Metabolic factors and the foveal avascular zone of the retina in diabetes mellitus

The Effect of Reduced Oxygen Saturation on Retinal Microvascularization in COVID-19 Patients with Bilateral Pneumonia Based on Optical Coherence Tomography Study

The aim of the study was to evaluate changes in the retinal thickness and microvasculature based on optical coherence tomography (OCT) depending on baseline oxygen saturation (SpO2) in patients hospitalized due to COVID-19 bilateral pneumonia. The prospective study was carried out among 62 patients with COVID-19 pneumonia who underwent ophthalmic examination after hospital discharge. They were divided into three groups depending on the oxygen saturation (SpO2) on admission: ≤90% (group 1), >90% and ≤95% (group 2), and >95% (group 3). The following parameters were assessed in the ophthalmological examination and correlated with the baseline SpO2: ganglion cell layer (GCL), the retinal nerve fiber layer (RNFL) in the macular area, RNFL in the peripapillary area, the foveal avascular zone (FAZ) in superficial capillary plexus (SCP) and deep capillary plexus (DCP), vessel density (VD) in SCP, in DCP, and in the choriocapillaris plexus (CC). Baseline saturation ≤90% in COVID-19 patients caused a decrease of VD in some areas of SCP and DCP and an increase in FAZ area in SCP and DCP. In the group of patients with SpO2 ≤ 90% statistically significant thinning of the retina in the inner superior ring (ISR) (p = 0.029), the inner temporal ring (ITR) (p = 0.34), the outer superior ring (OSR) (p = 0.012), and the outer temporal ring (OTR) (p= 0.004)] was observed. The statistically significant thickening of RNFL optic disc and thinning of RNFL retina in some macular areas in patients with SpO2 ≤ 90% were reported. The size of FAZ area in SCP and vessel density were significantly greater in some areas of SCP, DCP, and CC in patients with SpO2 ≤ 90% (p = 0.025). Baseline oxygen saturation ≤90% has been found to influence the ocular parameters of OCT in COVID-19 patients. We noticed a widened FAZ zone in SCP and increased VD in some regions of the retina and choroid as a response to systemic hypoxia.

Diabetic macular ischaemia- a new therapeutic target?

Diabetic macular ischaemia (DMI) is traditionally defined and graded based on the angiographic evidence of an enlarged and irregular foveal avascular zone. However, these anatomical changes are not surrogate markers for visual impairment. We postulate that there are vascular phenotypes of DMI based on the relative perfusion deficits of various retinal capillary plexuses and choriocapillaris. This review highlights several mechanistic pathways, including the role of hypoxia and the complex relation between neurons, glia, and microvasculature. The current animal models are reviewed, with shortcomings noted. Therefore, utilising the advancing technology of optical coherence tomography angiography (OCTA) to identify the reversible DMI phenotypes may be the key to successful therapeutic interventions for DMI. However, there is a need to standardise the nomenclature of OCTA perfusion status. Visual acuity is not an ideal endpoint for DMI clinical trials. New trial endpoints that represent disease progression need to be developed before irreversible vision loss in patients with DMI. Natural history studies are required to determine the course of each vascular and neuronal parameter to define the DMI phenotypes. These DMI phenotypes may also partly explain the development and recurrence of diabetic macular oedema. It is also currently unclear where and how DMI fits into the diabetic retinopathy severity scales, further highlighting the need to better define the progression of diabetic retinopathy and DMI based on both multimodal imaging and visual function. Finally, we discuss a complete set of proposed therapeutic pathways for DMI, including cell-based therapies that may provide restorative potential.

Measuring the foveal avascular zone in diabetes: A study using optical coherence tomography angiography

Aims/Introduction

Diabetes is a global issue that currently affects 425 million people worldwide. One observable microvascular complication of this condition is a change in the foveal avascular zone (FAZ). In this study, we used optical coherence tomography angiography to investigate the effect of diabetes on the FAZ.

Materials and Methods

A total of 11 participants with diabetes and 11 participants without diabetes took part in this study. Participants in both groups were matched for age (P = 0.217) and sex (P = 0.338), and had no history of ocular disease. Macular optical coherence tomography angiography (OCT‐A) scans of participants’ right and left eyes were taken. Glycosylated hemoglobin (HbA_1c) and blood glucose levels were also measured. The FAZ area was manually segmented at the levels of the superficial capillary plexus (FAZ_SCP) and deep capillary plexus (FAZ_DCP).

Results

There was a strong relationship between the FAZ area of participants’ right and left eyes (P ≤ 0.001) in both diabetes and non‐diabetes groups. In the diabetes group, the FAZ_SCP (P = 0.047) and FAZ_DCP (P = 0.011) areas was significantly larger than in the non‐diabetes group. Moreover, multiple linear regression analysis predicted a 0.07‐mm² increase in the FAZ_SCP and FAZ_DCP areas of individuals with diabetes for every 1% increase in their HbA_1c level.

