Individual-Specific Modeling of Rat Optic Nerve Head Biomechanics in Glaucoma.

Glaucoma is the second leading cause of blindness worldwide and is characterized by the death of retinal ganglion cells (RGCs), the cells that send vision information to the brain. Their axons exit the eye at the optic nerve head (ONH), the main site of damage in glaucoma. The importance of biomechanics in glaucoma is indicated by the fact that elevated intraocular pressure (IOP) is a causative risk factor for the disease. However, exactly how biomechanical insult leads to RGC death is not understood. Although rat models are widely used to study glaucoma, their ONH biomechanics have not been characterized in depth. Therefore, we aimed to do so through finite element (FE) modeling. Utilizing our previously described method, we constructed and analyzed ONH models with individual-specific geometry in which the sclera was modeled as a matrix reinforced with collagen fibers. We developed eight sets of scleral material parameters based on results from our previous inverse FE study and used them to simulate the effects of elevated IOP in eight model variants of each of seven rat ONHs. Within the optic nerve, highest strains were seen inferiorly, a pattern that was consistent across model geometries and model variants. In addition, changing the collagen fiber direction to be circumferential within the peripapillary sclera resulted in more pronounced decreases in strain than changing scleral stiffness. The results from this study can be used to interpret data from rat glaucoma studies to learn more about how biomechanics affects RGC pathogenesis in glaucoma.

Differential Effects of Aging in the Macular Retinal Layers, Neuroretinal Rim, and Peripapillary Retinal Nerve Fiber Layer.

PURPOSE: We determined the differential aging effects of the inner 6 layers of the macula in contrast to the minimum neuroretinal rim width (MRW) and peripapillary retinal nerve fiber layer (RNFL) thickness. DESIGN: Cross-sectional, multicenter study. PARTICIPANTS: An approximately equal number of white subjects with a normal ocular and visual field examination in each decade group from 20 to 90 years. METHODS: OCT of the macula, optic nerve head, and peripapillary retina. MAIN OUTCOME MEASURES: Sectoral measurements of the inner 6 layers of the macula; age-related decline of each of these layers; strength of the associations with age of the macular parameters, MRW, and peripapillary RNFL thickness; and association between ganglion cell layer (GCL) thickness and MRW and peripapillary RNFL thickness. RESULTS: The study sample comprised 1 eye of 246 subjects with a median (range) age of 52.9 (19.8-87.3) years. Of the 6 layers, there was a statistically significant decline with age of only the GCL, inner plexiform layer, and inner nuclear layer thickness with rates of -0.11 µm/year, -0.07 µm/year, and -0.03 µm/year, respectively. These rates corresponded to 2.82%, 2.10%, and 0.78% loss per decade, respectively, and were generally uniform across sectors. The rate of loss of MRW and peripapillary RNFL thickness was -1.22 µm/year and -0.20 µm/year, corresponding to 3.75% and 2.03% loss per decade. However, the association of GCL thickness change with age (R2 = 0.28) was approximately twice that of MRW and RNFL thickness (R2 = 0.14 for each). CONCLUSIONS: In concordance with histopathologic studies showing age-related loss of retinal ganglion cell axons, we showed a significant decline in GCL thickness, as well as MRW and peripapillary RNFL thickness. The stronger relationship between aging and GCL thickness compared with the rim or peripapillary RNFL may indicate that GCL thickness could be better suited to measure progression of structural glaucomatous loss.

A Methodology for Individual-Specific Modeling of Rat Optic Nerve Head Biomechanics in Glaucoma.

Glaucoma is the leading cause of irreversible blindness and involves the death of retinal ganglion cells (RGCs). Although biomechanics likely contributes to axonal injury within the optic nerve head (ONH), leading to RGC death, the pathways by which this occurs are not well understood. While rat models of glaucoma are well-suited for mechanistic studies, the anatomy of the rat ONH is different from the human, and the resulting differences in biomechanics have not been characterized. The aim of this study is to describe a methodology for building individual-specific finite element (FE) models of rat ONHs. This method was used to build three rat ONH FE models and compute the biomechanical environment within these ONHs. Initial results show that rat ONH strains are larger and more asymmetric than those seen in human ONH modeling studies. This method provides a framework for building additional models of normotensive and glaucomatous rat ONHs. Comparing model strain patterns with patterns of cellular response seen in studies using rat glaucoma models will help us to learn more about the link between biomechanics and glaucomatous cell death, which in turn may drive the development of novel therapies for glaucoma.

