The Curvature, Collagen Network Structure, and Their Relationship to the Pressure-Induced Strain Response of the Human Lamina Cribrosa in Normal and Glaucoma Eyes.

The lamina cribrosa (LC) is a connective tissue in the optic nerve head (ONH). The objective of this study was to measure the curvature and collagen microstructure of the human LC, compare the effects of glaucoma and glaucoma optic nerve damage, and investigate the relationship between the structure and pressure-induced strain response of the LC in glaucoma eyes. Previously, the posterior scleral cups of 10 normal eyes and 16 diagnosed glaucoma eyes were subjected to inflation testing with second harmonic generation (SHG) imaging of the LC and digital volume correlation (DVC) to calculate the strain field. In this study, we applied a custom microstructural analysis algorithm to the maximum intensity projection of SHG images to measure features of the LC beam and pore network. We also estimated the LC curvatures from the anterior surface of the DVC-correlated LC volume. Results showed that the LC in glaucoma eyes had larger curvatures p≤0.03), a smaller average pore area (p = 0.001), greater beam tortuosity (p < 0.0001), and more isotropic beam structure (p = 0.01) than in normal eyes. The difference measured between glaucoma and normal eyes may indicate remodeling of the LC with glaucoma or baseline differences that contribute to the development of glaucomatous axonal damage.

Regional Gene Expression in the Retina, Optic Nerve Head, and Optic Nerve of Mice with Optic Nerve Crush and Experimental Glaucoma.

A major risk factor for glaucomatous optic neuropathy is the level of intraocular pressure (IOP), which can lead to retinal ganglion cell axon injury and cell death. The optic nerve has a rostral unmyelinated portion at the optic nerve head followed by a caudal myelinated region. The unmyelinated region is differentially susceptible to IOP-induced damage in rodent models and human glaucoma. While several studies have analyzed gene expression changes in the mouse optic nerve following optic nerve injury, few were designed to consider the regional gene expression differences that exist between these distinct areas. We performed bulk RNA-sequencing on the retina and separately micro-dissected unmyelinated and myelinated optic nerve regions from naïve C57BL/6 mice, mice after optic nerve crush, and mice with microbead-induced experimental glaucoma (total = 36). Gene expression patterns in the naïve unmyelinated optic nerve showed significant enrichment of the Wnt, Hippo, PI3K-Akt, and transforming growth factor ß pathways, as well as extracellular matrix-receptor and cell membrane signaling pathways, compared to the myelinated optic nerve and retina. Gene expression changes induced by both injuries were more extensive in the myelinated optic nerve than the unmyelinated region, and greater after nerve crush than glaucoma. Changes present three and fourteen days after injury largely subsided by six weeks. Gene markers of reactive astrocytes did not consistently differ between injury states. Overall, the transcriptomic phenotype of the mouse unmyelinated optic nerve was significantly different from immediately adjacent tissues, likely dominated by expression in astrocytes, whose junctional complexes are inherently important in responding to IOP elevation.

Toward a new definition of glaucomatous optic neuropathy for clinical research.

PURPOSE OF REVIEW: A process is ongoing to produce a definition of glaucomatous optic neuropathy (GON) using quantitative, objective data from structural and functional tests. At present, a common practice is to define GON by subjective features said to be 'characteristic' as judged by those experienced in glaucoma care. RECENT FINDINGS: An objective definition would standardize the comparison of clinical research results across studies, without precluding simultaneous use of idiosyncratic definitions in the same reports. To achieve this goal, expert opinion was solicited to reach optimal agreement on one or more consensus, GON definitions. An interactive period of online discussion by 176 international experts led to 110 responses in an online survey that narrowed possible definitional structures into testable criteria. SUMMARY: Two approaches to validation of one or more sets of criteria for definite and possible GON are ongoing. The general principles include definition for each eye individually, inclusion of a borderline category, no intraocular pressure criterion, and both structural and functional defects in appropriate physical locations. Each validation approach uses clinician diagnosis as a standard against which objective criteria are compared, with the initial approach using a three-level categorical scale, and the second approach using 0--100 scaling.

