Ocular hypertension: general characteristics and estimated cerebrospinal fluid pressure. The Beijing Eye Study 2011

Glaucoma: from pathogenic mechanisms to retinal glial cell response to damage

Glaucoma is a neurodegenerative disease of the retina characterized by the irreversible loss of retinal ganglion cells (RGCs) leading to visual loss. Degeneration of RGCs and loss of their axons, as well as damage and remodeling of the lamina cribrosa are the main events in the pathogenesis of glaucoma. Different molecular pathways are involved in RGC death, which are triggered and exacerbated as a consequence of a number of risk factors such as elevated intraocular pressure (IOP), age, ocular biomechanics, or low ocular perfusion pressure. Increased IOP is one of the most important risk factors associated with this pathology and the only one for which treatment is currently available, nevertheless, on many cases the progression of the disease continues, despite IOP control. Thus, the IOP elevation is not the only trigger of glaucomatous damage, showing the evidence that other factors can induce RGCs death in this pathology, would be involved in the advance of glaucomatous neurodegeneration. The underlying mechanisms driving the neurodegenerative process in glaucoma include ischemia/hypoxia, mitochondrial dysfunction, oxidative stress and neuroinflammation. In glaucoma, like as other neurodegenerative disorders, the immune system is involved and immunoregulation is conducted mainly by glial cells, microglia, astrocytes, and Müller cells. The increase in IOP produces the activation of glial cells in the retinal tissue. Chronic activation of glial cells in glaucoma may provoke a proinflammatory state at the retinal level inducing blood retinal barrier disruption and RGCs death. The modulation of the immune response in glaucoma as well as the activation of glial cells constitute an interesting new approach in the treatment of glaucoma.

Evaluation of the nutraceutical Palmitoylethanolamide in reducing intraocular pressure (IOP) in patients with glaucoma or ocular hypertension: a systematic review and meta-analysis

Intraocular pressure (IOP) positively correlates with both normal and high-tension glaucoma. To date, IOP targeting remains the validated pharmacological approach in counteracting glaucoma progression as well as in halting vision loss. Among the different adjuvant compounds, evidence highlighted the potential effectiveness of Palmitoylethanolamide (PEA), an endogenous fatty acid amide. Thus, a systematic review of the literature was conducted, thoroughly evaluating PEA treatment regimen in decreasing IOP in patients with eye disorders. We checked for articles across the scientific databases Pubmed (MEDLINE), Embase (OVID), and Web of Science from the inception to 30 August 2023, and a total of 828 articles were recovered. Six of these studies (199 patients) were included in the systematic review after the study selection process, and three studies for meta-analysia. Overall, PEA showed significant efficacy in reducing IOP in patients, this encourages its clinical use in glaucoma as well as across different forms of eye disorders.

Effect of Prefilled vs Vial-Drawn Syringes on Sustained Increases in Intraocular Pressure in Patients Treated With Aflibercept

Purpose: To evaluate the effect of syringe type on developing sustained intraocular pressure (IOP) increases. Methods: This retrospective cohort study included patients in a single academic center receiving antivascular endothelial growth factor (anti-VEGF) injections from 2012 to 2022 for various indications. Patients were grouped by anti-VEGF treatment of either vial-drawn or prefilled syringe delivery. Trends in IOP were recorded for 1 year after treatment began. Development of sustained IOP increase, ocular hypertension, and glaucoma was recorded. Sustained IOP increase was defined as ≥5 mm Hg above baseline for at least 4 weeks. Results: Of 257 total patients, 6 (2.3%) developed sustained IOP increases throughout the study's duration. No significant differences were noted with respect to prefilled versus vial-drawn syringe status on the development of sustained IOP increases or incident glaucoma (IOP: 1.8% vs 2.7%, respectively, P = .65; glaucoma: 0.0% vs 2.0%, respectively, P = .14). Patients treated with prefilled syringes were significantly less likely to develop ocular hypertension (2.8% vs 8.8%, P < .05). Conclusions: This study found that aflibercept intravitreal injection with prefilled syringes was not associated with a significant increase in IOP-related adverse effects when compared with those treated with vial-drawn syringes.

