Anatomical and functional choroidal lobuli

The vascular geometry of the choriocapillaris is associated with spatially heterogeneous molecular exchange with the outer retina

Vision relies on the continuous exchange of material between the photoreceptors, retinal pigment epithelium and choriocapillaris, a dense microvascular bed located underneath the outer retina. The anatomy and physiology of the choriocapillaris and their association with retinal homeostasis have proven difficult to characterize, mainly because of the unusual geometry of this vascular bed. By analysing tissue dissected from 81 human eyes, we show that the thickness of the choriocapillaris does not vary significantly over large portions of the macula or with age. Assessments of spatial variations in the anatomy of the choriocapillaris in three additional human eyes indicate that the location of arteriolar and venular vessels connected to the plane of the choriocapillaris is non-random, and that venular insertions cluster around arteriolar ones. Mathematical models built upon these anatomical analyses reveal that the choriocapillaris contains regions where the transport of passive elements is dominated by diffusion, and that these diffusion-limited regions represent areas of reduced exchange with the outer retina. The width of diffusion-limited regions is determined by arterial flow rate and the relative arrangement of arteriolar and venular insertions. These analyses demonstrate that the apparent complexity of the choriocapillaris conceals a fine balance between several anatomical and functional parameters to effectively support homeostasis of the outer retina. KEY POINTS: The choriocapillaris is the capillary bed supporting the metabolism of photoreceptors and retinal pigment epithelium, two critical components of the visual system located in the outer part of the retina. The choriocapillaris has evolved a planar multipolar vascular geometry that differs markedly from the branched topology of most vasculatures in the human body. Here, we report that this planar multipolar vascular geometry is associated with spatially heterogenous molecular exchange between choriocapillaris and outer retina. Our data and analyses highlight a necessary balance between choriocapillaris anatomical and functional parameters to effectively support homeostasis of the outer retina.

Bruch's Membrane Calcification in Pseudoxanthoma Elasticum: Comparing Histopathology and Clinical Imaging

Purpose

To investigate the histology of Bruch's membrane (BM) calcification in pseudoxanthoma elasticum (PXE) and correlate this to clinical retinal imaging.

Design

Experimental study with clinicopathological correlation.

Subjects and Controls

Six postmortem eyes from 4 PXE patients and 1 comparison eye from an anonymous donor without PXE. One of the eyes had a multimodal clinical image set for comparison.

Methods

Calcification was labeled with OsteSense 680RD, a fluorescent dye specific for hydroxyapatite, and visualized with confocal microscopy. Scanning electron microscopy coupled with energy-dispersive x-ray spectroscopy (SEM-EDX) and time-of-flight secondary ion mass spectrometry (TOF-SIMs) were used to analyze the elemental and ionic composition of different anatomical locations. Findings on cadaver tissues were compared with clinical imaging of 1 PXE patient.

Main Outcome Measures

The characteristics and topographical distribution of hydroxyapatite in BM in eyes with PXE were compared with the clinical manifestations of the disease.

Results

Analyses of whole-mount and sectioned PXE eyes revealed an extensive, confluent OsteoSense labeling in the central and midperipheral BM, transitioning to a speckled labeling in the midperiphery. These areas corresponded to hyperreflective and isoreflective zones on clinical imaging. Scanning electron microscopy coupled with energy-dispersive x-ray spectroscopy and TOF-SIMs analyses identified these calcifications as hydroxyapatite in BM of PXE eyes. The confluent fluorescent appearance originates from heavily calcified fibrous structures of both the collagen and the elastic layers of BM. Calcification was also detected in an aged comparison eye, but this was markedly different from PXE eyes and presented as small snowflake-like deposits in the posterior pole.

Conclusions

Pseudoxanthoma elasticum eyes show extensive hydroxyapatite deposition in the inner and outer collagenous and elastic BM layers in the macula with a gradual change toward the midperiphery, which seems to correlate with the clinical phenotype. The snowflake-like calcification in BM of an aged comparison eye differed markedly from the extensive calcification in PXE.

Financial Disclosures

Proprietary or commercial disclosure may be found in the Footnotes and Disclosures at the end of this article.

Changes in choroidal hemodynamics of form-deprivation myopia in Guinea pigs

PURPOSE

We studied changes in the choroid, particularly variation in blood flow, during the development of myopia. The hemodynamic mechanism in play remains unclear. We evaluated blood flow by quantitating indocyanine green (ICG) fluorescence in a guinea pig model of form-deprivation myopia.

METHODS

Guinea pigs were divided into form-deprivation myopia (FDM) and normal control (NC) groups. Ocular biometric and choroidal hemodynamics parameters were quantitatively derived via ICG imaging, and included the maximal ICG fluorescence intensity (Imax), rising time (Trising), blood flow index (BFI), and mean transit time (MTT).

RESULTS

Form deprivation was associated with significant interocular differences in terms of both refractive error and axial length. ICG fluorescence hemodynamic maps of fundal blood flow and vasculature density were evident. In deprived eyes, the fluorescence signals exhibited significantly longer Trising and MTT but lower Imax and BFI than fellow eyes and NC group. The interocular differences in terms of the ocular biometric and hemodynamic parameters were significantly correlated. Hemodynamic analysis of choriocapillaris lobules revealed weakened fluorescence intensity and prolonged arrival and filling times in deprived eyes. Form deprivation reduced the number of lobulated choriocapillaris structures.

CONCLUSION

Form-deprivation myopia triggered changes in the hemodynamic and vascular network structures of the choroid and choriocapillaris. The ICG fluorescence imaging/analysis method provides a unique tool for further myopia research.

Effect of perfluoropropane (C3F8) versus sulfurhexafluoride (SF6) tamponades on the retinal microvasculature after macular hole surgery

PURPOSE

To determine the effects of C3F8 and SF6 gasses by using optical coherence tomography angiography (OCTA) in patients with surgically closed idiopathic full-thickness macular holes (FTMH).

METHODS

A prospective, comparative study, in which 38 eyes of 38 patients with an idiopathic FTMH were studied. Twenty patients were randomized to the C3F8 group and 18 patients to the SF6 group. All patients underwent pars plana vitrectomy, internal limiting membrane peeling with 14 % C3F8 or 20 % SF6 gasses. The superficial capillary plexus (SCP) and deep capillary plexus (DCP) vessel densities (VD), foveal avascular zone (FAZ) area in SCP, the choriocapillaris flow area; and subfoveal choroidal thickness (SFCT) were examined at preoperative and postoperative first- and third-month controls using OCTA.

RESULTS

When the changes in the FAZ, SFCT, SCP and DCP VDs were compared, no significant differences were found between the groups (p>0.05 for all). It was determined that the 1-mm radius flow area increases in the C3F8 group at the first and third months after the surgery were significantly higher than in the SF6 group (p<0.05). A significant gain was observed in the BCVA values compared to their preoperative values for both groups; however any differences between the C3F8 and SF6 groups in terms of BCVA were not detected in this study.