Conclusions

Our findings show that there is enlargement of the FAZ in individuals with diabetes compared with individuals without diabetes. In the diabetes group, this enlargement appears to be correlated with HbA_1c level. OCT‐A imaging could, therefore, be a useful tool to monitor the FAZ and identify potential early microvasculopathy in diabetes.

Quantitative assessment and determinants of foveal avascular zone in healthy volunteers

Objectives

To evaluate the foveal avascular zone (FAZ) area in healthy volunteers using optical coherence tomography angiography (OCTA) and identify factors that influence the FAZ.

Methods

This single-center cross-sectional study included 526 eyes of 263 healthy volunteers who underwent macular scanning by Zeiss OCTA. A linear mixed model was used to investigate the effects of systemic factors (age, sex, blood pressure, height, and weight) and ocular factors (intraocular pressure, biometric parameters, and central macular thickness) on FAZ.

Results

In total, 520 eyes of 262 healthy volunteers were included in the analysis. The mean volunteer age was 38.59 ± 22.03 years (range, 5–84 years); 124 volunteers were male (47.33%) and 138 volunteers were female (52.67%). The mean FAZ area was 0.30 ± 0.03 mm² (95% confidence interval [CI], 0.29–0.31 mm²). Univariate analysis showed that FAZ area was associated with age (β = 0.0011), anterior chamber depth (β = −0.0513), and axial length (β = −0.0202). Multivariate analysis showed that FAZ area was negatively correlated with axial length (β = −0.0181).

Conclusions

The mean FAZ area in healthy volunteers, measured using Zeiss OCTA, was 0.30 ± 0.03 mm². Furthermore, FAZ area was negatively associated with axial length; this relationship should be considered in clinical practice.

Factors Affecting the Foveal Avascular Zone Area in Healthy Eyes among Young Chinese Adults

Purpose

To evaluate the influence of systemic and ocular factors on the foveal avascular zone (FAZ) area in young Chinese subjects' healthy eyes.

Methods

The current observational, cross-sectional study included 344 eyes from 172 healthy individuals (103 women, 69 men). Optical coherence tomography angiography realized with the split-spectrum amplitude-decorrelation angiography (SSADA) algorithm was used to assess the area of superficial FAZ. To determine the related factors and to reveal their potential correlations with the FAZ area, comprehensive examinations including both systemic and ocular ones were executed. Systemic examination involved factors including age, gender, and body mass index, while ocular examination involved factors including BCVA, refractive error, intraocular pressure, axial length (AL), anterior chamber depth, and central corneal thickness. Especially for fundus examination, central macular thickness (CMT), retinal volume, mean retinal thickness, macular blood flow area/vessel density in the superficial retinal layer (SRL) and deep retinal layer (DRL), mean retinal nerve fiber layer (RNFL) thickness, ganglion cell layer (GCL) thickness, C/D rate, rim area, and subfoveal choroid thickness were assessed, using mixed-effects regression models to appropriately account for intereye correlation. Subgroup analyses were performed based on gender and high myopia categories.

Results

The mean FAZ area was 0.30 ± 0.11 mm² and varied significantly across gender (P = 0.0024). AL, CMT, and RNFL thickness were found significantly correlated with the FAZ area in the univariate regression analysis (AL, P = 0.0005; CMT, P < 0.0001; and RNFL thickness, P = 0.0461). According to the multivariate results, CMT and macular blood flow in SRL were negatively correlated with FAZ (CMT: P < 0.0001; macular blood flow in SRL: P = 0.00223). Mean retinal thickness, mean GCL thickness, and macular blood flow in DRL were positively correlated with FAZ (mean retinal thickness: P = 0.0005; mean GCL thickness: P < 0.0001; and macular blood flow in DRL: P = 0.0099). Correlation results among these filtered factors and FAZ were more pronounced in non-high-myopic eyes than in high-myopic eyes and had a significant difference when data of male and female subjects were processed separately from each other.

Conclusion

The present cross-sectional study performed comprehensive systemic and ocular examinations in young Chinese adults and filtered factors affecting FAZ. We indicated that among all the assessed candidate factors, gender, AL, retinal thickness, macular blood flow, RNFL, and GCL thickness affected the FAZ area most significantly. Such findings would facilitate future research concerning the role of FAZ variation in fundus diseases.

