Controversies in the vascular theory of glaucomatous optic nerve degeneration

Vascular resistance indices are higher in the superior than inferior optic nerve head and retina

Retinal vascular resistance is of interest in glaucoma research, as a potential link between retinal ganglion cell loss and observed phenomena including disrupted vascular autoregulation, altered biomechanical stiffness, and impaired neurovascular coupling. It can now be assessed in vivo, using laser speckle flowgraphy. However, continued progress in the field requires better understanding of its physiology. In this study, we test the hypothesis of homogeneity of vascular resistance indices between regions of the retina: specifically, between superior and inferior hemifields. The resistivity index (maximum flow minus minimum flow, as a proportion of the maximum) and pulsatility index (maximum minus minimum, as a proportion of the mean) were measured in major vessels within the optic nerve head, in the remaining tissue within the optic nerve head, and in peripapillary branch retinal arteries, separated in each case into superior and inferior quadrants. This was performed in 378 eyes of 189 participants with suspected, early or moderate glaucoma; and in 99 eyes of 50 participants without any ocular pathology. In the glaucoma cohort, the resistivity index was on average 9% higher superiorly than inferiorly in vessels within the optic nerve head; 8% higher superiorly in remaining tissue; and 8% higher superiorly in peripapillary vessels (all p < 0.001). The pulsatility index was on average 11% higher superiorly in all three locations (all p < 0.001). Average flow was slightly higher superiorly in major vessels in the nerve head, but higher inferiorly elsewhere. In the healthy control cohort, resistivity index was higher superiorly by 10% in vessels and 8% in tissue within the optic nerve head; pulsatility index was 12% and 10% higher superiorly respectively (all p < 0.001). The fact that these differences were similar between the two cohorts suggests that they are not caused by the disease process. However, it is notable that glaucomatous loss most frequently occurs first in the superior visual field, corresponding with the inferior retina. The finding that vascular resistance indices are consistently higher in the superior retina warrants further investigation, both for its causes and consequences.

Asymmetric Glaucoma and Corresponding Hearing Impairment

Background/Objectives: This study aims to explore the potential relationship between unilateral or asymmetric glaucoma and ipsilateral hearing impairment. Methods: In this retrospective study, visual and hearing functions were assessed in patients with unilateral or asymmetric glaucoma. Correlations between retinal nerve fiber layer (RNFL) thickness, visual field mean deviation (MD) values, and pure tone audiometry (PTA) measurements across various frequencies were analyzed to explore potential associations between visual and ipsilateral hearing functions. Differences in PTA values between ears ipsilateral to the more affected glaucomatous eyes and the contralateral ears were studied for statistical significance. Results: Twenty-six patients with unilateral or asymmetric glaucoma were included in the study. Significant differences in hearing thresholds between the ears corresponding to the more severely glaucomatous eyes and the contralateral ears were found at 0.7, 1, 1.5, and 3 kHz (p < 0.05). Additionally, a statistically significant difference was observed in the speech frequencies (0.5, 0.7, 1, 1.5, 2, 3, and 4 kHz) between ears corresponding to glaucomatous or more affected glaucomatous eyes and the contralateral ears (p = 0.016). Furthermore, a moderately positive correlation was found between differences in MD and PTA values at 0.125 kHz (r = 0.50; p = 0.01). Conclusions: This study highlights a potential association between unilateral or asymmetric glaucoma and ipsilateral hearing impairment, particularly at speech-relevant frequencies. These findings underscore the importance of integrated sensory assessment in the management of glaucoma patients, suggesting that early detection and intervention for concurrent hearing loss could enhance overall quality of life.

The Role of Optical Coherence Tomography Angiography in Glaucoma

Glaucoma is the leading cause of irreversible vision loss and comprises a group of chronic optic neuropathies characterized by progressive retinal ganglion cell (RGC) loss. Various etiologies, including impaired blood supply to the optic nerve, have been implicated for glaucoma pathogenesis. Optical coherence tomography angiography (OCTA) is a non-invasive imaging modality for visualizing the ophthalmic microvasculature. Using blood flow as an intrinsic contrast agent, it distinguishes blood vessels from the surrounding tissue. Vessel density (VD) is mainly used as a metric for quantifying the ophthalmic microvasculature. The key anatomic regions for OCTA in glaucoma are the optic nerve head area including the peripapillary region, and the macular region. Specifically, VD of the superficial peripapillary and superficial macular microvasculature is reduced in glaucoma patients compared to unaffected subjects, and VD correlates with functional deficits measured by visual field (VF). This renders OCTA similar in diagnostic capabilities compared to structural retinal nerve fiber layer (RNFL) thickness measurements, especially in early glaucoma. Furthermore, in cases where RNFL thickness measurements are limited due to artifact or floor effect, OCTA technology can be used to evaluate and monitor glaucoma, such as in eyes with high myopia and eyes with advanced glaucoma. However, the clinical utility of OCTA in glaucoma management is limited due to the prevalence of imaging artifacts. Overall, OCTA can play a complementary role in structural OCT imaging and VF testing to aid in the diagnosis and monitoring of glaucoma.