The effects of age on mitochondria, axonal transport, and axonal degeneration after chronic IOP elevation using a murine ocular explant model.

The purpose of this study was to compare younger and older mice after chronic intraocular pressure (IOP) elevation lasting up to 4 days with respect to mitochondrial density, structure, and movement, as well as axonal integrity, in an ex vivo explant model. We studied 2 transgenic mouse strains, both on a C57BL/6J background, one expressing yellow fluorescent protein (YFP) in selected axons and one expressing cyan fluorescent protein (CFP) in all mitochondria. Mice of 4 months or 14 months of age were exposed to chronic IOP by anterior chamber microbead injection for 14 h, 1, 3, or 4 days. The optic nerve head of globe--optic nerve explants were examined by laser scanning microscopy. Mitochondrial density, structure, and movement were quantified in the CFP explants, and axonal integrity was quantified in YFP explants. In control mice, there was a trend towards decreased mitochondrial density (# per mm2) with age when comparing younger to older, control mice, but this was not significant (1947 ±â€¯653 vs 1412 ±â€¯356; p = 0.19). Mitochondrial density decreased after IOP elevation, significantly, by 31%, in younger mice (p = 0.04) but trending towards a decrease, by 22%, in older mice (p = 0.82) compared to age matched controls. Mitochondrial mean size was not altered after chronic IOP elevation for 14 h or more (p ≥ 0.16). When assessing mitochondrial movement, in younger mice, 5% were mobile at any given time; 4% in the anterograde direction and 1% retrograde. In younger untreated tissue, only 75% of explants had moving mitochondria (mean = 15.8 moving/explant), while after glaucoma induction only 24% of explants had moving mitochondria (mean = 4.2 moving/explant; difference from control, p = 0.03). The distance mitochondria traveled in younger mice was unchanged after glaucoma exposure, but in older glaucoma explants the distance traveled was less than half of older controls (p < 0.0003). In younger mice, mitochondrial speed increased after 14 h of elevated IOP (p = 0.006); however, in older glaucoma explants, movement was actually slower than controls (p = 0.02). In RGC-YFP explants, axonal integrity declined significantly after 4 days of IOP elevation to a similar degree in both younger and older mice. Older mice underwent greater loss of mitochondrial movement with chronic IOP elevation than younger mice, but suffered similar short-term axonal fragmentation in C57BL/6J mice. These transgenic strains, studied in explants, permit observations of alterations in intracellular structure and organelle activity in experimental glaucoma.

Neuroprotection for glaucoma: Requirements for clinical translation.

Within the field of glaucoma research, neuroprotection is defined as slowing the functional loss in glaucoma by a mechanism independent of lowering of intraocular pressure. There is currently a great potential for research surrounding neuroprotection as it relates to glaucoma. Anatomical targets for neuroprotection should focus on upstream rather than downstream factors, and could include any part of the retinal ganglion cell, the glia, especially astrocytes or Muller cells, and vasculature. The great number of anatomical targets is exceeded only by the number of possible biochemical pathways and potential treatments. Successful treatment may be accomplished through the targeting of one or even a combination of multiple pathways. Once a treatment is shown effective in vitro, it should be evaluated in vivo with carefully chosen animal models and studied in sufficient numbers to detect statistically and clinically significant effects. Such a drug should have few systemic side effects and its delivery should be optimized so as to encourage compliance. There are still a multitude of possible screens available to test the efficacy of a neuroprotective drug and a single gold standard is ideal for the accurate assessment and comparison of new drugs. Future studies in neuroprotection should investigate the genetic component of the disease, novel pharmaceutical agents for new or known pathways, modulations of scleral biomechanics, and relation to research of other complex disorders of the central nervous system.

A mouse ocular explant model that enables the study of living optic nerve head events after acute and chronic intraocular pressure elevation: Focusing on retinal ganglion cell axons and mitochondria.

