Comparison of Neurovascular Coupling between Normal Tension Glaucoma Patients and Healthy Individuals with Laser Speckle Flowgraphy

Neuroprotection beyond intraocular pressure: game changer or quiet addiction

The topic of neuroprotection in glaucoma and age-related macular degeneration (AMD) is well disseminated in the literature. However, the problem is providing ophthalmologists with clear, evidence-based messages to draw on. This review examines the landscape of neuroprotective therapies for glaucoma and AMD. While promising neuroprotective agents, such as citicoline and nicotinamide, have been explored for their potential to mitigate neurodegeneration in glaucoma, robust clinical evidence validating their efficacy remains limited and there is a need for further large-scale, long-term studies to substantiate the neuroprotective effects of these agents. Maintaining low intraocular pressure plays a vital role in preventing neuronal death in glaucoma. AMD has traditionally been considered a disease affecting the outer retinal layers; however, growing evidence suggests that the inner layers are also involved. Neuroprotection is an emerging area of research, with strategies focusing on alleviating oxidative stress, inflammation and apoptosis. A reassessment of clinical endpoints and methodologies in neuroprotection research is critical to better evaluate the efficacy of these therapies in glaucoma and AMD.

Response of capillaries and small arterioles to full-field flicker is not dependent on local ganglion cell thickness

To measure the influence of ganglion cell layer (GCL) thickness on the changes in size and red blood cell (RBC) flow in small retinal vessels evoked by full-field flicker. We used a dual-beam adaptive optics scanning laser ophthalmoscope to image 11 healthy young controls in two retinal areas with significantly different GCL thicknesses. All capillaries and arterioles of the superficial vascular plexus were responsive to the flicker stimulation. Average lumen dilation and RBC flow changes were greater in capillaries than in arterioles (vasodilation: 10.9%, 6.7%; RBC flow: 51%, 38%, respectively). No statistically significant differences regarding relative lumen diameter, RBC velocity, or RBC flow were found with respect to GCL thickness, or vessel size.

Factors Associated With Ocular Perfusion Measurements as Obtained With Laser Speckle Contrast Imaging

Purpose

To study the ocular and systemic factors affecting optic nerve head (ONH) perfusion data as obtained using a commercially available laser speckle flowgraphy (LSFG) device in a cohort of Caucasian subjects without ocular diseases. Also, to assess the intrasession repeatability and intersession reproducibility of ONH, macular, retinal, and choroidal perfusion.

Methods

Seventy-five healthy eyes of 75 Caucasian participants underwent LSFG and spectral-domain optical coherence tomography (SD-OCT) on the same visit. Perfusion of the ONH was assessed with LSFG, and SD-OCT was used to measure peripapillary retinal nerve fiber layer thickness (RNFLT) and macular ganglion cell plus inner plexiform layer thickness (GCIPLT). The intrasession repeatability and intersession reproducibility of ONH and macular perfusion and retinal and choroidal relative flow volume (RFV) were evaluated in 20 participants measured on three different days over a 6-month period.

Results

Intrasession and intersession intraclass correlation coefficients of LSFG parameters ranged from 0.787 to 0.967 and from 0.776 to 0.935, respectively. Intersession 95% prediction intervals for the ratio of two measurements were wider for RFV indices than for ONH and macular perfusion parameters. The multiple regression analysis indicated that higher ONH perfusion was associated with younger age, female sex, smaller optic disc area, and higher RNFLT. RNFLT was an independent predictor of ONH perfusion, whereas GCIPLT was not. Each 1-µm increase in RNFLT was associated with a 0.272 arbitrary unit increase in ONH perfusion.

Conclusions

LSFG measurements of optic disc perfusion are influenced by sex, age, and anatomical variations in optic disc area and RNFLT.

Translational Relevance

Better evaluation of ocular blood flow will result in better diagnosis and treatment of various ocular diseases.

