Understanding racial disparities of glaucoma.

PURPOSE OF REVIEW: Increased prevalence, earlier onset, and more rapid progression to vision loss from glaucoma has demonstrated racial disparity in numerous studies over decades. Precise etiologies of these important differences among patients of African and Hispanic ancestral background have not been elucidated. This review focuses on currently available epidemiologic/population, genetic, socioeconomic and physiologic studies of racial disparities in this blinding disease. RECENT FINDINGS: In depth reviews of several landmark studies of glaucoma prevalence in various racial groups have highlighted potential challenges of lack of recruitment of diverse populations in genetic studies and clinical trials, challenges of racial stratification of subjects, and the impact of socioeconomic variables. SUMMARY: Through a more comprehensive analysis of racial disparities of glaucoma, both clinicians and researchers may provide more effective population screening and management with a holistic approach for individualized patient care to provide improved outcomes. Future studies of interventions in sociodemographic factors and genetic/physiologic variables that influence the prevalence, access, and consequential vision loss from glaucoma will be crucial to minimize/eliminate racial disparities and improve outcomes for all.

Trabecular Meshwork Mitochondrial Function and Oxidative Stress: Clues to Racial Disparities of Glaucoma.

Purpose: To identify racial differences of oxidative damage and stress and mitochondrial function in human trabecular meshwork (TM). Design: Experimental study. Participants: One hundred seventy-three eyes of 173 patients undergoing intraocular surgery provided aqueous humor (AH) for analysis. Trabecular meshwork tissues from eye bank donors were used as healthy controls for primary cell culture. Methods: Enzyme-linked immunosorbent assay methods were used to measure 8-hydroxy-2-deoxyguanosine (8-OHdG), an oxidative damage marker, in AH comparing Black and White Americans. Human TM primary cultured cells from Black and White donors were used for adenosine triphosphate (ATP) measurement under high and low oxygen culture conditions. Complex I activity was measured in mitochondrial fractions isolated from cultured TM cells. Mitochondrial quantification was performed by translocase of outer mitochondrial membrane 20 (TOMM20) Western blot. Intracellular reactive oxygen species (ROS) production was measured in live TM cells. Main Outcome Measures: Oxidative damage in AH, ATP production, complex I activity, mitochondrial quantification, and intracellular ROS in cultured TM cells stratified by racial background. Results: Aqueous humor samples (75 Black, 98 White) displayed significantly higher 8-OHdG levels (P = 0.024) in Black compared with White patients with severe stage glaucoma. Using cultured healthy donor TM cells, ATP production was higher in Black than White TM cells (P = 0.002) in low oxygen culture conditions. Complex I activity was not statistically different in Black compared with White TM cells, but TOMM20 expression was higher in Black versus White cells (P = 0.001). In response to hydrogen peroxide challenge, ROS production was significantly higher in Black compared to White TM cells (P = 0.004). Conclusions: Significantly higher 8-OHdG levels in AH of Black compared with White patients with severe glaucoma indicated that oxidative damage may be a risk factor in glaucoma pathogenesis or the result of distinct pathologic features in the Black population. To identify potential origins or causes of this damage, our data showed that healthy Black cultured TM cells have higher ATP and ROS levels, with increased quantity of mitochondria, compared with White TM cells. These findings indicate that mitochondrial alterations and increased oxidative stress may influence racial disparities of glaucoma.

Racial Disparities in Glaucoma: From Epidemiology to Pathophysiology.

Among individuals of African and Latinx descent compared to those of European background, there is a higher prevalence, earlier onset, more rapid progression of primary open angle glaucoma and greater incidence of blindness. Although some suggest that outreach, education and screening programs may expand earlier diagnosis, and attention to access, cost of treatment, and adherence will improve outcomes, there is increasing evidence of genetic and physiologic differences which may be associated with these disease disparities.

Compositional Analysis of Extracellular Aggregates in the Eyes of Patients With Exfoliation Syndrome and Exfoliation Glaucoma.