Biomechanical aspects of axonal damage in glaucoma: A brief review.

The biomechanical environment within the optic nerve head (ONH) is complex and is likely directly involved in the loss of retinal ganglion cells (RGCs) in glaucoma. Unfortunately, our understanding of this process is poor. Here we describe factors that influence ONH biomechanics, including ONH connective tissue microarchitecture and anatomy; intraocular pressure (IOP); and cerebrospinal fluid pressure (CSFp). We note that connective tissue factors can vary significantly from one individual to the next, as well as regionally within an eye, and that the understanding of ONH biomechanics is hindered by anatomical differences between small-animal models of glaucoma (rats and mice) and humans. Other challenges of using animal models of glaucoma to study the role of biomechanics include the complexity of assessing the degree of glaucomatous progression; and inadequate tools for monitoring and consistently elevating IOP in animal models. We conclude with a consideration of important open research questions/challenges in this area, including: (i) Creating a systems biology description of the ONH; (ii) addressing the role of astrocyte connective tissue remodeling and reactivity in glaucoma; (iii) providing a better characterization of ONH astrocytes and non-astrocytic constituent cells; (iv) better understanding the role of ONH astrocyte phagocytosis, proliferation and death; (v) collecting gene expression and phenotype data on a larger, more coordinated scale; and (vi) developing an implantable IOP sensor.

Comparing three different modes of electroretinography in experimental glaucoma: diagnostic performance and correlation to structure.

PURPOSE: To compare diagnostic performance and structure-function correlations of multifocal electroretinogram (mfERG), full-field flash ERG (ff-ERG) photopic negative response (PhNR) and transient pattern-reversal ERG (PERG) in a non-human primate (NHP) model of experimental glaucoma (EG). METHODS: At baseline and after induction of chronic unilateral IOP elevation, 43 NHP had alternating weekly recordings of retinal nerve fiber layer thickness (RNFLT) by spectral domain OCT (Spectralis) and retinal function by mfERG (7F slow-sequence stimulus, VERIS), ff-ERG (red 0.42 log cd-s/m2 flashes on blue 30 scotopic cd/m2 background, LKC UTAS-E3000), and PERG (0.8° checks, 99% contrast, 100 cd/m2 mean, 5 reversals/s, VERIS). All NHP were followed at least until HRT-confirmed optic nerve head posterior deformation, most to later stages. mfERG responses were filtered into low- and high-frequency components (LFC, HFC, >75 Hz). Peak-to-trough amplitudes of LFC features (N1, P1, N2) and HFC RMS amplitudes were measured and ratios calculated for HFC:P1 and N2:P1. ff-ERG parameters included A-wave (at 10 ms), B-wave (trough-to-peak) and PhNR (baseline-to-trough) amplitudes as well as PhNR:B-wave ratio. PERG parameters included P50 and N95 amplitudes as well as N95:P50 ratio and N95 slope. Diagnostic performance of retinal function parameters was compared using the area under the receiver operating characteristic curve (A-ROC) to discriminate between EG and control eyes. Correlations to RNFLT were compared using Steiger's test. RESULTS: Study duration was 15 ± 8 months. At final follow-up, structural damage in EG eyes measured by RNFLT ranged from 9% above baseline (BL) to 58% below BL; 29/43 EG eyes (67%) and 0/43 of the fellow control eyes exhibited significant (>7%) loss of RNFLT from BL. Using raw parameter values, the largest A-ROC findings for mfERG were: HFC (0.82) and HFC:P1 (0.90); for ff-ERG: PhNR (0.90) and PhNR:B-wave (0.88) and for PERG: P50 (0.64) and N95 (0.61). A-ROC increased when data were expressed as % change from BL, but the pattern of results persisted. At 95% specificity, the diagnostic sensitivity of mfERG HFC:P1 ratio was best, followed by PhNR and PERG. The correlation to RNFLT was stronger for mfERG HFC (R = 0.65) than for PhNR (R = 0.59) or PERG N95 (R = 0.36), (p = 0.20, p = 0.0006, respectively). The PhNR flagged a few EG eyes at the final time point that had not been flagged by mfERG HFC or PERG. CONCLUSIONS: Diagnostic performance and structure-function correlation were strongest for mfERG HFC as compared with ff-ERG PhNR or PERG in NHP EG.

