Automation improves repeatability of retinal oximetry measurements

Purpose

Retinal oximetry is a technique based on spectrophotometry where images are analyzed with software capable of calculating vessel oxygen saturation and vessel diameter. In this study, the effect of automation of measurements of retinal vessel oxygen saturation and vessel diameter is explored.

Methods

Until now, operators have had to choose each vessel segment to be measured explicitly. A new, automatic version of the software automatically selects the vessels once the operator defines a measurement area. Five operators analyzed image pairs from the right eye of 23 healthy subjects with semiautomated retinal oximetry analysis software, Oxymap Analyzer (v2.5.1), and an automated version (v3.0). Inter- and intra-operator variability was investigated using the intraclass correlation coefficient (ICC) between oxygen saturation measurements of vessel segments in the same area of the retina.

Results

For semiautomated saturation measurements, the inter-rater ICC was 0.80 for arterioles and venules. For automated saturation measurements, the inter-rater ICC was 0.97 for arterioles and 0.96 for venules. For semiautomated diameter measurements, the inter-rater ICC was 0.71 for arterioles and venules. For automated diameter measurements the inter-rater ICC was 0.97 for arterioles and 0.95 for venules. The inter-rater ICCs were different (p < 0.01) between the semiautomated and automated version in all instances.

Conclusion

Automated measurements of retinal oximetry values are more repeatable compared to measurements where vessels are selected manually.

Nasalization of Central Retinal Vessel Trunk Predicts Rapid Progression of Central Visual Field in Open-Angle Glaucoma

Central visual field (CVF) loss is important in maintaining vision-related quality of life in eyes with open-angle glaucoma (OAG). The present study investigated whether nasalized location of central retinal vessel trunk (CRVT) at baseline is associated with rapid rate of CVF loss in early-stage OAG eyes. This study included 76 OAG eyes with high nasalization CRVT [HNL] group and 75 OAG eyes with low nasalization CRVT [LNL] group matched for glaucoma severity at baseline that showed progressive visual field (VF) loss. The rates of mean threshold changes at various regions were compared in the two groups using a linear mixed model. Clinical variables associated with rapid rate of CVF progression were also identified using a linear mixed model. The rate of CVF loss in the central 10° was significantly higher in the HNL group than that in the LNL group (-0.452 dB/year vs. -0.291 dB/year, P < 0.001). The average and inferior hemi-macular ganglion cell inner plexiform layer (GCIPL) progression rates were significantly faster in the HNL group than in the LNL group (P < 0.05). Nasalized location of CRVT was an independent predictor of a more rapid VF loss in the central 10° region (P < 0.05).

Association of serum lutein and zeaxanthin with quantitative measures of retinal vascular parameters

To evaluate the association between serum carotenoids and quantitative measures of retinal vasculature in elderly Singapore Chinese subjects. The following details were collected in 128 healthy subjects: sociodemographics, lifestyle information, medical and drug history, and anthropometric measurements. Serum concentrations of carotenoids were estimated in fasting venous blood using high performance liquid chromatography. Retinal vascular parameters were quantitatively measured from retinal photographs using a computer-assisted program (Singapore I Vessel Assessment). The mean age of the population was 54.1 years (range 40 to 81 years). In multiple linear regression analysis, per SD decrease in retinal arteriolar caliber [β = 0.045 (0.003 to 0.086), p = 0.036], per SD increase in retinal venular caliber [β = -0.045 (-0.086 to -0.003), p = 0.036] and per SD increase in arteriolar branching angle [β = -0.039 (-0.072 to -0.006), p = 0.021] were associated with decreased serum lutein. Per SD increase in retinal venular tortuosity [β = -0.0075 (-0.0145 to -0.0004), p = 0.039] and per SD increase in arteriolar branching angle (β = -0.0073 [-0.0142 to -0.0059], p = 0.041) were associated with decreased serum zeaxanthin. None of the other carotenoids demonstrated meaningful relationship with quantitative measures of retinal vasculature. Lower levels of lutein and zeaxanthin demonstrated significant relationship with adverse quantitative measures of retinal vasculature in elderly healthy subjects.

Immunohistochemical expression of CD117 and vascular endothelial growth factor in retinoblastoma: possible targets of new therapies

CD117 (C-kit) is thought to play an important role in tumourigenesis. There are limited data in the literature concerning C-kit expression in retinoblastoma. To date, no immunohistochemical studies have been performed to assess the possible association of C-kit with vascular endothelial growth factor (VEGF) in retinoblastoma. This study was designed to investigate C-kit and VEGF immunoexpression in retinoblastoma, their relationship with prognostic parameters as well as the correlation between them. A prospective immunohistochemical study was conducted on 56 retinoblastoma cases. Patients who had received preoperative chemotherapy were excluded. Positive C-kit and VEGF immunoreactivity was observed in 48.2% and 76.8% of retinoblastoma cases respectively. No C-kit immunostaining was seen in the adjacent uninvolved retina. However, VEGF expression was detected within its vasculature. Retinoblastomas with combined pattern of tumour growth revealed a highly significant positive C-kit expression (P = 0.002) compared to cases with endophytic or exophytic growths. Also, positive C-kit expression was statistically higher in cases with optic nerve invasion (P = 0.001) and choroidal invasion (P ≤ 0.01) compared to negative cases. A highly significant positive VEGF expression was detected in cases with optic nerve invasion (P = 0.013) compared to negative cases. Moreover, a highly significant positive correlation was detected between C-kit and VEGF expression (P = 0.006). C-kit is a feature of more aggressive retinoblastomas, with increased expression in tumours spreading beyond the retina. Moreover, VEGF is vastly expressed in retinoblastoma and is associated with optic nerve invasion. Both C-kit and VEGF may represent potential therapeutic targets for retinoblastomas.

Oximetry of retinal capillaries by multicomponent analysis

Retinal oximetry of capillaries was performed for early detection of retinal vascular abnormalities, which are caused predominantly by complications of systemic circulatory diseases. As the conventional method for determining absorbance is not applicable to capillaries, multicomponent analysis was used to estimate the absorbance spectra of the retinal blood vessels. In this analysis, the capillary spectrum was classified as intermediate between those of the retinal arteries and veins, enabling relative estimation of oxygen saturation in the capillaries. This method could be useful for early recognition of disturbances in the peripheral circulation. Furthermore, a spectroscopic ophthalmoscope system based on the proposed method was developed to examine the human retina. A clinical trial of this system demonstrated that oximetry of the retinal capillaries may be an improvement over the present diagnosis for patients of malignant hypertension.