Purpose: Exfoliation syndrome (XFS) is a condition characterized by the production of insoluble fibrillar aggregates (exfoliation material; XFM) in the eye and elsewhere. Many patients with XFS progress to exfoliation glaucoma (XFG), a significant cause of global blindness. We used quantitative mass spectrometry to analyze the composition of XFM in lens capsule specimens and in aqueous humor (AH) samples from patients with XFS, patients with XFG and unaffected individuals. Methods: Pieces of lens capsule and samples of AH were obtained with consent from patients undergoing cataract surgery. Tryptic digests of capsule or AH were analyzed by high-performance liquid chromatography-mass spectrometry and relative differences between samples were quantified using the tandem mass tag technique. The distribution of XFM on the capsular surface was visualized by SEM and super-resolution light microscopy. Results: A small set of proteins was consistently upregulated in capsule samples from patients with XFS and patients with XFG, including microfibril components fibrillin-1, latent transforming growth factor-ß-binding protein-2 and latent transforming growth factor-ß-binding protein-3. Lysyl oxidase-like 1, a cross-linking enzyme associated with XFS in genetic studies, was an abundant XFM constituent. Ligands of the transforming growth factor-ß superfamily were prominent, including LEFTY2, a protein best known for its role in establishing the embryonic body axis. Elevated levels of LEFTY2 were also detected in AH from patients with XFG, a finding confirmed subsequently by ELISA. Conclusions: This analysis verified the presence of suspected XFM proteins and identified novel components. Quantitative comparisons between patient samples revealed a consistent XFM proteome characterized by strong expression of fibrillin-1, lysyl oxidase-like-1, and LEFTY2. Elevated levels of LEFTY2 in the AH of patients with XFG may serve as a biomarker for the disease.

Intraocular Oxygen and Antioxidant Status: New Insights on the Effect of Vitrectomy and Glaucoma Pathogenesis.

PURPOSE: The purpose of this study was to investigate correlations of partial pressure of oxygen (pO2) in the ocular anterior segment of human eyes and aqueous humor antioxidant levels of ascorbate (AsA) and total reactive antioxidant potential (TRAP) with glaucoma and vitreous status. METHODS: This prospective, cross-sectional study stratified patients (n = 288 eyes) by lens and vitreous status and the presence of primary open-angle glaucoma for statistical analyses. Intraocular pO2 concentrations were measured using a fiberoptic probe in patients at the beginning of planned glaucoma and/or cataract surgery. Aqueous humor specimens were obtained for antioxidant analysis of AsA and TRAP. RESULTS: Following prior pars plana vitrectomy, pO2 levels were significantly higher than in the reference group of cataract surgery in the anterior chamber angle (16.2 ± 5.0 vs. 13.0 ± 3.9 mm Hg; P = .0171) and in the posterior chamber (7.6 ± 3.1 vs. 3.9 ± 2.7 mm Hg; P < .0001). AsA and TRAP levels were significantly lower (1.1 ± 0.4 vs. 1.4 ± 0.5 mM, respectively; 403.3 ±116.5 vs. 479.0 ± 146.7 Trolox units, respectively; P = .004 and P = .024, respectively) in patients after vitrectomy. In patients with an intact vitreous, neither pO2 nor antioxidant status correlated with lens status or glaucoma. CONCLUSIONS: Increased pO2 and antioxidant depletion following vitrectomy suggests an alteration of the intraocular oxidant-antioxidant balance. Our study links physiologic factors such as increased pO2 in the anterior chamber angle and the posterior chamber to decreased antioxidant levels in aqueous humor following vitrectomy. Oxidative stress/damage to the trabecular meshwork in such post-vitrectomy cases may contribute to intraocular pressure elevation and increased risk of glaucoma. NOTE: Publication of this article is sponsored by the American Ophthalmological Society.

Monitoring Neurodegeneration in Glaucoma: Therapeutic Implications.

Glaucoma is one of the leading causes of blindness globally, and is characterized by loss of retinal ganglion cells (RGCs). Because vision loss in glaucoma is not reversible, therapeutic interventions early in disease are highly desirable. However, owing to the current limitations in evaluating glaucomatous neurodegeneration, it is challenging to monitor the disease severity and progression objectively, and to design rational therapeutic strategies accordingly. Therefore, there is a clear need to identify quantifiable molecular biomarkers of glaucomatous neurodegeneration. As such, in our opinion, molecular biomarker(s) that specifically reflect stress or death of RGCs, and which correlate with disease severity, progression, and response to therapy, are highly desirable.

Effects of Vitrectomy and Lensectomy on Older Rhesus Macaques: Oxygen Distribution, Antioxidant Status, and Aqueous Humor Dynamics.