Glaucoma, Pseudoexfoliation and Hearing Loss: A Systematic Literature Review

Purpose: To investigate the relationship between glaucoma, pseudoexfoliation and hearing loss (HL). Methods: A systematic literature search following PRISMA guidelines was conducted using the PubMed, Embase, Scopus and Cochrane databases from 1995 up to 28 August 2023. Results: Thirty studies out of the 520 records screened met the inclusion criteria and were included. Most articles (n = 20) analysed the association between pseudoexfoliation syndrome (XFS) and HL, showing XFS patients to have higher prevalence of sensorineural hearing loss (SNHL) at both speech frequencies (0.25, 0.5, 1 and 2 kHz), and higher frequencies (4 and 8 kHz) compared to controls in most cases. No significant differences in prevalence or level of HL between XFS and pseudoexfoliative glaucoma (XFG) were detected in most studies. Eight articles analysed the relationship between primary open-angle glaucoma (POAG) and HL. Overall, a positive association between the two conditions was highlighted across all studies except for two cases. Similarly, articles focusing on NTG and HL (n = 4) showed a positive association in most cases. The role of autoimmunity and, in particular, the presence of antiphosphatidylserine antibodies (APSA) in patients with NTG and HL suggested an underlying autoimmune or vascular mechanism contributing to their pathogenesis. Only one study analysed the relationship between angle-closure glaucoma (ACG) and HL, showing higher incidence of ACG in patients with SNHL compared to normal hearing controls. Conclusions: Most studies detected an association between XFS and HL as well as POAG/NTG/ACG and HL, suggesting the presence of a similar pathophysiology of neurodegeneration. However, given the strength of the association of XFS with HL, it remains unclear whether the presence of XFG is further associated with SNHL. Further research specifically targeted to assess the correlation between glaucoma, XFS and HL is warranted to provide a more comprehensive understanding of this association.

Is Primary Open-Angle Glaucoma a Vascular Disease? Assessment of the Relationship between Retinal Arteriolar Morphology and Glaucoma Severity Using Adaptive Optics

BACKGROUND

Retinal vascular abnormalities may be associated with glaucomatous damage. Adaptive optics (AO) is a new technology that enables the analysis of retinal vasculature at the cellular level in vivo. The purpose of this study was to evaluate retinal arteriolar parameters using the rtx1 adaptive optics fundus camera (AO-FC) in patients with primary open-angle glaucoma (POAG) at different stages and to investigate the relationship between these parameters and changes in spectral-domain optical coherence tomography (SD-OCT) and perimetry.

METHODS

Parameters of the retinal supratemporal and infratemporal arterioles (wall thickness (WT), lumen diameter (LD), total diameter (TD), wall-to-lumen ratio (WLR), and cross-sectional area of the vascular wall (WCSA)) were analysed with the rtx1 in 111 POAG eyes, which were divided into three groups according to the severity of the disease, and 70 healthy eyes. The associations between RTX1 values and the cup-to-disk ratio, SD-OCT parameters, and visual field parameters were assessed.

RESULTS

Compared with the control group, the POAG groups showed significantly smaller TD and LD values (p < 0.05) and significantly higher WLR and WT values (p < 0.05) for the supratemporal and infratemporal arterioles. TD was significantly positively correlated with the retinal nerve fibre layer (RNFL) and ganglion cell complex (GCC) (p < 0.05). LD was significantly positively correlated with the RNFL, GCC, and rim area (p < 0.05). The WLR was significantly negatively correlated with the RNFL, GCC, rim area, and MD (p < 0.05), while it was significantly positively correlated with the cup-to-disc ratio and PSD (p < 0.05).

CONCLUSIONS

The results suggest that vascular dysfunction is present in POAG, even at a very early stage of glaucoma, and increases with the severity of the disease.

Factors Contributing to the Development of Choroidal Microvasculature Dropout in Glaucoma Suspects and Patients with Glaucoma