Observation of persistent fundus fluorescence after internal limiting membrane peeling assisted by indocyanine green solution of different concentrations

PURPOSE

To investigate how long indocyanine green (ICG) remains in the fundus after vitreoretinal surgery assisted with ICG, and to identify factors that influence the persistence duration.

METHODS

Fifty five eyes diagnosed as idiopathic macular hole (Stage 2 and 3) were randomly divided into five groups. ICG solution at concentrations of 5, 2.5, 2.5, 1.25, and 0.5 mg/ml, employed in cases of Group I to V respectively, was applied to stain the internal limiting membrane (ILM) during the procedure of internal limiting membrane peeling. A prospective study was carried out after pars plana vitrectomy and ILM peeling were performed on 55 eyes with Stage 2, 3, or 4 idiopathic macular holes. Infrared fundus pictures were obtained in all patients before and after surgery.

RESULTS

High levels of fluorescence from residual ICG (ICG hyperfluorescence) were mainly localized at the posterior pole of the fundus after surgery. In Group Ⅰ, Ⅱ, III, IV and V, the duration of persistence of flurorescence from ICG was 8.33±0.87, 3.59±0.94, 3.75±0.79, 2.30±0.48, and 1.29±0.49 months, respectively. Although no significant difference was detected between Group Ⅱ and Group III, the general inter-group difference was significant among the five groups in which different ICG concentration was applied. In Group III, even though 90% of the macular holes acquired anatomical closure, ICG hyperfluorescence was detected in the macular area.

CONCLUSION

ICG remains in the fundus for a period of months. The persistence duration of fluorescence from ICG is positively correlated with the concentration and the staining time of ICG. Hyaluronan is beneficial in reducing the amount of ICG residue in the macular area.

Gene expression profiles of ATP-binding cassette transporter A and C subfamilies in mouse retinal vascular endothelial cells

The purpose of this study was to quantify gene expression levels of the ATP-binding cassette (ABC) transporter A and C subfamilies ABCA1-A9, and ABCC1-6/Mrp1-6, C10/Mrp7 in mouse retinal vascular endothelial cells (RVEC) using a combination of a magnetic isolation method for mouse RVEC and real-time quantitative PCR analysis. The transcript level of endothelial cell markers, such as CD31, Tie-2, claudin-5, occludin, ABCB1a/mdr1a, and ABCG2, were more than 20-fold higher than those in the non-RVEC fraction, suggesting that RVEC in the RVEC fraction are concentrated at least 20-fold compared with those of the non-RVEC fraction. In the ABCA1 to A9 families, the transcript level of ABCA3 and A9 in the RVEC fraction was 1.2- and 32-fold higher than that in the non-RVEC fraction. Although ABCA3 was expressed in both the RVEC and non-RVEC fractions, A9 is predominantly expressed in the RVEC fraction. In the ABCC1 to C6 and C10 families, the transcript level of ABCC3, C4, and C6 in the RVEC fraction was 27-, 251-, and 242-fold higher, respectively, than that in the non-RVEC fraction, suggesting that ABCC3, C4, and C6 are predominantly expressed in the RVEC. In conclusion, ABCA3, ABCA9, ABCC3, ABCC4, and ABCC6 mRNAs are predominantly expressed at the inner blood-retina barrier (inner BRB) and appear to play a major role in the efflux transport of their substrates at the inner BRB.

Caveolin-1 is up-regulated in transdifferentiated lens epithelial cells but minimal in normal human and murine lenses

Caveolae are flask-shaped invaginations of the plasma membrane found in many cell types. Caveolae play a role in lipid transport, endocytosis, signal transduction, and cell transformation. Expression of caveolin-1, the principal component of caveolae and a regulator of caveolae-dependent signaling and endocytosis, was investigated in lens epithelial cells and lens fiber cells in wild-type (wt) and SPARC-null mice and normal human donors in vivo and in vitro. RT-PCR, immunofluorescence and immunoblot analyses of human and murine ocular tissues revealed that caveolin-1 was expressed in the corneal epithelium, corneal endothelial cells, and blood vessels of iris, ciliary body and retina, but minimal in the normal lens epithelia or fiber cells of murine and human lens. In contrast, caveolin-1 was significantly up-regulated in mesenchymal-transdifferentiated lens epithelia in SPARC-null cataract lenses. In addition, lens epithelial cells from primary culture or from cultures of immortalized lens epithelial cell lines expressed significant amounts of caveolin-1. The lens epithelial cells expressed epidermal growth factor (EGF) receptor and were responsive to EGF-mediated cell proliferation, but they did not show EGF-dependent caveolin-1 tyrosine phosphorylation. Caveolin-1 might have a role in the process of epithelial-mesenchymal transdifferentiation (EMT) in the lens, the most common cause of vision loss in human secondary cataracts.

Kv1.5 is a major component underlying the A-type potassium current in retinal arteriolar smooth muscle

Little is known about the molecular characteristics of the voltage-activated K⁺ (K_v) channels that underlie the A-type K⁺ current in vascular smooth muscle cells of the systemic circulation. We investigated the molecular identity of the A-type K⁺ current in retinal arteriolar myocytes using patch-clamp techniques, RT-PCR, immunohistochemistry, and neutralizing antibody studies. The A-type K⁺ current was resistant to the actions of specific inhibitors for K_v3 and K_v4 channels but was blocked by the K_v1 antagonist correolide. No effects were observed with pharmacological agents against K_v1.1/2/3/6 and 7 channels, but the current was partially blocked by riluzole, a K_v1.4 and K_v1.5 inhibitor. The current was not altered by the removal of extracellular K⁺ but was abolished by flecainide, indicative of K_v1.5 rather than K_v1.4 channels. Transcripts encoding K_v1.5 and not K_v1.4 were identified in freshly isolated retinal arterioles. Immunofluorescence labeling confirmed a lack of K_v1.4 expression and revealed K_v1.5 to be localized to the plasma membrane of the arteriolar smooth muscle cells. Anti-K_v1.5 antibody applied intracellularly inhibited the A-type K⁺ current, whereas anti-K_v1.4 antibody had no effect. Co-expression of K_v1.5 with K_vβ1 or K_vβ3 accessory subunits is known to transform K_v1.5 currents from delayed rectifers into A-type currents. K_vβ1 mRNA expression was detected in retinal arterioles, but K_vβ3 was not observed. K_vβ1 immunofluorescence was detected on the plasma membrane of retinal arteriolar myocytes. The findings of this study suggest that K_v1.5, most likely co-assembled with K_vβ1 subunits, comprises a major component underlying the A-type K⁺ current in retinal arteriolar smooth muscle cells.