Expansions of the neurovascular scleral canal and contained optic nerve occur early in the hypertonic saline rat experimental glaucoma model.

PURPOSE: To characterize early optic nerve head (ONH) structural change in rat experimental glaucoma (EG). METHODS: Unilateral intraocular pressure (IOP) elevation was induced in Brown Norway rats by hypertonic saline injection into the episcleral veins and animals were sacrificed 4 weeks later by perfusion fixation. Optic nerve cross-sections were graded from 1 (normal) to 5 (extensive injury) by 5 masked observers. ONHs with peripapillary retina and sclera were embedded, serial sectioned, 3-D reconstructed, delineated, and quantified. Overall and animal-specific EG versus Control eye ONH parameter differences were assessed globally and regionally by linear mixed effect models with significance criteria adjusted for multiple comparisons. RESULTS: Expansions of the optic nerve and surrounding anterior scleral canal opening achieved statistical significance overall (p < 0.0022), and in 7 of 8 EG eyes (p < 0.005). In at least 5 EG eyes, significant expansions (p < 0.005) in Bruch's membrane opening (BMO) (range 3-10%), the anterior and posterior scleral canal openings (8-21% and 5-21%, respectively), and the optic nerve at the anterior and posterior scleral canal openings (11-30% and 8-41%, respectively) were detected. Optic nerve expansion was greatest within the superior and inferior quadrants. Optic nerve expansion at the posterior scleral canal opening was significantly correlated to optic nerve damage (R = 0.768, p = 0.042). CONCLUSION: In the rat ONH, the optic nerve and surrounding BMO and neurovascular scleral canal expand early in their response to chronic experimental IOP elevation. These findings provide phenotypic landmarks and imaging targets for detecting the development of experimental glaucomatous optic neuropathy in the rat eye.

Bruch's Membrane Opening Minimum Rim Width and Retinal Nerve Fiber Layer Thickness in a Normal White Population: A Multicenter Study.

PURPOSE: Conventional optic disc margin-based neuroretinal rim measurements lack a solid anatomic and geometrical basis. An optical coherence tomography (OCT) index, Bruch's membrane opening minimum rim width (BMO-MRW), addresses these deficiencies and has higher diagnostic accuracy for glaucoma. We characterized BMO-MRW and peripapillary retinal nerve fiber layer thickness (RNFLT) in a normal population. DESIGN: Multicenter cross-sectional study. PARTICIPANTS: Normal white subjects. METHODS: An approximately equal number of subjects in each decade group (20-90 years of age) was enrolled in 5 centers. Subjects had normal ocular and visual field examination results. We obtained OCT images of the optic nerve head (24 radial scans) and peripapillary retina (1 circular scan). The angle between the fovea and BMO center (FoBMO angle), relative to the horizontal axis of the image frame, was first determined and all scans were acquired and analyzed relative to this eye-specific FoBMO axis. Variation in BMO-MRW and RNFLT was analyzed with respect to age, sector, and BMO shape. MAIN OUTCOME MEASURES: Age-related decline and between-subject variability in BMO-MRW and RNFLT. RESULTS: There were 246 eyes of 246 subjects with a median age of 52.9 years (range, 19.8-87.3 years). The median FoBMO angle was -6.7° (range, 2.5° to -17.5°). The BMO was predominantly vertically oval with a median area of 1.74 mm(2) (range, 1.05-3.40 mm(2)). Neither FoBMO angle nor BMO area was associated with age or axial length. Both global mean BMO-MRW and RNFLT declined with age at a rate of -1.34 µm/year and -0.21 µm/year, equivalent to 4.0% and 2.1% loss per decade of life, respectively. Sectorially, the most rapid decrease occurred inferiorly and the least temporally; however, the age association was always stronger with BMO-MRW than with RNFLT. There was a modest relationship between mean global BMO-MRW and RNFLT (r = 0.35), whereas sectorially the relationship ranged from moderate (r = 0.45, inferotemporal) to nonexistent (r = 0.01, temporal). CONCLUSIONS: There was significant age-related loss of BMO-MRW in healthy subjects and notable differences between BMO-MRW and RNFLT in their relationship with age and between each other. Adjusting BMO-MRW and RNFLT for age and sector is important in ensuring optimal diagnostics for glaucoma.