Retinal microvascular alterations related to diabetes assessed by optical coherence tomography angiography: A cross-sectional analysis

Fluorescein angiography has been so far the gold-standard test to assess diabetic macular ischemia (DMI), a cause of irreversible visual impairment in diabetic patients. The aim of this study was to investigate foveal avascular zone (FAZ) and perifoveal microcirculation changes in eyes with nonproliferative diabetic retinopathy (NPDR) using optical coherence tomography angiography (OCTA), a new and noninvasive vascular imaging technique.Cross-sectional study including eyes of diabetic patients with NPDR.All patients underwent medical history, best-corrected visual acuity (BCVA) measurement, slit-lamp and fundus examination, multicolor imaging, SD-OCT, and swept-source OCT. OCTA was performed in order to assess macular superficial and deep capillary plexus, and swept-source OCT was performed to evaluate the central choroidal thickness.Fifty-eight eyes of 35 patients with a mean age of 61.8 years (±12.1) with mean HbA1C level of 7.6% (±1.5) were included in this study. Among them, 19 eyes had mild NPDR, 24 eyes had moderate NPDR, and 15 eyes had severe NPDR. There was a significant progression between NPDR stages for FAZ grade (P < 0.0001), surface (P = 0.0036) and perimeter (P = 0.0001), and for superficial capillary plexus nonperfusion index (NPI) (P = 0.0009). Moreover, a significant correlation was found between NPI and BCVA (P = 0.007).OCT angiography is a useful noninvasive tool to explore early phases of diabetic retinopathy, which are not routinely explore with fluorescein angiography and not precisely enough with color photographs. NPI and foveal avascular zone parameters are correlated with glycated hemoglobin in patients with NPDR. If confirmed by further studies, these results could represent a mean to sensibilize diabetic patients to their disease.

Optical coherence tomography angiography versus fluorescein angiography in the diagnosis of ischaemic diabetic maculopathy

PURPOSE

To evaluate the efficacy of optical coherence tomography (OCT) angiography versus fluorescein angiography (FA) in terms of retinal vessel imaging in ischaemic diabetic maculopathy defined according to the Early Treatment Diabetic Retinopathy Study (ETDRS) classification.

METHODS

Twenty patients (31 eyes) with ischaemic diabetic maculopathy and 17 control subjects (27 eyes) were enrolled in this prospective study. Patients and control subjects underwent complete ophthalmic examination, including best-corrected visual acuity (BCVA), intraocular pressure, FA, Fourier domain optical coherence tomography (FD-OCT) and OCT angiography. Fluorescein angiograms and OCT angiography images were graded according to the foveal avascular zone (FAZ) of the ETDRS group. Ganglion cell complex (GCC) thickness was evaluated with FD-OCT.

RESULTS

Optical coherence tomography (OCT) angiography images closely correlated with FA in terms of FAZ parameters. The correlation was strongest with OCT angiography deep imaging. The average GCC thickness was smaller in patients than in controls. Neither GCC parameters nor FAZ was correlated to BCVA.

CONCLUSIONS

Given the correlation between FA and OCT angiography in terms of FAZ parameters, the newer method can be considered a valid, reliable and easy-to-perform method with which to evaluate ischaemic diabetic maculopathy without contrast injection, and thus to visualize and quantify non-perfusion areas without risks of anaphylactic reactions.

Vision, retinal thickness, and foveal avascular zone size after intravitreal bevacizumab for diabetic macular edema

INTRODUCTION

To investigate three monthly intravitreal bevacizumab (IVB) injections effects in chronic diabetic macular edema (DME).

METHODS

A prospective, noncomparative study in which inclusion criteria were; DME with central macular thickness (CMT) of at least 250 μm, and no treatment for diabetic retinopathy (DR) within 4 months before the first injection. All eyes received three monthly 1.25 mg IVB injections. CMT by optical coherence tomography, visual acuity (VA), foveal avascular zone (FAZ) greatest linear dimension (GLD), and area of FAZ by fundus fluorescein angiography were documented initially and 1 month after last injection. Outcomes (P<0.05 were significant) and correlations (r values) were analyzed.

RESULTS

A total of 29 eyes of 29 patients (group 1, 19 female, 10 male), aged 60.7±6.6 years were analyzed. The patients were split into two groups; group 2 included 15 mild-to-moderate nonproliferative DR, and group 3 included 14 more-severe DR. VA gain was significant in all groups (P<0.05). Mean CMT decrease was approximately 46, 36, and 55 μm in groups 1, 2, and 3, respectively (P<0.05 only in group 1). A 0.045-mm2 increase in FAZ area was obtained in group 1 (P<0.05). In group 2, an increase in GLD and area of FAZ was 0.048 mm and 0.058 mm2, respectively (P<0.05), whereas in group 3, FAZ enlargement was nonsignificant. VA and CMT were significantly correlated (r values=0.5-0.6), except for the final VA-final CMT in group 2. FAZ dimensions and other parameters (VA and CMT) were noncorrelated.

CONCLUSION

According to the authors' short-term results, three monthly IVB injections can be used for chronic DME regardless of VA, CMT, or FAZ dimensions, despite the FAZ enlargement encountered, especially in cases with milder DR.