Optical microangiography provides correlation between microstructure and microvasculature of optic nerve head in human subjects

Aging Effects on Optic Nerve Neurodegeneration

Common risk factors for many ocular pathologies involve non-pathologic, age-related damage to the optic nerve. Understanding the mechanisms of age-related changes can facilitate targeted treatments for ocular pathologies that arise at any point in life. In this review, we examine these age-related, neurodegenerative changes in the optic nerve, contextualize these changes from the anatomic to the molecular level, and appreciate their relationship with ocular pathophysiology. From simple structural and mechanical changes at the optic nerve head (ONH), to epigenetic and biochemical alterations of tissue and the environment, multiple age-dependent mechanisms drive extracellular matrix (ECM) remodeling, retinal ganglion cell (RGC) loss, and lowered regenerative ability of respective axons. In conjunction, aging decreases the ability of myelin to preserve maximal conductivity, even with "successfully" regenerated axons. Glial cells, however, regeneratively overcompensate and result in a microenvironment that promotes RGC axonal death. Better elucidating optic nerve neurodegeneration remains of interest, specifically investigating human ECM, RGCs, axons, oligodendrocytes, and astrocytes; clarifying the exact processes of aged ocular connective tissue alterations and their ultrastructural impacts; and developing novel technologies and pharmacotherapies that target known genetic, biochemical, matrisome, and neuroinflammatory markers. Management models should account for age-related changes when addressing glaucoma, diabetic retinopathy, and other blinding diseases.

Optical Microangiography and Progressive Ganglion Cell-Inner Plexiform Layer Loss in Primary Open-Angle Glaucoma

PURPOSE

To evaluate the association between optical microangiography (OMAG) measurements and progressive ganglion cell-inner plexiform layer (GCIPL) loss in patients with primary open-angle glaucoma (POAG).

DESIGN

Prospective case series.

METHODS

Sixty-three eyes of 38 patients with POAG were studied for ≥2 years and with ≥ 3 optical coherence tomography examinations. Only those hemifields with mild to moderate functional damage at baseline (106 hemifields) were included in the analysis. OMAG imaging was performed at the baseline visit. The effects of clinical parameters (age, gender, central corneal thickness, presence of disc hemorrhage, and mean and fluctuation of intraocular pressure), baseline mean deviation, retinal nerve fiber layer, and GCIPL thickness and baseline OMAG measurements (peripapillary and macular perfusion density [PD] and vessel density [VD]) on the rate of change of GCIPL thickness were evaluated using linear mixed models.

RESULTS

Average (± standard deviation) mean deviation, quadrant retinal nerve fiber layer, and sector GCIPL thickness of the analyzed hemifields respectively at baseline were -5.2 ± 2.8 dB, 94.5 ± 20.0 µm, and 72.4 ± 8.7 µm, respectively. Peripapillary PD and VD in the quadrant were 43.1% ± 7.0% and 17.0 ± 2.6 mm/mm², respectively. Macular PD and VD in the quadrant were 37.2% ± 6.9% and 15.1 ± 2.6 mm/mm², respectively. Rate of sector GCIPL change was -0.97 ± 0.15 µm per year. Multivariate mixed models showed that lower peripapillary PD (coefficient 0.04, P = .01) and VD (coefficient 0.09, P = .05) were significantly associated with a faster rate of GCIPL loss.

CONCLUSIONS

Lower baseline peripapillary OMAG measurements were significantly associated with a faster rate of GCIPL loss in patients with mild to moderate POAG.

Optical Microangiography and Progressive Retinal Nerve Fiber Layer Loss in Primary Open Angle Glaucoma

PURPOSE

To evaluate the association between optical microangiography (OMAG) measurements and progressive retinal nerve fiber layer (RNFL) loss in primary open angle glaucoma (POAG).

DESIGN

Prospective case series.