We aimed to characterize and compare the occurrence of peripapillary microvasculature dropout (MvD) between glaucoma suspects and patients with glaucoma. In addition, the factors related to the development of parapapillary MvD in glaucoma suspects and patients with glaucoma were investigated. Of a total 150 eyes, 68 eyes of glaucoma suspects and 82 eyes of glaucoma patients were analyzed in this study. Univariate and multivariate logistic regression analyses were used to identify factors associated with MvD development. The classification of glaucoma patients or glaucoma suspects was not significantly associated with MvD development (beta 1.368, 95% CI, 0.718-2.608, p = 0.341). In the regression analysis of the glaucoma suspect group, greater axial length (beta 1.520, 95% CI, 1.008-2.291, p = 0.046) and baseline cup volume (beta 3.993, 95% CI, 1.292-12.345, p = 0.035) among the baseline factors and the slope of ganglion cell-inner plexiform layer (GCIPL) thickness (beta 0.027, 95% CI, 0.072-0.851, p = 0.027) and central visual field (VF) progression (beta 7.040, 95% CI, 1.781-16.306, p = 0.014) among follow-up factors were significantly associated with MvD development. In the glaucoma group, central VF progression (beta 5.985, 95% CI, 1.474-24.083, p = 0.012) and ONH depression (beta 3.765, 95% CI, 1.301-10.895, p = 0.014) among follow-up elements were observed as significant factors and the baseline factor had little relationship. MvD appears not only as a result of the progression of axonal loss of RGC in glaucoma but may also be developed due to structural changes and mechanical susceptibility of the ONH associated with baseline characteristics. Analyzing the structural susceptibility of the ONH can predict the occurrence of MvD, which can be helpful in predicting the progression of glaucoma.

The Relationship between Transcranial Doppler Ultrasonography and Visual Field Test Results in Glaucoma and Glaucoma Suspect Patients

PURPOSE

To evaluate the relationships between parameters of transcranial ultrasonography and results of visual field tests in patients with open angle glaucoma or suspected of having glaucoma.

METHODS

This retrospective study was based on data from medical records of patients who visited the Department of Ophthalmology in Kangbuk Samsung Hospital from January 1, 2016, to October 17, 2019, and underwent transcranial Doppler ultrasonography as part of a routine health examination. Ophthalmic data were visual acuity, intraocular pressure, optical coherence tomography, and Humphrey visual field test results. Retinal nerve fiber layer defect was confirmed by a glaucoma specialist. Patients' ophthalmic data, such as average ganglion cell layer thickness, visual field index, pattern standard deviation, and mean deviation, were divided into quartiles. Each ophthalmic artery parameter from transcranial Doppler ultrasonography was compared between quartiles.

RESULTS

A total of 162 patients were reviewed. There was no difference in Doppler ophthalmic artery (OA) parameters between patients with or without retinal nerve fiber layer defect. None of the quartile groups of average ganglion cell layer thickness showed significant difference in any OA parameters. Patients in the low-visual field index quartile showed significant low peak systolic velocities of OAs when adjusted for age, sex, and presence of diabetes mellitus or hypertension (p = 0.016). A higher pattern standard deviation showed lower peak systolic velocity (p = 0.046). There was no significant tendency between any other OA parameter and mean deviation value.

CONCLUSIONS

Our study suggests that hemodynamic parameters of ophthalmic arteries might be associated with visual field status of patients. Further large-population studies are needed in order to better understand the relationship between visual function and ocular blood flow.

Optical Coherence Tomography Angiography (OCTA) Differences in Vessel Perfusion Density and Flux Index of the Optic Nerve and Peri-Papillary Area in Healthy, Glaucoma Suspect and Glaucomatous Eyes

Purpose

To assess the ability of vascular perfusion parameters determined by optical coherence tomography angiography (OCTA) to detect and monitor glaucoma.

Methods

This prospective study included healthy, glaucoma suspect and glaucomatous eyes. All eyes underwent comprehensive glaucoma examination, including visual field tests and ocular imaging scans by OCTA. Parameters measured included retinal nerve fiber layer (RNFL) thickness, ganglion cell analysis (GCA), vascular perfusion density (VPD) and flux index (FI) of the optic nerve and peri-papillary area. Ocular parameters in healthy, glaucoma suspect, and glaucomatous eyes were compared by generalized estimating equations (GEE) with adjustments for age, with their relationships analyzed by Pearson's correlation coefficient. Rates of change per year were compared in glaucomatous eyes with and without glaucoma progression.

Results

This study enrolled 238 eyes, including 56 healthy, 79 glaucoma suspect, and 103 glaucomatous eyes. After adjustments for age, the average VPD (45.40 ± 0.19% vs 45.05 ± 0.22% vs 42.89 ± 0.32%, p < 0.001) and FI (0.4210 ± 0.0055 vs 0.4105 ± 0.0039 vs 0.3801 ± 0.0048, p < 0.001) in these three groups differed significantly. Average VPD in the glaucoma group was inversely associated with the severity of glaucoma, being 43.99 ± 0.32%, 42.63 ± 0.43% and 39.27 ± 0.48% in eyes with early, moderate and severe glaucoma, respectively (p < 0.001). Average VPD, as well as VPD in the superior and inferior quadrants correlated well with both OCT determined RNFL and visual field parameters. The decreases per year in both superior (-0.012 vs -0.001, p = 0.002) and inferior (-0.008 vs -0.003, p = 0.007) FI were significantly greater in glaucomatous eyes with than without glaucoma progression.