Severe systemic adverse reactions to ophthalmic timolol in a CYP2D6 homozygous *4 allele carrier: a case report

A woman with ocular hypertension suffered from severe bradycardia, hypotension and syncope attacks in temporal relation with ophthalmic timolol application. Topically applied timolol is nasally absorbed and has been shown to reach potentially relevant systemic concentrations. Timolol is mainly metabolized by CYP2D6, which exhibits interindividual metabolic capacity due to genetic variations. A reactive pharmacogenetic panel test identified the patient as a CYP2D6 homozygous *4 allele carrier, which has been associated with a poor metabolizer phenotype and lacking enzyme activity. Thus, the adverse drug reactions possibly resulted from increased systemic timolol exposure. This case report highlights that pharmacogenetic panel testing can contribute to safe and effective pharmacotherapy, even for topically applied drugs.

Mechanically Active Materials and Devices for Bio-Interfaced Pressure Sensors-A Review

Pressures generated by external forces or by internal body processes represent parameters of critical importance in diagnosing physiological health and in anticipating injuries. Examples span intracranial hypertension from traumatic brain injuries, high blood pressure from poor diet, pressure-induced skin ulcers from immobility, and edema from congestive heart failure. Pressures measured on the soft surfaces of vital organs or within internal cavities of the body can provide essential insights into patient status and progression. Challenges lie in the development of high-performance pressure sensors that can softly interface with biological tissues to enable safe monitoring for extended periods of time. This review focuses on recent advances in mechanically active materials and structural designs for classes of soft pressure sensors that have proven uses in these contexts. The discussions include applications of such sensors as implantable and wearable systems, with various unique capabilities in wireless continuous monitoring, minimally invasive deployment, natural degradation in biofluids, and/or multiplexed spatiotemporal mapping. A concluding section summarizes challenges and future opportunities for this growing field of materials and biomedical research.

Problems in CSF and Ophthalmic Disease Research

There has been significant interest and progress in the understanding of cerebrospinal fluid pressure and its relationship to glaucoma and other ophthalmic diseases. However, just as every physiologic fluid pressure fluctuates, cerebrospinal fluid pressure (CSFP) is similarly dynamic. Coupling this with the difficulty in measuring the pressure, there are many obstacles in furthering this field of study. This review highlights some of the difficulties in CSFP research, including fluid compartmentalization, estimation equations, and pressure fluctuation. Keeping these limitations in mind will hopefully improve the quality and context of this burgeoning field.

The Intertwined Roles of Oxidative Stress and Endoplasmic Reticulum Stress in Glaucoma

Glaucoma is the leading cause of irreversible blindness worldwide, and the burden of the disease continues to grow as the global population ages. Currently, the only treatment option is to lower intraocular pressure. A better understanding of glaucoma pathogenesis will help us to develop novel therapeutic options. Oxidative stress has been implicated in the pathogenesis of many diseases. Oxidative stress occurs when there is an imbalance in redox homeostasis, with reactive oxygen species producing processes overcoming anti-oxidant defensive processes. Oxidative stress works in a synergistic fashion with endoplasmic reticulum stress, to drive glaucomatous damage to trabecular meshwork, retinal ganglion cells and the optic nerve head. We discuss the oxidative stress and endoplasmic reticulum stress pathways and their connections including their key intermediary, calcium. We highlight therapeutic options aimed at disrupting these pathways and discuss their potential role in glaucoma treatment.

Three-Decade Evaluation of Cerebrospinal Fluid Pressure in Open-Angle Glaucoma at a Tertiary Care Center

Elevated intraocular pressure (IOP) is the most prevalent risk factor for primary open-angle glaucoma. However, IOP alone does not fully describe a mechanical basis for disease in patients with normal tension glaucoma or primary open-angle glaucoma. The translaminar pressure difference (TLPD) theory proposes that the pressure gradient generated by the difference of IOP and cerebrospinal fluid pressure (CSFp) acting at the level of the optic nerve can lead to cupping and glaucoma when IOP is higher than normal and/or CSFp is lower than normal. The study results to date have generally supported the TLPD theory; however, varying methods, populations, and sample sizes make it difficult to compare results. To further assess whether there is an association between low CSFp and open-angle glaucoma, 30 years of clinical data that assess 96,543 lumbar punctures were analyzed. Patients with open-angle glaucoma showed a significantly lower CSFp than randomly selected normal control patients (9.9 ± 3 mm·Hg (n = 86) versus 12.1 ± 3.6 mm·Hg (n = 114), p < 0.001) following adjustment for age and sex. This retrospective study provides strong evidence for an association between open-angle glaucoma and low CSFp.