METHODS

Sixty-four eyes of 40 patients with POAG (108 quadrants) with mild to moderate functional damage were longitudinally studied for at least 2 years and with a minimum of 3 optical coherence tomography examinations. OMAG imaging was performed at the baseline visit. Effect of clinical parameters (age, sex, presence of systemic diseases, central corneal thickness, presence of disc hemorrhage, and mean and fluctuation of intraocular pressure during follow-up), baseline hemifield mean deviation, baseline quadrant optical coherence tomography RNFL and ganglion cell inner plexiform layer thickness), and OMAG (peripapillary and macular perfusion density [PD] and vessel density [VD]) on the rate of RNFL change was evaluated using linear mixed models.

RESULTS

Average (±SD) mean deviation, RNFL, and ganglion cell inner plexiform layer thickness of the analyzed quadrants at baseline were -5.5 ± 2.9 dB, 96.5 ± 17.9 µm, and 73.8 ± 8.6 µm, respectively. Peripapillary PD and VD in the quadrant were 44.6% ± 5.9% and 17.5 ± 2.2 mm/mm², respectively. Rate of quadrant RNFL change was -1.8 ± 0.6 µm/y. Multivariate mixed models showed that lower peripapillary PD (coefficient = 0.08, P = .01) and lower VD (coefficient = 0.21, P = .02) were significantly associated with a faster rate of RNFL loss.

CONCLUSIONS

Lower baseline peripapillary PD and VD measured using OMAG were significantly associated with a faster rate of RNFL loss in POAG. OMAG imaging provides useful information about the risk of glaucoma progression and the rate of disease worsening.

Referenced scans improve the repeatability of optical coherence tomography angiography measurements in normal and glaucoma eyes

AIM

To compare the repeatability of peripapillary perfusion density and flux index measurements on referenced and non-referenced optical microangiography (OMAG) scans in normal, glaucoma suspect and glaucoma eyes.

METHODS

In a cross-sectional study, 48 eyes (33 subjects) underwent three repeat, non-referenced peripapillary OMAG scans in the same session and 43 eyes (25 subjects) underwent three referenced peripapillary OMAG scans. In the referenced scan group, repeat scans (second and the third scan) were acquired exactly on the baseline (first) scan using the 'track to prior scan' option on the device. Repeatability estimates of the mean and four-sector (temporal, superior, nasal and inferior) OMAG measurements on the non-referenced and referenced scans were assessed using within-subject coefficient of repeatability (CR_w) and variation (CV_w).

RESULTS

CR_w (%) of peripapillary perfusion density measurements (range: 2.0-4.1) on non-referenced scans were significantly higher than that on referenced scans (range: 1.4-2.7). CV_w (%) on non-referenced and referenced scans ranged from 1.7 to 3.1 and from 1.2 to 2.1, respectively . CR_w of flux index on non-referenced and referenced scans ranged from 4.4 to 5.8 and from 3.6 to 4.8, respectively. CV_w on non-referenced and referenced scans ranged from 4.1 to 5.2 and from 3.3 to 4.5, respectively.

CONCLUSIONS

Repeatability estimates of OMAG measurements were better on referenced scans compared with non-referenced scans. Perfusion density measurements had lower variability than flux index. OCTA-measured perfusion density of referenced scans is preferable for monitoring vascular change in glaucoma.

Intereye Comparison of the Characteristics of the Peripapillary Choroid in Patients with Unilateral Normal-Tension Glaucoma

PURPOSE

To compare the characteristics of the peripapillary choroid (PPC) between the 2 eyes of patients with unilateral treatment-naïve normal-tension glaucoma (NTG).

DESIGN

Observational case series.

PARTICIPANTS

Sixty-nine patients (138 eyes) with treatment-naïve unilateral NTG.

METHODS

The characteristics of PPC vasculature were evaluated by measuring PPC thickness and assessing the presence of parapapillary deep-layer microvasculature dropout (MvD). Peripapillary choroid thickness was measured by enhanced depth imaging OCT. Microvasculature dropout was assessed using OCT angiography. The area and maximum radial width of β-zone parapapillary atrophy (PPA) were measured on infrared images using the built-in caliper tool of the Spectralis OCT (Heidelberg Engineering).