Purpose: The purpose of this study is to evaluate effects of vitrectomy (PPV) and lens extraction with intraocular lens implantation (PE/IOL) on molecular oxygen (pO2) distribution, aqueous humor antioxidant-oxidant balance, aqueous humor dynamics, and histopathologic changes in the trabecular meshwork (TM) in the older macaque monkey. Methods: Six rhesus monkeys underwent PPV followed by PE/IOL. pO2, outflow facility, and intraocular pressure (IOP) were measured. Aqueous and vitreous humor specimens were analyzed for antioxidant status and 8-hydroxy-2'-deoxyguanosine (8-OHdG), a marker of oxidative damage. TM specimens were obtained for immunohistochemical and quantitative PCR analysis. Results: pO2 at baseline revealed steep gradients in the anterior chamber and low levels in the posterior chamber (PC) and around the lens. Following PPV and PE/IOL, pO2 significantly increased in the PC, around the IOL, and angle. IOP increased following both surgical interventions, with no change in outflow facility. Histopathologic analysis did not show changes in TM cell quantification, but there was an increase in 8-OHdG. Quantitative PCR did not reveal significant differences in glaucoma-related gene expression. Aqueous and vitreous humor analysis revealed decreased ascorbate and total reactive antioxidant potential and increased 8-OHdG in the aqueous humor only in the surgical eyes. Conclusions: Oxygen distribution in the older rhesus monkey is similar to humans at baseline and following surgical interventions. Our findings of histopathologic changes of TM oxidative damage and alterations in the oxidant-antioxidant balance suggest a potential correlation of increased oxygen exposure with oxidative stress/damage and the development of open angle glaucoma.

GDF15 is elevated in mice following retinal ganglion cell death and in glaucoma patients.

Glaucoma is the second leading cause of blindness worldwide. Physicians often use surrogate endpoints to monitor the progression of glaucomatous neurodegeneration. These approaches are limited in their ability to quantify disease severity and progression due to inherent subjectivity, unreliability, and limitations of normative databases. Therefore, there is a critical need to identify specific molecular markers that predict or measure glaucomatous neurodegeneration. Here, we demonstrate that growth differentiation factor 15 (GDF15) is associated with retinal ganglion cell death. Gdf15 expression in the retina is specifically increased after acute injury to retinal ganglion cell axons and in a murine chronic glaucoma model. We also demonstrate that the ganglion cell layer may be one of the sources of secreted GDF15 and that GDF15 diffuses to and can be detected in aqueous humor (AH). In validating these findings in human patients with glaucoma, we find not only that GDF15 is increased in AH of patients with primary open angle glaucoma (POAG), but also that elevated GDF15 levels are significantly associated with worse functional outcomes in glaucoma patients, as measured by visual field testing. Thus, GDF15 maybe a reliable metric of glaucomatous neurodegeneration, although further prospective validation studies will be necessary to determine if GDF15 can be used in clinical practice.

Impact of Corneal Endothelial Dysfunctions on Intraocular Oxygen Levels in Human Eyes.

PURPOSE: We studied the implications of corneal endothelial dysfunctions on oxidative stress in the anterior segment via in vivo measurements of oxygen partial pressure (pO2) in the anterior chamber (AC) of human eyes. METHODS: We recruited 51 patients undergoing cataract surgery and/or endothelial keratoplasty (EK). Endothelial cell density (ECD; n = 33) and central corneal thickness (CCT; n = 41) were measured on patients with relatively clear corneas. Before surgery, an oxygen sensor was introduced into the AC via a peripheral corneal paracentesis. In all patients, seven measurements of pO2 were obtained by positioning the flexible tip near the endothelium at the central cornea, at four cardinal subendothelial locations near the midperipheral cornea, and in the mid-AC and AC angle. In patients with pseudophakia or eyes undergoing cataract surgery, pO2 also was measured near the lens surface and in the posterior chamber. RESULTS: Consistent with our previous reports, a steep oxygen gradient was noted in the anterior segment of normal controls (n = 24). In patients with endothelial dysfunctions (n = 27), there was a significant increase of pO2 at all five subendothelial locations without a significant increase of pO2 in the AC angle. By regression analyses, subendothelial pO2 correlated inversely with ECD and positively with CCT in patients with endothelial dysfunctions. CONCLUSIONS: This study demonstrates an even steeper intraocular oxygen gradient in eyes with corneal endothelial dysfunctions. It suggests that the reduced oxygen consumption in corneal endothelial cells may increase oxidative stress in the AC and the existence of an alternative aqueous inflow pathway that maintains a relatively low and constant pO2 at the AC angle.

Central corneal thickness correlates with oxygen levels in the human anterior chamber angle.

