Normal and pathological mechanisms in retinal vascular development

Image-free recognition of moderate ROP from mild with machine learning algorithm on plasma Raman spectrum

The retinopathy of prematurity (ROP) can cause serious clinical consequences and, fortunately, it is remediable while the time window for treatment is relatively narrow. Therefore, it is urgent to screen all premature infants and diagnose ROP degree timely, which has become a large workload for pediatric ophthalmologists. We developed a retinal image-free procedure using small amount of blood samples based on the plasma Raman spectrum with the machine learning model to automatically classify ROP cases before medical intervention was performed. Statistical differences in infrared Raman spectra of plasma samples were found among the control, mild (ZIIIS1), moderate (ZIIIS2 & ZIIS1), and advanced (ZIIS2) ROP groups. With the different wave points of Raman spectra as the inputs, the outputs of our support vector machine showed that the area under the curves in the receiver operating characteristic (AUC) were 0.763 for the pair comparisons of the control with the mild groups, 0.821 between moderate and advanced groups (ZIIS2), while more than 90% in comparisons of the other four pairs: control vs. moderate (0.981), control vs. advanced (0.963), mild vs. moderate (0.936), and mild vs. advanced (0.953), respectively. Our study could advance principally the ROP diagnosis in two dimensions: the moderate ROPs have been classified remarkably from the mild ones, which leaves more time for the medical treatments, and the procedure of Raman spectrum with a machine learning model based on blood samples can be conveniently promoted to those hospitals lacking of the pediatric ophthalmologists with experience in reading retinal images.

Roles of EphA2 in Development and Disease

The Eph family of receptor tyrosine kinases (RTKs) has been implicated in the regulation of many aspects of mammalian development. Recent analyses have revealed that the EphA2 receptor is a key modulator for a wide variety of cellular functions. This review focuses on the roles of EphA2 in both development and disease.

Intraocular and systemic levels of vascular endothelial growth factor in advanced cases of retinopathy of prematurity

PURPOSE

To measure vitreous, aqueous, subretinal fluid and plasma levels of vascular endothelial growth factor in late stages of retinopathy of prematurity.

METHODS

Interventional study. We enrolled patients with clinical diagnoses of bilateral stage V retinopathy of prematurity, confirmed by b-scan ultrasound and programmed for vitrectomy. During surgery we took samples from blood, aqueous, vitreous, and subretinal fluids. The vascular endothelial growth factor concentration in each sample was measured by ELISA reaction. A control sample of aqueous, vitreous and blood was taken from patients with congenital cataract programmed for phacoemulsification. For statistical analysis, a Mann-Whitney and a Wilcoxon W test was done with a significant P value of 0.05.

RESULTS

We took samples of 16 consecutive patients who met the inclusion criteria. The vascular endothelial growth factor levels in the study group were: aqueous, 76.81 ± 61.89 pg/mL; vitreous, 118.53 ± 65.87 pg/mL; subretinal fluid, 1636.58 ± 356.47 pg/mL; and plasma, 74.64 ± 43.94 pg/mL. There was a statistical difference between the study and the control group (P < 0.001) in the aqueous and vitreous samples.

CONCLUSION

Stage 5 retinopathy of prematurity has elevated intraocular levels of vascular endothelial growth factor, which remains high despite severe retinal lesion. There was no statistical difference in plasma levels of the molecule between the control and study group.

Maturation of rod function in preterm infants with and without retinopathy of prematurity

OBJECTIVES

To establish normal development of rod electroretinograms in preterm infants and to assess the effects of retinopathy of prematurity (ROP).

STUDY DESIGN

We measured 88 Naka-Rushton functions from 41 preterm infants at maturities from 30 to 72 weeks postmenstrual age (PMA). Outcomes (log sigma, retinal sensitivity and V(max), retinal responsivity) were compared between control (no ROP), untreated ROP, and treated ROP.

RESULTS

In control infants, sensitivity increased by 1.5 log units from 30 to 40 weeks PMA and by a further 0.5 log units by 50 weeks PMA but was 0.5 log units less than in similarly-mature, healthy, term-born infants. Average retinal responsivity increased from 23 microV to 90 microV between 30 and 40 weeks PMA and was 35 muV greater at 40 weeks PMA than in similarly-mature term-born infants. At around 36 weeks PMA, (when onset of ROP peaks), infants with untreated ROP had average retinal sensitivity 0.2 log units lower than control infants; sensitivity was reduced further in infants treated for ROP. Retinal responsiveness did not differ between control subjects and untreated infants with ROP but was greatly reduced in infants treated for ROP.