Divergent Distribution in Vascular and Avascular Mammalian Retinae Links Neuroglobin to Cellular Respiration

The visual function of the vertebrate retina relies on sufficient supply with oxygen. Neuroglobin is a respiratory protein thought to play an essential role in oxygen homeostasis of neuronal cells. For further understanding of its function, we compared the distribution of neuroglobin and mitochondria in both vascular and avascular mammalian retinae. In the vascular retinae of mouse and rat, oxygen is supplied by the outer choroidal, deep retinal, and inner capillaries. We show that in this type of retina, mitochondria are concentrated in the inner segments of photoreceptor cells, the outer and the inner plexiform layers, and the ganglion cell layer. These are the same regions in which oxygen consumption takes place and in which neuroglobin is present at high levels. In the avascular retina of guinea pig the deep retinal and inner capillaries are absent. Therefore, only the inner segments of the photoreceptors adjacent to choroidal capillaries display an oxidative metabolism. We demonstrate that in the retina of guinea pigs both neuroglobin and mitochondria are restricted to this layer. Our results clearly demonstrate an association of neuroglobin and mitochondria, thus supporting the hypothesis that neuroglobin is a respiratory protein that supplies oxygen to the respiratory chain.

Special report: Noninvasive multi-parameter functional optical imaging of the eye

Advancement in the treatment of blindness depends on the development of new technologies that enable early detection, follow-up, and treatment of disease. The authors describe direct, noninvasive imaging of four parameters: blood flow, blood oximetry, metabolic state, and hidden vasculature, particularly capillaries. These are functional parameters of the retina known to be degraded by retinal disease. The new Retinal Function Imager (Optical Imaging, Ltd., Rehovot, Israel) can image all four parameters as intrinsic reflectance intensity differences over the retina's surface. During the past 2 decades, imaging of small optical signals has been a powerful tool for high-resolution functional mapping in the neocortex. In this article, this technology is applied to the retina and demonstrates a general tool for noninvasively probing retinal function in many modalities. Imaging functional changes before anatomic consequences arise holds promise as a powerful tool for early diagnosis and treatment of retinal disease.

Diabetic retinopathy: VEGF, bFGF and retinal vascular pathology

BACKGROUND

Previous research indicated that the development of diabetic retinopathy (DR) is closely related to the excessive expression of growth factors. This paper was to study the relationship of DR with vascular endothelial growth factor (VEGF), basic fibroblast growth factor (bFGF) and the retinal vascular pathological change.

METHODS

Fifty-five Wistar rats, weighing 100 - 200 g, were selected and randomly divided into four groups: control group (no streptozocin injection, n = 10), M1 group (streptozocin induced diabetes for 1 month, n = 15), M3 group (streptozocin induced diabetes for 3 months, n = 15), and M5 group (streptozocin induced diabetes for 5 months, n = 15). In situ hybridization and immunohistochemistry were used to investigate the expressions of bFGF and VEGF on retinal vascular, and retinal vessels were observed by transmission electron microscope.

RESULTS

There was no difference in the number of pericytes between M1 and control group (P > 0.05), but the number of pericytes decreased obviously in M3 and M5 groups compared with the control group (P < 0.01, P < 0.001, respectively). Capillary embolization and non-cell capillary were seen in M5 group. Positive expression of VEGF was found in M5 group using in situ hybridization and immunohistochemistry respectively. Positive expression of bFGF could be seen in M3 (78%) and M5 group (89%). Most remarkable changes of vessels were observed in M5 group including fragmental thickness, split of basement membrane, swelling and distortion of endothelial cells.

CONCLUSIONS

In retinal vascular of the streptozocin (STZ) rats, there shows the expression of bFGF at the third month and that of VEGF at the fifth month.

Role of protein kinase C on the expression of platelet-derived growth factor and endothelin-1 in the retina of diabetic rats and cultured retinal capillary pericytes

Increased expression of endothelin-1 (ET-1) is associated with diabetic retinopathy and vasculopathy, although the molecular explanation has not been defined. The effects of high glucose and protein kinase C (PKC) activation on platelet-derived growth factor (PDGF)-BB and of ET-1 expression in the retina of streptozotocin (STZ)-induced diabetic rats and bovine retinal pericytes (BRPC) were examined. In 4-week diabetic rats, PDGF-B and prepro-ET-1 (ppET-1) mRNA levels increased significantly by 2.8- and 1.9-fold, respectively, as quantified by RT-PCR. Treatment with PKC-beta isoform-specific inhibitor (LY333531) or insulin normalized retinal ET-1 and PDGF-B expression. In BRPC, high glucose levels increased ppET-1 and PDGF-B mRNA expression by 1.7- and 1.9-fold, respectively. The addition of PDGF-BB but not PDGF-AA increased expression of ppET-1 and vascular endothelial growth factor mRNA by 1.6- and 2.1-fold, respectively, with both inhibited by AG1296, a selective PDGF receptor kinase inhibitor. A general PKC inhibitor, GF109203X, suppressed PDGF-BB's induction of ET-1 mRNA. Thus, increased ET-1 expression in diabetic retina could be due to increased expression of PDGF-BB, mediated via PDGF-beta receptors in part by PKC activation. The novel demonstration of elevated expression of PDGF-B and its induction by PKC activation identifies a potential new molecular step in the pathogenesis of diabetic retinopathy.

Retinal neovascular markers in retinopathy of prematurity: aetiological implications

AIM

(1) To determine if expression of the blood-tissue barrier associated glucose transporter GLUT1 is preserved by the neovasculature of retinopathy of prematurity (ROP), in contrast with the reported loss of GLUT1 expression in preretinal vessels of proliferative diabetic retinopathy. (2) To compare the vascular immunophenotype of ROP to juvenile haemangioma, another perinatal neovascular disorder that has recently been shown to express placental type vascular antigens, including GLUT1 and Lewis Y antigen.