The non-human primate experimental glaucoma model.

The purpose of this report is to summarize the current strengths and weaknesses of the non-human primate (NHP) experimental glaucoma (EG) model through sections devoted to its history, methods, important findings, alternative optic neuropathy models and future directions. NHP EG has become well established for studying human glaucoma in part because the NHP optic nerve head (ONH) shares a close anatomic association with the human ONH and because it provides the only means of systematically studying the very earliest visual system responses to chronic intraocular pressure (IOP) elevation, i.e. the conversion from ocular hypertension to glaucomatous damage. However, NHPs are impractical for studies that require large animal numbers, demonstrate spontaneous glaucoma only rarely, do not currently provide a model of the neuropathy at normal levels of IOP, and cannot easily be genetically manipulated, except through tissue-specific, viral vectors. The goal of this summary is to direct NHP EG and non-NHP EG investigators to the previous, current and future accomplishment of clinically relevant knowledge in this model.

Rat optic nerve head anatomy within 3D histomorphometric reconstructions of normal control eyes.

The purpose of this study is to three-dimensionally (3D) characterize the principal macroscopic and microscopic relationships within the rat optic nerve head (ONH) and quantify them in normal control eyes. Perfusion-fixed, trephinated ONH from 8 normal control eyes of 8 Brown Norway Rats were 3D histomorphometrically reconstructed, visualized, delineated and parameterized. The rat ONH consists of 2 scleral openings, (a superior neurovascular and inferior arterial) separated by a thin connective tissue strip we have termed the "scleral sling". Within the superior opening, the nerve abuts a prominent extension of Bruch's Membrane (BM) superiorly and is surrounded by a vascular plexus, as it passes through the sclera, that is a continuous from the choroid into and through the dural sheath and contains the central retinal vein (CRV), (inferiorly). The inferior scleral opening contains the central retinal artery and three long posterior ciliary arteries which obliquely pass through the sclera to obtain the choroid. Bruch's Membrane Opening (BMO) is irregular and vertically elongated, enclosing the nerve (superiorly) and CRV and CRA (inferiorly). Overall mean BMO Depth, BMO Area, Choroidal Thickness and peripapillary Scleral Thickness were 29 µm, 56.5 × 10(3) µm(2), 57 µm and 104 µm respectively. Mean anterior scleral canal opening (ASCO) and posterior scleral canal opening (PSCO) radii were 201 ± 15 µm and 204 ± 16 µm, respectively. Mean optic nerve area at the ASCO and PSCO were 46.3 × 10(3)±4.4 × 10(3) µm(2) and 44.1 × 10(3)±4.5 × 10(3) µm(2) respectively. In conclusion, the 3D complexity of the rat ONH and the extent to which it differs from the primate have been under-appreciated within previous 2D studies. Properly understood, these anatomic differences may provide new insights into the relative susceptibilities of the rat and primate ONH to elevated intraocular pressure.

The morphological difference between glaucoma and other optic neuropathies.

The clinical phenomenon of cupping has 2 principal pathophysiologic components in all optic neuropathies: prelaminar thinning and laminar deformation. We define prelaminar thinning to be the portion of cup enlargement that results from thinning of the prelaminar tissues due to physical compression and/or loss of retinal ganglion cell axons. We define laminar deformation or laminar cupping to be the portion of cup enlargement that results from permanent intraocular pressure (IOP)-induced deformation of the lamina cribrosa and peripapillary scleral connective tissues after damage and/or remodeling. We propose that the defining phenomenon of glaucomatous cupping is deformation and/or remodeling of the neural and connective tissues of the optic nerve head (ONH), which is governed by the distribution of IOP-related connective tissue stress and strain, regardless of the mechanism of insult or the level of IOP at which deformation and/or remodeling occurs. In other words, "glaucomatous cupping" is the term clinicians use to describe the clinical appearance and behavior the ONH assumes as its neural and connective tissues deform, remodel, or mechanically fail: 1) in a pattern and 2) by the several pathophysiologic processes governed by IOP-related connective tissue stress and strain. ONH biomechanics explains why a given ONH will demonstrate a certain form of "cupping" and at what level of IOP that might happen. Animal models are allowing us to tease apart the important components of cupping in IOP-related and non-IOP-related forms of optic neuropathy. A paradigm change in spectral domain optical coherence tomography ONH, retinal nerve fiber layer, and macular imaging should improve our ability to phenotype the ocular manifestations of many forms of damage to the visual system including glaucoma.