Conclusion

Both VPD and FI as measured by OCTA are promising ocular parameters that can distinguish between normal and glaucomatous eyes. VPD is sensitive in comparing eyes at different glaucoma stages, whereas FI can detect rates of glaucoma progression.

Trial Registration

Thai Clinical Trial Registry, TCTR20181031002.

The Association between Vascular Abnormalities and Glaucoma-What Comes First?

Glaucoma is a leading cause of irreversible blindness worldwide. While intraocular pressure (IOP) presents a major risk factor, the underlying pathophysiology still remains largely unclear. The correlation between vascular abnormalities and glaucoma has been deliberated for decades. Evidence for a role played by vascular factors in the pathogenesis of glaucomatous neurodegeneration has already been postulated. In addition, the fact that glaucoma causes both structural and functional changes to retinal blood vessels has been described. This review aims to investigate the published evidence concerning the relationship between vascular abnormalities and glaucoma, and to provide an overview of the "chicken or egg" dilemma in glaucoma. In this study, several biomarkers of glaucoma progression from a vascular perspective, including endothelin-1 (ET-1), nitric oxide, vascular endothelial growth factor (VEGF), and matrix metalloproteinases (MMPs), were identified and subsequently assessed for their potential as pharmacological intervention targets.

Natural History of Glaucoma Progression in the DBA/2J Model: Early Contribution of Müller Cell Gliosis

Glaucoma is a chronic optic neuropathy characterized by progressive degeneration of retinal ganglion cells (RGCs). Elevated intraocular pressure (IOP) and the resulting mechanical stress are classically considered the main causes of RGC death. However, RGC degeneration and ensuing vision loss often occur independent of IOP, indicating a multifactorial nature of glaucoma, with the likely contribution of glial and vascular function. The aim of the present study was to provide a comprehensive evaluation of the time course of neuro-glial-vascular changes associated with glaucoma progression. We used DBA/2J mice in the age range of 2-15 months as a spontaneous model of glaucoma with progressive IOP elevation and RGC loss typical of human open-angle glaucoma. We found that the onset of RGC degeneration at 10 months of age coincided with that of IOP elevation and vascular changes such as decreased density, increased lacunarity and decreased tight-junction protein zonula occludens (ZO)-1, while hypoxia-inducible factor (HIF)-1α and vascular endothelial growth factor (VEGF) were already significantly upregulated at 6 months of age together with the onset of Müller cell gliosis. Astrocytes, however, underwent significant gliosis at 10 months. These results indicate that Müller cell activation occurs well before IOP elevation, with probable inflammatory consequences, and represents an early event in the glaucomatous process. Early upregulation of HIF-1α and VEGF is likely to contribute to blood retinal barrier failure, facilitating RGC loss. The different time courses of neuro-glial-vascular changes during glaucoma progression provide further insight into the nature of the disease and suggest potential targets for the development of efficient therapeutic intervention aside from IOP lowering.

Influence of Cilioretinal Arteries on Flow Density in Glaucoma Patients Measured Using Optical Coherence Tomography Angiography

It has long been speculated whether the presence of a cilioretinal artery (CRA) can influence the development of glaucomatous damage in patients with open-angle glaucoma. Studies involving healthy patients have shown a change in flow density (FD) depending on the presence of a CRA. Similarly, studies that compared the optical coherence tomography angiography (OCTA) results of healthy controls and glaucoma cohorts identified a reduction in FD in certain retinal layers for glaucoma patients. These observations raise the question of whether FD is altered in glaucoma patients depending on the presence of CRA, with possible implications for the progression of glaucomatous damage. In this prospective study, 201 eyes of 134 primary and secondary open-angle glaucoma patients who visited the Department of Ophthalmology at the University of Muenster Medical Center, Germany were included. The patients were allocated to different groups according to the presence of CRAs and the level of glaucoma severity. The FD results obtained using OCTA for the CRA and non-CRA groups were compared. While FD differed noticeably between the CRA and non-CRA cohorts in the deep macular plexus, no differences in FD were observed between the two groups when adjusted for glaucoma severity. In both the CRA and non-CRA eyes, increasing glaucoma severity correlated most strongly with a reduction in peripapillary FD. Our results suggest that the presence of CRAs does not significantly affect retinal perfusion in glaucoma patients.

The Role of Color Doppler Imaging in the Diagnosis of Glaucoma: A Review of the Literature

Glaucoma is a progressive optic neuropathy and one of the leading causes of irreversible blindness worldwide. Elevated intraocular pressure (IOP) is the major risk factor for the onset and progression of glaucoma. In addition to elevated IOP, impaired intraocular blood flow is also considered to be involved in the pathogenesis of glaucoma. Various techniques have been used to assess ocular blood flow (OBF), including Color Doppler Imaging (CDI), a technique used in ophthalmology in recent decades. This article reviews the role of CDI in both the diagnosis and effective monitoring of glaucoma progression, presenting the protocol for imaging and its advantages, as well as the limitations of its use. Moreover, it analyzes the pathophysiology of glaucoma, focusing on vascular theory and its role in the onset and progression of the disease.