METHODS

A retrospective case report was carried out. Immunoreactivities for GLUT1 and Lewis Y antigen were assessed in a human eye with stage 3 ROP and compared with those in a control (paediatric) eye. The presence or absence of endothelial GLUT1 and Lewis Y immunoreactivity was determined in preretinal and intraretinal vessels.

RESULTS

Immunoreactivity was positive for GLUT1 and negative for Lewis Y in the intraretinal and preretinal neovasculature of the ROP affected eye and in the normal retinal vessels of the control eye.

CONCLUSIONS

Retention of immunoreactivity for GLUT1 distinguishes ROP from proliferative diabetic retinopathy. Furthermore, absence of Lewis Y antigen co-expression distinguishes ROP from juvenile haemangioma, a perinatal form of GLUT1 positive neovascularisation that has recently been linked to placental vasculature.

Melatonin MT-1-receptor immunoreactivity in the human eye

AIM

To examine the distribution of melatonin 1a (MT1) receptors in the human eye.

METHODS

Seven normal human eyes were examined by immunohistochemical staining of paraffin sections, using an anti-MT1 primary antibody and an ABC detection system.

RESULTS

MT1 receptor immunoreactivity (MT1-IR) was detected primarily in the inner segments of rods and cones and in retinal ganglion cells. In addition, MT1-IR was present in the adventitia of retinal arteries and veins, including the papillary region, but absent in ciliary and choroidal vessels. Mild staining of corneal endothelial cells and keratocytes was observed in all but two eyes.

CONCLUSION

MT1-IR is present in various ocular tissues with the highest density in photoreceptor cells and ganglion cells. The physiological function of these receptors deserves further investigation.

Contractile proteins in pericytes at the blood-brain and blood-retinal barriers

Evidence from a variety of sources suggests that pericytes have contractile properties and may therefore function in the regulation of capillary blood flow. However, it has been suggested that contractility is not a ubiquitous function of pericytes, and that pericytes surrounding true capillaries apparently lack the machinery for contraction. The present study used a variety of techniques to investigate the expression of contractile proteins in the pericytes of the CNS. The results of immunocytochemistry on cryosections of brain and retina, retinal whole-mounts and immunoblotting of isolated brain capillaries indicate strong expression of the smooth muscle isoform of actin (alpha-SM actin) in a significant number of mid-capillary pericytes. Immunogold labelling at the ultrastructural level showed that alpha-SM actin expression in capillaries was exclusive to pericytes, and endothelial cells were negative. Compared to alpha-SM actin, non-muscle myosin was present in lower concentrations. By contrast, smooth muscle myosin isoforms, were absent. Pericytes were strongly positive for the intermediate filament protein vimentin, but lacked desmin which was consistently found in vascular smooth muscle cells. These results add support for a contractile role in pericytes of the CNS microvasculature, similar to that of vascular smooth muscle cells.

[Apoptosis of retinal capillary cells in diabetic rats and expression of apoptosis-related genes]

OBJECTIVE

To determine the apoptosis of retinal capillary cells in early diabetic rats and observe the expression of apoptosis-related genes (bcl-2, Bax) in retinas of early diabetic rats.

METHODS

40 healthy adult Wistar rats were chosen and randomly divided into four groups: normal control (CON), diabetes mellitus one month (DM1), three months (DM3) and six months (DM6). Diabetic mellitus in rats was induced by streptozotocin (STZ) intraperitoneally. Retinal preparations of blood vessels and paraffin sections were stained by TdT-mediated dUTP nick end labeling (TUNEL) and immunohistochemical (ABC) method respectively and analyzed by computer-picture analytic system on the results of ABC method.

RESULTS

Positive pericyte nuclei labeled by TUNEL were emerged in DM3 and DM6, but positive endothelial cell nuclei only in DM6. No positive reaction was seen in CON and DM1. Chromatin of TUNEL positive nuclei was distributed unequally, showing apoptotic characteristics of ring-like and crescent nuclei. In ABC staining method, two genes' (bcl-2, Bax) proteins were expressed in retinal vessels. Along with the progression of diabetes, the intensity of positive reaction was increased in degrees. Moreover, pigment epithelial cells in DM3 showed Bcl-2 positive reaction that again extended further to inner rod segments and ganglion cells in DM6, while in DM6, Bax was expressed in ganglion cells.

CONCLUSIONS

The nature of pericyte dropout in early diabetic rats is apoptosis that also exists in endothelial cells; the expression of Bax and bcl-2 in retinas of early diabetic rats is enhancing.

Retina accumulates more glucose than does the embryologically similar cerebral cortex in diabetic rats

AIMS/HYPOTHESIS

The retina is embryologically similar to cerebral cortex and the tissues of both are exposed to similar blood glucose concentrations. Nevertheless, in diabetes the retina develops metabolic abnormalities and microvascular lesions from which cerebrum seems relatively protected. We directly compared glucose concentrations and expression of GLUT-1 (the major carrier transporting glucose from blood into the neural retina and cerebrum) in the two tissues from normal and diabetic rats.

METHODS

Tissue and intracellular glucose were measured using two methods: direct assay of glucose and assay of Amadori products on intracellular proteins. The expression of GLUT-1 was measured using western blots in tissue and in the isolated endothelial luminal membrane of the two vascular beds.

RESULTS

Both methods assessing intracellular glucose indicate that intracellular concentrations of glucose in diabetes increased significantly in the retina but not in cerebral cortex. Concentrations of free glucose and Amadori product in retinas of diabetic animals were increased above normal by 334% and 122%, respectively, whereas there was no statistically significant increase in either parameter in the cerebral cortex of diabetic animals. In contrast to the observed increase in glucose in the retina in diabetes, expression of GLUT-1 on the luminal plasmalemma of the retinal vascular endothelium and in homogenates of whole retina decreased to a statistically significant extent (55% and 36%, respectively compared to normal). In the luminal cell membrane of the cerebral vasculature, diabetes did not decrease expression of GLUT-1 but tended to increase it slightly.

CONCLUSIONS/INTERPRETATION

Even among tissues that do not require insulin for glucose uptake, tissue glucose concentration varies in diabetes. The greater increase in glucose concentration in retina than in cerebrum in diabetes probably contributes to the tissue differences in biochemical and histopathologic sequelae of the disease. The expression of GLUT-1 in the microvasculature is unlikely to account for the differences in tissue glucose between retina and cerebrum.

