Dual effect of the Valsalva maneuver on autonomic nervous system activity, intraocular pressure, Schlemm's canal, and iridocorneal angle morphology

Bidirectional causality of physical exercise in retinal neuroprotection

Physical exercise is recognized as an effective intervention to improve mood, physical performance, and general well-being. It achieves these benefits through cellular and molecular mechanisms that promote the release of neuroprotective factors. Interestingly, reduced levels of physical exercise have been implicated in several central nervous system diseases, including ocular disorders. Emerging evidence has suggested that physical exercise levels are significantly lower in individuals with ocular diseases such as glaucoma, age-related macular degeneration, retinitis pigmentosa, and diabetic retinopathy. Physical exercise may have a neuroprotective effect on the retina. Therefore, the association between reduced physical exercise and ocular diseases may involve a bidirectional causal relationship whereby visual impairment leads to reduced physical exercise and decreased exercise exacerbates the development of ocular disease. In this review, we summarize the evidence linking physical exercise to eye disease and identify potential mediators of physical exercise-induced retinal neuroprotection. Finally, we discuss future directions for preclinical and clinical research in exercise and eye health.

Evaluating the impact of caloric restriction, body mass index and exercise on primary open-angle glaucoma: A review

This literature review evaluates any possible links between primary open-angle glaucoma (POAG) and caloric restriction (CR), body mass index (BMI), and exercise, aiming to map the extent of the literature. Its primary objective is to recognise the nature and breadth of research evidence, identify possible gaps in these topics and develop future studies. The databases searched were MEDLINE (PudMed), Scopus and ScienceDirect, in April 2023 for articles published in English, with no date restriction. A total of 447 search results were retrieved. Of these, 73 were related to CR, 249 to BMI, and 125 to exercise. Records identified included systematic reviews, meta-analyses, randomised controlled trials, cohort studies and animal studies. CR has been shown to halt the degeneration of retinal ganglion cells and protect against various glaucomatous processes in animal models. Low BMI has been shown to be associated with an increased risk of POAG and a faster rate of visual field deterioration in POAG. However, the association between high BMI and POAG is not consistent. Exercise has been shown to cause mechanical, vascular, and neurobiological changes affecting the pathophysiology of POAG. The present review helps identify key characteristics and factors relating to the impacts of CR, BMI, or exercise on POAG.

The impact of different forms of exercise on intraocular pressure, blood flow, and the risk for primary open angle glaucoma

Primary open angle glaucoma (POAG) is a chronic disease characterized by progressive optic nerve damage and irreversible loss of vision, often diagnosed at late stages. Elevated intraocular pressure (IOP) is the major risk factor for its onset and progression while older age, myopia, genetic factors, blood pressure (BP), and reduced ocular blood flow (OBF) have also been linked to the disease. Different forms of exercise are known to have significant, but variable, effects on IOP, BP, ocular perfusion pressure (OPP), OBF and oxygen metabolism, and ultimately the risk for development and progression of POAG. While population-based studies lack agreement regarding the relationship between exercise and POAG status, data suggests that resistance training causes a short-term increase in IOP, BP, and OPP. Conversely, aerobic exercise has been shown to cause a short-term decrease in IOP and increase in BP and OPP. Research also suggests that following an exercise program over an extended period may lead to a long-term decrease in IOP, however its cessation results in a prompt return to baseline levels. Data suggests normal vascular autoregulation ensures minimal change in OBF following extended exercise unless OPP rises ∼70% above baseline. Although exercise may alter IOP, BP, and OBF, both acutely and chronically, it is currently uncertain if physical activity significantly alters risk for the onset and progression of POAG.

Evaluation of Retinal and Posterior Segment Vascular Changes Due to Systemic Hypoxia Using Optical Coherence Tomography Angiography