We developed an explant model of the mouse eye and optic nerve that facilitates the study of retinal ganglion cell axons and mitochondria in the living optic nerve head (ONH) in an ex vivo environment. Two transgenic mouse strains were used, one expressing yellow fluorescent protein in selected axons and a second strain expressing cyan fluorescent protein in all mitochondria. We viewed an explanted mouse eye and optic nerve by laser scanning microscopy at and behind the ONH, the site of glaucoma injury. Explants from previously untreated mice were studied with the intraocular pressure (IOP) set artificially at normal or elevated levels for several hours. Explants were also studied from eyes that had undergone chronic IOP elevation from 14 h to 6 weeks prior to ex vivo study. Image analysis in static images and video of individual mitochondria or axonal structure determined effects of acute and chronic IOP elevation. At normal IOP, fluorescent axonal structure was stable for up to 3 h under ex vivo conditions. After chronic IOP elevation, axonal integrity index values indicated fragmentation of axon structure in the ONH. In mice with fluorescent mitochondria, the normal density decreased with distance behind the ONH by 45% (p = 0.002, t-test). Density increased with prior chronic IOP elevation to 21,300 ± 4176 mitochondria/mm2 compared to control 16,110 ± 3159 mitochondria/mm2 (p = 0.025, t-test), but did not increase significantly after 4 h, acute IOP elevation (1.5% decrease in density, p = 0.83, t-test). Mean normal mitochondrial length of 2.3 ± 1.4 µm became 13% smaller after 4 h of IOP elevation ex vivo compared to baseline (p = 0.015, t-test, N-10). Normal mitochondrial speed of movement was significantly slower in the anterograde direction (towards the brain) than retrograde, but there were more mitochondria in motion and traveling longer lengths in anterograde direction. The percent of mitochondria in motion decreased by >50% with acute IOP increase to 30 mm Hg after 60 min. A new ocular explant model implemented with eyes from transgenic mice with fluorescent cellular components provided real time measurement of the early events in experimental glaucoma and quantitative outcomes for neuroprotection therapy experiments.

Scleral fibroblast response to experimental glaucoma in mice.

PURPOSE: To study the detailed cellular and molecular changes in the mouse sclera subjected to experimental glaucoma. METHODS: Three strains of mice underwent experimental bead-injection glaucoma and were euthanized at 3 days and 1, 3, and 6 weeks. Scleral protein expression was analyzed with liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS) using (16)O/(18)O labeling for quantification in 1- and 6-week tissues. Sclera protein samples were also analyzed with immunoblotting with specific antibodies to selected proteins. The proportion of proliferating scleral fibroblasts was quantified with Ki67 and 4',6-diamidino-2-phenylindole (DAPI) labeling, and selected proteins were studied with immunohistochemistry. RESULTS: Proteomic analysis showed increases in molecules involved in integrin-linked kinase signaling and actin cytoskeleton signaling pathways at 1 and 6 weeks after experimental glaucoma. The peripapillary scleral region had more fibroblasts than equatorial sclera (p=0.001, n=217, multivariable regression models). There was a sixfold increase in proliferating fibroblasts in the experimental glaucoma sclera at 1 week and a threefold rise at 3 and 6 weeks (p=0.0005, univariate regression). Immunoblots confirmed increases for myosin, spectrin, and actinin at 1 week after glaucoma. Thrombospondin-1 (TSP-1), HINT1, vimentin, actinin, and α-smooth muscle actin were increased according to immunohistochemistry. CONCLUSIONS: Scleral fibroblasts in experimental mouse glaucoma show increases in actin cytoskeleton and integrin-related signaling, increases in cell division, and features compatible with myofibroblast transition.

Changes in Anterior Segment Morphology and Predictors of Angle Widening after Laser Iridotomy in South Indian Eyes.