MAIN OUTCOME MEASURES

Between-eye differences in PPC thickness, MvD frequency, and the area and maximum width of β-zone PPA.

RESULTS

Eyes with NTG showed higher intraocular pressure (IOP), longer axial length, thinner PPC, larger area and maximum radial width of the β-zone PPA, and more frequent MvD (P < 0.01 for each) than contralateral healthy eyes. Multivariate conditional logistic regression analysis revealed that higher IOP, thinner PPC, larger maximum radial width of β-zone PPA, and the presence of MvD were associated independently with the risk of NTG (P < 0.03 for each). In eyes with NTG, MvD location and retinal nerve fiber layer defect were correlated topographically.

CONCLUSIONS

Peripapillary choroid vasculature characteristics are significantly more compromised in eyes with NTG than in contralateral healthy eyes of patients with unilateral NTG.

Effect of systemic blood pressure on optical coherence tomography angiography in glaucoma patients

BACKGROUND

The association between retinal microvascular structure and glaucoma has been revealed in multiple studies using optical tomography angiography (OCTA), but limited information on the macular vessel density (mVD) in patients with glaucoma is available. In this study, we tried to identity the factors that affected macular VD (mVD) in glaucomatous eyes.

METHODS

This retrospective cross-sectional study evaluated OCT and OCTA images from 92 eyes from 58 healthy subjects and 179 eyes from 103 glaucoma patients using the SD-OCT database from July 2017 to July 2018. Glaucomatous eyes were further divided into two groups according to history of disc haemorrhage (DH). Association between mVD and demographic characteristics, ganglion cell-inner plexiform layer (GCIPL) thickness, visual field mean deviation (MD) and systemic blood pressure was analysed in each group.

RESULTS

In both healthy and glaucomatous eyes, mVD was inversely associated with age (β = -0.035, P = 0.025; β = -0.039, P = 0.018). In the glaucomatous eyes, mVD was significantly decreased, as the MD value was worse (β = 0.109, P = 0.002). In glaucomatous eyes with DH, mVD decreased as blood pressure increased (β = -0.111, P = 0.003) CONCLUSIONS: Reduced mVD is more common in older individuals in both healthy and glaucomatous eyes, and correlates with functional deterioration than structural damage in glaucomatous eyes. In glaucomatous eyes with DH, high systemic BP is associated with a reduction in mVD. This may indicate that glaucoma patients with DH are more susceptible to vascular damage secondary to hypertension.

Optical Coherence Tomography Angiography in Glaucoma

Optical coherence tomography angiography (OCTA) is a relatively new, noninvasive, dye-free imaging modality that provides a qualitative and quantitative assessment of the vasculature in the retina and optic nerve head. OCTA also enables visualization of the choriocapillaris, but only in areas of parapapillary atrophy. With OCTA, the movement of red blood cells is used as a contrast to delineate blood vessels from static tissues. The features seen with OCTA in eyes with glaucoma are reduction in the superficial vessel density in the peripapillary and macular areas, and complete loss of choriocapillaris in localized regions of parapapillary atrophy (called deep-layer microvascular dropout). These OCTA changes correlate well topographically with the functional changes seen on visual field examination and structural changes seen on optical coherence tomography (OCT) (ie, parapapillary retinal nerve fiber layer changes and inner retinal layer thickness changes at macula). The OCTA measurements also have acceptable test-retest variability and well differentiate glaucomatous from normal eyes. OCTA measurements can be affected by various subject-related, eye-related, and disease-related factors. Vessel density reduction on OCTA reaches a base level (floor) at a more advanced disease stage than the structural changes on OCT and therefore has the potential to monitor progression in eyes with advanced glaucomatous damage. OCTA also adds information about glaucoma patients at risk of faster progression. OCTA, therefore, complements visual field and OCT examinations to diagnose glaucoma, detect progression, and assess risk of progression.

Peripapillary vessel parameters and mean ocular perfusion pressure in young healthy eyes: OCT angiography study

BACKGROUND

To investigate the relationship between estimated mean ocular perfusion pressure (MOPP) and peripapillary perfusion density (PD) or vessel density (VD) as measured by spectral-domain optical coherence tomography angiography (OCTA) in young healthy eyes.