Comparison of Lamina Cribrosa Morphology in Eyes with Ocular Hypertension and Normal-Tension Glaucoma

Purpose

To characterize differences in the lamina cribrosa (LC) morphology between healthy, ocular hypertension (OHT), and naive normal-tension glaucoma (NTG) eyes.

Methods

Each group consisted of 80 eyes of 80 participants who were matched for age, sex, and axial length. The participants underwent enhanced-depth-imaging volume scanning of the optic nerve head using spectral-domain optical coherence tomography. The lamina cribrosa curvature index (LCCI) and lamina cribrosa thickness (LCT) were measured in horizontal B-scan images spaced equidistantly across the vertical diameter of the optic disc.

Results

The LCCIs in all seven planes were smaller in both OHT and healthy eyes than in NTG eyes (all P < 0.001), and did not differ significantly between the OHT and healthy eyes. The LCTs in all three planes were greatest in OHT eyes followed by healthy and then NTG eyes (all P < 0.001). Overall, the larger LCCI was associated with smaller LCT (P < 0.001).

Conclusions

The LC was thin and steeply curved in NTG eyes than in healthy and OHT eyes. In OHT eyes, the LC was thick, and its curvature was comparable to healthy eyes. Longitudinal studies are required to examine whether the straight and thickened LCs in OHT eyes precede the onset of OHT or are a protective response to elevated intraocular pressure.

Evaluation of Cerebrospinal Fluid Pressure by a Formula and Its Role in the Pathogenesis of Glaucoma

Purpose

To investigate potential associations between intraocular pressure (IOP) and cerebrospinal fluid pressure (CSFP) in patients with primary open-angle glaucoma (POAG) and healthy subjects.

Methods

Forty-three subjects were recruited. Weight and height were measured to calculate body mass index (BMI), along with blood pressure, heart rate, visual acuity, and IOP. Biometrics exam, corneal pachymetry, peripapillary retinal nerve fiber layer (RNFL) thickness, and macular thickness were assessed. The visual field exam was performed on all patients, and both pattern standard deviation (PSD) and mean deviation (MD) were considered. CSFP was estimated indirectly by using the mathematical formula CSFP = 0.44 × BMI + 0.16 × diastolic pressure - 0.18 × age - 1.91, based on the previous scientific studies. The TLCPD was calculated as follows: IOP-CSFP.

Results

A significant (p < 0.05) difference was found between the two groups for several parameters. Specifically, the CSFP was lower in patients with POAG than in healthy subjects (8.14 ± 4.52 and 7.43 ± 2.06, p < 0.001, respectively). Anamnestic TLCPD was found to be significantly (p < 0.001) higher in patients with POAG compared to healthy subjects. A significant (p < 0.05) correlation was found between anamnestic TLCPD and MD (r = -0.31), inferior RNFL thickness (r = -0.29), superior RNFL thickness (r = -0.27), IOP (r = 0.22), and CSFP (r = -0.46).

Conclusion

The CSFP was lower in glaucomatous patients compared to healthy subjects, whereas the TLCPD was higher in glaucomatous patients compared to healthy subjects, even though this difference was not statistically significant. A higher TLCPD may damage the RNFL, resulting in functional visual field impairment.

