Low systemic vitamin D as a potential risk factor in primary open-angle glaucoma: a review of current evidence

Is fat the future for saving sight? Bioactive lipids and their impact on glaucoma

Glaucoma is characterized by a continuous loss of retinal ganglion cells. The cause of glaucoma is associated with an increase in intraocular pressure (IOP), but the underlying pathophysiology is diverse and, in most cases, unknown. There is an indisputable unmet need to identify new pathways involved in glaucoma pathogenesis. Increasing evidence suggests that bioactive lipids may be critical in the development and progression of glaucoma. Preclinical and clinical bioactive lipid targets exist and are being developed. In this review, we aim to shed light on the potential of bioactive lipids for the prevention, diagnosis, prognosis, and treatment of glaucoma by asking the question "is fat the future for saving sight".

The role of Vitamin D3 in ocular fibrosis and its therapeutic potential for the glaucomatous trabecular meshwork

Glaucoma is the leading cause of irreversible blindness globally. The most prevalent subtype, Primary Open Angle Glaucoma (POAG), is characterized by increased intraocular pressure (IOP), damage to the optic nerve head and irreversible visual loss. IOP increases aqueous humor (AqH) outflow is reduced through the trabecular meshwork (TM) and Schlemm's canal (SC). Increased outflow resistance is partly due to TM/SC dysregulation, including loss of normal trabecular meshwork cell (TMC) function, following increased levels of oxidative stress within TMC, dysregulated extracellular matrix (ECM) deposition and remodeling alongside alterations in TMC phenotype and apoptosis. Current widely available POAG treatments do not target the aberrant expression of ECM in the TM directly. As a result, most drug treatments can fail as the underlying pathological process continues unabated. Rho-kinase inhibitors have demonstrated the benefit of restoring TM/SC function, however there is a clear need to develop further treatment strategies that can target the underlying cellular processes which become dysregulated within the TMC during POAG pathogenesis. Vitamin D is suggested to be beneficial in alleviating the symptoms of fibrosis and inflammation in soft tissues. It has important functions in many major organ systems, including regulation of calcium, phosphate and parathyroid hormone. Evidence suggests that Vitamin D3 modulates ECM turnover through the conventional TGFβ-SMAD signaling, which is associated with the development of POAG. The link between Vitamin D3, inflammation and fibrosis within ocular tissues will be discussed and the potential roles of Vitamin D3 in the management of POAG patients will be explored within this review.

Clinical Tear Fluid Proteomics—A Novel Tool in Glaucoma Research

Tear fluid forms the outermost layer of the ocular surface and its characteristics and composition have been connected to various ocular surface diseases. As tear proteomics enables the non-invasive investigation of protein levels in the tear fluid, it has become an increasingly popular approach in ocular surface and systemic disease studies. Glaucoma, which is a set of multifactorial diseases affecting mainly the optic nerve and retinal ganglion cells, has also been studied using tear proteomics. In this condition, the complete set of pathophysiological changes occurring in the eye is not yet fully understood, and biomarkers for early diagnosis and accurate treatment selection are needed. More in-depth analyses of glaucoma tear proteomics have started to emerge only more recently with the implementation of LC-MS/MS and other modern technologies. The aim of this review was to examine the published data of the tear protein changes occurring during glaucoma, its topical treatment, and surgical interventions.

Association Between Serum Vitamin D Level and Rates of Structural and Functional Glaucomatous Progression

PRCIS

In a retrospective cohort study, serum vitamin D levels were not associated with rates of structural or functional loss in glaucoma patients, suggesting that low vitamin D level is not a risk factor for progression.

PURPOSE

To investigate the association between serum vitamin D level and rates of functional and structural glaucomatous loss over time.

METHODS

This study included 826 eyes of 536 glaucoma or suspect patients with an average follow-up of 4.8±1.9 years. All patients had at least 1 serum vitamin D measurement, and all eyes had at least 2 reliable standard automated perimetry (SAP) tests and 2 spectral-domain optical coherence tomography (SD OCT) tests with a minimum follow-up of 6 months. Multivariable linear mixed-effects models were used to estimate the association of vitamin D level with rates of change in SAP mean deviation (MD) and OCT retinal nerve fiber layer (RNFL) thickness over time while adjusting for potential confounding factors.

RESULTS

Patients had an average of 3.4±1.7 SAP tests, 4.8±1.9 SD OCT tests, and 2.3±1.9 vitamin D measurements. The average serum vitamin D level was 33.9±13.2 ng/mL. Mean rates of MD and RNFL change were -0.03±0.08 dB/y and -0.68±0.64 µm/y, respectively. After controlling for confounding factors, there was no statistically significant association between mean vitamin D level and rates of MD (β=0.038, 95% CI: -0.006, 0.082, P =0.09) or RNFL loss over time (β=-0.018, 95% CI: -0.092, 0.055, P =0.62).

CONCLUSIONS

We did not find a significant association between vitamin D level and rates of visual field or RNFL loss over time in individuals with glaucoma and glaucoma suspect patients.