PURPOSE: To measure oxygen (pO2) in eyes of patients undergoing intraocular surgery and identify correlations with central corneal thickness (CCT). DESIGN: Prospective, cross-sectional study. METHODS: setting: Institutional. patient population: 124 patients undergoing cataract and/or glaucoma surgery. observation procedure: Prior to surgery, an oxygen sensor was introduced into the anterior chamber (AC) via peripheral corneal paracentesis. The tip of the flexible fiberoptic probe was positioned for 3 measurements in all patients: (1) near central corneal endothelium; (2) in mid-AC; and (3) in AC angle. In patients undergoing cataract extraction, additional measurements were taken (4) at the anterior lens surface and (5) in the posterior chamber. main outcome measures: pO2 measurements at 5 locations within the eye were compared to central corneal thickness measurements by multivariate regression analyses. RESULTS: There was a statistically significant inverse correlation between CCT and pO2 in the anterior chamber angle (P = .048). pO2 was not significantly related to CCT at any other location, including beneath the central cornea. Regression analysis relating CCT to age, race, and oxygen levels in all 5 locations in the anterior segment revealed an association of a thinner cornea with increasing age (P = .007). CONCLUSIONS: Physiologic correlations with central corneal thickness may provide clues to understanding why a thinner cornea increases the risk of open glaucoma. Associations between glaucoma risk, CCT, and pO2 in the AC angle suggest that exposure of the outflow system to increased oxygen or oxygen metabolites may increase oxidative damage to the trabecular meshwork cells, resulting in elevation of intraocular pressure.

Mutation of the melastatin-related cation channel, TRPM3, underlies inherited cataract and glaucoma.

Inherited forms of cataract are a clinically important and genetically heterogeneous cause of visual impairment that usually present at an early age with or without systemic and/or other ocular abnormalities. Here we have identified a new locus for inherited cataract and high-tension glaucoma with variable anterior segment defects, and characterized an underlying mutation in the gene coding for transient receptor potential cation channel, subfamily M, member-3 (TRPM3, melastatin-2). Genome-wide linkage analysis mapped the ocular disease locus to the pericentric region of human chromosome 9. Whole exome and custom-target next-generation sequencing detected a heterozygous A-to-G transition in exon-3 of TRPM3 that co-segregated with disease. As a consequence of alternative splicing this missense mutation was predicted to result in the substitution of isoleucine-to-methionine at codon 65 (c.195A>G; p.I65 M) of TRPM3 transcript variant 9, and at codon 8 (c.24A>G; p.I8 M) of a novel TRPM3 transcript variant expressed in human lens. In both transcript variants the I-to-M substitution was predicted in silico to exert damaging effects on protein function. Furthermore, transient expression studies of a recombinant TRPM3-GFP reporter product predicted that the I-to-M substitution introduced an alternative translation start-site located 89 codons upstream from the native initiator methionine found in eight other TRPM3 transcript variants (1-8). Collectively, these studies have provided the first evidence that TRPM3 is associated with inherited ocular disease in humans, and further provide support for the important role of this cation channel in normal eye development.

Preserve the (intraocular) environment: the importance of maintaining normal oxygen gradients in the eye.

Oxygen levels in the eye are generally low and tightly regulated. Oxygen enters the eye largely by diffusion from retinal arterioles and through the cornea. In intact eyes, oxygen from the retinal arterioles diffuses into the vitreous body. There is a decreasing oxygen gradient from the retina to the lens, established by oxygen consumption by ascorbate in the vitreous fluid and lens metabolism. Age-related degeneration of the vitreous body or removal during vitrectomy exposes the posterior of the lens to increased oxygen, causing nuclear sclerotic cataracts. Lowering oxygen in the vitreous, as occurs in patients with ischemic diabetic retinopathy, protects against cataracts after vitrectomy. Vitrectomy and cataract surgery increase oxygen levels at the trabecular meshwork and with it the risk of open angle glaucoma. Two additional risk factors for glaucoma, African heritage and having a thinner cornea, are also associated with increased oxygen in the anterior chamber angle. Preservation of the vitreous body and the lens, two important oxygen consumers, would protect against nuclear sclerotic cataracts and open angle glaucoma. Delaying removal of the lens for as long as possible after vitrectomy would be an important step in delaying ocular hypertension and glaucoma progression.

Randomized, prospective, comparative trial of EX-PRESS glaucoma filtration device versus trabeculectomy (XVT study).