Astrocytes and blood vessels define the foveal rim during primate retinal development

PURPOSE

To investigate the relationship between development of the perifoveal blood vessels and formation of the foveal depression.

METHODS

Retinal sections and flatmounts from monkeys aged between fetal day (Fd)80 and 2 years of age were double labeled using antisera to CD31 or von Willebrand factor to detect vascular endothelial cells and antiserum to glial fibrillary acidic protein to detect astrocytes. Sections were studied by fluorescence or confocal microscopy.

RESULTS

From Fd88 to 115, vessels on the horizontal meridian were found only at the level of the ganglion cell layer (GCL)-inner plexiform layer (IPL) border where they form the ganglion cell layer plexus (GCP). Stellate astrocytes accompany GCP vessels and extend closer to the fovea than vessels. The foveal avascular zone was present within the GCP at Fd101, and at Fd105 a shallow foveal depression encircled by the GCP was present. The GCP foveal margin had the same dimensions as the adult foveal pit. Both blood vessels and astrocytes were excluded from the emerging fovea throughout development. After Fd140, capillary plexuses in the outer retina anastomosed with the GCP on the foveal slope to form a perifoveal plexus, but this plexus did not mature until a month or more after birth. After Fd142, astrocytes rapidly disappeared from the GCP and most of central retina.

CONCLUSIONS

An avascular area is outlined by the GCP before the foveal pit begins to form, suggesting that molecular factors in this region exclude both vessels and astrocytes. These factors may also guide neuronal migration to form the pit. Because the perifoveal plexus is formed during late gestation, both capillary growth and foveal development may be affected adversely by prematurity.

Three dimensional analysis of microaneurysms in the human diabetic retina

The retinal vasculature of postmortem normal human and diabetic eyes was studied using an immunohistochemical technique in conjunction with confocal laser scanning microscopy. The technique, which stained for von Willebrand factor, allowed both large areas of the retinal vasculature to be visualised and abnormalities to be studied in detail without disturbing the tissue architecture. Only one microaneurysm, defined as any focal capillary dilation, was observed in 10 normal eyes but numerous microaneurysms were seen in 4 out of 5 diabetic retinas; counts varied between 0 and 26 per 0.41 mm2 sample area. Microaneurysms were classified into 3 categories according to morphology: saccular, fusiform and focal bulges. Most were saccular, these having no preferred orientation. The majority of microaneurysms were associated with just 2 vessels suggesting they were unlikely to develop at vascular junctions. The majority were observed to originate from the inner nuclear layer and were therefore in the deeper part of the inner retinal capillary plexus. Variation in the staining of microaneurysms may correlate with endothelial dysfunction seen clinically as dye leakage during fluorescein angiography.

An immunohistochemical study of endothelin-1 in the human eye

PURPOSE

Endothelin-1 (ET-1) is a potent vasoconstrictive and neural peptide that has been demonstrated to be present and functionally active and important in the eye. This study was undertaken to examine for the first time the cellular distribution of ET-1 in the whole human eye.

METHODS

Twelve human eyes were examined by immunohistochemical staining of paraffin sections, using an anti-ET-1 primary antibody and an ABC-detection system.

RESULTS

Endothelin-1-immunoreactivity (ET-1-IR) was detected primarily in the fibrovascular stroma of the iris, ciliary body and choroid, in the retinal blood vessels, the ciliary and optic nerves, and in the corneal and the non-pigmented ciliary epithelium.

CONCLUSION

In the eye, ET-1-IR is present in fibrovascular, neural and epithelial structures. Changes in the distribution and concentration of ET-1 may be relevant to a variety of ocular diseases including diabetes mellitus, hypertension, sickle cell disease, optic neuritis, AION, papilledema, corneal ulcer, corneal epithelial dystrophy or after keratoplasty.

Evidence for upregulation and redistribution of vascular endothelial growth factor (VEGF) receptors flt-1 and flk-1 in the oxygen-injured rat retina

There is considerable evidence that vascular endothelial growth factor (VEGF) is important in the pathogenesis of retinal neovascular diseases. The effects of this endothelial cell-specific mitogen are mediated by specific cell surface receptors. In this study we probed for the two VEGF receptors (VEGFRs) known to have highest affinity in the rat--flt-1 and flk-1. Using a well-characterized rat model of the neovascular disease retinopathy of prematurity (ROP), we performed immunohistochemical assays on methacrylate sections of eyes from normal and oxygen-injured animals at the time neovascularization is first observed (16 days of age) and at its peak (day 20). In day 16 room air retinas there was light, diffuse labeling of the inner nuclear layer and outer plexiform layer. In contrast, in 4 of 5 oxygen-injured eyes on day 16, there was specific labeling of small neovascular growths and normal retinal vessels, and the outermost (sclerad) limit of the label had shifted inward to the vitread border of the inner nuclear layer and the inner plexiform layer. Day 20 room air eyes showed a pattern similar to day 16, although with stronger labeling. However, in oxygen-injured eyes on day 20 the labeling pattern had shifted toward the vitreous, with extremely strong labeling of the preretinal neovascular growths. As on day 16 there was also labeling of the inner plexiform layer and the inner portion of the inner nuclear layer, but not the outer plexiform layer. Comparison of VEGF protein immunolabel with both of the VEGFR immunolabels revealed overlap and strong similarity on day 20 in the oxygen-injured eyes. This is the first report of VEGF receptor protein being concentrated in preretinal neovascular growths in a model of ROP. These results lend themselves to further investigation of the roles of VEGFRs in preretinal neovascularization in ROP and other retinal diseases and suggest avenues of research toward therapies using VEGFR antagonists.

Time-course expression of vascular endothelial growth factor as related to the development of the retinochoroidal vasculature in rats

Growth factors involved in angiogenesis are critical to both the normal and pathological vascular development in the retina and choroid. In the present experiment, the relationship between the vascular endothelial growth factor (VEGF) expression and the retinochoroidal vasculogenesis in Sprague-Dawley rats was investigated using in situ hybridization and immunohistochemistry. It was found that VEGF was produced mainly by astrocytes and Muller cells in the neural retina, and this was correlated temporally and spatially with the retinal vasculogenesis. In addition, it was observed that, although the VEGF expression in the retinal pigment epithelium (RPE) decreased with increasing age, it persisted from the embryonic stage to adulthood. These findings indicate that the VEGF expression in RPE may play a role in the development of the choroidal vessels as well as in the maintenance of the normal structure and permeability of the choriocapillaris in adults.