CONCLUSION

This is the first report to compare the effects of C3F8 and SF6 gasses on idiopathic FTMH surgery by using OCTA. C3F8 and SF6 gasses may have similar effect on the remodeling process of vascular tissues.

Choroidal Microvasculature Dropout in the Absence of Parapapillary Atrophy in POAG

Purpose

To describe the parapapillary choroidal microvasculature dropout (CMvD) in glaucomatous eyes without β-zone parapapillary atrophy (β-PPA) and compare its characteristics with that of CMvD with β-PPA.

Methods

Peripapillary choroidal microvasculature was evaluated on en face images obtained using optical coherence tomography angiography. CMvD was defined as a focal sectoral capillary dropout with no visible microvascular network identified in the choroidal layer. Peripapillary and optic nerve head structures, including the presence of β-PPA, peripapillary choroidal thickness and lamina cribrosa curvature index were evaluated using the images obtained by enhanced depth-imaging optical coherence tomography.

Results

The study included 100 glaucomatous eyes with CMvD (25 without and 75 with β-PPA) and 97 eyes without CMvD (57 without and 40 with β-PPA). Regardless of the presence of β-PPA, eyes with CMvD tended to have a worse visual field at a given RNFL thickness than eyes without CMvD, with patients having eyes with CMvD having lower diastolic blood pressure and more frequent cold extremities than patients with eyes lacking CMvD. Peripapillary choroidal thickness was significantly smaller in eyes with than without CMvD, but was not affected by the presence of β-PPA. β-PPA without CMvD was not associated with vascular variables.

Conclusions

CMvD were found in the absence of β-PPA in glaucomatous eyes. CMvDs had similar characteristics in the presence and absence of β-PPA. Clinical and optic nerve head structural characteristics potentially relevant to compromised optic nerve head perfusion were dependent on the presence of CMvD, rather than the presence of β-PPA.

Visualization of erythrocyte stasis in the living human eye in health and disease

Blood cells trapped in stasis have been reported within the microcirculation, but their relevance to health and disease has not been established. In this study, we introduce an in vivo imaging approach that reveals the presence of a previously-unknown pool of erythrocytes in stasis, located within capillary segments of the CNS, and present in 100% of subjects imaged. These results provide a key insight that blood cells pause as they travel through the choroidal microvasculature, a vascular structure that boasts the highest blood flow of any tissue in the body. Demonstration of clinical utility using deep learning reveals that erythrocyte stasis is altered in glaucoma, indicating the possibility of more widespread changes in choroidal microvascular than previously realized. The ability to monitor the choroidal microvasculature at the single cell level may lead to novel strategies for tracking microvascular health in glaucoma, age-related macular degeneration, and other neurodegenerative diseases.

Assessment of Choroidal Vasculature and Innate Immune Cells in the Eyes of Albino and Pigmented Mice

The visualization of choroidal vasculature and innate immune cells in the eyes of pigmented mice has been challenging due to the presence of a retinal pigment epithelium (RPE) layer separating the choroid and retina. Here, we established methods for visualizing the choroidal macrophages, mast cells, and vasculature in eyes of albino and pigmented mice using cell type-specific staining. We were able to visualize the choroidal arterial and venous systems. An arterial circle around the optic nerve was found in mice similar to the Zinn-Haller arterial circle that exists in humans and primates. Three different structural patterns of choriocapillaris were observed throughout the whole choroid: honeycomb-like, maze-like, and finger-like patterns. Choroidal mast cells were relatively few but dense around the optic nerve. Mast cell distribution in the middle and periphery was different among strains. Macrophages were found in all layers of the choroid. Thus, utilizing the simple and reliable methods described herein will allow the evaluation of transgenic and preclinical mouse models of ocular diseases that affect the choroid, including age-related macular degeneration (AMD), diabetic choroidopathy, and retinopathy of prematurity. These studies will advance our understanding of the pathophysiology, and molecular and cellular mechanisms that can be targeted therapeutically, in these diseases.

Choroidal Vasculature Changes in Age-Related Macular Degeneration: From a Molecular to a Clinical Perspective

The contribution of choroidal vasculature to the pathogenesis of age-related macular degeneration (AMD) has been long debated. The present narrative review aims to discuss the primary molecular and choroidal structural changes occurring with aging and AMD with a brief overview of the principal multimodal imaging modalities and techniques that enable the optimal in vivo visualization of choroidal modifications. The molecular aspects that target the choroid in AMD mainly involve human leukocyte antigen (HLA) expression, complement dysregulation, leukocyte interaction at Bruch’s membrane, and mast cell infiltration of the choroid. A mechanistic link between high-risk genetic loci for AMD and mast cell recruitment has also been recently demonstrated. Recent advances in multimodal imaging allow more detailed visualization of choroidal structure, identifying alterations that may expand our comprehension of aging and AMD development.

Choroidal vascularity index changes with phacovitrectomy for vitreoretinal interface disorders

Purpose

Vitreomacular interface disorders have long been argued to change choroidal structure. The aim of this study was to determine the choroidal vascularity index (CVI) changes following internal limiting membrane peeling for epiretinal membrane (ERM) and full thickness macular hole (FTMH).

Methods

Fifty-nine patients with unilateral ERM and 56 with unilateral FTMH were included in the study. Axial length, pre- and post-surgery intraocular pressure, baseline and post-phacovitrectomy CVI were calculated and compared with the normal fellow eyes. To compare the baseline and the final measurements, Wilcoxon test was used. Mann-Whitney U test was used for independent data comparisons. Median and standard deviations were compared.

Results

Axial length, pre- and post-surgery intraocular pressure differences were insignificant between study and fellow eyes within all groups. CVI were significantly lower in post-vitrectomy study eyes of all groups compared with pre-surgery (P < 0.001). There were no significant changes before and after the surgeries in fellow eyes. Baseline CVI of ERM study eyes (median 65.90%) and FTHM study eyes (median 65.59%) did not differ significantly between groups (U = 1336, P = 0.07, r = 0.16).

Conclusion

There are conflicting results of vitreoretinal interface disorders CVI in the literature. In this study, both FTMH and ERM eyes showed reduced CVI postoperatively compared with the baseline. Preoperatively, there were no difference between study eyes and the fellow eyes.