PURPOSE: To compare anterior segment optical coherence tomography (ASOCT) angle morphology before and after laser peripheral iridotomy (LPI) in a cohort of South Indian subjects with primary angle-closure suspect (PACS) or primary angle-closure/primary angle-closure glaucoma (PAC/PACG) and to examine baseline parameters associated with angle widening. DESIGN: Prospective observational study. PARTICIPANTS: A total of 244 subjects aged ≥30 years with PACS or PAC/PACG in at least 1 eye. METHODS: The ASOCT images and angle gonioscopic grades were analyzed for all subjects at baseline and 2 weeks after LPI. Multivariable linear and logistic regression models were used to determine predictors of angle widening (change in mean angle opening distance [AOD750]) and angle opening (all 4 quadrants with trabecular meshwork [TM] visible on gonioscopy after LPI). MAIN OUTCOME MEASURES: Change in ASOCT parameters with LPI and baseline predictors of angle widening. RESULTS: Laser peripheral iridotomy resulted in angle widening on ASOCT with significant increases in AOD750, angle recess area, and trabecular iris surface area (P < 0.05 for all). Gonioscopically, 44.7% of all subjects had open angles in all 4 quadrants after LPI, with a greater percentage of angles open in the PACS group compared with the PAC/PACG group (52.4% vs. 36.4%; P = 0.01). In multivariable regression analyses, greater postoperative angle widening as defined by change in AOD750 was associated with shorter baseline AOD750 and axial length, and greater baseline anterior chamber depth, iris curvature, and lens vault (P ≤ 0.002 for all). Gonioscopic angle opening after LPI was more common with wider baseline angle width (modified Shaffer grade) and lower cup-to-disc ratio (P < 0.001 for both). CONCLUSIONS: In a South Indian population with PACS or PAC/PACG, LPI results in significant anterior chamber angle widening seen on both ASOCT and gonioscopy, although some degree of persistent iridotrabecular contact was present in approximately half of PACS eyes and approximately two thirds of PAC/PACG eyes on gonioscopy. The greatest widening by ASOCT was observed in eyes with features most consistent with greater baseline pupillary block.

Subconjunctival Delivery of Dorzolamide-Loaded Poly(ether-anhydride) Microparticles Produces Sustained Lowering of Intraocular Pressure in Rabbits.

Topical medications that inhibit the enzyme carbonic anhydrase (CAI) are widely used to lower intraocular pressure in glaucoma; however, their clinical efficacy is limited by the requirement for multiple-daily dosing, as well as side effects such as blurred vision and discomfort on drop instillation. We developed a biodegradable polymer microparticle formulation of the CAI dorzolamide that produces sustained lowering of intraocular pressure after subconjunctival injection. Dorzolamide was ion paired with sodium dodecyl sulfate (SDS) and sodium oleate (SO) with 0.8% and 1.5% drug loading in poly(lactic-co-glycolic acid) (PLGA), respectively. Encapsulating dorzolamide into poly(ethylene glycol)-co-poly(sebacic acid) (PEG3-PSA) microparticles in the presence of triethylamine (TEA) resulted in 14.9% drug loading and drug release that occurred over 12 days in vitro. Subconjunctival injection of dorzolamide-PEG3-PSA microparticles (DPP) in Dutch belted rabbits reduced IOP as much as 4.0 ± 1.5 mmHg compared to untreated fellow eyes for 35 days. IOP reduction after injection of DPP microparticles was significant when compared to baseline untreated IOPs (P < 0.001); however, injection of blank microparticles (PEG3-PSA) did not affect IOP (P = 0.9). Microparticle injection was associated with transient clinical vascularity and inflammatory cell infiltration in conjunctiva on histological examination. Fluorescently labeled PEG3-PSA microparticles were detected for at least 42 days after injection, indicating that in vivo particle degradation is several-fold longer than in vitro degradation. Subconjunctival DPP microparticle delivery is a promising new platform for sustained intraocular pressure lowering in glaucoma.

Functional genomic screening identifies dual leucine zipper kinase as a key mediator of retinal ganglion cell death.

Glaucoma, a major cause of blindness worldwide, is a neurodegenerative optic neuropathy in which vision loss is caused by loss of retinal ganglion cells (RGCs). To better define the pathways mediating RGC death and identify targets for the development of neuroprotective drugs, we developed a high-throughput RNA interference screen with primary RGCs and used it to screen the full mouse kinome. The screen identified dual leucine zipper kinase (DLK) as a key neuroprotective target in RGCs. In cultured RGCs, DLK signaling is both necessary and sufficient for cell death. DLK undergoes robust posttranscriptional up-regulation in response to axonal injury in vitro and in vivo. Using a conditional knockout approach, we confirmed that DLK is required for RGC JNK activation and cell death in a rodent model of optic neuropathy. In addition, tozasertib, a small molecule protein kinase inhibitor with activity against DLK, protects RGCs from cell death in rodent glaucoma and traumatic optic neuropathy models. Together, our results establish a previously undescribed drug/drug target combination in glaucoma, identify an early marker of RGC injury, and provide a starting point for the development of more specific neuroprotective DLK inhibitors for the treatment of glaucoma, nonglaucomatous forms of optic neuropathy, and perhaps other CNS neurodegenerations.