Retrolaminar Demyelination of Structurally Intact Axons in Nonhuman Primate Experimental Glaucoma.

Purpose: To determine if structurally intact, retrolaminar optic nerve (RON) axons are demyelinated in nonhuman primate (NHP) experimental glaucoma (EG). Methods: Unilateral EG NHPs (n = 3) were perfusion fixed, EG and control eyes were enucleated, and foveal Bruch's membrane opening (FoBMO) 30° sectoral axon counts were estimated. Optic nerve heads were trephined; serial vibratome sections (VSs) were imaged and colocalized to a fundus photograph establishing their FoBMO location. The peripheral neural canal region within n = 5 EG versus control eye VS comparisons was targeted for scanning block-face electron microscopic reconstruction (SBEMR) using micro-computed tomographic reconstructions (µCTRs) of each VS. Posterior laminar beams within each µCTR were segmented, allowing a best-fit posterior laminar surface (PLS) to be colocalized into its respective SBEMR. Within each SBEMR, up to 300 axons were randomly traced until they ended (nonintact) or left the block (intact). For each intact axon, myelin onset was identified and myelin onset distance (MOD) was measured relative to the PLS. For each EG versus control SBEMR comparison, survival analyses compared EG and control MOD. Results: MOD calculations were successful in three EG and five control eye SBEMRs. Within each SBEMR comparison, EG versus control eye axon loss was -32.9%, -8.3%, and -15.2% (respectively), and MOD was increased in the EG versus control SBEMR (P < 0.0001 for each EG versus control SBEMR comparison). When data from all three EG eye SBEMRs were compared to all five control eye SBEMRs, MOD was increased within the EG eyes. Conclusions: Structurally intact, RON axons are demyelinated in NHP early to moderate EG. Studies to determine their functional status are indicated.

OCT Optic Nerve Head Morphology in Myopia IV: Neural Canal Scleral Flange Remodeling in Highly Myopic Eyes.

PURPOSE: To compare the prevalence, location and magnitude of optic nerve head (ONH) OCT-detected, exposed neural canal (ENC), externally oblique choroidal border tissue (EOCBT) and exposed scleral flange (ESF) regions in 122 highly myopic (Hi-Myo) versus 362 nonhighly myopic healthy (Non-Hi-Myo-Healthy) eyes. DESIGN: Cross-sectional study. METHODS: After OCT radial B-scan, ONH imaging, Bruch's membrane opening (BMO), the anterior scleral canal opening (ASCO), and the scleral flange opening (SFO) were manually segmented in each B-scan and projected to BMO reference plane. The direction and magnitude of BMO/ASCO offset and BMO/SFO offset as well as the location and magnitude of ENC, EOCBT and ESF regions, perineural canal (pNC) retinal nerve fiber layer thickness (RNFLT) and pNC choroidal thickness (CT) were calculated within 30° sectors relative to the Foveal-BMO (FoBMO) axis. Hi-ESF eyes were defined to be those with an ESF region ≥100 µms in at least 1 sector. RESULTS: Hi-Myo eyes more frequently demonstrated Hi-ESF regions (87/122) than Non-Hi-myo-Healthy eyes (73/362) and contained significantly larger ENC, EOCBT, and ESF regions (P < .001) which were greatest in magnitude and prevalence within the inferior-temporal FoBMO sectors where Hi-Myo pNC-RNFLT and pNCCT were thinnest. BMO/ASCO offset and the BMO/SFO offset were both significantly increased (P < .001) in the Hi-Myo eyes, with the latter demonstrating a greater increase. CONCLUSIONS: ENC region tissue remodeling that includes the scleral flange is enhanced in Hi-Myo compared to Non-Hi-Myo-Healthy eyes. Longitudinal studies are necessary to determine whether the presence of an ENC region influences ONH susceptibility to aging and/or glaucoma.

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.

Enhanced detection of open-angle glaucoma with an anatomically accurate optical coherence tomography-derived neuroretinal rim parameter.