Characterization of Choroidal Morphology and Vasculature in the Phenotype of Pachychoroid Diseases by Swept-Source OCT and OCTA

The objective of this study was to characterize the choroidal morphology and vasculature in pachychoroid diseases (PCD). A total of 49 eyes with polypoidal choroidal vasculopathy (PCV), 43 eyes with neovascular age-related macular degeneration (nAMD), and 50 eyes with central serous chorioretinopathy (CSC), along with 80 healthy eyes, were enrolled in this nested case-control study. The swept-source optical coherent tomography (OCT), OCT angiography, and En face images were quantitatively analyzed. Multivariate logistic regression models showed that older age and increased vessel density (VD) in the choriocapillaris (CC) layer were independent risk factors for both PCV (page < 0.001, pVD = 0.004), and nAMD (page < 0.001, pVD = 0.005). Decreased VD in the Sattler’s layer was an independent risk factor for PCV (p = 0.014). Increased VD in the Haller’s layer was an independent risk factor for CSC (p = 0.001). The proportion of the diffuse type of collateral circulation in the Sattler’ layer in CSC group was significantly higher than in the other three groups (p < 0.001). We concluded that the involvement of the blood flow in the CC, Haller’s, and Sattler’s layers are differently affected in CSC, nAMD, and PCV eyes, indicating the different pathological mechanism underlying the phenotype of PCD. The age-dependent establishment of collateral circulation in the Sattler’s layer may play a compensatory role regarding ischemic injury in the development of PCD.

Variability in Retinal Neuron Populations and Associated Variations in Mass Transport Systems of the Retina in Health and Aging

Aging is associated with a broad range of visual impairments that can have dramatic consequences on the quality of life of those impacted. These changes are driven by a complex series of alterations affecting interactions between multiple cellular and extracellular elements. The resilience of many of these interactions may be key to minimal loss of visual function in aging; yet many of them remain poorly understood. In this review, we focus on the relation between retinal neurons and their respective mass transport systems. These metabolite delivery systems include the retinal vasculature, which lies within the inner portion of the retina, and the choroidal vasculature located externally to the retinal tissue. A framework for investigation is proposed and applied to identify the structures and processes determining retinal mass transport at the cellular and tissue levels. Spatial variability in the structure of the retina and changes observed in aging are then harnessed to explore the relation between variations in neuron populations and those seen among retinal metabolite delivery systems. Existing data demonstrate that the relation between inner retinal neurons and their mass transport systems is different in nature from that observed between the outer retina and choroid. The most prominent structural changes observed across the eye and in aging are seen in Bruch's membrane, which forms a selective barrier to mass transfers at the interface between the choroidal vasculature and the outer retina.

The characteristics of choriocapillaris flow void in the unilateral polypoidal choroidal vasculopathy fellow eyes

To evaluate the morphological characteristics of flow void (FV) in the fellow eyes of the unilateral polypoidal choroidal vasculopathy (PCV). Fifty PCV fellow eyes (PCVF) and 31 age-matched normal ocular circulation controls were recruited in this retrospective study. The number of FV was analyzed according to the size in a centered 5 × 5 mm swept source optical coherence tomography angiography scans. We used indocyanine green angiography images to determine whether choroidal vascular hyperpermeability (CVH) has occurred. For the PCVF, the prevalence rate of CVH was 70% (35 of 50) The number of FVs was significantly lower in 400-25,000 μm2 (P = 0.005), 400-500 μm2 (P = 0.001), 525-625 μm2 (P = 0.001) and 650-750 μm2 (P = 0.018). compared to the controls. And showed no difference in size from 775 to 1125 μm2 between the two groups. The area under the receiver operating characteristic curve of PCVF with CVH and controls was 0.94 (95% CI 0.88-1.00) (P < 0.001). We found that the number of small FVs was significantly lower in the PCV fellow eyes than that in the eyes with control group.

Correlation of choriocapillaris hemodynamic data from dynamic indocyanine green and optical coherence tomography angiography

To investigate the correlation between posterior pole choroidal blood flow evaluated with digital subtraction indocyanine green angiography and enface optical coherence tomography angiography (OCTA). Imaging in animal study. The anatomy of 2 cynomogulus monkeys was studied. Each monkey was given a 0.75 mg/kg injection of indocyanine green in the saphenous vein. The dynamic angiographic filling sequence was recorded at 15 frames per second using the Heidelberg Spectralis. After image registration, sequential frame subtraction was used to image the dye front moving through the choroid. The OCTA was obtained by frame averaging nine separate choriocapillaris slab flow images obtained from the Zeiss Plex Elite 9000. Posterior pole choriocapillaris filling pattern in relation to the choriocapillaris anatomy as imaged by OCTA. In the posterior pole, the choriocapillaris fills in the pattern of discrete units with variable sizes and shapes. The cycle of dye filling begins in the peripapillary area and progresses toward the periphery in a wavelike manner. This filling pattern repeats in a cyclical manner, consistent with the cardiac cycle. OCTA shows a uniform mesh of vessels. While OCTA shows a uniform meshwork appearance of the choriocapillaris, the dynamic dye angiography suggests an irregular configuration of functional units partitioned by pressure gradients as opposed to structural boundaries. Disturbance of local perfusion pressure within choroidal vasculature may result in abnormal flow patterns, which could be evaluated in the clinic using commercially available equipment.

Choriocapillaris: Fundamentals and advancements

The choriocapillaris is the innermost structure of the choroid that directly nourishes the retinal pigment epithelium and photoreceptors. This article provides an overview of its hemovasculogenesis development to achieve its final architecture as a lobular vasculature, and also summarizes the current histological and molecular knowledge about choriocapillaris and its dysfunction. After describing the existing state-of-the-art tools to image the choriocapillaris, we report the findings in the choriocapillaris encountered in the most frequent retinochoroidal diseases including vascular diseases, inflammatory diseases, myopia, pachychoroid disease spectrum disorders, and glaucoma. The final section focuses on the development of imaging technology to optimize visualization of the choriocapillaris as well as current treatments of retinochoroidal disorders that specifically target the choriocapillaris. We conclude the article with pertinent unanswered questions and future directions in research for the choriocapillaris.

Age-Related Macular Degeneration: Role of Oxidative Stress and Blood Vessels

Age-related macular degeneration (AMD) is a common irreversible ocular disease characterized by vision impairment among older people. Many risk factors are related to AMD and interact with each other in its pathogenesis. Notably, oxidative stress and choroidal vascular dysfunction were suggested to be critically involved in AMD pathogenesis. In this review, we give an overview on the factors contributing to the pathophysiology of this multifactorial disease and discuss the role of reactive oxygen species and vascular function in more detail. Moreover, we give an overview on therapeutic strategies for patients suffering from AMD.

Evaluation of the different thresholding strategies for quantifying choriocapillaris using optical coherence tomography angiography

BACKGROUND

In this paper, we evaluate the different thresholding strategies that have been used for the quantification of the choriocapillaris (CC) and explore their repeatability and the interchangeability of the measurements resulting from its application.