Comparison of resident and glaucoma faculty practice patterns in the care of open-angle glaucoma.

BACKGROUND: Previous studies suggest there are large variations in adherence of ophthalmologists with the American Academy of Ophthalmology's Preferred Practice Patterns (PPPs). The purpose of this study was to compare rates of compliance with glaucoma care guidelines between resident and glaucoma faculty physicians at a single institution. METHODS: Charts of resident continuity clinic or glaucoma faculty patients with primary open angle glaucoma (POAG), ocular hypertension (OHTN), or suspicion of glaucoma were reviewed during the 2005-6 academic year. Performance within care measures specified by the 2005 PPP guidelines was compared between resident and faculty physicians using univariate and multivariable logistic regression models. RESULTS: 112 resident and 100 faculty charts were reviewed. The mean compliance rate for all 7 care measures for resident physicians was significantly lower than that of faculty physicians (78% vs. 96%, p < 0.001). As compared to glaucoma faculty, resident physicians were less likely to have documented 6 of the 7 individual care measures (p ≤ 0.001 for all); the exception was optic nerve (ON) description. In multivariable analyses, resident patients were more likely to have at least one undocumented care measure than faculty patients (OR = 10.1, 95% CI = 5.1 to 20.0, p < 0.001). Among resident patients, undocumented care measures were more common among patients with poorer visual acuity (VA) in the better eye. CONCLUSIONS: Though unmeasured differences in clinic structure and patient characteristics may have partially contributed to poorer resident performance, residents were more likely than faculty to omit PPP care measures and significantly underperformed faculty in global assessment of glaucoma care. Resident education should focus on integration of PPPs into residency training and monitoring of resident compliance with evidence-based guidelines.

Collagen structure and mechanical properties of the human sclera: analysis for the effects of age.

The objective of this study was to measure the collagen fiber structure and estimate the material properties of 7 human donor scleras, from age 53 to 91. The specimens were subjected to inflation testing, and the full-field displacement maps were measured by digital image correlation. After testing, the collagen fiber structure was mapped using wide-angle X-ray scattering. A specimen-specific inverse finite element method was applied to calculate the material properties of the collagen fibers and interfiber matrix by minimizing the difference between the experimental displacements and model predictions. Age effects on the fiber structure and material properties were estimated using multivariate models accounting for spatial autocorrelation. Older age was associated with a larger matrix stiffness (p = 0.001), a lower degree of fiber alignment in the peripapillary sclera (p = 0.01), and a lower mechanical anisotropy in the peripapillary sclera (p = 0.03).

Effects of age and diabetes on scleral stiffness.

The effects of diabetes on the collagen structure and material properties of the sclera are unknown but may be important to elucidate whether diabetes is a risk factor for major ocular diseases such as glaucoma. This study provides a quantitative assessment of the changes in scleral stiffness and collagen fiber alignment associated with diabetes. Posterior scleral shells from five diabetic donors and seven non-diabetic donors were pressurized to 30 mm Hg. Three-dimensional surface displacements were calculated during inflation testing using digital image correlation (DIC). After testing, each specimen was subjected to wide-angle X-ray scattering (WAXS) measurements of its collagen organization. Specimen-specific finite element models of the posterior scleras were generated from the experimentally measured geometry. An inverse finite element analysis was developed to determine the material properties of the specimens, i.e., matrix and fiber stiffness, by matching DIC-measured and finite element predicted displacement fields. Effects of age and diabetes on the degree of fiber alignment, matrix and collagen fiber stiffness, and mechanical anisotropy were estimated using mixed effects models accounting for spatial autocorrelation. Older age was associated with a lower degree of fiber alignment and larger matrix stiffness for both diabetic and non-diabetic scleras. However, the age-related increase in matrix stiffness was 87% larger in diabetic specimens compared to non-diabetic controls and diabetic scleras had a significantly larger matrix stiffness (p = 0.01). Older age was associated with a nearly significant increase in collagen fiber stiffness for diabetic specimens only (p = 0.06), as well as a decrease in mechanical anisotropy for non-diabetic scleras only (p = 0.04). The interaction between age and diabetes was not significant for all outcomes. This study suggests that the age-related increase in scleral stiffness is accelerated in eyes with diabetes, which may have important implications in glaucoma.