Intraocular Pressure-Induced Endothelial Dysfunction of Retinal Blood Vessels Is Persistent, but Does Not Trigger Retinal Ganglion Cell Loss

Research has been conducted into vascular abnormalities in the pathogenesis of glaucoma, but conclusions remain controversial. Our aim was to test the hypothesis that retinal endothelial dysfunction induced by elevated intraocular pressure (IOP) persists after IOP normalization, further triggering retinal ganglion cell (RGC) loss. High intraocular pressure (HP) was induced in mice by episcleral vein occlusion (EVO). Retinal vascular function was measured via video microscopy in vitro. The IOP, RGC and their axons survival, levels of oxidative stress and inflammation as well as vascular pericytes coverage, were determined. EVO caused HP for two weeks, which returned to baseline afterwards. Mice with HP exhibited endothelial dysfunction in retinal arterioles, reduced density of RGC and their axons, and loss of pericytes in retinal arterioles. Notably, these values were similar to those of mice with recovered IOP (RP). Levels of oxidative stress and inflammation were increased in HP mice but went back to normal in the RP mice. Our data demonstrate that HP induces persistent endothelial dysfunction in retinal arterioles, which persists one month after RP. Oxidative stress, inflammation, and loss of pericytes appear to be involved in triggering vascular functional deficits. Our data also suggest that retinal endothelial dysfunction does not affect RGC and their axon survival.

Pericyte dysfunction and loss of interpericyte tunneling nanotubes promote neurovascular deficits in glaucoma

Reduced blood flow and impaired neurovascular coupling are recognized features of glaucoma, the leading cause of irreversible blindness worldwide, but the mechanisms underlying these defects are unknown. Retinal pericytes regulate microcirculatory blood flow and coordinate neurovascular coupling through interpericyte tunneling nanotubes (IP-TNTs). Using two-photon microscope live imaging of the mouse retina, we found reduced capillary diameter and impaired blood flow at pericyte locations in eyes with high intraocular pressure, the most important risk factor to develop glaucoma. We show that IP-TNTs are structurally and functionally damaged by ocular hypertension, a response that disrupted light-evoked neurovascular coupling. Pericyte-specific inhibition of excessive Ca²⁺ influx rescued hemodynamic responses, protected IP-TNTs and neurovascular coupling, and enhanced retinal neuronal function as well as survival in glaucomatous retinas. Our study identifies pericytes and IP-TNTs as potential therapeutic targets to counter ocular pressure-related microvascular deficits, and provides preclinical proof of concept that strategies aimed to restore intrapericyte calcium homeostasis rescue autoregulatory blood flow and prevent neuronal dysfunction.

Treatment of Glaucoma with Natural Products and Their Mechanism of Action: An Update

Glaucoma is one of the leading causes of irreversible blindness. It is generally caused by increased intraocular pressure, which results in damage of the optic nerve and retinal ganglion cells, ultimately leading to visual field dysfunction. However, even with the use of intraocular pressure-lowering eye drops, the disease still progresses in some patients. In addition to mechanical and vascular dysfunctions of the eye, oxidative stress, neuroinflammation and excitotoxicity have also been implicated in the pathogenesis of glaucoma. Hence, the use of natural products with antioxidant and anti-inflammatory properties may represent an alternative approach for glaucoma treatment. The present review highlights recent preclinical and clinical studies on various natural products shown to possess neuroprotective properties for retinal ganglion cells, which thereby may be effective in the treatment of glaucoma. Intraocular pressure can be reduced by baicalein, forskolin, marijuana, ginsenoside, resveratrol and hesperidin. Alternatively, Ginkgo biloba, Lycium barbarum, Diospyros kaki, Tripterygium wilfordii, saffron, curcumin, caffeine, anthocyanin, coenzyme Q10 and vitamins B3 and D have shown neuroprotective effects on retinal ganglion cells via various mechanisms, especially antioxidant, anti-inflammatory and anti-apoptosis mechanisms. Extensive studies are still required in the future to ensure natural products' efficacy and safety to serve as an alternative therapy for glaucoma.

Association Between Diabetes, Diabetic Retinopathy, and Glaucoma

PURPOSE OF REVIEW

The strength of the relationship between diabetes, diabetic retinopathy (DR), and glaucoma remains controversial. We review evidence supporting and refuting this association and explore mechanistic pathological and treatment relationships linking these diseases.