METHODS

Observational study. Eighteen eyes from nine healthy volunteers aged >18 years were imaged four consecutive times with a SD-OCTA system (Heidelberg Engineering, Germany) using a 10°×10° high-resolution protocol centered on the fovea. Projection artifacts were removed, and the CC was bracketed between 10 and 30 µm below Bruch's membrane. For the quantification of CC, we used four flow deficits (FD) parameters: FD number, mean FD size, total FD area and FD density. We performed a systematic review of literature to collect the thresholding methods that have been used for the quantification of CC. The CC quantification parameters were then evaluated after applying each of the thresholding strategies. Intraclass correlation coefficient (ICC) and Pearson's correlation analysis were used to compare the repeatability and interchangeability among the different thresholding strategies for quantifying the CC.

RESULTS

A total of 72 optical coherence tomography angiography (OCTA) examinations were considered. The systematic review allowed us to conclude that three local thresholding strategies (Phansalkar, mean and Niblack) and three global thresholding strategies (mean, default, Otsu) have been used for CC quantification. These strategies were evaluated in our observational study. We found a high agreement within the same method in the quantification of FD number, mean FD size, total FD area and FD density but a poor agreement with different strategies. Local strategies achieved a significantly superior ICC than global ones in CC quantification.

CONCLUSIONS

In conclusion, the interchangeability of the CC quantification using different thresholding strategies is low, and direct comparisons should not be performed. Local thresholding strategies are significantly superior to global ones for quantifying CC and should be preferred. There is an unmet need for a uniform strategy to quantify CC in future studies.

Correlations Between Different Choriocapillaris Flow Deficit Parameters in Normal Eyes Using Swept Source OCT Angiography

PURPOSE

Choriocapillaris (CC) imaging of normal eyes with swept-source optical coherence tomographic angiography (SS-OCTA) was performed, and the percentage of CC flow deficits (FD%) and the average area of CC flow deficits (FDa) were compared within the given macular regions.

DESIGN

A prospective, cross-sectional study.

METHODS

Subjects with normal eyes ranging in age from their 20s through their 80s were imaged with SS-OCTA (PLEX Elite 9000; Carl Zeiss Meditec, Dublin, California, USA) using both 3×3-mm and 6×6-mm macular scan patterns. The CC images were generated using a previously published and validated algorithm. In both 3×3-mm and 6×6-mm scans, the CC FD% and FDa were measured in circular regions centered on the fovea with diameters as 1 mm and 2.5 mm (C1 and C2.5). In 6×6-mm scans, the FD% and FDa were measured within an additional circular region with diameter as 5 mm (C5). The correlations between FD% and FDa from each region were analyzed with Pearson correlation coefficients.

RESULTS

A total of 164 eyes were analyzed. There was excellent correlation between CC FDa and FD% measurements from each region. In the 3×3-mm scans, the correlations in the C1 and C2.5 regions were 0.83 and 0.90, respectively. In the 6×6-mm scans, the correlations in C1, C2.5, and C5 regions were 0.90, 0.89, and 0.89, respectively.

CONCLUSIONS

When measuring CC FDs, we found excellent correlations between FDa and FD% in regions from 3×3-mm and 6×6-mm scans. Further studies are needed to determine if one parameter is more useful when studying diseased eyes.

Quantification of Choriocapillaris with Optical Coherence Tomography Angiography: A Comparison Study

PURPOSE

To demonstrate the variation in quantitative choriocapillaris (CC) metrics with various binarization approaches using optical coherence tomography angiography (OCTA).

DESIGN

Retrospective, observational, cross-sectional case series.

METHODS

Macular OCTA scans, 3- × 3-mm and 6- × 6-mm, were obtained from normal eyes and from eyes with drusen secondary to age-related macular degeneration (AMD). The CC slab was extracted, and the CC flow deficits (FDs) were segmented with 2 previously published algorithms: the fuzzy C-means approach (FCM method) and Phansalkar's local thresholding (Phansalkar method). Four different values for the radius were used in order to investigate the effect on the FD segmentation when using the Phansalkar method. FD density (FDD), mean FD size (MFDS), FD number (FDN), FD area (FDA) and intercapillary distance (ICD) were calculated for comparison. Repeatability was assessed as coefficient of variation (CV), and Pearson's correlation analysis was conducted.

RESULTS

Six eyes from 6 subjects with normal eyes and 6 eyes from 6 subjects with drusen secondary to AMD were scanned. The 3- × 3-mm scans resulted in higher repeatability than the 6- × 6-mm scans. For the Phansalkar method, larger values of the radius resulted in higher repeatability. ANOVA tests resulted in significant differences (P < 0.001) among the FCM method and the Phansalkar method with different radius options for all CC metrics and scan sizes investigated. In 3- × 3-mm scans, significant correlation was found between the FCM method and the Phansalkar method for all quantitative CC metrics other than FDN (all P < 0.001; 0.90 < r <0.99).

CONCLUSIONS

Quantitative CC analysis with commercially available OCTA is complicated and researchers need to pay close attention to how they conduct such analyses.

Microvascular contributions to age-related macular degeneration (AMD): from mechanisms of choriocapillaris aging to novel interventions

Aging of the microcirculatory network plays a central role in the pathogenesis of a wide range of age-related diseases, from heart failure to Alzheimer's disease. In the eye, changes in the choroid and choroidal microcirculation (choriocapillaris) also occur with age, and these changes can play a critical role in the pathogenesis of age-related macular degeneration (AMD). In order to develop novel treatments for amelioration of choriocapillaris aging and prevention of AMD, it is essential to understand the cellular and functional changes that occur in the choroid and choriocapillaris during aging. In this review, recent advances in in vivo analysis of choroidal structure and function in AMD patients and patients at risk for AMD are discussed. The pathophysiological roles of fundamental cellular and molecular mechanisms of aging including oxidative stress, mitochondrial dysfunction, and impaired resistance to molecular stressors in the choriocapillaris are also considered in terms of their contribution to the pathogenesis of AMD. The pathogenic roles of cardiovascular risk factors that exacerbate microvascular aging processes, such as smoking, hypertension, and obesity as they relate to AMD and choroid and choriocapillaris changes in patients with these cardiovascular risk factors, are also discussed. Finally, future directions and opportunities to develop novel interventions to prevent/delay AMD by targeting fundamental cellular and molecular aging processes are presented.

Angiographic features of drug-induced bilateral angle closure and transient myopia with Ciliochoroidal effusion

Background

To report five cases of acute drug-induced angle closure and transient myopia with ciliochoroidal effusion and to analyze angiographic findings of these cases.

Methods

This study is an observational case series. Five patients with acute drug-induced angle closure and transient myopia with ciliochoroidal effusion were examined by fluorescein angiography, indocyanine green angiography (ICGA) and ultrasound biomicroscopy (UBM).