METHODS

132 healthy participants (264 eyes) under 45 years of age underwent optic disc OCTA scan sized 3×3 mm to acquire PD and VD in the superficial vascular complex (SVC). Optic nerve head (ONH) parameters including retinal nerve fibre layer (RNFL) thickness, rim area and disc area were measured. MOPP was estimated from systemic blood pressure and intraocular pressure (IOP). A linear mixed model was used to find the systemic and ocular factors associated with PD and VD.

RESULTS

The average age of the subjects was 25.8±6.5 years. PD and VD showed a significant correlation with RNFL thickness (r=0.224, p<0.001 and r=0.214, p<0.001, respectively), but with MOPP, the correlation was only marginally significant (r=0.105, p=0.09 and r=0.112, p=0.07, respectively). After controlling for confounding factors, including age, sex, IOP, central corneal thickness, axial length and OCTA signal strength, PD and VD were significantly associated with ONH parameters (all p<0.05) but not with estimated MOPP (all p>0.05).

CONCLUSION

PD and VD in the SVC were significantly associated with ONH parameters while showing no association with estimated MOPP. OCTA-derived VD may not represent perfusion pressure, but is rather more dependent on peripapillary structure.

Factors associated with macular vessel density measured by optical coherence tomography angiography in healthy and glaucomatous eyes

PURPOSE

To investigate factors associated with macular vessel density and to analyze their effects according to glaucoma stage.

STUDY DESIGN

Retrospective cross-sectional study.

METHODS

A total of 72 healthy eyes and 147 open-angle glaucomatous eyes were studied. All eyes underwent optical coherence tomography and visual field examinations. Clinical variables were compared according to the glaucoma stage. Relationships between macular vessel density (mVD) and other variables were analyzed using linear regression and segmented analyses.

RESULTS

Age (P = 0.010) and signal strength (P < 0.001) were associated with macular vessel density in healthy eyes. In glaucomatous eyes, age, signal strength, ganglion cell-inner plexiform layer (GCIPL) thickness, and mean deviation (MD) correlated with macular vessel density (all P ≤ 0.005). When analyzed by glaucoma stage, age correlated with macular vessel density in early (P = 0.017 and all P ≤ 0.012, respectively) and moderate (P = 0.002 and all P ≤ 0.001, respectively) glaucoma. Conversely, GCIPL thickness was associated with macular vessel density (P = 0.004). According to segmented analysis between MD and mVD, the MD value at the change point for mVD was -17.92 dB, which was much lower than that for GCIPL thickness (-5.83 dB).

CONCLUSION

Signal strength was the most significant factor associated with macular vessel density in healthy and glaucomatous eyes. Other than signal strength, factors associated with macular vessel density of glaucomatous eyes vary according to the glaucoma stage. The segmented analysis suggests that mVD could be better than GCIPL thickness in predicting MD changes in moderate-to-advanced glaucoma.

The Difference in Repeatability of Automated Superficial Retinal Vessel Density according to the Measurement Area Using OCT Angiography

Purpose

To evaluate the difference in the repeatability of automated superficial retinal vessel density and foveal avascular zone (FAZ) metrics according to the measurement area of optical coherence tomography angiography (OCTA).

Methods

A total of 127 normal eyes from 127 healthy subjects were included. Macular angiography images were acquired from all subjects using the Zeiss Cirrus 5000 with AngioPlex^™ OCTA software. Scans of 3 × 3 mm and 6 × 6 mm were each performed twice in a randomly arranged sequence. Vessel density (VD), perfusion density (PD), and FAZ metrics of the superficial capillary plexus were calculated automatically for all scans, and the repeatabilities for both scan patterns were assessed based on intraclass correlation (ICC), coefficient of variation (CV), and coefficient of repeatability (CR) parameters. The average measured values in the two scan patterns were also compared.