OBJECTIVE: Neuroretinal rim assessment based on the clinical optic disc margin (DM) lacks a sound anatomic basis for 2 reasons: (1) The DM is not reliable as the outer border of rim tissue because of clinically and photographically invisible extensions of Bruch's membrane (BM) inside the DM and (2) nonaccountability of rim tissue orientation in the optic nerve head (ONH). The BM opening-minimum rim width (BMO-MRW) is a parameter that quantifies the rim from its true anatomic outer border, BMO, and accounts for its variable orientation. We report the diagnostic capability of BMO-MRW. DESIGN: Case control. PARTICIPANTS: Patients with open-angle glaucoma (n = 107) and healthy controls (n = 48). METHODS: Spectral-domain optical coherence tomography (SD-OCT) with 24 radial and 1 circumpapillary B-scans, centered on the ONH, and confocal scanning laser tomography (CSLT) were performed. The internal limiting membrane (ILM) and BMO were manually segmented in each radial B-scan. Three SD-OCT parameters were computed globally and sectorally: (1) circumpapillary retinal nerve fiber layer thickness (RNFLT); (2) BMO-horizontal rim width (BMO-HRW), the distance between BMO and ILM in the BMO reference plane; and (3) BMO-MRW, the minimum distance between BMO and ILM. Moorfields Regression Analysis (MRA) with CLST was performed globally and sectorally to yield MRA1 and MRA2, where "borderline" was classified as normal and abnormal, respectively. MAIN OUTCOME MEASURES: Sensitivity, specificity, and likelihood ratios (LRs) for positive and negative test results (LR+/LR-). RESULTS: The median (interquartile range) age and mean deviation of patients and controls were 69.9 (64.3-76.9) and 65.0 (58.1-74.3) years and -3.92 (-7.87 to -1.62) and 0.33 (-0.32 to 0.98) dB, respectively. Globally, BMO-MRW yielded better diagnostic performance than the other parameters. At 95% specificity, the sensitivity of RNFLT, BMO-HRW, and BMO-MRW was 70%, 51%, and 81%, respectively. The corresponding LR+/LR- was 14.0/0.3, 10.2/0.5, and 16.2/0.2. Sectorally, at 95% specificity, the sensitivity of RNFLT ranged from 31% to 59%, of BMO-HRW ranged from 35% to 64%, and of BMO-MRW ranged from 54% to 79%. Globally and in all sectors, BMO-MRW performed better than MRA1 or MRA2. CONCLUSIONS: The higher sensitivity at 95% specificity in early glaucoma of BMO-MRW compared with current BMO methods is significant, indicating a new structural marker for the detection and risk profiling of glaucoma.

Asymmetry of Peripapillary Retinal Blood Vessel and Retinal Nerve Fiber Layer Thickness Between Healthy Right and Left Eyes.

Purpose: The purpose of this study was to determine if there is asymmetry in retinal blood vessel (RBV) position and thickness between right and left eyes (R-L) and evaluate whether R-L asymmetry in RBV thickness is related to R-L asymmetry of retinal nerve fiber layer thickness (RNFLT). Methods: We analyzed peripapillary circle scan optical coherence tomography (OCT) examinations from healthy White subjects to measure RNFLT and RBV thickness and position relative to the fovea to Bruch's membrane opening axis, for all visible RBV. The R-L asymmetries of RNFLT and RBV thickness were computed for each A-scan. Four major vessels (superior temporal artery [STA] and superior temporal vein [STV], inferior temporal artery [ITA], and vein [ITV]) were identified using infrared images. Results: We included 219 individuals. The mean (standard deviation) number of RBV measured per eye was 15.0 (SD = 2.2). The position of the STV and STA was more superior in left eyes than in right eyes, by 2.4 degrees and 3.7 degrees, respectively (P < 0.01). There was no region with significant R-L asymmetry in RBV thickness. RNFLT was thicker in right eyes in the temporal superior region and thicker in left eyes in the superior and nasal superior regions, with the asymmetry profile resembling in a "W" shape. This shape was also present in post hoc analyses in two different populations. The R-L asymmetries of RBV and RNFLT at each A-scan were not significantly associated (P = 0.37). Conclusions: There is little R-L asymmetry in RBV, and it is not related to RNFLT asymmetry. This study suggests that R-L RNFLT asymmetry is due to factors other than RBV.

OCT Optic Nerve Head Morphology in Myopia II: Peri-Neural Canal Scleral Bowing and Choroidal Thickness in High Myopia-An American Ophthalmological Society Thesis.