Background/Objectives: Retinal vascular occlusions are a significant cause of visual impairment in older adults, resulting in ischemic retinal damage and sudden vision loss. This study evaluates the retinal, optic nerve head (ONH), and choroidal capillary networks in chronic and acute-on-chronic hypoxia compared to normal controls using optical coherence tomography angiography (OCT-A). Methods: We evaluated a prospective study including twenty patients in the hypoxic group (mean age 61.2 ± 10.2) in two phases, chronic hypoxia and acute-on-chronic hypoxia, and 21 control subjects (mean age 59 ± 9.4 years). All patients underwent a comprehensive eye examination, OCT, and OCT-A imaging. The data were analyzed using OCT-A analysis software (Zeiss OCT-A software 2.1.0.55513) and Fiji software (1.51a). Vascular density of the retina and ONH, choriocapillaries, and foveal avascular zone (FAZ) size were measured. Results: The superficial peripapillary vascular density was higher for the control group (0.387 ± 0.03) compared to the hypoxic patients with (0.383 ± 0.03) and without O2 supplementation (0.383 ± 0.03; p = 0.018). No retinal angiographic differences were identified between the two study groups. The ganglion cell layer (GCL) was thinner in the hypoxic group. Both hypoxic subgroups demonstrated denser choriocapillaries (mean 13,073 ± 1812 and 12,689 ± 1815, with and without O2 supplementation, respectively) compared to the control group (mean 9749 ± 2881, p < 0.001 for both groups). Hypoxic patients demonstrated increased area size of choriocapillaries (+O2 supplementation-mean 44,347 ± 10,563; -O2 supplementation-mean 46,984 ± 12,822) compared to the control group (mean 30,979 ± 9635; p < 0.01 and p < 0.001, respectively). Conclusions: Chronic and acute-on-chronic hypoxia did not affect the retinal vascular network, most probably due to the strong autoregulation of vascular function of the retina. However, compared to the control group, GCL, ONH vasculature density, and most choriocapillaries indices were significantly altered among hypoxic patients.

Pathological Mechanism and Clinical Therapy Progress of Schlemm's Canal

Schlemm's canal (SC) is a small circular canal in the deep part of the sclera at the junction of the sclera and cornea. As an integral component of the aqueous humor outflow, its structure and function are essential in regulating intraocular pressure (IOP). If SC develops lesions, the drainage of aqueous humor would be obstructed, leading to increased intraocular pressure and injury to the optic nerve. With the rapid development of minimally invasive glaucoma surgery, an increasing number of surgeons became familiar with SC, and the area generated substantial academic attention. The pathological mechanism and the therapy for SC that had been studied in recent years are summarized in this article, hoping to provide ideas for the treatment of glaucoma in the future.

Effects of low-pressure Valsalva maneuver on changes in cerebral arterial stiffness and pulse wave velocity

The Valsalva maneuver (VM), commonly used to assess cardiovascular and autonomic nervous system functions, can induce changes in hemodynamic function that may affect cerebral vascular functionality, such as arterial elasticity. This study aimed to investigate the effects of low-pressure VM on cerebral arterial stiffness and cerebral vascular dynamics. Thirty-one healthy young participants (average age 21.58±1.72 years) were recruited for this study. These participants were instructed to maintain an expiratory pressure of 30-35 mmHg for 15 seconds. We measured the vasoconstriction and vasodilation diameters (VCD and VDD) of the common carotid artery (CCA), as well as systolic and diastolic blood pressures (SBP and DBP), before and after VM (PRE_VM and POST_VM). Additionally, we assessed mean arterial pressure (MAP), pulse pressure (PP), pulse wave velocity (PWV), and arterial stiffness. Our findings revealed significant increases in both the VCD and VDD of the CCA (2.15%, p = 0.039 and 4.55%, p<0.001, respectively), MAP (1.67%, p = 0.049), and DBP (1.10%, p = 0.029) following low-pressure VM. SBP showed an increasing trend, but this was not statistically significant (p = 0.108). Interestingly, we observed significant decreases in arterial stiffness and PWV in POST_VM when comparing with PRE_VM (p<0.001 and p<0.001, respectively). In conclusion, our study demonstrated the effectiveness of low-pressure VM in reducing the PWV and stiffness of the CCA. This suggests that low-pressure VM can be a simple and cost-effective method to reduce cerebrovascular stiffness in a brief interval, without the need for specific environmental conditions.

Acute macular neuroretinopathy following Valsalva manoeuvre: an insight into the pathophysiology

Acute macular neuroretinopathy (AMN) affects the outer retina and is most likely induced by non-inflammatory ischaemia of the retinal deep capillary plexus and choriocapillaris. A man in his early 20s developed Valsalva retinopathy following weightlifting at the gym and presented with blurring of vision in the left eye 1 month after the initial retinal haemorrhages had resolved. A diffuse, purplish, donut-shaped, perifoveal lesion was seen on funduscopy and was well defined by an optical coherence tomography angiography (OCTA) en face image in the left eye. Outer retinal changes on optical coherence tomography (OCT) and a dense co-localised scotoma on a visual field (VF) examination confirmed the diagnosis of AMN, and the patient was started on a tapering dose of oral steroids. Improvement was seen in OCT, OCTA and VF during the 6-month follow-up visit. The use of OCTA en face imaging enabled the accurate identification of the lesion in the affected layers of the retina.