Global prevalence of glaucoma and projections of glaucoma burden through 2040: a systematic review and meta-analysis.

PURPOSE: Glaucoma is the leading cause of global irreversible blindness. Present estimates of global glaucoma prevalence are not up-to-date and focused mainly on European ancestry populations. We systematically examined the global prevalence of primary open-angle glaucoma (POAG) and primary angle-closure glaucoma (PACG), and projected the number of affected people in 2020 and 2040. DESIGN: Systematic review and meta-analysis. PARTICIPANTS: Data from 50 population-based studies (3770 POAG cases among 140,496 examined individuals and 786 PACG cases among 112 398 examined individuals). METHODS: We searched PubMed, Medline, and Web of Science for population-based studies of glaucoma prevalence published up to March 25, 2013. Hierarchical Bayesian approach was used to estimate the pooled glaucoma prevalence of the population aged 40-80 years along with 95% credible intervals (CrIs). Projections of glaucoma were estimated based on the United Nations World Population Prospects. Bayesian meta-regression models were performed to assess the association between the prevalence of POAG and the relevant factors. MAIN OUTCOME MEASURES: Prevalence and projection numbers of glaucoma cases. RESULTS: The global prevalence of glaucoma for population aged 40-80 years is 3.54% (95% CrI, 2.09-5.82). The prevalence of POAG is highest in Africa (4.20%; 95% CrI, 2.08-7.35), and the prevalence of PACG is highest in Asia (1.09%; 95% CrI, 0.43-2.32). In 2013, the number of people (aged 40-80 years) with glaucoma worldwide was estimated to be 64.3 million, increasing to 76.0 million in 2020 and 111.8 million in 2040. In the Bayesian meta-regression model, men were more likely to have POAG than women (odds ratio [OR], 1.36; 95% CrI, 1.23-1.52), and after adjusting for age, gender, habitation type, response rate, and year of study, people of African ancestry were more likely to have POAG than people of European ancestry (OR, 2.80; 95% CrI, 1.83-4.06), and people living in urban areas were more likely to have POAG than those in rural areas (OR, 1.58; 95% CrI, 1.19-2.04). CONCLUSIONS: The number of people with glaucoma worldwide will increase to 111.8 million in 2040, disproportionally affecting people residing in Asia and Africa. These estimates are important in guiding the designs of glaucoma screening, treatment, and related public health strategies.

Experimental scleral cross-linking increases glaucoma damage in a mouse model.

The purpose of this study was to assess the effect of a scleral cross-linking agent on susceptibility to glaucoma damage in a mouse model.CD1 mice underwent 3 subconjunctival injections of 0.5 M glyceraldehyde (GA) in 1 week, then had elevated intraocular pressure (IOP) induced by bead injection. Degree of cross-linking was measured by enzyme-linked immunosorbent assay (ELISA), scleral permeability was measured by fluorescence recovery after photobleaching (FRAP), and the mechanical effects of GA exposure were measured by inflation testing. Control mice had buffer injection or no injection in 2 separate glaucoma experiments. IOP was monitored by Tonolab and retinal ganglion cell (RGC) loss was measured by histological axon counting. To rule out undesirable effects of GA, we performed electroretinography and detailed histology of the retina. GA exposure had no detectable effects on RGC number, retinal structure or function either histologically or electrophysiologically. GA increased cross-linking of sclera by 37% in an ELISA assay, decreased scleral permeability (FRAP, p = 0.001), and produced a steeper pressure-strain behavior by in vitro inflation testing. In two experimental glaucoma experiments, GA-treated eyes had greater RGC axon loss from elevated IOP than either buffer-injected or control eyes, controlling for level of IOP exposure over time (p = 0.01, and 0.049, multivariable regression analyses). This is the first report that experimental alteration of the sclera, by cross-linking, increases susceptibility to RGC damage in mice.