PURPOSE: To use optical coherence tomography (OCT) to characterize optic nerve head (ONH) peri-neural canal (pNC) scleral bowing (pNC-SB) and pNC choroidal thickness (pNC-CT) in 69 highly myopic and 138 healthy, age-matched, control eyes. DESIGN: Cross-sectional, case control study. METHODS: Within ONH radial B-scans, Bruch membrane (BM), BM opening (BMO), anterior scleral canal opening (ASCO), and pNC scleral surface were segmented. BMO and ASCO planes and centroids were determined. pNC-SB was characterized within 30° foveal-BMO (FoBMO) sectors by 2 parameters: pNC-SB-scleral slope (pNC-SB-SS), measured within 3 pNC segments (0-300, 300-700, and 700-1000 µm from the ASCO centroid); and pNC-SB-ASCO depth relative to a pNC scleral reference plane (pNC-SB-ASCOD). pNC-CT was calculated as the minimum distance between the scleral surface and BM at 3 pNC locations (300, 700, and 1100 µm from the ASCO). RESULTS: pNC-SB increased and pNC-CT decreased with axial length (P < .0133; P < .0001) and age (P < .0211; P < .0004) among all study eyes. pNC-SB was increased (P < .001) and pNC-CT was decreased (P < .0279) in the highly myopic compared to control eyes, and these differences were greatest in the inferior quadrant sectors (P < .0002). Sectoral pNC-SB was not related to sectoral pNC-CT in control eyes, but was inversely related to sectoral pNC-CT (P < .0001) in the highly myopic eyes. CONCLUSIONS: Our data suggest that pNC-SB is increased and pNC-CT is decreased in highly myopic eyes and that these phenomena are greatest in the inferior sectors. They support the hypothesis that sectors of maximum pNC-SB may predict sectors of greatest susceptibility to aging and glaucoma in future longitudinal studies of highly myopic eyes. NOTE: Publication of this article is sponsored by the American Ophthalmological Society.

Patients with Low Vision Struggle with Placing Eye Drops and Benefit from an Eye Drop Aid.

PURPOSE: To evaluate eye drop self-administration in a low-vision patient population and test whether a nose-pivoted drop delivery device (NPDD, GentleDrop) can improve eye drop delivery in these patients. DESIGN: Repeated-measures case series. PARTICIPANTS: Thirty subjects (58 eyes) with low vision, defined as best-corrected visual acuity worse than 20/60 or visual field worse than 20° in the better-seeing eye. METHODS: We video-recorded subjects while self-administering eye drops using their own traditional delivery at baseline, after a standardized teaching, and with an NPDD. Two masked graders independently reviewed each drop delivery. Primary success was defined as the drop reaching the eye without the bottle touching the eye or eyelids. Subjects rated ease-of-use (1-10 scale, 10 = easiest) after each drop delivery and completed a satisfaction survey, which included asking whether subjects could place drops independently (1-5 scale, 5 = most independent). MAIN OUTCOME MEASURES: Logistic-transformed generalized estimating equation regression to compare technique satisfaction, ease-of-use, independence, no contact, and success. RESULTS: Primary success was observed in 30 (52%) of 58 eyes at baseline and increased to 44 eyes (76%) with an NPDD (P = 0.013). Bottle tip contact occurred in 23 (40%) of 58 eyes at baseline and 8 eyes (14%) with an NPDD (P = 0.004). Mean ease-of-use scores were 6.7 ± 3.1 at baseline and 8.3 ± 1.8 (P < 0.001) with an NPDD. Likewise, the NPDD improved success, bottle tip contact, and ease-of-use compared with post-teaching traditional delivery (P < 0.01). Twenty-two (73%) of 30 subjects preferred the NPDD to traditional delivery. Twenty-nine (97%) thought the NPDD was comfortable to use, and all would recommend the device. A subgroup analysis was performed on 16 subjects that self-reported difficulty instilling drops at baseline. The NPDD showed similar results, and it increased confidence in placing drops independently (4.6 ± 0.9) compared with baseline (2.7 ± 1.6, P < 0.001). Fifteen (94%) subjects in this subgroup preferred the NPDD. CONCLUSIONS: Low-vision subjects struggled to self-administer eye drops. An NPDD can improve bottle tip contact, ease-of-use, satisfaction, and independence. Eye care providers could consider screening low-vision patients about difficulty with eye drop self-administration and recommending eye drop aids. FINANCIAL DISCLOSURE(S): Proprietary or commercial disclosure may be found in the Footnotes and Disclosures at the end of this article.