Results

VD was significantly greater in the 3 × 3 mm scan than in the 6 × 6 mm scan according to all parameters, whereas PD was significantly less in the 3 × 3 mm scan than in the 6 × 6 mm scan. The ICCs for VDs in the central fovea were 0.826 and 0.741 for the 3 × 3 and 6 × 6 mm scans, respectively, and the CVs were 8.00% and 12.75%. For PDs, the ICCs were 0.839 and 0.762 and the CVs were 9.32% and 14.90%. The FAZ metrics in the 3 × 3 mm scan showed good repeatability with an ICC >0.75 and a CV <10.0%. However, all ICCs for the 6 × 6 mm scans were <0.75, and the CVs were all >10%.

Conclusions

The 6 × 6 mm macular angiography scans resulted in lower repeatabilities than the 3 × 3 mm scans according to all OCTA parameters, particularly in the central fovea and FAZ metrics. The 3 × 3 mm scan was more suitable than the 6 × 6 mm scan for analyzing macular microvascular density and FAZ metrics.

Simultaneous detection of cerebral blood perfusion and cerebral edema using swept-source optical coherence tomography

The progression of ischemic cerebral edema (CE) is closely related to the level of cerebral blood perfusion (CBP) and affects each other. Simultaneous detection of CBP and CE is helpful in understanding the mechanisms of ischemic CE development. In this article, a wide field of view swept-source optical coherence tomography system was used to detect CE status and CBP levels simultaneously in middle cerebral artery occlusion rats. Images reflecting these two physiological states can be reconstructed with only one C-scan. We quantify these two physiological states into four parameters, which contain two vascular parameters (vascular displacement distance and vascular perfusion density) and two edema parameters (optical attenuation coefficient and edema area). The association between the two vascular parameters and the two edema parameters was analyzed. The results show that there is a strong linear relationship between blood flow parameters and edema parameters. This work provides a new option for CE in vivo detection, and is very likely to play an important role in the development of relevant drugs or in selection of treatment options.

RELATIONSHIP BETWEEN ABNORMALITIES OF PHOTORECEPTOR MICROSTRUCTURES AND MICROVASCULAR STRUCTURES DETERMINED BY OPTICAL COHERENCE TOMOGRAPHY ANGIOGRAPHY IN EYES WITH BRANCH RETINAL VEIN OCCLUSION

PURPOSE

To determine whether the size of the foveal avascular zone (FAZ) is significantly correlated with the best-corrected visual acuity (BCVA) and to examine the relationship between the size and microstructural changes of the photoreceptors in eyes with a branch retinal vein occlusion.

METHODS

The medical records of 69 eyes of patients (mean age, 64.6 ± 11.7 years) with a branch retinal vein occlusion were reviewed after the resolution of macular edema. All the patients underwent optical coherence tomography angiography for measurement of the FAZ area and spectral domain optical coherence tomography for determination of microstructural changes of the photoreceptors at the fovea.

RESULTS

The superficial and deep FAZ areas in eyes with a branch retinal vein occlusion were 0.39 ± 0.36 mm and 0.63 ± 0.18 mm, respectively, and both were significantly larger than those observed in the fellow eyes (both, P < 0.001). The superficial FAZ area correlated with the posttreatment BCVA (r = 0.285, P = 0.027) but not with any parameters regarding the microstructures of the photoreceptors. Multivariate linear regression analysis showed that the pretreatment BCVA (β = 0.519, P < 0.001) and integrity of the external limiting membrane (β = -0.373, P = 0.001) were independent factors that significantly correlated with the posttreatment BCVA.

CONCLUSION

There was no significant correlation between the FAZ area and microstructural parameters. However, the integrity of the external limiting membrane was significantly correlated with the posttreatment BCVA in eyes with a branch retinal vein occlusion.