Results

Five patients presented with bilateral visual loss and ocular pain after intake of topiramate, methazolamide, phendimetrazine tartrate or mefenamic acid. All patients showed elevated intraocular pressure (IOP) with shallow anterior chamber and myopic shift from − 0.5 to − 17.0 diopters (D). UBM showed ciliochoroidal effusions with diffuse thickening of the ciliary body in all cases. Rapid normalization of IOP and decrease of myopic shift occurred in all patients after discontinuing the suspected drugs. We classified the ICGA findings into 2 major signs (hypofluorescent dark spots, hyperfluorescent pinpoints) and 3 minor signs (diffuse choroidal hyperfluorescence, early hyperfluorescence of choroidal stromal vessel, and leakage and dilated retinal vessels).

Conclusions

The pathogenesis of acute drug-induced angle closure and transient myopia with ciliochoroidal effusion may be idiosyncratic reaction of uveal tissue to systemic drugs. Accumulation of extravascular fluid in the ciliochoroidal layer had a major role in the pathogenesis. ICGA could be a useful method to examine the pathophysiology of this condition by imaging of the choroidal layer.

Visualizing choriocapillaris using swept-source optical coherence tomography angiography with various probe beam sizes

Imaging choriocapillaris (CC) is a long-term challenge for commercial OCT angiography (OCTA) systems due to limited transverse resolution. Effects of transverse resolution on the visualization of a CC microvascular network are explored and demonstrated in this paper. We use three probe beams with sizes of ~1.12 mm, ~2.51 mm and ~3.50 mm at the pupil plane, which deliver an estimated transverse resolution at the retina of 17.5 µm, 8.8 µm and 7.0 µm, respectively, to investigate the ability of OCTA to resolve the CC capillary vessels. The complex optical microangiography algorithm is applied to extract blood flow in the CC slab. Mean retinal pigment epithelium (RPE) to CC (RPE-CC) distance, mean CC inter-vascular spacing and the magnitude in the radially-averaged power spectrum are quantified. We demonstrate that a clearer CC lobular capillary network is resolved in the angiograms provided by a larger beam size. The image contrast of the CC angiogram with a large beam size of 3.50 mm is 114% higher than that with a small beam size of 1.12 mm. While the measurements of the mean RPE-CC distance and CC inter-vascular spacing are almost consistent regardless of the beam sizes, they are more reliable and stable with the larger beam size of 3.50 mm. We conclude that the beam size is a key parameter for CC angiography if the purpose of the investigation is to visualize the individual CC capillaries.

Choroidal binarization analysis: clinical application

INTRODUCTION

Image processing of optical coherence tomography scans through binarization techniques represent a non-invasive way to separately asses and measure choroidal components, in vivo. In this review, we systematically search the scientific literature regarding binarization studies published so far.

METHODS

A systematic research was conducted at PubMed database, including English literature articles for all of the following terms in various combinations: binarization, choroid/al, enhanced depth spectral domain/swept source optic coherence tomography, and latest publications up to November 2018 were reviewed.

RESULTS

Thirty-seven articles were included and analyzed regarding studied disease, binarization method, studied variables, and outcomes. Most of the studies have focused on the more common retinal pathologies, such as age-related macular degeneration, central serous chorioretinopathy and diabetic retinopathy but binarization techniques have also been applied to the study of choroidal characteristics in ocular inflammatory diseases, corneal dystrophies and in postsurgical follow-up. Advantages and disadvantages of binarization techniques are also discussed.

CONCLUSION

Binarization of choroidal images seems to represent a promising approach to study choroid subcomponents in an increasingly detailed manner.

Optical coherence tomography angiography features in patients with idiopathic full-thickness macular hole, before and after surgical treatment

Purpose

To present optical coherence tomography (OCT) angiography features in patients with idiopathic full-thickness macular hole before and after vitrectomy.

Study design

Prospective case series study.

Materials and methods

Patients presenting with an idiopathic full-thickness macular hole (IMH) who underwent posterior vitrectomy with internal limiting membrane peeling and gas tamponade were included in the study. En face OCT and OCT angiography (OCTA) was performed pre- and postoperatively using 3×3 mm scans (Optovue, XR Avanti). Foveal avascular zone (FAZ) area, macular hole size (MHS), central retinal thickness (CRT), macular parafoveal choriocapillary flow area (MCFA), and fovea vessel density (FVDS) were measured and assessed using OCTA. Best-corrected visual acuity (BCVA) was examined before and 3 months after surgery.

Results

Twenty-eight eyes of 28 patients were included in the study. The mean age of patient group was 68.28 years. The hole was closed in all eyes after the initial surgery. OCTA showed enlargement of FAZ and increased CRT in foveal area. Mean preoperative FAZ area was 0.39±0.07 mm². En face images of the middle retina showed a range of preoperative cystic patterns surrounding the hole. BCVA was improved from 0.1±0.11 preoperatively to 0.42±0.17 postoperatively. Mean FAZ area was reduced to 0.24±0.07 mm² postoperatively with resolution of macular hole and adjacent cystic areas. Mean CRT was reduced from 396±62.6 µm pre-operatively to 272±30.7 µm postoperatively. After vitrectomy, the parafoveal choriocapillary flow area and FVDS of IMH eyes increased compared with the preoperative measurements.

Conclusion

Quantitative evaluation of vascular and morphological changes following IMH surgery using OCTA shows the potential for recovery due to vascular and neuronal plasticity. OCTA showing vascular changes and their quantitative characteristics might be a useful tool for the assessment of macular holes before and after surgical treatment.

Improving visualization and quantitative assessment of choriocapillaris with swept source OCTA through registration and averaging applicable to clinical systems

Choriocapillaris (CC) visualization and quantification remains challenging. We propose an innovative three-step registration and averaging approach using repeated swept source optical coherence tomography angiography (SS-OCTA) scans to conduct automatic quantitative assessment on CC. Six subjects were enrolled, each imaged at several locations with SS-OCTA from macular to equatorial regions using 3 mm × 3 mm scanning pattern. Five repeated volumes were collected for each subject. The complex optical microangiography (OMAG) algorithm was applied to identify blood flow in CC slab. An automatic three-step registration of translation, affine and B-Spline was applied to en face OCTA images of CC, followed with averaging. A fuzzy clustering approach was used to segment vasculature and flow deficits from the averaged images. The improvement in visualization of CC was evaluated and the average intercapillary distance was estimated by calculating the averaged capillary lumen spacing. A series of quantitative indices of flow deficit density, number, size, complexity index and aspect ratio index (FDD, FDN, FDS, FDCI and FDARI) were designed and validated with the increase of repeated scan numbers for averaging. Quantitative assessment was applied and compared on CC in macular and equatorial regions. The intercapillary distance was observed to be around 24 µm at macula and increased toward equatorial regions. All five quantitative indices (FDD, FDN, FDS, FDCI and FDARI) showed significant changes with multiple averaging and tend to become stable with repeated number of 4. Our proposed registration and averaging algorithm significantly improved the visualization of CC with SS-OCTA. The designed five indices for CC provide more options in the quantitative assessment of CC and are of great potentials in assisting the understanding of disease pathology, early diagnosis and treatment monitoring.