RECENT FINDINGS

While studies have shown diabetes/DR may increase the risk for glaucoma, this remains inconsistently demonstrated. Diabetes/DR may contribute toward glaucomatous optic neuropathy indirectly (either by increasing intraocular pressure or vasculopathy) or through direct damage to the optic nerve. However, certain elements of diabetes may slow glaucoma progression, and diabetic treatment may concurrently be beneficial in glaucoma management. Diabetes plays a significant role in poor outcomes after glaucoma surgery. While the relationship between diabetes/DR and glaucoma remains controversial, multiple mechanistic links connecting pathophysiology and management of diabetes, DR, and glaucoma have been made. However, a deeper understanding of the causes of disease association is needed.

Pathophysiology of the comorbidity of glaucoma with obstructive sleep apnea: A postulation

Glaucoma is a serious and progressive optic neuropathy, the exact pathophysiology of which is still poorly understood. Furthermore, glaucoma exhibits significant comorbidity with obstructive sleep apnea (OSA) that warrants an in-depth study in view of highly probable beneficial and far-reaching clinical implications. In this brief paper, the authors have studied the existing theories in an attempt to explain the comorbidity and its underlying pathophysiology. From the ensuing evidence, the role of connective tissue strength has emerged as a major factor and which appears to play a pivotal role not only in the development of glaucoma but also in the underlying pathophysiology of its enigmatic comorbidity with OSA. Understanding the pathophysiology of the comorbidity can stimulate newer therapeutic strategies targeted toward strengthening of connective tissues that may at least retard if not arrest the progression of glaucomatous changes and their complications.

Glaucoma detection in Latino population through OCT's RNFL thickness map using transfer learning

PURPOSE

Glaucoma is the leading cause of irreversible blindness worldwide. It is estimated that over 60 million people around the world have this disease, with only part of them knowing they have it. Timely and early diagnosis is vital to delay/prevent patient blindness. Deep learning (DL) could be a tool for ophthalmologists to give a more informed and objective diagnosis. However, there is a lack of studies that apply DL for glaucoma detection to Latino population. Our contribution is to use transfer learning to retrain MobileNet and Inception V3 models with images of the retinal nerve fiber layer thickness map of Mexican patients, obtained with optical coherence tomography (OCT) from the Instituto de la Visión, a clinic in the northern part of Mexico.

METHODS

The IBM Foundational Methodology for Data Science was used in this study. The MobileNet and Inception V3 topologies were chosen as the analytical approaches to classify OCT images in two classes, namely glaucomatous and non-glaucomatous. The OCT files were collected from a Zeiss OCT machine at the Instituto de la Visión, and classified by an expert into the two classes under study. These images conform a dataset of 333 files in total. Since this research work is focused on RNFL thickness map images, the OCT files were cropped to obtain only the RNFL thickness map images of the corresponding eye. This action was carried out for images in both classes, glaucomatous and non-glaucomatous. Since some images were damaged (with black spots in which data was missing), these images were cut-out and cut-off. After the preparation process, 50 images per class were used for training. Fifteen images per class, different than the ones used in the training stage, were used for running predictions. In total, 260 images were used in the experiments, 130 per eye. Four models were generated, two trained with MobileNet, one for the left eye and one for the right eye, and another two trained with Inception V3. TensorFlow was used for running transfer learning.

RESULTS

The evaluation results of the MobileNet model for the left eye are, accuracy: 86%, precision: 87%, recall: 87%, and F1 score: 87%. The evaluation results of the MobileNet model for the right eye are, accuracy: 90%, precision: 90%, recall: 90%, and F1 score: 90%. The evaluation results of the Inception V3 model for the left eye are, accuracy: 90%, precision: 90%, recall: 90%, and F1 score: 90%. The evaluation results of the Inception V3 model for the right eye are, accuracy: 90%, precision: 90%, recall: 90%, and F1 score: 90%.

CONCLUSION

In average, the evaluation results for right eye images were the same for both models. The Inception V3 model showed slight better average results than the MobileNet model in the case of classifying left eye images.

Review of a new concept of glaucoma pathogenesis based on the glymphatic theory of cerebrospinal fluid circulation

General aspects of glaucoma: Glaucoma is a heterogeneous multi-factorial disease that is one of the main causes of blindness, along with degeneration of retinal ganglion cells and optic nerve atrophy.

Theories of pathogenesis: There are three theories of glaucoma pathogenesis: biomechanical, vascular, and biochemical.

Basic theory of the glymphatic system: The classical knowledge of cerebrospinal fluid circulation has been revised, and in 2012 a new concept of glial-perivascular – glymphatic perfusion of the brain parenchyma was introduced. Due to experimental and clinical studies, it is approved by many scientists, especially in relation to Alzheimer’s disease (AD), in which amyloid pathology is the result of dysfunction of the para-/perivascular transport/cleansing pathways.