Signal Strength as an Important Factor in the Analysis of Peripapillary Microvascular Density Using Optical Coherence Tomography Angiography

The quality of the scan image is important in peripapillary circulation analysis using optical coherence tomography angiography (OCTA). We aimed to investigate the effects of signal strength (SS) on the peripapillary microvascular density acquired from OCTA. A total of 259 eyes from 259 young healthy subjects were included. Peripapillary OCTA images using 3 × 3 mm angiography scan were acquired from all participants. Subjects were divided into four groups according to the SS: SS 7, SS 8, SS 9, and SS 10. Vessel density (VD) and perfusion density (PD) of the superficial capillary plexus were calculated. VD and PD were compared among the four groups, and linear regression analyses were performed to identify and evaluate the clinical factors associated with average VD. As the SS increased from 7 to 10, the average VD and PD increased; these increases were statistically significant (all, p < 0.001). Regression analyses showed that four factors were significantly correlated with average VD: age (partial r = 0.133), average retinal nerve fiber layer thickness (partial r = 0.169), cup/disc ratio (partial r =-0.481), and SS (partial r = 0.413). SS is a significant factor affecting peripapillary microvascular density, and its influence is similar to well-known structural parameters associated with glaucoma.

Factors Affecting Repeatability of Assessment of the Retinal Microvasculature Using Optical Coherence Tomography Angiography in Healthy Subjects

Various factors can affect repeatability of optical coherence tomography angiography (OCTA) measurements, and they have not been studied sufficiently. We aimed to investigate the factors associated with the repeatability of automated superficial retinal vessel density (VD) and foveal avascular zone (FAZ) metrics acquired from OCTA. A total of 141 normal eyes from 141 healthy subjects were included, and two consecutive macular 6 × 6-mm angiography scans were performed. VD, perfusion density (PD), and FAZ of the superficial capillary plexus were calculated automatically. Reproducibility was assessed based on intraclass correlations (ICCs) and coefficients of variation (CVs). VD (ICC: 0.824, CV: 3.898) and PD (ICC: 0.845, CV: 4.042) over the entire 6-mm scan area showed better repeatability than VD (ICC: 0.752, CV: 17.470) and PD (ICC: 0.752, CV: 18.552) in the 1-mm scan, and with respect to the obtained FAZ metrics (ICC < 0.75, CV > 10.0%). Regression analyses showed that two factors, signal strength (p = 0.004) and average VD over the total 6-mm scan area (p < 0.001), were significantly correlated with the CV of the VD. Signal strength was associated with the repeatability of OCTA measurements and should be considered in the analysis of retinal VD and FAZ.

Changes in Ganglion Cell-Inner Plexiform Layer Thickness and Retinal Microvasculature in Hypertension: An Optical Coherence Tomography Angiography Study

PURPOSE

To investigate retinal blood flow in patients with hypertension using optical coherence tomography angiography (OCTA) and the relationship between blood flow metrics and ganglion cell-inner plexiform layer (GC-IPL) thickness.

DESIGN

Retrospective, cross-sectional study.

METHODS

A total of 201 eyes from 117 healthy subjects and 84 hypertensive patients without any ocular abnormalities were included. Hypertensive patients were divided into the 2 groups according to disease periods (<5 years: Hypertension Group 1; ≥5 years: Hypertension Group 2). Macular 3 × 3-mm angiography was acquired using the Zeiss Cirrus 5000 OCT instrument. Vessel density (VD), perfusion density (PD), and foveal avascular zone metrics of the superficial capillary plexus were automatically calculated, and the thicknesses of the central fovea, GC-IPL, and peripapillary retinal nerve fiber layer (RNFL) were measured. All measurements were compared among the 3 groups, and retinal blood flow metrics were correlated with the thickness of each retinal layer. Logistic regression analyses were performed to determine the factors associated with prolonged hypertension.

RESULTS

The average GC-IPL (P < .001) and peripapillary RNFL (P = .048) thicknesses in Hypertension Group 2 were significantly thinner compared to the control group. The 3 mm total area of the VD and PD was also decreased compared to the control group and Hypertension Group 1 (all P < .05), and was significantly correlated with the GC-IPL (VD: r = 0.450, P = .001; PD: r = 0.467, P < .001) and peripapillary RNFL (VD: r = 0.314, P = .027; PD: r = 0.328, P = .023) thicknesses in Hypertension Group 2. Using multivariate logistic analyses, only the average GC-IPL thickness was a significant factor for prolonged hypertension (odds ratio = 0.911, P = .002).

