Central retinal artery pressure and carotid artery stenosis

Physics-informed deep generative learning for quantitative assessment of the retina

Disruption of retinal vasculature is linked to various diseases, including diabetic retinopathy and macular degeneration, leading to vision loss. We present here a novel algorithmic approach that generates highly realistic digital models of human retinal blood vessels, based on established biophysical principles, including fully-connected arterial and venous trees with a single inlet and outlet. This approach, using physics-informed generative adversarial networks (PI-GAN), enables the segmentation and reconstruction of blood vessel networks with no human input and which out-performs human labelling. Segmentation of DRIVE and STARE retina photograph datasets provided near state-of-the-art vessel segmentation, with training on only a small (n = 100) simulated dataset. Our findings highlight the potential of PI-GAN for accurate retinal vasculature characterization, with implications for improving early disease detection, monitoring disease progression, and improving patient care.

Retinal artery occlusion after ophthalmic surgery under regional anaesthesia: A narrative review

Two recent cases of central retinal artery occlusion under otherwise uncomplicated sub-Tenon's block that resulted in significant visual loss after cataract surgery prompted us to undertake a literature review of such cases. We identified 97 cases of retinal artery occlusion after ophthalmic surgery under regional anaesthesia that had no immediate signs of block-related complications. These occurred after various intraocular (87%) and extraocular (13%) operations, across a wide range of ages (19-89 years) on patients with (59%) or without (39%) known risk factors. The anaesthetic techniques included 40 retrobulbar blocks, 36 peribulbar blocks, 19 sub-Tenon's blocks, one topical anaesthetic and one unspecified local anaesthetic. Different strengths of lidocaine, bupivacaine, mepivacaine and ropivacaine, either alone or in various combinations, were used. The details of the anaesthetic techniques were often incomplete in the reports, which made comparison and analysis difficult. Only nine cases had their cause (optic nerve sheath injury) identified, while the mechanism of injury was unclear in the remaining patients. Various mechanisms were postulated; however, the cause was likely to be multifactorial due to patient, surgical and anaesthetic risk factors, especially in those with compromised retinal circulation. As there were no definite risk factors identified, no specific recommendations could be made to avoid this devastating outcome. We have provided rationales for some general considerations, which may reduce this risk, and propose anaesthetic options for ophthalmic surgery on the fellow eye if required, based both on our literature review and our personal experience.

Retinal microvasculature and cerebral hemodynamics in patients with internal carotid artery stenosis

Purpose

To investigate the relationship between retinal microvasculature and cerebral hemodynamics in patients with internal carotid artery (ICA) stenosis.

Methods

Patients with unilateral moderate or severe ICA stenosis(≥50%) from West China hospital, Sichuan university were consecutively and prospectively recruited enrolled in the current study. En face angiograms of the superficial vascular complex (SVC), deep vascular complex (DVC), superficial vascular plexus (SVP), intermediate capillary plexus (ICP), and deep capillary plexus (DCP) were generated by automatic segmentation using swept-source optical coherence tomography angiography (SS-OCTA) to assess the retinal microvascular perfusion. The cerebral blood flow perfusion on bilateral middle cerebral artery territories measured at the basal ganglia level was assessed by brain computed tomography perfusion (CTP). CTP data were postprocessed to generate maps of different perfusion parameters including cerebral blood flow (CBF), cerebral blood volume (CBV), time to peak (TTP), mean transit time (MTT) and permeability surface(PS). Relative perfusion parameters (rPS, rCBF, etc.) were calculated as the ratio of the value on the contralateral side to that on the ipsilateral side.

Results

In the final analysis, 31 patients were included, of whom 11 patients had a moderate ICA stenosis (50–69%) and 20 with a severe ICA stenosis(≥70%). A total of 55 eyes were analyzed in the study, 27 eyes from the ipsilateral side (ie, side with stenosis) and 28 eyes from the contralateral side. In the patients with ICA stenosis, there was a strong correlation between the retinal microvascular perfusion of SVC with rCBV(B = 0.45, p = 0.03), rCBF(B = 0.26, p = 0.02) and rPS(B = 0.45, p < 0.001) after adjustment for age, sex and vascular risk factors. Similar correlations were also found between microvasculature in SVP and cerebral perfusion changes. There were no any significant associations of microvascular perfusion in both DVC and DCP with CTP parameters(all p > 0.05).