[Expression of basic fibroblast growth factor and fibroblast growth factor receptor 1 in the experimental retinal vein occlusion model]

Retinal ischemia promotes retinal neovascularization. Vascular endothelial growth factor (VEGF) and fibroblast growth factor (FGF) are important growth factors for neovascularization. We did experimental retinal vein occlusion (RVO) and examined the expression of basic FGF and FGF receptor 1(one of the basic FGF receptors) by in situ hybridization. We used adult pigmented rats (Brown-Norway strain). Dye laser photocoagulation (577 nm) was applied to the retinal arteries and veins within two disc diameters of the optic nerve head to injure the retinal vessels. After one week, laser photocoagulation was applied to only the retinal veins to occlude them (RVO model). As a control, laser photocoagulation was applied to the posterior retina avoiding the retinal vessels. After treatment, the eyes were removed and 10 microns thick cryostat-cut chorioretinal section were used for in situ hybridization with probes as mentioned above. In the RVO model, expression of messenger RNA of basic FGF (b-FGF) and FGF receptor 1 increased in the inner nuclear layer and the inner segment of the photoreceptors, and appeared in the retinal vessel wall in the early stage. This shows that b-FGF and FGF receptor 1 increased in the ischemic retina, and were produced on the retinal vessel wall. This suggests that b-FGF may be involved in protection, regeneration, and proliferation of the retinal vascular endothelial cells in retinal circulatory disturbance.

Antagonists of integrin alpha v beta 3 inhibit retinal neovascularization in a murine model

Integrin alpha v beta 3 is differentially expressed in angiogenic blood vessels in skin granulation tissue, and alpha v beta 3 antagonists inhibit angiogenesis in chick chorioallantoic membranes. In this study, we investigated the role of alpha v beta 3 in retinal neovascularization. There was no detectable signal for alpha v beta 3 by immunohistochemistry in normal human retina, but neovascular tissue removed from the surface of the retina of patients with diabetic retinopathy showed intense staining for alpha v beta 3 within the endothelial cells of new blood vessels. In a murine model of oxygen-induced ischemic retinopathy, there was intense staining for alpha v beta 3 in endothelial cells participating in neovascularization but no detectable staining in normal retinal blood vessels of adult mice. Synthetic peptides that bind alpha v beta 3 and perturb alpha v beta 3-mediated adhesion in vitro inhibited retinal neovascularization in the murine model when given by intraperitoneal or periocular injections. These data suggest that alpha v beta 3 antagonists may provide a useful adjunct for the treatment of retinal neovascularization.

Localization of thrombomodulin in a rabbit eye

PURPOSE

To show the distribution of an anticoagulant factor, thrombomodulin, in a rabbit eye.

METHODS

Immunohistochemical staining using polyclonal anti-rabbit thrombomodulin antibody was performed with the excised eyes of pigmented adult rabbits. Streptavidin-biotin method was used to obtain intense staining.

RESULTS

The endothelium of the chorioretinal vessels showed positive linear staining. The ciliary non-pigmented epithelium showed granular staining, while the pigmented epithelium stained negatively. The positive staining was also detected in the trabecular plexus endothelium. The vascular endothelium of the ciliary body stained weakly.

CONCLUSIONS

It is suggested that thrombomodulin in the vessel walls and the aqueous drainage apparatus works to maintain normal blood fluidity and aqueous outflow. The role of nonvascular thrombomodulin in the ciliary non-pigmented epithelium is unclear.

The temporal and spatial vascular endothelial growth factor expression in retinal vasculogenesis of rat neonates

Vascular endothelial growth factor (VEGF) has been identified as an endothelial cell-specific mitogen with potent angiogenic properties. VEGF is overexpressed in pathologic angiogenesis observed in tumor growth, rheumatoid arthritis, and retinal angiogenic diseases such as diabetic retinopathy and retinopathy of prematurity. VEGF expression in physiologic angiogenesis, i.e., vasculogenesis, has also been reported in the embryonic organs such as brain, kidney, spleen, and lung. However, the details of VEGF expression in vasculogenesis remain largely unclear. To determine if VEGF contributes to vasculogenesis in the developing tissues, VEGF expression was studied by both immunohistochemistry and in situ hybridization in newborn rat retinas on postnatal days 3, 7, 14, and 30. Vasculogenesis was assessed by both the ink perfusion method and a histologic examination. To identify the cell types of VEGF-expressing cells, immunohistochemistry for cell markers such as glial fibrillary acidic protein and von Willebrand factor was performed. On postnatal days 3 and 7, when retinal vasculogenesis was active, VEGF mRNA and protein(s) were prominently expressed in the ganglion cell and the inner nuclear layers. In rats, as well as humans, these two layers are where the retinal vessels develop, and these two layers depend solely on the retinal vessels. In addition to the ganglion and the inner nuclear layers, VEGF protein(s) were located in the endothelial cells of the developing vessels and the angioblasts, i.e., endothelial precursors. On postnatal day 14, when vasculogenesis became inactive, VEGF mRNA expression markedly decreased. These results indicated that VEGF expression in the developing retinas is temporally and spatially correlated with retinal vasculogenesis.

Histological study of oxalosis in the eye and adnexa of AIDS patients

Review of a series of 98 eyes removed at autopsy from 86 AIDS patients identified 12 cases (14%) showing varying degrees of microscopic calcium oxalate deposition. The oxalate crystals were birefringent using polarisation microscopy and were stained histochemically by the silver nitrate-rubeanic acid method (Yasue), a stain considered to be specific for calcium oxalate. In two cases, the deposition was extensive and involved the surface of the ciliary processes, ciliary body and pars plana of the retina, the retinal and optic nerve blood vessel wall, a few retinal pigment cells, and the anterior inner sclera. A lesser degree of intraocular involvement was observed in the remaining 10 cases. In all but two eyes, where a peripheral active area of cytomegalovirus retinitis was present, no other significant microscopical abnormality was found. Clinically, these patients were asymptomatic. At autopsy, oxalate deposits were found in the kidney and/or thyroid in seven of the patients.