Role of 24-Hour Intraocular Pressure Monitoring in Glaucoma Management

Glaucoma is the leading cause of irreversible blindness worldwide and the prevalence is on the rising trend. Intraocular pressure (IOP) reduction is the mainstay of treatment. The current practice of IOP monitoring is based on spot measurements during clinic visits during office hours. However, there are up to 50% of glaucoma patients who had normal initial IOP, while some treated patients continued to have progressive glaucomatous optic nerve damage even with a low IOP. Recent studies have shown that the IOP of glaucoma patients fluctuated during the day with different patterns, and some of them had peak IOP outside office hours. These findings provided us with new insights on the role of 24-hour IOP monitoring in managing normal tension glaucoma and patients with progressive deterioration despite apparently well-controlled IOP. Nevertheless, results to date are rather inconsistent, and there is no consensus yet. In this review, we briefly highlighted the current modalities of 24-hour IOP monitoring and summarized the characteristic 24-hour IOP pattern and the clinical relevance of IOP parameters in predicting glaucomatous progression in different glaucoma subtypes. We also discussed the therapeutic efficacy of current glaucoma treatment modalities with respect to the mentioned 24-hour IOP profiles, so as to strengthen the role of 24-hour IOP monitoring in identifying and stratifying the risks of progression in glaucoma patients, as well as optimizing treatments according to their IOP profiles.

Noninvasive evaluation of cerebrospinal fluid pressure in ocular hypertension: a preliminary study

PURPOSE

To compare the orbital cerebral spinal fluid pressure (CSFP) and trans-lamina cribrosa pressure difference (TLCPD) determined noninvasively in ocular hypertensive (OH) subjects and controls.

METHODS

Cross-sectional observational study. Magnetic resonance imaging was used to measure orbital subarachnoid space width (OSASW). The CSFP (mm Hg) was estimated from a published formula as 17.54 × MRI derived OSASW at 15 mm behind the globe + 0.47 × body mass index + 0.13 × mean arterial blood pressure -21.52. Estimated TLCPD was calculated as IOP- CSFP.

RESULTS

The orbital subarachnoid space width was significantly wider (p = 0.01) in the OH group than in the control group at all three measurement locations. The MRI derived CSFP value in OH (14.9 ± 2.9 mm Hg) was significantly higher than in the normal group (12.0 ± 2.8 mm Hg; p < 0.01). The estimated TLCPD value in OH (9.0 ± 4.2 mm Hg) was significantly higher than in controls (3.6 ± 3.0 mm Hg; p < 0.01).

CONCLUSION

The wider OSASW and higher estimated CSFP in OH subjects suggest a higher orbital CSFP. Despite a higher orbital CSFP that could be protective, the higher TLCPD in OH may play a significant role in the risk of developing glaucoma.

Translaminar pressure in Caucasian normal tension glaucoma patients

PURPOSE

The aim of this study was to examine the translaminar pressure difference (TLP) in Caucasian patients with normal tension glaucoma (NTG) and its possible impact onto the pathogenesis of NTG.

METHODS

Retrospective analysis of medical records of patients with open-angle glaucoma (OAG) in the period from 2005 to 2015 from the Ophthalmology Department, Cantonal Hospital Aarau, Switzerland. A total of 67 eyes of 38 patients (mean age 68.6 ± 11.3 years, 21 women and 17 men) fulfilled the diagnostic criteria of progressive NTG and underwent lumbar puncture (LP) during computer-assisted cisternography (CT - cisternography). The intraocular pressure (IOP) and lumbar cerebrospinal fluid pressure (CSF-p) were analysed and the TLP calculated. The TLP was compared with the mean defect (MD) of visual fields. Statistical analysis was performed with the one and two-tailed paired and unpaired t-test and the non-parametric Spearman correlation test.

RESULTS

The mean lumbar opening CSF-p measured 11.6 ± 3.7 mmHg. The mean IOP in the right eye measured 14.7 ± 2.4 mmHg, in the left eye 14.7 ± 2.5 mmHg. The calculated mean TLP was 3.0 ± 4.2 mmHg in the right and 3.3 ± 4.3 mmHg in the left eye. There was no significant correlation between TLP and the MD of visual fields in both eyes.

CONCLUSIONS

This study did not confirm either a lower lumbar CSF-p or increased TLP compared to previous retrospective and prospective studies. As cerebrospinal fluid (CSF) flow is not homogenous throughout all CSF spaces and CSF-p and IOP fluctuate, the current view on TLP needs modifications to improve its validity.