CONCLUSIONS

In patients with hypertension lasting more than 5 years, inner retinal layer thinning, particularly GC-IPL thinning, was observed, which was significantly correlated with a decrease in retinal blood flow. Therefore, physicians should consider the effects of hypertension on the GC-IPL.

The Importance of Signal Strength in Quantitative Assessment of Retinal Vessel Density Using Optical Coherence Tomography Angiography

The quality of the scan image is important in microvascular circulation analysis using optical coherence tomography (OCTA). We aimed to investigate the effect of signal strength (SS) on OCTA metrics and minimum SS level that could be considered optimal. Macular 6 × 6 mm angiography images were acquired, and all subjects were divided into four groups according to the SS (SS 7, SS 8, SS 9, and SS 10) of the OCTA image. Vessel density (VD), perfusion density (PD), and foveal avascular zone (FAZ) metrics of the superficial capillary plexus were compared. In total, 446 eyes from young healthy subjects were included. As the SS increased from 7 to 10, the VD and PD of the total area, and the FAZ area increased significantly (all, p < 0.001), but there were no significant difference between SS 9 and SS 10 in all metrics. Correlation analysis between the SS and each parameter showed a high correlation coefficient (VD, r = 0.668; PD, r = 0.671; FAZ area, r = 0.570; all, p < 0.001). The measurements of VD, PD, and FAZ using OCTA varied significantly with the SS, and at least 9 of SS is recommended. The physician should be careful in the analyses of OCTA measurements showing different values of the SS.

Macular Displacement After Vitrectomy in Eyes With Idiopathic Macular Hole Determined by Optical Coherence Tomography Angiography

PURPOSE

To determine whether the macula is displaced after vitrectomy with internal limiting membrane (ILM) peeling in eyes with an idiopathic macular hole.

DESIGN

A retrospective, observational case series.

METHODS

Optical coherence tomography angiography was used to obtain 3 mm × 3 mm en face images before and 2, 4, and 8 weeks after the vitrectomy with ILM peeling for 20 eyes of 20 patients with an idiopathic macular hole. The displacements of easily identifiable retinal vessel bifurcations were measured relative to the fovea and the optic disc.

RESULTS

The distance between the optic disc and vessel bifurcations was significantly shorter in all 4 quadrants throughout the postoperative period (P < .001). This distance was significantly greater in the temporal quadrant (P < .001). The distance of the bifurcations was significantly correlated with the preoperative distance from the optic disc (r = -0.579, P < .001). A significantly greater downward displacement was observed in the superior quadrant (P < .001). The change in the angle of bifurcations was significantly correlated with the preoperative angle to the optic disc (r = -0.632, P < .001). The change in the distance in the inner region was significantly greater than that in the outer region in all quadrants. A significant reduction was observed in the mean foveal avascular zone area during the follow-up period.

CONCLUSIONS

The retina in the macular region was displaced nasally, probably owing to movement of the retina toward the optic disc because of a contraction after the ILM removal. There is also a possibility of a rotation downward by buoyancy from gas tamponade, and centripetal contraction during the process of hole closure.

Optical coherence tomography angiography: Technical principles and clinical applications in ophthalmology

Optical coherence tomography angiography (OCTA) is a functional extension of OCT that provides information on retinal and choroidal circulations without the need for dye injections. With the recent development of high-speed OCT systems and efficient algorithms, OCTA has become clinically feasible. In this review article, we discuss the technical principles of OCTA, including image processing and artifacts, and its clinical applications in ophthalmology. We summarize recent studies which qualitatively or quantitatively assess disease presentation, progression, and/or response to treatment.