PURPOSE: To compare the clinical outcomes of the EX-PRESS glaucoma filtration device placed under a partial-thickness scleral flap with trabeculectomy. DESIGN: Randomized, prospective, multicenter trial. METHODS: A total of 120 eyes in 120 subjects were analyzed, including 59 eyes treated with EX-PRESS and 61 eyes treated with trabeculectomy. Both the EX-PRESS and the trabeculectomy groups were treated intraoperatively with mitomycin C and followed postoperatively for 2 years. Surgical success was defined as 5 mm Hg ≤ intraocular pressure ≤ 18 mm Hg, with or without medications, without further glaucoma surgery. RESULTS: Mean intraocular pressure was significantly reduced compared with baseline in both groups (P < 0.001). Average intraocular pressure and number of medications were similar in both groups during follow-up, with mean intraocular pressure at 2 years after surgery of 14.7 ± 4.6 mm Hg and 14.6 ± 7.1 mm Hg in the EX-PRESS and trabeculectomy groups, respectively (P = 0.927). At 2 years after surgery, the success rate was 83% and 79% in the EX-PRESS and trabeculectomy groups, respectively (P = 0.563). Although visual acuity (logMAR) was significantly decreased on day 1 in both groups, the vision was not significantly different compared with baseline at 1 month after EX-PRESS implant (P = 0.285) and 3 months after trabeculectomy (P = 0.255). The variance of early postoperative intraocular pressure values was similar between groups on the first postoperative day but higher after trabeculectomy compared with EX-PRESS implant on day 7 (P = 0.003). The total number of postoperative complications was higher after trabeculectomy than after EX-PRESS implantation (P = 0.013). CONCLUSIONS: Mean intraocular pressures, medication use, and surgical success were similar at 2 years after treatment with the EX-PRESS device and trabeculectomy. Vision recovery between groups was also similar throughout the study, although return to baseline vision was more rapid in the EX-PRESS group. Intraocular pressure variation was lower during the early postoperative period, and postoperative complications were less common after EX-PRESS implantation compared with trabeculectomy.

The development of a decision analytic model of changes in mean deviation in people with glaucoma: the COA model.

PURPOSE: To create and validate a statistical model predicting progression of primary open-angle glaucoma (POAG) assessed by loss of visual field as measured in mean deviation (MD) using 3 landmark studies of glaucoma progression and treatment. DESIGN: A Markov decision analytic model using patient level data described longitudinal MD changes over 7 years. PARTICIPANTS: Patient-level data from the Collaborative Initial Glaucoma Treatment Study (n = 607), the Ocular Hypertension Treatment Study (OHTS; n = 148; only those who developed POAG in the first 5 years of OHTS) and Advanced Glaucoma Intervention Study (n = 591), the COA model. METHODS: We developed a Markov model with transition matrices stratified by current MD, age, race, and intraocular pressure categories and used a microsimulation approach to estimate change in MD over 7 years. Internal validation compared model prediction for 7 years to actual MD for COA participants. External validation used a cohort of glaucoma patients drawn from university clinical practices. MAIN OUTCOME MEASURES: Change in visual field as measured in MD in decibels (dB). RESULTS: Regressing the actual MD against the predicted produced an R(2) of 0.68 for the right eye and 0.63 for the left. The model predicted ending MD for right eyes of 65% of participants and for 63% of left eyes within 3 dB of actual results at 7 years. In external validation the model had an R(2) of 0.79 in the right eye and 0.77 in the left at 5 years. CONCLUSIONS: The COA model is a validated tool for clinicians, patients, and health policy makers seeking to understand longitudinal changes in MD in people with glaucoma.

Racial differences in ocular oxidative metabolism: implications for ocular disease.

OBJECTIVE: To compare the Po(2) distribution in different regions in the eyes of patients undergoing intraocular surgery. METHODS: Before initiation of intraocular cataract and/or glaucoma surgery, an optical oxygen sensor was introduced into the anterior chamber via a peripheral corneal paracentesis. The tip of the flexible fiberoptic probe was positioned by the surgeon for 3 measurements in all patients: (1) near the central corneal endothelium, (2) in the mid-anterior chamber, and (3) in the anterior chamber angle. In patients scheduled to undergo cataract extraction, Po(2) was also measured (4) at the anterior lens surface and (5) in the posterior chamber just behind the iris. Oxygen measurements at the 5 locations were compared using a 2-tailed unpaired t test and multivariate regression. RESULTS: The Po(2) value was significantly higher in African American patients at all 5 locations compared with Caucasian patients. Adjusting for age increased the significance of this association. Adjusting for race revealed that age was associated with increased Po(2) beneath the central cornea. CONCLUSIONS: Racial differences in oxygen levels in the human eye reflect an important difference in oxidative metabolism in the cornea and lens and may reflect differences in systemic physiologic function. Increased oxygen or oxygen metabolites may increase oxidative stress, cell damage, intraocular pressure, and the risk of developing glaucoma. Oxygen use by the cornea decreases with age.