Pax6 regulation of Sox9 in the mouse retinal pigmented epithelium controls its timely differentiation and choroid vasculature development

The synchronized differentiation of neuronal and vascular tissues is crucial for normal organ development and function, although there is limited information about the mechanisms regulating the coordinated development of these tissues. The choroid vasculature of the eye serves as the main blood supply to the metabolically active photoreceptors, and develops together with the retinal pigmented epithelium (RPE). Here, we describe a novel regulatory relationship between the RPE transcription factors Pax6 and Sox9 that controls the timing of RPE differentiation and the adjacent choroid maturation. We used a novel machine learning algorithm tool to analyze high resolution imaging of the choroid in Pax6 and Sox9 conditional mutant mice. Additional unbiased transcriptomic analyses in mutant mice and RPE cells generated from human embryonic stem cells, as well as chromatin immunoprecipitation and high-throughput analyses, revealed secreted factors that are regulated by Pax6 and Sox9. These factors might be involved in choroid development and in the pathogenesis of the common blinding disease: age-related macular degeneration (AMD).

CLASSIFICATION OF HALLER VESSEL ARRANGEMENTS IN ACUTE AND CHRONIC CENTRAL SEROUS CHORIORETINOPATHY IMAGED WITH EN FACE OPTICAL COHERENCE TOMOGRAPHY

PURPOSE

To compare the prevailing patterns of Haller vessel arrangements at the posterior pole between healthy eyes and those with central serous chorioretinopathy (CSC) using en face optical coherence tomography.

METHODS

Eyes of normal subjects and patients with acute or chronic CSC underwent optical coherence tomography imaging (RTVue 100; Optovue Inc, Fremont, CA). En face sections at the level of the Haller layer were classified by two masked graders into five mutually exclusive morphologic categories (temporal herringbone, branched from below, laterally diagonal, double arcuate, and reticular). The relative prevalence of each Haller vessel arrangement pattern was determined for each phenotype.

RESULTS

Numbers of eyes examined were as follows: 154 eyes of 77 normal subjects; 41 eyes of 31 patients with acute CSC; and 39 eyes of 33 patients with chronic CSC. The mean age of participants was 44.4 ± 14.6 years for healthy subjects (M:F = 37:40), 48.5 ± 8.2 years (M:F = 24:7) for acute CSC, and 65.3 ± 13.1 years (M:F = 28:5) for chronic CSC. The relative prevalence of each Haller vessel arrangement pattern differed by phenotype. The temporal herringbone pattern was most prevalent in healthy eyes (49.2%), whereas a reticular pattern was most prevalent in eyes with acute and/or chronic CSC (combined, 48.8%).

CONCLUSION

A significant difference was observed in the prevalence of respective Haller vessel arrangement patterns between eyes of normal subjects and those of patients with either acute or chronic CSC. Although further study is needed to determine the mechanistic factors underlying these differences, and the hemodynamic implications, our data suggest that en face optical coherence tomography may find a formal role in choroidal disease classification.

Optical coherence tomography angiography

Optical coherence tomography (OCT) was one of the biggest advances in ophthalmic imaging. Building on that platform, OCT angiography (OCTA) provides depth resolved images of blood flow in the retina and choroid with levels of detail far exceeding that obtained with older forms of imaging. This new modality is challenging because of the need for new equipment and processing techniques, current limitations of imaging capability, and rapid advancements in both imaging and in our understanding of the imaging and applicable pathophysiology of the retina and choroid. These factors lead to a steep learning curve, even for those with a working understanding dye-based ocular angiography. All for a method of imaging that is a little more than 10 years old. This review begins with a historical account of the development of OCTA, and the methods used in OCTA, including signal processing, image generation, and display techniques. This forms the basis to understand what OCTA images show as well as how image artifacts arise. The anatomy and imaging of specific vascular layers of the eye are reviewed. The integration of OCTA in multimodal imaging in the evaluation of retinal vascular occlusive diseases, diabetic retinopathy, uveitis, inherited diseases, age-related macular degeneration, and disorders of the optic nerve is presented. OCTA is an exciting, disruptive technology. Its use is rapidly expanding in clinical practice as well as for research into the pathophysiology of diseases of the posterior pole.

Dilatation of Asymmetric Vortex Vein in Central Serous Chorioretinopathy

PURPOSE

To characterize the outer choroidal vessels in normal control eyes and those with central serous chorioretinopathy (CSC).

DESIGN

Prospective case-control study.

PARTICIPANTS

Thirty-eight eyes of 35 patients with acute CSC and 39 age-matched normal subjects.

METHODS

Swept-source optical coherence tomography was performed to obtain B-scan and en face images in the posterior pole in both groups. All patients with CSC underwent fluorescein angiography (FA) and indocyanine green angiography (ICGA).

MAIN OUTCOME MEASURES

Ascertainment of the patterns of the outer choroidal vessels in the en face and B-scan images in normal controls and patients, and the relationship between the en face images and dye leakage in the FA images and hyperpermeability in the ICGA images.

RESULTS

En face and ICGA images showed 2 choroidal drainage routes that served the upper and lower halves of the posterior pole. Twenty-four of the 39 eyes (62%) of the normal subjects had symmetrically distributed outer choroidal vessels; 15 eyes (38%) had asymmetrically distributed outer choroidal vessels. Asymmetry was seen in all 38 eyes (100%) of the 35 patients with CSC. The outer choroidal vessels all had vortex veins on en face and ICGA images. In eyes with CSC, a dominant vortex vein served the macular region (9 eyes) or the posterior pole (24 eyes) or extended beyond the vascular arcades (5 eyes). Dominant vortex veins were relatively dilated in normal controls but dilated markedly in CSC, with the distal ends in the macular region abruptly dilated. The sites of dye leakage on the FA images and hyperpermeability on the ICGA images corresponded to the dilated dominant vortex veins.

CONCLUSION

The presence of an asymmetric vortex vein was a common variation (38%) in normal subjects; this asymmetry was seen in all eyes (100%) with CSC. Dominant vortex veins were dilated markedly in CSC. Congestion of the dominant vortex veins might enhance the permeability of fenestrated choriocapillaris in the macular region. Asymmetric dominant vortex veins appear to be a predisposing factor for CSC.