Acute Effects of Resistance Exercise on Intraocular Pressure in Healthy Adults: A Systematic Review

ABSTRACT

Hackett, DA, Li, J, Wang, B, Way, KL, Cross, T, and Tran, DL. Acute effects of resistance exercise on intraocular pressure in healthy adults: A systematic review. J Strength Cond Res 38(2): 394-404, 2024-Intraocular pressure (IOP) tends to fluctuate during a resistance exercise (RE). This systematic review examines the acute effects of RE on IOP in healthy adults and factors that influence changes in IOP. Five electronic databases were searched using terms related to RE and IOP. A strict inclusion criterion was applied, which included being 55 years or younger with no medical conditions and RE intensity needing to be quantifiable (e.g., based on a maximal effort). Thirty-four studies met the inclusion criteria for this review. Isometric and isotonic contractions produced similar changes in IOP during RE up to 28.7 mm Hg. Exercises that involved larger muscle mass, such as squats and leg press, were found to produce changes in IOP during exercise ranging from 3.1 to 28.7 mm Hg. Smaller changes in IOP during RE were found for exercises engaging less muscle mass (e.g., handgrip and bicep curls). Intraocular pressure was found to increase during RE when lifting heavier loads and with longer exercise durations (e.g., greater repetitions). The Valsalva maneuver (VM) and breath-hold during RE accentuated the change in IOP, with more extreme changes observed with the VM. However, most studies showed that postexercise IOP returned to baseline after approximately 1 minute of recovery. An acute increase in IOP is observed during RE in healthy adults with fluctuations of varying magnitude. Factors that independently increase IOP during RE include exercises involving larger muscle mass, heavy loads, greater set duration, and when the VM or breath-hold is performed.

Fluctuation of Intraocular Pressure and Vascular Factors Are Associated With the Development of Epiretinal Membrane in Glaucoma

PURPOSE

To identify factors associated with the development of epiretinal membranes (ERM) in glaucoma patients.

DESIGN

Multicenter, propensity-score matched, case-control study.

METHODS

One hundred ninety-two eyes of 192 patients with glaucoma from the Catholic Medical Center Glaucoma Suspect Cohort Study were analyzed. We identified 64 eyes who developed ERM from the cohort, and 128 eyes without ERM were selected by propensity score matching (1:2) according to baseline age and mean deviation (MD) of the visual field (VF). Demographic, systemic, and ocular characteristics were determined at baseline. Intraocular pressure (IOP) was measured, including baseline, mean IOP, and IOP fluctuation. Early-stage ERM, defined as translucent membrane with no underlying retinal distortion, was detected by fundus photography and optical coherence tomography. Central VF progression was considered when new VF defets developed in one either or both hemifields or when there was an increase of 3 or more abnormal points within 12 points of central 10° fixation. Autonomic nervous system status was evaluated by heart rate variability.

RESULTS

Patients who developed ERM were more frequently receiving medication for systemic hypertension and had higher systolic blood pressure, greater IOP fluctuation, more frequent disc hemorrhage (DH), worse VF MD, and a higher rate of central VF progression than patients without ERM. Additionally, patients with early glaucoma who developed ERM had higher rate of autonomic imbalance while patients with moderate-to-advanced glaucoma who developed ERM had greater baseline and peak IOP and worse MD of the last follow-up VF (MD < 6.0 dB). Older age (P = .048), medication for systemic hypertension (P < .001), IOP fluctuation (P < .001), presence of DH (P < .001), and worse last MD of VF (P = .033) were significantly associated with ERM in Cox proportional hazard analysis.

CONCLUSIONS

Early stage of ERMs in glaucomatous eyes are significantly associated with glaucoma progression, medication of systemic hypertension, presence of DH, and IOP fluctuation. These suggest that glaucoma patients who develop early stage of ERMs should be carefully monitored in terms of IOP fluctuation, vascular factors, and glaucoma progression.

Abnormal Systemic and Ocular Responses to the Valsalva Manoeuvre in Primary Open-Angle Glaucoma: A Case for Autonomic Failure?

OBJECTIVE

This study aimed to examine the association of primary open-angle glaucoma (POAG) with autonomic dysfunction by assessing the differences in systemic and ocular responses to an autonomic provocation test, the Valsalva manoeuvre (VM), between POAG patients and normal subjects.

METHODS

Forty POAG and forty control subjects were subjected to the VM. Systemic and ocular parameters were measured at baseline, phase 2, and phase 4 of the VM (VM2 and VM4), where VM2 and VM4 are sympathetic and parasympathetic nervous activation states, respectively. Heart rate variability was used to assess the autonomic nervous activity, among which the high-frequency component (HF) and the low-frequency (LF)/HF ratio were used as indices of parasympathetic and sympathetic activation, respectively.