Susceptibility to glaucoma damage related to age and connective tissue mutations in mice.

The purpose of this research was to study the effects of age and genetic alterations in key connective tissue proteins on susceptibility to experimental glaucoma in mice. We used mice haploinsufficient in the elastin gene (EH) and mice without both alleles of the fibromodulin gene (FM KO) and their wild type (WT) littermates of B6 and CD1 strains, respectively. FM KO mice were tested at two ages: 2 months and 12 months. Intraocular pressure (IOP) was measured by Tonolab tonometer, axial lengths and widths measured by digital caliper post-enucleation, and chronic glaucoma damage was measured using a bead injection model and optic nerve axon counts. IOP in EH mice was not significantly different from WT, but FM KO were slightly lower than their controls (p = 0.04). Loss of retinal ganglion cell (RGC) axons was somewhat, but not significantly greater in young EH and younger or older FM KO strains than in age-matched controls (p = 0.48, 0.34, 0.20, respectively, multivariable regression adjusting for IOP exposure). Older CD1 mice lost significantly more RGC axons than younger CD1 (p = 0.01, multivariable regression). The CD1 mouse strain showed age-dependence of experimental glaucoma damage to RGC in the opposite, and more expected, direction than in B6 mice in which older mice are more resistant to damage. Genetic alteration in two genes that are constituents of sclera, fibromodulin and elastin do not significantly affect RGC loss.

Long-term Remodeling Response in the Lamina Cribrosa Years after Intraocular Pressure Lowering by Suturelysis after Trabeculectomy.

OBJECTIVE: To measure the remodeling of the lamina cribrosa (LC) years after intraocular pressure (IOP) lowering by suturelysis. DESIGN: Cohort study. PARTICIPANTS: Glaucoma patients were imaged 20 minutes after laser suturelysis after trabeculectomy surgery and at their follow-up appointment 1 to 4 years later (16 image pairs; 15 persons). INTERVENTION: Noninvasive OCT imaging of the eye. MAIN OUTCOME MEASURES: Deformation calculated by correlating OCT scans of the LC immediately after IOP lowering by suturelysis and those acquired years later (defined as remodeling strain). RESULTS: The LC anterior border moved 60.9 ± 54.6 µm into the eye (P = 0.0007), and the LC exhibited regions of large local stretch in the anterior-posterior direction on long-term, maintained IOP lowering, resulting in a mean anterior-posterior remodeling strain of 14.0% ± 21.3% (P = 0.02). This strain and the LC border movement was 14 times and 124 times larger, respectively, than the direct response to IOP lowering by suturelysis. A larger anterior LC border movement was associated with greater mean anterior-posterior remodeling strain (P = 0.004). A thinner retinal nerve fiber layer at suturelysis was also associated with greater mean anterior-posterior remodeling strain at follow-up (P = 0.05). Worsening visual field indexes during follow-up were associated with a greater mean circumferential remodeling strain (P = 0.02), due to regions of large local circumferential stretch of the LC. Eyes with a more compliant LC torsional shear strain response at lysis were associated with worse mean deviation at follow-up (P = 0.03). CONCLUSIONS: Strains and LC border position changes measured years after IOP lowering are far larger than the immediate response to IOP lowering and indicate dramatic remodeling of the LC anatomical structure caused by IOP lowering and glaucoma progression. The remodeling strains indicate substantial local stretch in the anterior-posterior direction and are associated with movement of the LC anterior border into the eye. Eyes with greater direct strain response to IOP lowering, greater glaucoma damage at suturelysis, and greater worsening of visual field at follow-up experienced greater remodeling. TRIAL REGISTRATION: ClinicalTrials.gov Identifier: NCT03267849. FINANCIAL DISCLOSURE(S): Proprietary or commercial disclosure may be found in the Footnotes and Disclosures at the end of this article.