Stimulus type and duration affect magnitude and evolution of flicker-induced hyperemia measured by laser speckle flowgraphy at the optic disc and peripapillary vessels

Neurovascular coupling is a vital mechanism employed by the cerebrovascular system, including the eye, to regulate blood flow in periods of neuronal activation. This study aims to investigate if laser speckle flowgraphy (LSFG) can detect coupling response elicited by flickering light stimuli and how variations in stimulus type and duration can affect the magnitude and evolution of blood flow in the optic nerve head (ONH) and peripapillary vessels. Healthy adults were exposed to two types of 10-Hz flicker stimuli: a photopic negative response-like stimulus (PhNR-S) or a visual evoked potential-like stimulus (VEP-S)-each presented in separate 10- and 60-s epochs. Both PhNR-S and VEP-S significantly increased ONH blood flow (p < 0.001) immediately after flicker cessation, with a trend of 60-s stimuli (PhNR-S = 11.6%; VEP-S = 10.4%) producing a larger response than 10-s stimuli (PhNR-S = 7.5%; VEP-S = 6.2%). Moreover, exposure to 60-s stimuli elicited a significantly prolonged ONH hyperemic response, especially with PhNR-S. Lastly, stimulation with either 60-s stimuli elicited a robust increase in blood flow within the peripapillary arterioles (p < 0.01) and venules (p < 0.01) as well. Flicker stimulation with common visual electrophysiology stimuli (PhNR-S and VEP-S) induced a demonstrable increase in ONH and peripapillary vessel blood flow, which varied with flicker duration. Our results validate that LSFG is a robust method to quantify flicker-induced hyperemic responses and to study neurovascular coupling in humans.

Acute Increase in Ocular Microcirculation Blood Flow Upon Cholesterol Removal. The Eyes Are the Window of the Heart

BACKGROUND

Lipoprotein apheresis acutely increases coronary microvascular blood flow. However, measurement techniques are time-consuming, costly, and invasive. The ocular vasculature may be an appropriate surrogate and an easily accessible window to investigate the microcirculation. Recent advances in ocular imaging techniques enable quick, noninvasive quantification of ocular microcirculation blood flow. The insights from these techniques represent a significant opportunity to study the short-term changes in optic disk blood flow after lipoprotein apheresis for inherited hypercholesterolemia.

METHODS

This study was performed at the Italian Reference Center for Inherited Dyslipidemias in Tuscany. The study sample was comprised of 22 patients with inherited hypercholesterolemia who were previously studied for coronary microcirculation. Laser speckle flowgraphy (LSFG) was used to measure optic disk blood flow before and after lipoprotein apheresis. The main outcomes measures were average tissue blood flow (referred to as mean tissue) and arteriolar/venular average blood flow (referred to as mean vessel). Eyes were divided into 2 groups based on pre-lipoprotein apheresis optic disk blood flow values. P < .05 was considered statistically significant.

RESULTS

After each lipoprotein apheresis treatment resulting in the reduction of plasma lipids, there was a concurrent increase in all optic disk microcirculatory parameters. The increase was statistically significant in eyes with lower pre-apheresis optic disk blood flow values (mean tissue +7.0%, P < .005; mean vessel +7.2%, P < .05).

CONCLUSIONS

A single lipoprotein apheresis session resulted in a statistically significant short-term increase in optic disk blood flow. These findings together with previous coronary microcirculation data suggest a similar ocular and coronary blood flow response to lipoprotein apheresis. Ocular microcirculation may represent a versatile biomarker for evaluating systemic microcirculatory health, including coronary microcirculation. Hence, it is plausible that plasma lipoprotein levels may influence optic disk blood flow.

Measuring optic nerve head perfusion to monitor glaucoma: a study on structure-function relationships using laser speckle flowgraphy

PURPOSE

We aimed to describe the global and localized correlations among visual field (VF) sensitivity, optic nerve head (ONH) perfusion measured by laser speckle flowgraphy (LSFG) and neural structure measured by optical coherence tomography (OCT) in open-angle glaucoma (OAG) and to compare the floor effect for LSFG and OCT.