Association of intraocular pressure-related factors and retinal vessel diameter with optic disc rim area in subjects with and without primary open angle glaucoma

IMPORTANCE

The data may support the notion that the intra-ocular pressure (IOP)-related factors and vascular factors were implicated concurrently in glaucomatous optic nerve damage.

BACKGROUND

To study the association of intraocular pressure (IOP)-related factors, IOP, trans-lamina cribrosa pressure difference (TLCPD), cerebrospinal fluid pressure (CSFP) and retinal vessel diameters (RVD), central retinal arteriolar equivalent (CRAE), central retinal venular equivalent (CRVE) with neuro-retinal rim area (RA).

DESIGN

A population-based, cross-sectional study.

PARTICIPANTS

A total of 6830 people aged 30 years and over.

METHODS

All participants underwent a comprehensive eye examination, fundus photograph-based measurements of RVD and Heidelberg retinal tomogram (HRT) measurement of optic disc.

MAIN OUTCOME MEASURES

RA, CRAE, CRVE, IOP, body mass index (BMI), CSFP and TLCPD.

RESULTS

Primary open-angle glaucoma (POAG) was diagnosed using two separate methods: 67 from expert consensus, and 125 from the International Society of Geographical and Epidemiologic Ophthalmology (ISGEO) classification. After excluding of those with high myopia or without gradable HRT images, 4194 non-glaucoma and 40 POAG were analysed for determinants of RA. On multivariable analysis determinants of reduced RA were POAG (P < 0.001), higher IOP (P = 0.03), higher refractive error (P < 0.01), longer axial length (P = 0.01), CRVE (P < 0.001), lower BMI (P = 0.015), older age (P < 0.001) smaller disc area (P < 0.001) and higher TLCPD (P = 0.03). When age and/or BMI were omitted from the model, reduced RA was also associated with lower CSFP (P < 0.001).

CONCLUSIONS AND RELEVANCE

Reduced RA is associated with narrow CRVE and higher IOP or lower CSFP. The data supports the concurrent role of IOP-related and vascular factors in glaucomatous optic nerve damage.

Estimated Trans-Lamina Cribrosa Pressure Differences in Low-Teen and High-Teen Intraocular Pressure Normal Tension Glaucoma: The Korean National Health and Nutrition Examination Survey

BACKGROUND

To investigate the association between estimated trans-lamina cribrosa pressure difference (TLCPD) and prevalence of normal tension glaucoma (NTG) with low-teen and high-teen intraocular pressure (IOP) using a population-based study design.

METHODS

A total of 12,743 adults (≥ 40 years of age) who participated in the Korean National Health and Nutrition Examination Survey (KNHANES) from 2009 to 2012 were included. Using a previously developed formula, cerebrospinal fluid pressure (CSFP) in mmHg was estimated as 0.55 × body mass index (kg/m2) + 0.16 × diastolic blood pressure (mmHg)-0.18 × age (years)-1.91. TLCPD was calculated as IOP-CSFP. The NTG subjects were divided into two groups according to IOP level: low-teen NTG (IOP ≤ 15 mmHg) and high-teen NTG (15 mmHg < IOP ≤ 21 mmHg) groups. The association between TLCPD and the prevalence of NTG was assessed in the low- and high-teen IOP groups.

RESULTS

In the normal population (n = 12,069), the weighted mean estimated CSFP was 11.69 ± 0.04 mmHg and the weighted mean TLCPD 2.31 ± 0.06 mmHg. Significantly higher TLCPD (p < 0.001; 6.48 ± 0.27 mmHg) was found in the high-teen NTG compared with the normal group. On the other hand, there was no significant difference in TLCPD between normal and low-teen NTG subjects (p = 0.395; 2.31 ± 0.06 vs. 2.11 ± 0.24 mmHg). Multivariate logistic regression analysis revealed that TLCPD was significantly associated with the prevalence of NTG in the high-teen IOP group (p = 0.006; OR: 1.09; 95% CI: 1.02, 1.15), but not the low-teen IOP group (p = 0.636). Instead, the presence of hypertension was significantly associated with the prevalence of NTG in the low-teen IOP group (p < 0.001; OR: 1.65; 95% CI: 1.26, 2.16).