Retinal neurons and vessels are not fractal but space-filling

Many branched patterns in nature are hypothesized to be fractal, i.e., statistically self-similar across a range of scales. We tested this hypothesis on the two-dimensional arbors of retinal neurons and blood vessels. First, we measured fractalness on synthetic fractal and nonfractal patterns. The synthetic fractal patterns exhibited self-similarity over a decade of scale, but the nonfractal "controls" showed hardly any self-similarity. Neuronal and vascular patterns showed no greater self-similarity than the controls. Second, we manipulated a synthetic fractal pattern to remove its self-similarity and found this to be reflected in a loss of measured fractalness. The same manipulation of the nonfractal control and also of the neural and vascular patterns did not alter their measured fractalness. Third, we "grew" patterns of branched line segments according to a variety of nonfractal algorithms. These patterns were, if anything slightly more fractal than the neural and vascular patterns. We conclude that the biological patterns studied here are not fractal. Finally, we measured extended versions of these patterns: a contiguous array of homotypic neuron arbors and a vascular pattern with a high degree of total detail. These patterns showed a "fractal dimension" of 2, which implies that down to some cut-off scale they fill space completely. Thus, neural and vascular patterns might best be described as quasi-regular lattices.

Type II collagen is a major component of bovine retinal microvessel extracellular matrix

OBJECTIVE

To determine which interstitial collagen types may be present in bovine retinal microvessel extracellular matrix (ECM).

METHODS

Dissociated bovine microvessels were treated with detergents and the resultant purified ECM monitored by transmission electron microscopy (TEM). Pepsin-extracted soluble ECM collagens were identified by Western blots. Collagens were further purified by neutral salt precipitation and carboxymethyl cellulose (CMC) chromatography before cyanogen bromide (CNBr) peptide mapping and two-dimensional peptide mapping of CMC-generated fractions. Interstitial collagens were localized by immunofluorescence on frozen sections.

RESULTS

Transmission electron microscopy of detergent-purified microvessel ECM demonstrated numerous 10-50-nm collagen fibrils associated with basal laminae regardless of vessel diameter. Western blots showed that soluble ECM collagens were strongly positive for type II, moderate for type III, and weak for type I. CNBr peptide maps and two-dimensional maps of neutral salt and CMC-purified fractions confirmed the presence of type II collagen. Immunofluorescence localized type II collagen in large and small vessels of the retina.

CONCLUSIONS

Type II collagen is an unexpected major component of bovine microvessel ECM, whereas types I and III are present in minor amounts. Type V collagen is also a substantial ECM component. Accordingly, all four types may contribute to a heterogeneous population of collagenous fibrils identified by TEM in intact isolated retinal microvessel ECM.

Yield of fluorescence from indocyanine green in plasma and flowing blood

The purpose of this work was to obtain more quantitative knowledge about the yield of fluorescence from retinal vessels during indocyanine green angiography (ICG). The yield of fluorescence from blood was investigated for various shear rates, concentrations of ICG, and layer thicknesses. Measurements were performed in vitro on samples of human blood in a cone-plate shear chamber using frontal illumination as in scanning laser angiography. In blood and in plasma, the yield of fluorescence of ICG increased with concentration up to 0.05 and 0.1 mg/ml, respectively. At higher concentrations, the yield decreased for all layer thicknesses. For increasing layer thicknesses, both in plasma and in blood, the yield of ICG fluorescence increased nonlinearly for concentrations higher than 0.012 mg/ml. Saturation occurred for layers thicker than 200 microns in combination with ICG concentrations of 0.4 mg/ml and higher. Application of shear rates within the physiological range of the microcirculation (88/sec and 528/sec) increased the yield of fluorescence from the blood sample compared with stasis. The high transparency of blood for the excitation and emission light of ICG that was demonstrated will lead to superposition of fluorescence from superficial and deeper layers. This superposition precludes quantitative indocyanine angiography of ocular vessels.

Isoforms of platelet-derived growth factor and its receptors in epiretinal membranes: immunolocalization to retinal pigmented epithelial cells

Epiretinal membranes (ERMs) form on the inner surface of the retina in conjunction with various ocular disease processes, but the factors controlling their development are not understood. The predominant cell types involved are retinal pigmented epithelial (RPE) cells and retinal glia. Cultured RPE cells secrete platelet-derived growth factor (PDGF), which is chemotactic and mitogenic for both RPE cells and retinal glia and, therefore, could be involved in the development of ERMs. In the present study, we performed immunohistochemical staining for PDGF A chain (PDGF-A), PDGF B chain (PDGF-B), and both types of PDGF receptors (PDGFr alpha and PDGFr beta) on ERMs associated with various disease processes. PDGF-A is detected in most ERMs, regardless of the associated disease process, and it appears to be localized predominantly in RPE cells, recognized by the presence of pigment and the immunohistochemical demonstration of some or all of the following RPE-associated epitopes: class III beta-tubulin, keratin, the 65-kDa microsomal protein recognized by the RPE9 antibody, and cellular retinaldehyde-binding protein. PDGF-B is found only in minor subpopulations of cells in about half of the ERMs evaluated and, with only occasional exceptions, appears to be localized almost entirely in blood-borne cells found in and around vessels in vascularized ERMs. Both PDGFr alpha and PDGFr beta are demonstrated in most ERMs with neither isotype consistently predominating: they are found predominantly on RPE cells with many cells expressing both receptor types. ERMs with little or no RPE cell component contain little or no PDGF and PDGF receptor, whereas those in which the RPE cell represents the major cell type, have widespread PDGF and PDGF receptor positivity. These findings show that RPE cells in ERMs produce PDGF-A and PDGF alpha and PDGF beta receptors and suggest that autocrine and paracrine stimulation with PDGF may be involved in ERM pathogenesis.

[Endothelin receptors in bovine retinal vessels--quantitative receptor autographic analysis with radioluminography]

Endothelin (ET) receptors in bovine retinal macrovessels, microvessels, and nonvascular tissues were characterized using a quantitative receptor autoradiographic method with 125I-endothelin-1 (125I-ET-1), ET-1, ET-, ET-3, BQ123 (a selective antagonist for the ETA receptor) and sarafotoxin S6c (an agonist for the ETB receptor). A quantitation was made with a computerized radioluminographic system and imaging plates. The method we used revealed that there were specific binding sites for 125I-ET-1 in the bovine retinal macrovessels, microvessels, and nonvascular tissues. There was no difference in the dissociation constant (Kd) showing binding characteristics between the retinal macrovessels and the microvessels. The bindings to the retinal macrovessels and the microvessels were effectively displaced by BQ123, whereas the binding to the retinal nonvascular tissues was displaced by sarafotoxin S6c. Thus, we obtained evidence that macrovessels and microvessels of the bovine retina have ETA receptor, and that the nonvascular tissues have ETB receptors.