METHODS

Cross-sectional, multicenter study including one eye each from fifty OAG patients (mean age 69.3 years; average VF mean deviation, MD, -8.5 dB, range -25.17 to 0.85 dB) and fifty-one controls. Patients underwent SITA standard 24-2 automated perimetry and measurement of ONH perfusion, peripapillary retinal nerve fibre layer thickness (RNFLT) and macular ganglion cell-inner plexiform layer thickness (GCIPLT). We tested the presence of a significant change (breakpoint) in the correlation slope with VF sensitivity to assess floor effect.

RESULTS

The correlation between the LSFG parameter Mean All (MA) of the global disc area and MD (r = 0.56, p < 0.001) did not show a breakpoint, in contrast to the correlations between MD and OCT global parameters, which showed breakpoints at -8.53 and -4.05 dB for RNFLT and GCIPLT, respectively. Global and localized correlations with VF sensitivity were stronger for LSFG compared to OCT. In particular, LSFG outperformed OCT in the correlation with the central VF sector (r = 0.50, p < 0.001 and r = 0.06, p = 0.67 for MA and RNFLT, respectively).

CONCLUSION

The global and sectoral correlations with VF sensitivity and the favourable floor effect compared to OCT indicate LSFG as a promising tool to monitor progression particularly in late-stage glaucoma. Further longitudinal studies are warranted.

Longitudinal Study of Optic Disk Perfusion and Retinal Structure in Leber's Hereditary Optic Neuropathy

Purpose

The purpose of this study was to evaluate optic disk perfusion and neural retinal structure in patients with subacute Leber's hereditary optic neuropathy (LHON) and LHON carriers, as compared with healthy controls.

Methods

This study included 8 patients with LHON in the subacute stage, 10 asymptomatic carriers of a LHON-associated mitochondrial DNA mutation, and 40 controls. All subjects underwent measurement of the retinal nerve fiber layer (RNFL) thickness, the ganglion cell-inner plexiform layer (GCIPL) thickness using optical coherence tomography and optic disk microvascular perfusion (Mean Tissue [MT]) using laser speckle flowgraphy (LSFG). Patients were re-examined after a median interval of 3 months from the baseline visit.

Results

LHON carriers had higher values of RNFL thickness, GCIPL thickness, and disk area than controls (P < 0.05), whereas MT was not different between the two groups (P = 0.936). Median MT and RNFL thickness were 32% and 15% higher in the early subacute stage of the disease than in controls (P < 0.001 and P = 0.001). MT declined below the values of controls during the late subacute stage (P = 0.024), whereas RNFL thickness declined later during the dynamic stage (P < 0.001). GCIPL thickness was lower in patients with LHON than in controls independently of the stage of the disease (P < 0.001).

Conclusions

The high blood flow at the optic disk during the early subacute stage may be the consequence of vasodilation due to nitric oxide release as compensation to mitochondrial impairment. Optic disk perfusion as measured by LSFG is a promising biomarker for LHON diagnosis and monitoring as well as an objective outcome measure for assessing response to therapies.

Short-term changes in retinal and choroidal relative flow volume after anti-VEGF treatment for neovascular age-related macular degeneration

The effects of anti-vascular endothelial growth factor (anti-VEGF) agents on the native ocular vasculature are poorly understood. This pilot study aimed to assess short-term changes in retinal and choroidal perfusion after anti-VEGF treatment for neovascular exudative age-related macular degeneration (nAMD) using the relative flow volume (RFV) parameter derived from laser speckle flowgraphy. Ten treatment-naïve nAMD patients underwent measurements of mean, maximum, minimum, and differential RFV within a retinal arteriolar segment and a choroidal vessel segment outside the neovascular area. Measurement of retinal RFV (rRFV), choroidal RFV (cRFV), and subfoveal choroidal thickness (SCT) was repeated 9 and 35 days after a single anti-VEGF injection. The treatment caused a statistically significant decrease in the mean rRFV, mean cRFV, and SCT during the follow-up (p < 0.05). At the intermediate visit, the mean cRFV and SCT were − 17.6% and − 6.4% compared to baseline, respectively. However, at the final measurement, the mean cRFV was not different from the baseline value, which indicated waning of the anti-VEGF effect. In conclusion, a single anti-VEGF injection in treatment-naïve nAMD resulted in a decrease in retinal arteriolar and choroidal perfusion, according to the RFV parameter, which is a promising tool to simultaneously assess retinal and choroidal perfusion changes in response to anti-VEGF therapy.