Conclusions

Retinal perfusion changes in superficial vascular layer (SVC and SVP) were correlated with brain hemodynamic compromise in patients with unilateral moderate or severe ICA stenosis(≥50%). Given the limited size of our study, future studies with larger sample size are needed to confirm our findings.

Optical Coherence Tomography Angiography as a Noninvasive Assessment of Cerebral Microcirculatory Disorders Caused by Carotid Artery Stenosis

Purpose

Using retinal optical coherence tomography angiography (OCTA), we aimed to investigate the changes in important indicators of cerebral microcirculatory disorders, such as the properties of the radial peripapillary capillaries, vascular complexes, and the retinal nerve fiber layer, caused by carotid stenosis and postoperative reperfusion.

Methods

In this prospective longitudinal cohort study, we recruited 40 carotid stenosis patients and 89 healthy volunteers in the First Affiliated Hospital of Harbin Medical University (Harbin, China). Eyes with ipsilateral carotid stenosis constituted the experimental group, while the fellow eyes constituted the contralateral eye group. Digital subtraction angiography, CT perfusion imaging (CTP), and OCTA examinations were performed in all subjects. The vessel density of the radial peripapillary capillaries (RPC), superficial retinal vascular complexes (SVC), deep vascular complexes (DVC), choriocapillaris (CC), and the thickness of the retinal nerve fiber layer (RNFL) were assessed. Propensity-matched analysis was undertaken to adjust for covariate imbalances. Intergroup comparative analysis was conducted, and the paired sample t-test was used to evaluate the preoperative and postoperative changes in OCTA variables.

Results

The ocular vessel density in the experimental group was significantly lower than that in the control group (RPC: 55.95 vs. 57.24, P = 0.0161; SVC: 48.65 vs. 52.22, P = 0.0006; DVC: 49.65 vs. 57.50, P < 0.0001). Participants with severe carotid stenosis have reduced contralateral ocular vessel density (RPC 54.30; SVC 48.50; DVC 50.80). Unilateral stenosis removal resulted in an increase in vessel density on both sides, which was detected by OCTA on the 4^th day (RPC, P < 0.0001; SVC, P = 0.0104; DVC, P = 0.0104). Moreover, the ocular perfusion was consistent with that established by CTP.

Conclusion

OCTA can be used for sensitive detection and accurate evaluation of decreased ocular perfusion caused by carotid stenosis and may thus have the potential for application in noninvasive detection of cerebral microcirculation disorders. This trial is registered with NCT04326842.

Retinal vessel dynamic functionality in the eyes of asymptomatic patients with significant internal carotid artery stenosis

BACKGROUND

The goal of this study was to assess the retinal microvascular function in asymptomatic patients with hemodynamically significant internal carotid artery stenosis (ICAS) and to assess the potential efficacy of carotid endarterectomy (CEA) for the improvement of vessel functionality.

METHODS

Retinal vessel caliber and reactions to flicker stimulation were assessed in both eyes of 65 asymptomatic patients with unilateral hemodynamically significant ICAS and 34 healthy subjects. Subsequently, the recruited ICAS patients were referred for standard unilateral CEA procedure. The full ophthalmologic examination of both eyes and vessel analysis were performed 1 day before and 3 months after CEA.

RESULTS

The venous responses to flicker stimulation were significantly lower in the EIS (eyes ipsilateral to stenosis) and ECS (eyes contralateral to stenosis) compared with those in the controls (P<0.0001 and P<0.0001, respectively). No changes were identified in retinal vascular flicker responses after CEA in both groups of eyes compared with the baseline values. We observed a decrease in CRVE (central retinal venular equivalent) after the CEA both in eyes ipsilateral (P=0.01) and contralateral (P=0.04) to CEA. Likewise, a decrease in CRAE (central retinal arteriolar equivalent) was identified in the eyes ipsilateral to CEA (P<0.001).

CONCLUSIONS

This outcome strongly indicates that microvascular dysfunction is long-lasting despite the recovery of the flow in the carotid artery.