Peripheral leptochoroid: clinical and anatomical findings

BACKGROUND/AIMS

To investigate the clinical findings and anatomical characteristics of patients with a thinned peripheral choroid (leptochoroid) presenting with bilateral macular geographical hyperpigmented fundus and compare with matched controls.

METHODS

A retrospective, observational case series of 44 eyes (24 patients): 22 study eyes (12 study patients) with clinical findings of leptochoroid (geographical hyperpigmented fundus centred in the macula) matched with 22 control eyes (12 control patients). All eyes received enhanced depth imaging optical coherence tomography at Memorial Sloan Kettering Cancer Center. Two independent observers performed all measurements. Statistical analysis was used to correlate interobserver findings, and compare patient and eye characteristics.

RESULTS

Study patients had a female predominance and median age of 70 years. Iris colour and refractive error of these eyes were varied: 8 eyes were myopic (one of which was highly myopic with a refractive error of -9.00) and 14 eyes were emmetropic or hyperopic (up to+3.00). The best-corrected visual acuity was 20/40 or better in all study eyes. The geographical macular areas of relative hyperpigmentation correspond to normal choroidal thickness compared with controls (p=0.74). The relative hypopigmented surrounding fundus had significantly thinner choroid compared with controls (p value=0.0001). Choroidal thickness had a strong interobserver correlation (r=0.99, p<0.0001).

CONCLUSION

Described here is a clinical entity referred to as peripheral leptochoroid. It appears as geographical hyperpigmented fundus centred in the macula, with adjacent relative hypopigmented fundus. Compared with matched normal subjects, the hyperpigmented and hypopigmented fundus correspond with equivocal and decreased choroidal thickness, respectively.

Dark Signals in the Choroidal Vasculature on Optical Coherence Tomography Angiography: An Artefact or Not?

Optical coherence tomography angiography (OCTA) based on mathematical processing of sequentially acquired structural OCT images has been applied widely in both retinal and choroidal research and may have advantages over traditional angiography. Images obtained by OCTA are rendered under the assumption that the only moving entity in the retina is blood flow. Optical phenomena and image processing algorithms may create imaging artefacts. Therefore, OCTA images require careful interpretation. This review discusses the dark signals seen in the choroidal vasculature on OCTA using multiple factor analysis. For accurate and comprehensive interpretation of the choroidal vasculature, we recommend simultaneous consideration of the laser light penetration depth and masking effect of retinal pigment epithelium, the orientation of vessels in relation to the scanning lasers and blood flow, the range of regional detectable velocity of blood flow, atrophic tissues in the periphery, and absorption of superior vessels on the scanning laser.

Form, shape and function: segmented blood flow in the choriocapillaris

The development of fluid transport systems was a key event in the evolution of animals and plants. While within vertebrates branched geometries predominate, the choriocapillaris, which is the microvascular bed that is responsible for the maintenance of the outer retina, has evolved a planar topology. Here we examine the flow and mass transfer properties associated with this unusual geometry. We show that as a result of the form of the choriocapillaris, the blood flow is decomposed into a tessellation of functional vascular segments of various shapes delineated by separation surfaces across which there is no flow, and in the vicinity of which the transport of passive substances is diffusion-limited. The shape of each functional segment is determined by the distribution of arterioles and venules and their respective relative flow rates. We also show that, remarkably, the mass exchange with the outer retina is a function of the shape of each functional segment. In addition to introducing a novel framework in which the structure and function of the metabolite delivery system to the outer retina may be investigated in health and disease, the present work provides a general characterisation of the flow and transfers in multipole Hele-Shaw configurations.

Choriocapillaris Flow Features Follow a Power Law Distribution: Implications for Characterization and Mechanisms of Disease Progression

PURPOSE

To investigate flow characteristics of the choriocapillaris using optical coherence tomography angiography.

DESIGN

Retrospective observational case series.

METHODS

Visualization of flow in individual choriocapillary vessels is below the current resolution limit of optical coherence tomography angiography instruments, but areas of absent flow signal, called flow voids, are resolvable. The central macula was imaged with the Optovue RTVue XR Avanti using a 10-μm slab thickness in 104 eyes of 80 patients who ranged in age from 24 to 99 years of age. Automatic local thresholding of the resultant raw data with the Phansalkar method was analyzed with generalized estimating equations.

RESULTS

The distribution of flow voids vs size of the voids was highly skewed. The data showed a linear log-log plot and goodness-of-fit methods showed the data followed a power law distribution over the relevant range. A slope intercept relationship was also evaluated for the log transform and significant predictors for variables included age, hypertension, pseudodrusen, and the presence of late age-related macular degeneration (AMD) in the fellow eye.

CONCLUSIONS

The pattern of flow voids forms a scale invariant pattern in the choriocapillaris starting at a size much smaller than a choroidal lobule. Age and hypertension affect the choriocapillaris, a flat layer of capillaries that may serve as an observable surrogate for the neural or systemic microvasculature. Significant alterations detectable in the flow pattern in eyes with pseudodrusen and in eyes with late AMD in the fellow eye offer diagnostic possibilities and impact theories of disease pathogenesis.

En Face Optical Coherence Tomography for Visualization of the Choroid

BACKGROUND AND OBJECTIVE

To assess posterior pole choroid patterns in healthy eyes using en face optical coherence tomography (OCT).

PATIENTS AND METHODS

This observational study included 154 healthy eyes of 77 patients who underwent en face OCT. The mean age of the patients was 31.2 years (standard deviation: 13 years); 40 patients were women, and 37 patients were men. En face imaging of the choroidal vasculature was assessed using an OCT Optovue RTVue (Optovue, Fremont, CA). To generate an appropriate choroid image, the best detectable vessels in Haller's layer below the retinal pigment epithelium surface parallel plane were selected.

RESULTS

Images of diverse choroidal vessel patterns at the posterior pole were observed and recorded with en face OCT. Five different patterns of Haller's layer with different occurrences were assessed. Pattern 1 (temporal herringbone) represented 49.2%, pattern 2 (branched from below) and pattern 3 (laterally diagonal) represented 14.2%, pattern 4 (doubled arcuate) was observed in 11.9%, and pattern 5 (reticular feature) was observed in 10.5% of the reference plane.

CONCLUSION

In vivo assessment of human choroid microvasculature in healthy eyes using en face OCT demonstrated five different patterns. The choroid vasculature pattern may play a role in the origin and development of neuroretinal pathologies, with potential importance in chorioretinal diseases and circulatory abnormalities.