AxoNet 2.0: A Deep Learning-Based Tool for Morphometric Analysis of Retinal Ganglion Cell Axons.

Purpose: Assessment of glaucomatous damage in animal models is facilitated by rapid and accurate quantification of retinal ganglion cell (RGC) axonal loss and morphologic change. However, manual assessment is extremely time- and labor-intensive. Here, we developed AxoNet 2.0, an automated deep learning (DL) tool that (i) counts normal-appearing RGC axons and (ii) quantifies their morphometry from light micrographs. Methods: A DL algorithm was trained to segment the axoplasm and myelin sheath of normal-appearing axons using manually-annotated rat optic nerve (ON) cross-sectional micrographs. Performance was quantified by various metrics (e.g., soft-Dice coefficient between predicted and ground-truth segmentations). We also quantified axon counts, axon density, and axon size distributions between hypertensive and control eyes and compared to literature reports. Results: AxoNet 2.0 performed very well when compared to manual annotations of rat ON (R2 = 0.92 for automated vs. manual counts, soft-Dice coefficient = 0.81 ± 0.02, mean absolute percentage error in axonal morphometric outcomes < 15%). AxoNet 2.0 also showed promise for generalization, performing well on other animal models (R2 = 0.97 between automated versus manual counts for mice and 0.98 for non-human primates). As expected, the algorithm detected decreased in axon density in hypertensive rat eyes (P ≪ 0.001) with preferential loss of large axons (P < 0.001). Conclusions: AxoNet 2.0 provides a fast and nonsubjective tool to quantify both RGC axon counts and morphological features, thus assisting with assessing axonal damage in animal models of glaucomatous optic neuropathy. Translational Relevance: This deep learning approach will increase rigor of basic science studies designed to investigate RGC axon protection and regeneration.

Optic disc margin anatomy in patients with glaucoma and normal controls with spectral domain optical coherence tomography.

OBJECTIVE: To characterize optic nerve head (ONH) anatomy related to the clinical optic disc margin with spectral domain-optical coherence tomography (SD-OCT). DESIGN: Cross-sectional study. PARTICIPANTS: Patients with open-angle glaucoma with focal, diffuse, and sclerotic optic disc damage, and age-matched normal controls. METHODS: High-resolution radial SD-OCT B-scans centered on the ONH were analyzed at each clock hour. For each scan, the border tissue of Elschnig was classified for obliqueness (internally oblique, externally oblique, or nonoblique) and the presence of Bruch's membrane overhanging the border tissue. Optic disc stereophotographs were co-localized to SD-OCT data with customized software. The frequency with which the disc margin identified in stereophotographs coincided with (1) Bruch's membrane opening (BMO), defined as the innermost edge of Bruch's membrane; (2) Bruch's membrane/border tissue, defined as any aspect of either outside BMO or border tissue; or (3) border tissue, defined as any aspect of border tissue alone, in the B-scans was computed at each clock hour. MAIN OUTCOME MEASURES: The SD-OCT structures coinciding with the disc margin in stereophotographs. RESULTS: There were 30 patients (10 with each type of disc damage) and 10 controls, with a median (range) age of 68.1 (42-86) years and 63.5 (42-77) years, respectively. Although 28 patients (93%) had 2 or more border tissue configurations, the most predominant one was internally oblique, primarily superiorly and nasally, frequently with Bruch's membrane overhang. Externally oblique border tissue was less frequent, observed mostly inferiorly and temporally. In controls, there was predominantly internally oblique configuration around the disc. Although the configurations were not statistically different between patients and controls, they were among the 3 glaucoma groups. At most locations, the SD-OCT structure most frequently identified as the disc margin was some aspect of Bruch's membrane and border tissue external to BMO. Bruch's membrane overhang was regionally present in the majority of patients with glaucoma and controls; however, in most cases it was not visible as the disc margin. CONCLUSIONS: The clinically perceived disc margin is most likely not the innermost edge of Bruch's membrane detected by SD-OCT. These findings have important implications for the automated detection of the disc margin and estimates of the neuroretinal rim.