CONCLUSIONS

TLCPD was significantly associated with the prevalence of NTG in high-teen IOP subjects, but not low-teen IOP subjects, in whom hypertension may be more closely associated. This study suggests that the underlying mechanisms may differ between low-teen and high-teen NTG patients.

Translamina Cribrosa Pressure Difference as Potential Element in the Pathogenesis of Glaucomatous Optic Neuropathy

The main proven risk factor for glaucomatous optic neuropathy (GON) is an intraocular pressure (IOP) higher than the pressure sensibility of the optic nerve head allows. Fulfilling Koch postulates, numerous studies have shown that the presence of high IOP leads to GON, that lowering IOP stops the progression of GON, and that a re-increase in IOP again causes the progression of GON. There are, however, many patients with glaucoma who have statistically normal or low IOP, and despite low IOP values, they develop progressing GON. These observations led to findings that IOP is only 1 of 2 determinants of the translamina cribrosa pressure difference (TLCPD), which is the main pressure-related parameter for the physiology and pathophysiology of the optic nerve head. The second parameter influencing TLCPD is orbital cerebrospinal fluid pressure (CSFP) as the counter pressure against IOP across the lamina cribrosa. Recent experimental and clinical studies have suggested that a low CSFP could be associated with GON in normal-pressure glaucoma. These investigations included studies with an experimental long-term reduction in CSFP in monkeys, population-based studies, and clinical retrospective and prospective investigations on patients with normal-pressure glaucoma. Besides TLCPD, other ocular parameters influenced by CSFP may be choroidal thickness, retinal vein pressure and diameter, occurrence of retinal vein occlusions, and occurrence and severity of diabetic retinopathy.

Ocular Perfusion Pressure vs Estimated Trans-Lamina Cribrosa Pressure Difference in Glaucoma: The Central India Eye and Medical Study (An American Ophthalmological Society Thesis)

PURPOSE

To test the hypothesis that taking translamina pressure difference into consideration changes associations between ocular perfusion pressure and glaucomatous optic neuropathy.

METHODS

The population-based Central India Eye and Medical Study included 4711 subjects. Ocular perfusion pressure was calculated as follows: ⅔ [diastolic blood pressure + ⅓ × (systolic blood pressure - diastolic blood pressure)] - IOP. Cerebrospinal fluid pressure (mm Hg) was estimated as follows: 0.44 body mass index (kg/m(2)) + 0.16 diastolic blood pressure (mm Hg) - 0.18 × age (years) - 1.91. Translamina pressure difference was IOP minus cerebrospinal fluid pressure.

RESULTS

In multivariate analysis, higher open-angle glaucoma prevalence was associaed with higher IOP (P<.001; odds ratio [OR], 1.19; 95% CI, 1.15, 1.24) or with higher translamina pressure difference (P<.001; OR, 1.15; 95% CI, 1.10, 1.19), but not with ocular perfusion pressure (P<.37). A smaller neuroretinal rim area was correlated with higher IOP (P<.001; standardized coefficient beta -0.09) or larger translamina pressure difference (P<.001; β -0.10), but not with ocular perfusion pressure (P=.26). Greater prevalence of angle-closure glaucoma was associated with higher IOP (P<.001; OR, 1.22; 95% CI, 1.15, 1.28) or higher translamina pressure difference (P<.001; OR, 1.19; 95% CI, 1.13, 1.25) or lower ocular perfusion pressure (P<.04; OR, 0.95; 95% CI, 0.90, 0.996). Correlation coefficients were highest for the association with IOP and lowest for ocular perfusion pressure. A smaller rim area was correlated with higher IOP (P<.001; beta -0.08) and higher translamina pressure difference (P<.001; beta -0.08); rim area and ocular perfusion pressure were not significantly associated (P=.25).

CONCLUSIONS

The present study provides information on the relationship of translamina pressure difference to the development of optic nerve damage in what is presently called glaucoma. It does not provide support of the idea that ocular perfusion pressure plays a major role in the pathogenesis of optic neuropathy.