Features of the optic nerve and the cribriform plate: The cribriform plate forms a barrier at the border of intraocular (IOP) and intracranial (ICP) pressures, thus affecting the para-/periarterial flow of cerebrospinal fluid to the optic nerve and retina, as well as the para-/perivenous cleansing outflow.

Morphofunctional evidence of an ocular glymphatic system: The presence of an ocular glymphatic system is confirmed by in vivo experiments with the transfer of labeled substances through para-/perivascular structures from the ventricular or subarachnoid space to the optic nerve and by postmortem morphology.

Clinical evidence for the glymphatic system hypothesis: There is some clinical, including case-based, and epidemiological evidence for similarities between glaucomatous optic nerve/retinal injuries and AD, since both occur in the form of improper secretion of neurotoxic metabolites, and both are often diagnosed together.

The Neurovascular Unit in Glaucomatous Neurodegeneration

Glaucoma is a neurodegenerative disease of the visual system and leading cause of blindness worldwide. The disease is associated with sensitivity to intraocular pressure (IOP), which over a large range of magnitudes stresses retinal ganglion cell (RGC) axons as they pass through the optic nerve head in forming the optic projection to the brain. Despite clinical efforts to lower IOP, which is the only modifiable risk factor for glaucoma, RGC degeneration and ensuing loss of vision often persist. A major contributor to failure of hypotensive regimens is the multifactorial nature of how IOP-dependent stress influences RGC physiology and structure. This stress is conveyed to the RGC axon through interactions with structural, glial, and vascular components in the nerve head and retina. These interactions promote pro-degenerative pathways involving biomechanical, metabolic, oxidative, inflammatory, immunological and vascular challenges to the microenvironment of the ganglion cell and its axon. Here, we focus on the contribution of vascular dysfunction and breakdown of neurovascular coupling in glaucoma. The vascular networks of the retina and optic nerve head have evolved complex mechanisms that help to maintain a continuous blood flow and supply of metabolites despite fluctuations in ocular perfusion pressure. In healthy tissue, autoregulation and neurovascular coupling enable blood flow to stay tightly controlled. In glaucoma patients evidence suggests these pathways are dysfunctional, thus highlighting a potential role for pathways involved in vascular dysfunction in progression and as targets for novel therapeutic intervention.

Intra-Subject Variability and Diurnal Cycle of Ocular Perfusion Pressure as Characterized by Continuous Telemetry in Nonhuman Primates

Purpose

To characterize ocular perfusion pressure (OPP) fluctuations with continuous telemetry over 24-hour periods across multiple days in nonhuman primates (NHPs) to test the hypotheses that OPP differs among NHPs and that the diurnal cycle of OPP is characterized by low OPP during sleep.

Methods

We have developed and validated two implantable radiotelemetry systems that allow continuous measurement of intraocular pressure (IOP), arterial blood pressure (BP), and OPP up to 500 Hz. OPP was measured unilaterally in 12 male NHPs for periods of 38 to 412 days. IOP transducers were calibrated directly via anterior chamber manometry, and OPP was calculated continuously as central retinal artery BP minus IOP. OPP data were corrected for signal drift between calibrations and averaged hourly.

Results

OPP varied widely among animals, with daily averages ranging from ∼47 to 65 mm Hg. In eight of 12 NHPs, OPP was significantly lower during sleep compared to waking hours. In three animals, the diurnal cycle was reversed and OPP was significantly higher during sleep (P < 0.05), and one NHP showed no diurnal cycle. Day-to-day OPP variability within NHPs was the largest source of overall OPP variability, even larger than the differences between NHPs. Average daily OPP showed an unexplained ∼32-day cyclic pattern in most NHPs.

Conclusions

Average OPP varied widely and exhibited differing diurnal cycles in NHPs, a finding that matches those of prior patient studies and indicates that OPP studies in the NHP model are appropriate. Infrequent snapshot measurements of either IOP or BP are insufficient to capture true IOP, BP, and OPP and their fluctuations.

Association of endothelial nitric oxide synthase (NOS3) gene polymorphisms with primary open-angle glaucoma in a Saudi cohort

Aim

To investigate the association of endothelial nitric oxide synthase (NOS3) gene polymorphisms in patients with primary open-angle glaucoma (POAG) of Saudi origin.

Methods

This case-control study included 173 patients with POAG (94 men and 79 women) and 171 controls (98 men and 73 women). Genotyping of rs2070744 (T-786C) and rs1799983 (G894T) variants of the NOS3 gene was performed using TaqMan^® assay.