Histopathology of bone spicule pigmentation in retinitis pigmentosa

PURPOSE

To evaluate bone spicule pigmentation, a fundus feature in retinitis pigmentosa (RP) formed by migration of pigment-containing cells to perivascular sites in the inner retina.

METHODS

The authors performed light and electron microscopy, including immunocytochemistry, on the retinas from ten patients with RP and five normal donors.

RESULTS

The pigment-containing cells in regions of bone spicule pigmentation were derived from the retinal pigment epithelium (RPE). The translocated cells were remarkably polarized with a number of specializations characteristic of RPE cells in situ, but they did not contain lipofuscin granules and were not immunoreactive for cellular retinaldehyde-binding protein. The cells were linked by junctional complexes and formed epithelial layers around retinal vessels and next to the inner limiting membrane. Adjacent Müller cell processes contained glial fibrillary acidic protein-positive filaments and formed microvilli and intermediate junctions, resembling those in the external limiting membrane. Vascular endothelial cells adjacent to the translocated RPE cells were thin and fenestrated, resembling the choriocapillaris, and were separated from the pigmented cells by a layer of extracellular matrix similar in organization to Bruch membrane. Thickening of the matrix layer caused narrowing and occlusion of the vascular lumina.

CONCLUSIONS

The lack of lipofuscin granules and cellular retinaldehyde-binding protein immunoreactivity in the translocated RPE cells is probably related to the loss of photoreceptors. The development of fenestrations in the endothelial cells correlates with the leakiness of retinal vessels to fluorescein observed in some cases of RP. Narrowing and occlusion of vascular lumina by thickening of the surrounding layer of extracellular matrix may contribute to the loss of inner retinal neurons found in RP. These changes in the RPE, blood vessels, glia, and inner neurons warrant consideration in designing therapies to restore vision to degenerate retinas.

Vascular endothelial growth factor plays a role in hyperpermeability of diabetic retinal vessels

In rat diabetic retinas, we immunohistochemically looked for vascular endothelial growth factor (VEGF) which is also known as vascular permeability factor (VPF). In nondiabetic retinas, VEGF immunoreactivity was weak and restricted to the nerve fiber and ganglion cell layers. On the other hand, in diabetic retinas, VEGF immunoreactivity was markedly increased and was observed in all layers of the retina, especially in the perivascular area. Hyperpermeability of these vessels was confirmed by immunohistochemically detecting extravasation of albumin. These findings indicate that vascular endothelial growth factor plays an important role in blood-retinal barrier breakdown in diabetic retinopathy.

Heterogeneity in collagen biosynthesis by sprouting retinal endothelial cells

Bovine retinal microvascular endothelial cells can display two distinct and reversible morphologies in culture: 'cobblestone' and 'sprouting'. The cobblestone morphology resembles the resting cells lining the lumen of mature vessels while the sprouting morphology resembles the angiogenic cells involved in the formation of new vessels. Retinal cells displayed some heterogeneity in the shape of the cells making up the cobblestone monolayer. In contrast, all cell lines displayed an identical sprouting morphology. We have investigated the synthesis of matrix macromolecules by retinal endothelial cells displaying either the cobblestone or the sprouting morphology. Type IV was the only collagen synthesised by eight different lines of early-passage (between one and six) cobblestone endothelial cells. Collagen types I and III were not detected in these cultures. In contrast, heterogeneity was observed in the types of collagen synthesized by four lines of early-passage cells displaying the sprouting morphology. That is, two lines synthesised collagen types, II, III and IV, whereas two other lines continued to synthesise only type IV collagen. Both cobblestone and sprouting cells synthesised fibronectin and thrombospondin, although the relative amounts of these macromolecules varied with culture conditions. The pattern of collagen synthesis by cobblestone cells was also affected by in vitro "ageing": 4/5 lines examined above passage eight synthesised collagen types I, III and IV. Our results indicate that there is heterogeneity in the sprouting phenotype displayed by retinal endothelial cells, and that this phenotype is not necessarily associated with the synthesis of type I collagen. We suggest that differences in the spectrum of matrix macromolecules synthesised by sprouting endothelial cells may play a role in the control of angiogenesis.

Identification and partial characterisation of a low Mr collagen synthesised by bovine retinal pericytes. Apparent relationship to type X collagen

Bovine retinal pericytes (BRP) in culture synthesise a low Mr collagenous polypeptide which appears similar, but not identical, to bovine type X collagen and which we have called 'BRP collagen'. This polypeptide displays the following characteristics: (i) it is sensitive to digestion by bacterial collagenase and is resistant to pepsin digestion; (ii) it has an apparent Mr of 45 kDa (pepsinised form); (iii) it is recognised by specific antibodies to type X collagen using immunoblotting; (iv) it is present in the cell layer/matrix but not in the medium of pericyte cultures; and (v) it is not disulphide-bonded into higher Mr multimers. The latter two properties distinguish BRP collagen from bovine type X collagen. We have recently shown that pericytes calcify in vitro. We now report that this calcification is associated with an increased synthesis of BRP collagen.

Organ and species specific differences in cytoskeletal protein profiles of cultured microvascular endothelial cells

1. Using two-dimensional gel electrophoresis and immunoblotting techniques we systematically document the structural diversity of cytoskeletal proteins in tight and leaky cultured microvascular endothelial cells (MEC). Bovine pulmonary and eel rete mirabile MEC primarily express cytokeratins 8 and 19. Cytokeratins 8 and 18 were found to be prominent in rat pulmonary MEC. Bovine retinal MEC contained cytokeratins 8, 18 and 19. Bovine adrenal MEC contain vimentin as their sole intermediate filament protein. 2. Four principal actin isoforms were resolved in micro/macrovascular endothelial cells as well as in vascular smooth muscle cells. Retinal pericytes expressed three principal actin isoforms. 3. These results indicate that MEC are diverse, highly differentiated cells displaying a large repertoire of cytoskeletal protein profiles suited for specific tissue functions.