Investigating the choriocapillaris and choroidal vasculature with new optical coherence tomography technologies

The body of knowledge of in vivo investigation of the choroid has been markedly enhanced by recent technological advances in optical coherence tomography (OCT). New insights elucidating the morphological features of the choriocapillaris and choroidal vasculature, in both physiological and pathological conditions, indicate that the choroid plays a pivotal role in many posterior segment diseases. In this article, a review of the histological characteristics of the choroid, which must be considered for the proper interpretation of in vivo imaging, is followed by a comprehensive discussion of fundamental principles of the current state-of-the-art in OCT, including cross-sectional OCT, en face OCT, and OCT angiography using both spectral domain OCT and swept source OCT technologies. A detailed review of the tomographic features of the choroid in the normal eye is followed by relevant findings in prevalent chorioretinal diseases, focusing on major causes of vision loss such as typical early and advanced age-related macular degeneration, polypoidal choroidal vasculopathy, central serous chorioretinopathy, pachychoroid spectrum disorders, diabetic choroidopathy, and myopia.

Regional morphology and pathophysiology of retinal vascular disease

Disturbances in the retinal vascular supply are involved in the pathophysiology of the most frequent diseases causing visual impairment and blindness in the Western World. These diseases are diagnosed by noting how morphological lesions in the retina vary in shape, size, location and dynamics, and subsequently concluding the presence of a specific disease entity. This diagnostic approach can be used to identify the site of a retinal vascular occlusion, to assess whether retinal diseases are primarily due to changes in the larger retinal vessels or the microcirculation, and to differentiate the relative involvement of the choroidal and the retinal vascular systems. However, a number of morphological manifestations of retinal vascular disease cannot presently be related to the underlying pathophysiology. The review concludes that there is a need for developing new methods for assessing vascular structure and function in the ciliary vascular system supplying the choroid and the optic nerve head. Presently, the study of these structures relies on imaging techniques with limited penetration and resolution into the tissue. Secondly, there is a need for studying oscillations in retinal vascular function occurring within days to weeks, and for studying regional manifestations of retinal vascular disease. This may constitute the basis for future research in retinal vascular pathophysiology and for the development of new treatment modalities to reduce blindness secondary to retinal vascular disease.

The epidemiology of retinal reticular drusen

PURPOSE

To describe the prevalence and 15-year cumulative incidence of and risk factors for reticular drusen.

DESIGN

Population-based prospective study.

METHODS

Four thousand nine hundred and twenty-six persons, 43 to 86 years of age, were included between 1988 and 1990, of whom 3,684, 2,764, and 2,119 participated in five-, 10-, and 15-year follow-up examinations, respectively, in Beaver Dam, Wisconsin. Main outcome measures included prevalence and 15-year incidence of reticular drusen determined by grading stereoscopic color fundus photographs.

RESULTS

The prevalence at baseline and the 15-year cumulative incidence in either eye of reticular drusen was 0.7% and 3.0%, respectively. The 15-year incidence of reticular drusen varied with age from 0.4% in those 43 to 54 years of age to 6.6% in those 75 years or older at baseline (P < .001). In a multivariate model, while controlling for age, risk factors statistically significantly associated with increased risk of incident reticular drusen included: being female (odds ratio [OR], 2.8), current smoking (OR vs never, 1.9), less education (OR per category, 1.7), B-vitamin complex use (OR vs none, 2.5), single vitamin B (OR vs none, 2.9), history of steroid eye drops use (OR, 5.9), glaucoma (OR, 2.8), and more severe drusen type (e.g., soft indistinct drusen; OR, 1.4), whereas diabetes (OR, 0.1) at baseline was associated with decreased risk. Right eyes with reticular drusen at baseline had higher cumulative incidence of geographic atrophy (21% vs 9%) and exudative age-related macular degeneration [AMD] (20% vs 10%) compared with eyes with soft indistinct drusen.

CONCLUSIONS

This population-based study documents the long-term cumulative incidence of reticular drusen and its risk factors and shows its association with a high risk of incident late AMD.

Blue flicker modifies the subfoveal choroidal blood flow in the human eye

The objective of the present study was to reveal an interaction between choroidal blood flow (ChBF) and light-induced photoreceptor activity, a physiological coupling that has been already demonstrated for retinal blood flow but rejected for ChBF. Ten healthy adults volunteered for this study. A real-time recording near-infrared laser-Doppler flowmeter was used to quantify the subfoveal ChBF while the luminance of blue flicker between 1 and 64 Hz was first increased and then decreased by 4.0 log units in 1.0-log unit steps between 0.0375 and 375 cd/m2. In separate testing, flash electroretinograms (ERGs) provided electrophysiological indexes of the relative response of short-wave cones (s-cones) and rods to blue light stimulation. Group-averaged, normalized ChBF measurements revealed that it was modulated by approximately 9% by flicker frequency. Increasing the blue flicker luminance from low to high attenuated the subfoveal ChBF, volume, and velocity by approximately 32%, approximately 30%, and approximately 5%, respectively. Decreasing the luminance from high to low over the same range had no effect on the subfoveal choroidal hemodynamics. The markedly different effects of reversed directions of change in blue flicker luminance on the subfoveal ChBF were linked to transitions between rod-dominated and s-cone-dominated retinal responses. Collectively, these findings indicate that the blue light-induced photoreceptor response is associated with a differential distribution of the ChBF across the ocular fundus according to the degree and type of retinal photoreceptor stimulated.

Immunohistochemical staining and morphometric analysis of the monkey choroidal vasculature

The purpose of this study was to develop a method for staining non-human primate choroidal blood vessels for combined whole mount and histologic analysis. Ten monkey eyes were used in this study. Diabetic and non-diabetic aged rhesus monkeys ranging in age from 16 to 31 years were killed and eyes were obtained immediately after death. Anterior segments were removed and retinas dissected from the posterior eyecup. Eyecups were soaked in 0.1% EDTA for 1hr to remove the retinal pigment epithelium (RPE). The whole choroids were dissected from the sclera, fixed in 2% paraformaldehyde and processed for immunohistochemical demonstration of perlecan, a heparan sulfate proteoglycan, using a streptavidin alkaline phosphatase technique. The alkaline phosphatase reaction product was developed using Histomark Red. Following immunohistochemical staining, choroids were incubated for the enzyme histochemical demonstration of non-specific esterase to label granulocytes. Anti-perlecan was localized to the endothelial cells of viable choroidal blood vessels and provided excellent staining of the choriocapillaris in all regions. Morphometric measurements of choriocapillaris were made in wet preparations using digitized images and image analysis software. The staining was absent in degenerated choroidal capillaries (lacking endothelial cells), thus allowing for sites of pathology to be identified and analysed. The reaction product was retained within the tissue throughout the flat-embedding process and allowed for precise site-specific identification of angiopathic lesions en bloc during sectioning. This technique provides a method of staining monkey choroidal blood vessels in situ and allows for identification and analysis of pathologic changes associated with aging or diseases.