Results

Rs1799983 genotypes showed a significant association with POAG but did not survive Bonferroni correction (p_correction = 0.01). The minor ‘T’ allele was significantly associated with the risk of POAG among men (p = 0.025, odds ratio (OR) = 1.77, 95% confidence interval (CI) = 1.07–2.94). Likewise, the genotypes were significantly associated with POAG among men in dominant (p = 0.030, OR = 1.92, 95% CI = 1.06–3.48) and log-additive models (p = 0.022, OR = 1.82, 95% CI = 1.08–3.07), and after adjustment for age and smoking. Genotype and allele frequencies of rs2070744 were not significantly different between POAG cases and controls, and after sex stratification. CG haplotype was significantly protective (p = 0.011, OR = 0.52, 95% CI = 0.32–0.87) and CT haplotype conferred significantly increased risk of POAG (p = 0.016, OR = 2.60, 95% CI = 1.16–5.82) among men. Rs1799983 showed trend (p = 0.054) towards risk of POAG independent of age, gender, smoking, and rs2070744 polymorphism in logistic regression analysis. Both the polymorphisms showed no association with POAG phenotypes such as intraocular pressure and cup/disc ratio.

Conclusion

Our results suggest that the polymorphism rs1799983 and the haplotypes of rs20707440 and rs1799983 in the NOS3 gene may significantly modulate the risk of POAG in Saudi’s, particularly among men. Further larger studies are needed to confirm these findings.

Positive predictive value of optic disc haemorrhages for open angle glaucoma

OBJECTIVES

To determine the positive predictive value (PPV) of disc haemorrhages (DHs) for the diagnosis of open angle glaucoma (OAG).

METHODS

A retrospective review of 618 consecutive new referrals by community optometrists to a hospital glaucoma service, including 54 patients with DHs. All patients had a comprehensive eye examination. The primary outcome was whether the patient was diagnosed with OAG in either eye, with a secondary outcome of whether they were discharged at the first visit (first visit discharge rate, FVDR).

RESULTS

54 of 618 patients (8.7%) had a DH noted at the time of referral, including 21 referred with DH alone. 29 patients with DHs were diagnosed with OAG for a PPV of 54% (95% CI 40-67%), falling to 24% (95% CI 8-47%) in those with DH alone. The overall FVDR was 35%, increasing to 57% in those referred due to DH alone. The FVDR for those referred with DH alone was significantly higher than the FDVR of 25% among the 564 patients referred with suspected glaucoma without a DH (P = 0.001). The FVDR decreased to 35% for patients with a DH plus one other feature of glaucoma and to 0% for patients with a DH and at least two other features suggestive of glaucoma.

CONCLUSIONS

Almost 60% of patients referred due to isolated DHs were discharged at the first visit to the glaucoma clinic, however almost one in four was diagnosed with OAG. Patients with DH and other features suggestive of glaucoma had a higher probability of glaucoma diagnosis.

Hypothesis: Watershed zones in the human eye are a key for understanding glaucomatous retinal damage

The pathogenesis of glaucoma is complex which has led to numerous hypothesizes concerning the important factors creating this specific type of inner retinal degeneration namely apoptosis of retinal ganglion cells. We favor a primary vascular etiology and provide evidence that the pathogenesis of glaucoma should not be confined to changes exclusively at the optic nerve head but must include changes occurring in the peripheral retina with particular emphasis on the watershed zones of both the retina and choroid. This focus may help to sharpen ones awareness for early glaucoma treatment particularly in patients with minimal findings suggestive of glaucoma.

Risk Factors for Rapid Glaucoma Disease Progression

PURPOSE

To determine the intraocular and systemic risk factor differences between a cohort of rapid glaucoma disease progressors and nonrapid disease progressors.

DESIGN

Retrospective case-control study.

METHODS

Setting: Five private ophthalmology clinics.

STUDY POPULATION

Forty-eight rapidly progressing eyes (progression ≥1 dB mean deviation [MD]/year) and 486 non-rapidly progressing eyes (progression <1 dB MD/year). Patients were eligible if they had a diagnosis of glaucoma from their ophthalmologist and if they had greater than or equal to 5 Humphrey visual fields (24-2) conducted. Patients were excluded if their sequential visual fields showed an improvement in MD or if they had greater than 5 dB MD variation in between visits. Patients with obvious neurologic fields were excluded.

OBSERVATION PROCEDURE

Clinical and demographic data (age, sex, central corneal thickness [CCT], intraocular pressure [IOP], refraction, medications), as well as medical, surgical, and ocular histories, were collected.

MAIN OUTCOME MEASURES

Risk factor differences between the cohorts were measured using the independent t test, Wald χ², and binomial regression analysis.

RESULTS

Rapid progressors were older, had significantly lower CCT and baseline IOPs, and were more likely to have pseudoexfoliation, disc haemorrhages, ocular medication changes, and IOP-lowering surgery. They also had significantly higher rates of cardiovascular disease and hypotension. Subjects with cardiovascular disease were 2.33 times more likely to develop rapidly progressive glaucoma disease despite significantly lower mean and baseline IOPs.

CONCLUSION

Cardiovascular disease is an important risk factor for rapid glaucoma disease progression irrespective of IOP control.