RESULTS

POAG patients demonstrated higher sympathetic activation (LF/HF ratio median: 2.17 vs. 1.53, P=0.000) than controls at baseline and exhibited attenuated sympathetic and parasympathetic responses (a smaller change in LF/HF and HF values) during the VM than controls. During VM, the intraocular pressure (IOP), mean blood pressure (MAP), mean ocular perfusion pressure (MOPP), and the Schlemm's canal area (SCAR) increased from baseline to VM2 and then decreased from VM2 to VM4 in both the POAG and control groups (all P<0.05). However, when we compared the changes above, the fluctuations in IOP, MAP, and MOPP were more pronounced in POAG than in controls (all P<0.05), while the changes in amplitudes of SCAR were smaller in POAG (P<0.05). Furthermore, from VM2 to VM4, the choroid thickness (ChT) in the POAG group was significantly decreased, while it was unchanged in normal subjects (P=0.258). A regression analysis showed a significant correlation of the baseline LF/HF with IOP change values (ΔIOP) from baseline to VM2 in POAG (R²=0.147, P=0.014).

CONCLUSION

Patients with POAG showed more pronounced fluctuations in IOP, MAP, MOPP and ChT during the VM than controls. These reactions could be associated with autonomic dysfunction in POAG.

Choroidal vascularity index changes during the Valsalva manoeuvre in healthy volunteers

PURPOSE

To evaluate the effects of the Valsalva manoeuvre (VM) on the choroidal vascularity index (CVI) in healthy volunteers.

METHODS

This prospective, cross-sectional study included 60 eyes of 30 healthy volunteers. Enhanced depth imaging-optical coherence tomography scans of both eyes involving the fovea were taken, and a 1500 μm subfoveal choroidal area was selected for image binarization with open-access Fiji software. The binarized image was segmented into the stromal area (SA) and luminal area (LA), and CVI was calculated as the ratio (%) of LA to the total choroidal area (TCA). CVI, subfoveal choroidal thickness (SFCT), IOP, systolic and diastolic blood pressure were evaluated at rest and during the VM.

RESULTS

During the VM, a mean ± standard deviation increase in LA (0.02 ± 0.05 mm² , p < 0.001) and CVI (1.72 ± 2.83%, p < 0.001) was observed, whereas SA (-0.02 ± 0.05 mm² , p < 0.001) decreased. There was no significant change in TCA (0.00 ± 0.03 mm² , p = 0.55) or SFCT (1.05 ± 10.92 μm, p = 0.46). There was a moderate positive correlation between the spherical equivalent refractive error (SE) and SFCT both at rest and during VM (r₅₈  = 0.49, p < 0.0005 and r₅₈  = 0.49, p < 0.0005, respectively). However, there was no significant correlation between SE and CVI either at rest or during VM (p = 0.11 and 0.06, respectively). In a multiple linear regression analysis, CVI was only associated with SFCT; however, SFCT was also associated with SE, both at rest and during VM (p < 0.001).

CONCLUSION

Valsalva manoeuvre increases CVI by choroidal vascular dilation as demonstrated by an increase in LA and a decrease in SA. Researchers should be careful about unintentional VM during examinations.

Intraocular pressure fluctuation during resistance exercise

Objective

To evaluate the effect of weightlifting (leg press) on intraocular pressure (IOP).

Design

Prospective cohort study.

Subjects

A total of 24 participants met the inclusion criteria and completed the study procedures. Participants had an average age of 22.7±2.7 years and included nine women. The mean baseline IOP was 13.9 mm Hg (SD=2.4) with an average body mass index of 24.5 (SD= 3.1).

Methods

The maximum load for a single lift was found for each participant. Participants then performed three leg press regimens: one repetition using 95% of maximal load (1RM), six repetitions using 75% of maximal load (6RM) and isometric push against a weight much heavier than maximal load (ISO).

Main outcome measure

IOP was measured pre-exercise, during and immediately following the exercise using an iCare TA01i rebound tonometer. Blood pressure and HR were being monitored continuously during the lift. Optical coherence tomography images were obtained pre and postexercise session.

Results

The average maximum weight lifted by our participants was 331.9 Kg (SD=97.3). Transient increased IOP was observed across the 1RM, 6RM and ISO exercises with an average increase in 26.4 mm Hg (23.7 mm Hg to 28.7 mm Hg) to reach an average max IOP of 40.7 mm Hg (27.8 mm Hg to 54.2 mm Hg), with an absolute maximum of 70 mm Hg in one participant.

Conclusions

There is a transient and dramatic fluctuation in IOP with resistance training. This coupled with regular exposure to resistance training is potentially a significant risk factor for glaucoma. It should be noted that this study has been carried out in a healthy young population, and, thus, the external validity of these results in glaucoma participants requires further investigation.