Optical coherence tomography angiography: A comprehensive review of current methods and clinical applications

OCT has revolutionized the practice of ophthalmology over the past 10-20 years. Advances in OCT technology have allowed for the creation of novel OCT-based methods. OCT-Angiography (OCTA) is one such method that has rapidly gained clinical acceptance since it was approved by the FDA in late 2016. OCTA images are based on the variable backscattering of light from the vascular and neurosensory tissue in the retina. Since the intensity and phase of backscattered light from retinal tissue varies based on the intrinsic movement of the tissue (e.g. red blood cells are moving, but neurosensory tissue is static), OCTA images are essentially motion-contrast images. This motion-contrast imaging provides reliable, high resolution, and non-invasive images of the retinal vasculature in an efficient manner. In many cases, these images are approaching histology level resolution. This unprecedented resolution coupled with the simple, fast and non-invasive imaging platform have allowed a host of basic and clinical research applications. OCTA demonstrates many important clinical findings including areas of macular telangiectasia, impaired perfusion, microaneurysms, capillary remodeling, some types of intraretinal fluid, and neovascularization among many others. More importantly, OCTA provides depth-resolved information that has never before been available. Correspondingly, OCTA has been used to evaluate a spectrum of retinal vascular diseases including diabetic retinopathy (DR), retinal venous occlusion (RVO), uveitis, retinal arterial occlusion, and age-related macular degeneration among others. In this review, we will discuss the methods used to create OCTA images, the practical applications of OCTA in light of invasive dye-imaging studies (e.g. fluorescein angiography) and review clinical studies demonstrating the utility of OCTA for research and clinical practice.

Optic Disc Perfusion in Primary Open Angle and Normal Tension Glaucoma Eyes Using Optical Coherence Tomography-Based Microangiography

Purpose

To investigate optic disc perfusion differences in normal, primary open-angle glaucoma (POAG), and normal tension glaucoma (NTG) eyes using optical microangiography (OMAG) based optical coherence tomography (OCT) angiography technique.

Design

Cross-sectional, observational study.

Subjects

Twenty-eight normal, 30 POAG, and 31 NTG subjects.

Methods

One eye from each subject was scanned with a 68 kHz Cirrus HD-OCT 5,000-based OMAG prototype system centered at the optic nerve head (ONH) (Carl Zeiss Meditec Inc, Dublin, CA). Microvascular images were generated from the OMAG dataset by detecting the differences in OCT signal between consecutive B-scans. The pre-laminar layer (preLC) was isolated by a semi-automatic segmentation program.

Main Outcome Measures

Optic disc perfusion, quantified as flux, vessel area density, and normalized flux (flux normalized by the vessel area) within the ONH.

Results

Glaucomatous eyes had significantly lower optic disc perfusion in preLC in all three perfusion metrics (p<0.0001) compared to normal eyes. The visual field (VF) mean deviation (MD) and pattern standard deviation (PSD) were similar between the POAG and NTG groups, and no differences in optic disc perfusion were observed between POAG and NTG. Univariate analysis revealed significant correlation between optic disc perfusion and VF MD, VF PSD, and rim area in both POAG and NTG groups (p≤0.0288). However, normalized optic disc perfusion was correlated with some structural measures (retinal nerve fiber layer thickness and ONH cup/disc ratio) only in POAG eyes.

Conclusions

Optic disc perfusion detected with OMAG was significantly reduced in POAG and NTG groups compared to normal controls, but no difference was seen between POAG and NTG groups with similar levels of VF damage. Disc perfusion was significantly correlated with VF MD, VF PSD, and rim area in glaucomatous eyes. Vascular changes at the optic disc as measured using OMAG may provide useful information for diagnosis and monitoring of glaucoma.

Full-range Fourier domain Doppler optical coherence tomography based on sinusoidal phase modulation

A novel full-range Fourier domain Doppler optical coherence tomography (full-range FD-DOCT) using sinusoidal phase modulation for B-M scan is proposed. In this sinusoidal B-M scan, zero optical path difference (OPD) position does not move corresponding to lateral scanning points in contrast to linear B-M scan. Since high phase sensitivity arises around the zero OPD position, the proposed full-range FD-DOCT can achieve easily high velocity sensitivity without mirror image around the zero OPD position. Velocity sensitivity dependent on the OPD and the interval of scanning points is examined, and flow velocity detection capability is verified through Doppler imaging of a flow phantom and an in vivo biological sample.