CONCLUSIONS

Maturation of rod sensitivity appears to be slowed by preterm birth whereas maturation of rod responsivity is accelerated. ROP reduces retinal sensitivity, and treated ROP reduces both sensitivity and responsivity.

Time-course of experimental choroidal neovascularization in Dutch-Belted rabbit: clinical and histological evaluation

In order to study the pathogenesis of choroidal neovascularization (CNV) and explore a suitable animal model for assessing anti-angiogenic agents, rabbit CNV was induced by subretinal injection of a cocktail containing endotoxin and growth-factor, incorporated in Heparin-sepharose beads. The presence and development of CNV lesions was visualized by fluorescein angiography and quantified by image analysis. The time-course of experimental CNV was evaluated clinically and histologically, with some lesions followed up to 3-years. The suitability of this model for drug evaluation was appraised by the systemic administration of dexamethasone. The experimental results suggest two subsets of CNV, primary and secondary, observed in all treated eyes. Primary CNV, defined as neovascularization extending into the subretinal space and associated with injury to Bruch's membrane at the time of injection, was visible in 100% of eyes by 2-weeks and stable by 3-months. Secondary CNV, defined as neovascularization extending into the sub RPE space away from the initial injection related injury, became visible as early as 2-weeks in some of eyes and developed in 100% of eyes by 8-months. Both primary and secondary CNV were maintained and demonstrated leakage throughout the entire observation period. Atrophy of primary retinal pigmented epithelium (RPE) cells and hyper-proliferation of secondary RPE cells were observed in tissue sections with CNV lesions. The formation and growth of primary and secondary CNV were significantly inhibited by dexamethasone. This study indicates that a reproducible and quantitative model of rabbit CNV has been established utilizing subretinal administration of endotoxin and growth-factor. Studies of the stages of experimental CNV both clinically and histologically indicated an intimate relationship between CNV, macrophages and RPE. Furthermore, the inhibition observed with dexamethasone points to the possibility of being able to evaluate effective means of pharmacological intervention.

Development of the primate area of high acuity. 1. Use of finite element analysis models to identify mechanical variables affecting pit formation

Most primate retinas have an area dedicated for high visual acuity called the fovea centralis. Little is known about specific mechanisms that drive development of this complex central retinal specialization. The primate area of high acuity (AHA) is characterized by the presence of a pit that displaces the inner retinal layers. Virtual engineering models were analyzed with finite element analysis (FEA) to identify mechanical mechanisms potentially critical for pit formation. Our hypothesis is that the pit emerges within the AHA because it contains an avascular zone (AZ). The absence of blood vessels makes the tissue within the AZ more elastic and malleable than the surrounding vascularized retina. Models evaluated the contribution to pit formation of varying elasticity ratios between the AZ and surrounding retina, AZ shape, and width. The separate and interactive effects of two mechanical variables, intraocular pressure (IOP) and ocular growth-induced retinal stretch, on pit formation were also evaluated. Either stretch or IOP alone produced a pit when applied to a FEA model having a highly elastic AZ surrounded by a less elastic region. Pit depth and width increased when the elasticity ratio increased, but a pit could not be generated in models lacking differential elasticity. IOP alone produced a deeper pit than did stretch alone and the deepest pit resulted from the combined effects of IOP and stretch. These models predict that the pit in the AHA is formed because an absence of vasculature makes the inner retinal tissue of the AZ very deformable. Once a differential elasticity gradient is established, pit formation can be driven by either IOP or ocular growth-induced retinal stretch.

VEGF expression by ganglion cells in central retina before formation of the foveal depression in monkey retina: evidence of developmental hypoxia

In macaque monkeys the foveal depression forms between fetal day (Fd) 105 and birth (Fd 172 of gestation). Before this, the incipient fovea is identified by a photoreceptor layer comprising cones almost exclusively, a multilayered ganglion cell layer (GCL), and a "domed" profile. Vessels are absent from the central retina until late in development, leading to the suggestion that the GCL in the incipient fovea may be transitorily hypoxic. Vascular endothelial growth factor (VEGF), expressed by both glial and neuronal cells and mediated by the hypoxia-inducible transcription factor (HIF)-1, is the principal factor involved in blood vessel growth in the retina. We examined VEGF expression in macaque retinas between Fd 85 and 4 months postnatal. Digoxygenin-labeled riboprobes were generated from a partial-length human cDNA polymerase chain reaction fragment, detected using fluorescence confocal microscopy, and quantified using Scion Image. High levels of VEGF mRNA were detected in astrocytes associated with developing vessels. We also detected strong expression of VEGF mRNA in the GCL at the incipient fovea prior to Fd 105, with peak labeling in the incipient fovea that declined with distance in nasal and temporal directions. By Fd 152 peak labeling was in two bands associated with development of the inner nuclear layer (INL) capillary plexus: in the inner INL where Müller and amacrine cell somas are located, and in the outer INL where horizontal cells are found. The findings suggest that at the incipient fovea the GCL is hypoxic, supporting the hypothesis that the adaptive significance of the fovea centralis is in ensuring adequate oxygen supply to neuronal elements initially located within the avascular region.