Vitamin D, the Vitamin D Receptor, Calcitriol Analogues and Their Link with Ocular Diseases

The global prevalence of eye diseases continues to grow, bringing with it a reduction in the activity levels and quality of life of patients, and partial or complete blindness if left untreated. As such, there is considerable interest in identifying more effective therapeutic options and preventive agents. One such agent is vitamin D, known to have a range of anti-cancer, anti-angiogenic, anti-inflammatory and anti-oxidative properties, and whose deficiency is linked to the pathogenesis of a range of cardiovascular, cancer, and inflammatory diseases. This review presents the current stage of knowledge concerning the link between vitamin D and its receptor and the occurrence of eye disease, as well as the influence of analogues of calcitriol, an active metabolite of vitamin D. Generally, patients affected by various ocular disorders have vitamin D deficiency. In addition, previous findings suggest that vitamin D modulates the course of eye diseases and may serve as a marker, and that its supplementation could mitigate some disorders. However, as these studies have some limitations, we recommend further randomized trials to clarify the link between vitamin D and its activity with eye disease.

Study of vitamin D penetration in the human aqueous after topical administration

Purpose

this study was designed to measure the concentration of Vitamin D in the aqueous and to investigate if its topical application can increase quantities in aqueous humor.

Methods

29 patients scheduled for cataract surgery were divided into two groups. Group 1 was used as a control group, in group 2 patients were instructed to instill one drop of vitamin D eye drops three times daily 10 days before surgery .Aqueous humor was collected with a 30-gauge needle immediately before surgery. Vitamin D concentrations were analyzed by liquid chromatography tandem mass spectrometry.

Results

Aqueous humor (AH) samples in both groups had small but detectable vitamin D levels. In the AH concentrations of vitamin D were, respectively, 2.1ng/mL 土0.4 in group 1 and 2.1ng/mL土0.3 in group 2(P = 0.9).

Conclusion

Our study confirmed the presence of vitamin D in AH. No significant difference of vitamin D concentration in AH was observed between the treatment and control group.

Nicotinamide and Pyruvate for Neuroenhancement in Open-Angle Glaucoma: A Phase 2 Randomized Clinical Trial

Importance

Open-angle glaucoma may continue to progress despite significant lowering of intraocular pressure (IOP). Preclinical research has suggested that enhancing mitochondrial function and energy production may enhance retinal ganglion cell survival in animal models of glaucoma, but there is scant information on its effectiveness in a clinical setting.

Objective

To test the hypothesis that a combination of nicotinamide and pyruvate can improve retinal ganglion cell function in human glaucoma as measured with standard automated perimetry.

Design, Setting, and Participants

In this phase 2, randomized, double-blind, placebo-controlled clinical trial at a single academic institution, 197 patients were assessed for eligibility. Of these, 42 patients with treated open-angle glaucoma and moderate visual field loss in at least 1 eye were selected for inclusion and randomized. A total of 32 completed the study and were included in the final analysis. The mean (SD) age was 64.6 (9.8) years. Twenty-one participants (66%) were female. Participant race and ethnicity data were collected via self-report to ensure the distribution reflected that observed in clinical practice in the US but are not reported here to protect patient privacy. Recruitment took place in April 2019 and patients were monitored through December 2020. Data were analyzed from January to May 2021.

Interventions

Ascending oral doses of nicotinamide (1000 to 3000 mg) and pyruvate (1500 to 3000 mg) vs placebo (2:1 randomization).

Main Outcomes and Measures

Number of visual field test locations improving beyond normal variability in the study eye. Secondary end points were the rates of change of visual field global indices (mean deviation [MD], pattern standard deviation [PSD], and visual field index [VFI]).

Results

Twenty-two of 29 participants (76%) randomized to the intervention group and 12 of 13 participants (92%) randomized to placebo received their allocation, and 32 participants (32 eyes; ratio 21:11) completed the study (21 from the intervention group and 11 from the placebo group). Median (IQR) follow-up time was 2.2 (2.0-2.4) months. No serious adverse events were reported during the study. The number of improving test locations was significantly higher in the treatment group than in the placebo group (median [IQR], 15 [6-25] vs 7 [6-11]; P = .005). Rates of change of PSD suggested improvement with treatment compared with placebo (median, -0.06 vs 0.02 dB per week; 95% CI, 0.02 to 0.24; P = .02) but not MD (0.04 vs -0.002 dB per week; 95% CI, -0.27 to 0.09; P = .35) or VFI (0.09 vs -0.02% per week; 95% CI, -0.53 to 0.36; P = .71).

Conclusions and Relevance

A combination of nicotinamide and pyruvate yielded significant short-term improvement in visual function, supporting prior experimental research suggesting a role for these agents in neuroprotection for individuals with glaucoma and confirming the need for long-term studies to establish their usefulness in slowing progression.

Trial Registration

ClinicalTrials.gov Identifier: NCT03797469.