A Noninvasive Clinical Method to Measure in Vivo Mechanical Strains of the Lamina Cribrosa by OCT.

Objective: To measure mechanical strain of the lamina cribrosa (LC) after intraocular pressure (IOP) change produced 1 week after a change in glaucoma medication. Design: Cohort study. Participants: Adult glaucoma patients (23 eyes, 15 patients) prescribed a change in IOP-lowering medication. Intervention: Noninvasive OCT imaging of the eye. Main Outcome Measures: Deformation calculated by digital volume correlation of OCT scans of the LC before and after IOP lowering by medication. Results: Among 23 eyes, 17 eyes of 12 persons had IOP lowering ≥ 3 mmHg (reduced IOP group) with tensile anterior-posterior Ezz strain = 1.0% ± 1.1% (P = 0.003) and compressive radial strain (Err) = -0.3% ± 0.5% (P = 0.012; random effects models accounting inclusion of both eyes in some persons). Maximum in-plane principal (tensile) strain and maximum shear strain in the reduced-IOP group were as follows: Emax = 1.7% ± 1.0% and Γmax = 1.4% ± 0.7%, respectively (both P < 0.0001 vs. zero). Reduced-IOP group strains Emax and Γmax were significantly larger with greater % IOP decrease (P < 0.0001 and P < 0.0001, respectively). The compliances of the Ezz, Emax, and Γmax strain responses, defined as strain normalized by the IOP decrease, were larger with more abnormal perimetric mean deviation or visual field index values (all P ≤ 0.02). Strains were unrelated to age (all P ≥ 0.088). In reduced-IOP eyes, mean LC anterior border posterior movement was only 2.05 µm posteriorly (P = 0.052) and not related to % IOP change (P = 0.94, random effects models). Only Err was significantly related to anterior lamina depth change, becoming more negative with greater posterior LC border change (P = 0.015). Conclusions: Lamina cribrosa mechanical strains can be effectively measured by changes in eye drop medication using OCT and are related to degree of visual function loss in glaucoma. Financial Disclosures: Proprietary or commercial disclosure may be found in the Footnotes and Disclosures at the end of this article.

Optical Coherence Tomographic Optic Nerve Head Morphology in Myopia III: The Exposed Neural Canal Region in Healthy Eyes-Implications for High Myopia.

PURPOSE: To determine the prevalence and magnitude of optical coherence tomography (OCT) exposed neural canal (ENC), externally oblique choroidal border tissue (EOCBT), and exposed scleral flange (ESF) regions in 362 non-highly myopic (spherical equivalent -6.00 to 5.75 diopters) eyes of 362 healthy subjects. DESIGN: Cross-sectional study. METHODS: After OCT optic nerve head (ONH) imaging, Bruch membrane opening (BMO), the anterior scleral canal opening (ASCO), and the scleral flange opening (SFO) were manually segmented. BMO, ASCO, and SFO points were projected to the BMO reference plane. The direction and magnitude of BMO/ASCO offset as well as the magnitude of ENC, EOCBT, and ESF was calculated within 30° sectors relative to the foveal-BMO axis. Hi-ESF eyes demonstrated an ESF ≥100 µm in at least 1 sector. Sectoral peri-neural canal choroidal thickness (pNC-CT) was measured and correlations between the magnitude of sectoral ESF and proportional pNC-CT were assessed. RESULTS: Seventy-three Hi-ESF (20.2%) and 289 non-Hi-ESF eyes (79.8%) were identified. BMO/ASCO offset as well as ENC, EOCBT, and ESF prevalence and magnitude were greatest inferior temporally where the pNC-CT was thinnest. Among Hi-ESF eyes, the magnitude of each ENC region correlated with the BMO/ASCO offset magnitude, and the sectors with the longest ESF correlated with the sectors with proportionally thinnest pNC-CT. CONCLUSIONS: ONH BMO/ASCO offset, either as a cause or result of ONH neural canal remodeling, corresponds with the sectoral location of maximum ESF and minimum pNC-CT in non-highly myopic eyes. Longitudinal studies to characterize the development and clinical implications of ENC Hi-ESF regions in non-highly myopic and highly myopic eyes are indicated.