect on Fas-Ligand, Bax, Bcl-2, or cytochrome c. Neither IFN-␣ nor IFN-␥ alone induced HTF death, but each increased cell death 2 days after MMC treatment in a dose-dependent fashion. Combination IFN-␣ and IFN-␥ had a synergistic effect. IFN-␣ and IFN-␥ pretreatment increased Fas expression. Fas upregulation was associated with increased sensitivity to MMC. IFN pretreatment increased procaspase-8, procaspase-9, and procaspase-3 expression, and caspase-3 activation. Caspase-8, caspase-3, and broad caspase inhibitors, but not caspase-9 inhibitor, inhibited MMC-induced cell death in nonpretreated and IFN-pretreated cells. CONCLUSIONS. IFN-␣ and IFN-␥ enhance the susceptibility of HTFs to MMC-induced cell death through a Fas-mediated and a caspase-3-dependent pathway. Pretreatment with IFN primed HTFs to MMC, providing a potential means for initially slowing the healing response with IFN and subsequently terminating fibroblast activity through MMC-induced cell death. (Invest Ophthalmol Vis Sci