Association between vascular comorbidity and glaucoma progression: A four-year observational study

Glaucoma, one of the significant causes of blindness worldwide, is a chronic optic neuropathy, characterized by progressive loss of retinal ganglion cells and specific perimetric defects. This study aimed to assess the association between the risk of glaucoma progression and different systemic vascular abnormalities. A 4-year prospective study was carried out on 204 patients diagnosed with open-angle glaucoma. Associated systemic vascular pathology was documented in 102 cases. Progression was encountered in 57 (55.9%) patients with vascular comorbidities and only in 10 (9.8%) patients with no associated vascular diseases (OR 13.81, P<0.01). The vascular risk factors associated with glaucoma progression in the study group were diastolic hypotension (OR 5.444, P=0.027), ischemic cardiac disease (OR 5.826; P<0.01), peripheral vasospasm (OR 3.108, P=0.042) and arterial hypertension (OR 2.593, P=0.05). Diabetes was not significantly correlated with progression in the study group, but only patients without diabetic retinopathy were included. This study highlights that systemic comorbidities associated with endothelial lesions, atherosclerosis and hypoperfusion can lead to damage to the retinal nerve fiber layer and the underlying conjunctive tissue.

Time-Course Changes in Optic Nerve Head Blood Flow and Retinal Nerve Fiber Layer Thickness in Eyes with Open-angle Glaucoma

PURPOSE

To determine whether decreased optic nerve head (ONH) blood flow (BF) precedes or follows decreased circumpapillary retinal nerve fiber layer thickness (cpRNFLT) in eyes with open-angle glaucoma (OAG).

DESIGN

Retrospective, longitudinal study.

PARTICIPANTS

This study followed up 350 eyes of 225 OAG patients for at least 2 years and collected data from each patient from at least 5 examinations obtained with laser speckle flowgraphy (LSFG) and OCT.

METHODS

In the superior, temporal, and inferior ONH quadrants, tissue area mean blur rate (MT), representing ONH tissue BF, was measured with LSFG, whereas cpRNFLT was measured with OCT. A multivariate linear mixed-effects model was used to identify potential predictors of faster MT decrease, adjusting for possible confounding factors. Based on these results, each quadrant of each patient was assigned a risk point if the quadrant was the superior or temporal, if patient age was older than the median (61 years), and if patient pulse rate was higher than median (74 beats per minute). The quadrants were then compared with a mixed-effects Cox model for MT and cpRNFLT changes, defined as a difference between the baseline value and the values from the latest 2 consecutive follow-up visits of more than 1.96 × the corresponding coefficient of variation.

MAIN OUTCOME MEASURES

Ophthalmic and systemic variables and MT and cpRNFLT in the superior, temporal, and inferior quadrants.

RESULTS

The multivariate model showed that MT decrease was faster in older patients with higher pulse rate and slower in inferior quadrants (P < 0.05). Quadrants with 0 risk points showed primary cpRNFLT decrease (P = 0.048), 1-risk point quadrants showed simultaneous cpRNFLT and MT decrease (P = 0.260), and 2-risk point and 3-risk point quadrants showed primary MT decrease (P < 0.001).

CONCLUSIONS

Older patients with higher pulse rate are at greater risk of a primary reduction in ONH tissue BF, that is, preceding cpRNFLT decrease, in the superior and temporal quadrants.