Vascular endothelial growth factor-B and retinal vascular development in the mouse

PURPOSE

Vascular endothelial growth factor-A (VEGF-A) is crucial to retinal vascular growth, both normal and pathological. VEGF-B, recently characterized, is reported to be expressed in retinal tissues, but the importance of VEGF-B to retinal vascular development remained unknown. The aim of this study was to analyse retinal vascular growth in the Vegfb-/- knockout mouse.

METHODS

Retinal vascular growth was measured in Vegfb-/- knockout mice raised under normal conditions, and Vegfb-/- knockout mice with an oxygen-induced proliferative retinopathy. Wild type Vegfb+/+ mice served as controls. Vessels were perfused with ink and retinal flatmounts secondarily labelled with FITC-lectin (BS-1, Griffonia simplicifolia). Area and diameter of retinal growth and retinal vascular growth were recorded over days 0-20, and capillary density and mean diameter recorded from day 17 pups.

RESULTS

A variety of techniques confirmed that Vegfb+/+ mice expressed VEGF-B and that VEGF-B expression was absent in Vegfb-/- mice. Vegfb-/- mice raised in room air showed no significant differences from Vegfb+/+ controls. No differences were found in oxygen-induced retinopathy between Vegfb-/- and Vegfb+/+ pups in either the extent of the initial oxygen-induced ablation, or in the regrowth of retinal vessels or vitreal (neovascular) sprouts; vitreal sprouts are important markers of the abnormal proliferative response, and are maximally expressed on day 17 in this model of oxygen-induced retinopathy.

CONCLUSIONS

These results indicate that a lack of VEGF-B does not significantly affect development of the retinal vasculature under normal conditions, nor does it appear to affect the proliferative retinal responses seen in oxygen-induced retinopathy.

A clinicopathological study of venous loops and reduplications in diabetic retinopathy

PURPOSE

To study possible causes of the gradual venous occlusion that precedes the formation of venous loops and reduplications in diabetic retinopathy using histopathological techniques.

METHODS

Casts of the retinal vascular system from six eyes of five diabetic patients were used to identify venous loops and reduplications. Subsequently the lesions were studied by immunohistochemistry using antibodies against cellular and non-cellular components previously shown to be disturbed in the diabetic retina.

RESULTS

In all eyes the venous abnormalities identified on the casts were accompanied by abnormal wall partitions dividing the venous lumen. These partitions consisted of a double layer of flat cells displaying immunoreactivity to von Willebrand factor and actin (endothelial cells), but not to glial fibrillary acid protein or S-100 protein (glial cells), CD3, CD20, CD68, or neutrophil elastase (leucocytes). Neutrophile granulocytes adhering to the walls of larger retinal venules were unrelated to the venous partition and to capillary occlusion in the adjacent retinal areas.

CONCLUSIONS

Venous loops and reduplications are associated with partitions of the larger retinal venules consisting of a double layer of endothelial cells anchored to a thin basement membrane. An elucidation of the factors distinguishing this endothelial cell proliferation from preretinal new vessel formation may be important for understanding the pathophysiology of proliferative diabetic retinopathy.

Human retinal astroglia. A comparative study of adult and the 18 month postnatal developmental stage

The immunohistochemical location of glial fibrillary acidic protein (GFAP) was used to study the state of maturation of retinal astrocytes from an 18-mo-old infant and to compare it with the situation in the adult. Infant astrocytes showed intense GFAP immunoreactivity in the perikarya and possessed spindle-like enlargements in their processes, while in the adult immunoreactivity in the perikarya was scarce and the spindle-like enlargements were not evident. Two types of astrocyte were observed in adult and child retinas: elongated and star-shaped. In the adult, the star-shaped type tend to be more stylised and to have longer processes than in the infant. In the infant, numerous astrocyte cell bodies were observed over vessels, while in the adult these were scarce. In the infant, the star-shaped astrocytes made up a honeycomb plexus, but this was not fully developed. These results suggest that at 18 mo of postnatal development the retinal astrocytes are still increasing and growing into the astroglial structure found in adults.