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R W Flower

Publications and source records attributed to R W Flower.

At least 19 recordsLinked to original sources
PubMed1990

Perinatal ocular physiology and ROP in the experimental animal model.

In order to overcome the scarcity of premature human ocular tissues and the enormous obstacles to direct examination of immature human ocular vasculatures, a number of animal models have been employed by investigators in order to study various aspects of ROP. A variety of factors may influence selection of the particular model used, but ultimately it is the faithfulness with which the model mimics human ROP that is most important. The validity of the models has been and remains a controversial subject, but evidence appears strong in favor of the beagle puppy model for studying physiology of the ocular vasculatures during perinatal development. Human ROP pathology usually is defined in terms of static morphological state, physiological dysfunction being considerably more difficult to assess. Most of the animal models fall short of mimicking the pathological lesions found in human eyes, especially those associated with severe, or end-stage ROP, yet they do fairly well in terms of mimicking the retinal vascular physiological changes associated with onset of the disease. Unfortunately, where the physiological aspects of ROP are concerned, focus is primarily on the effects of hyperoxia; other physiological factors as well as the potential role of the choroid are essentially ignored. This paper discusses the potential of physiological changes which occur during the perinatal period to play a role in ROP pathogenesis.

Animals↗
PubMed1990

Pulsatile flow in the choroidal circulation: a preliminary investigation.

A preliminary investigation has been made of choroidal blood flow using a computer-aided image analysis approach to interpretation of indocyanine green (ICG) dye choroidal angiograms. The goal of the study was to characterise blood flow through the choroidal arteries vs. choroidal capillaries and veins. The methods of analysis used are briefly reviewed, and preliminary data obtained mainly from monkey eyes are presented. Preliminary conclusions are made regarding the relationship between compliance of choroidal arterial vessels and blood flow through them.

Angiography↗
PubMed1990

An image processing approach to characterizing choroidal blood flow.

Indocyanine green (ICG) dye angiography has made possible routine visualization of choroidal blood flow in the human eye; however, to date, its clinical utility has been limited. An overlying layer of densely pigmented tissue and the complex, multilayered vascular structure of the choroid combine to produce angiographic images of low contrast which are difficult to interpret. Conventional image processing can enhance individual images of the blood vessels, but this approach contributes no information about the dynamics of blood flow. Using relatively inexpensive, commercially available personal computer hardware, angiographic image processing algorithms were developed which appear to characterize uniquely a subject choroid in terms of various blood flow parameters. We believe this to be the first successfully demonstrated approach to routinely characterizing the human choroidal circulation in a way that conserves spatial distribution of blood flow dynamics across the entire observed choroidal area. The computer system allows acquisition of digital images from photographic film negatives; alternatively, real-time direct digitization of images from a high-resolution video camera is possible. Once acquired, the digitized data are manipulated according to various algorithms that employ time-sequence analysis to generate two-dimensional curves or three-dimensional surfaces which characterize the choroidal circulation. The unique correspondence of each three-dimensional surface to the subject choroidal circulation from which it was derived is demonstrated. Grouping the characteristic three-dimensional surfaces according to various topographic features in common may provide a basis for discriminating between normal and abnormal choroidal circulations.

Animals↗
PubMed1988

Physiology of the developing ocular vasculature.

A conservative view of some of the data discussed here would be that they are anecdotal, but the possibility that factors other than oxygen alone contribute to genesis of ROP is compelling, as is the possibility that clinically observed ROP is only a narrow range of a broad spectrum of retinopathies that could be produced in the immature retina were appropriate physiologic parameters varied outside the current clinically acceptable range. In this context, the significance of such preliminary investigations as these is that they should alert investigators and clinicians to look for correlations between incidence of ROP and factors other than oxygen alone.

Animals↗
PubMed1987

Visualization of a developing vasculature.

The events involved in vasculogenesis still remain obscure. One difficulty has been the techniques employed to visualize angioblasts, i.e., vascular precursors, during the genesis of blood vessels. The retina provides a unique model for studying these events since it is not completely vascularized in some mammals at birth. Using a previously published magnesium-dependent ATPase technique to visualize the developing retinal vasculature and its precursors, and embedding this tissue in JB-4 methacrylate for serial sectioning, has permitted examination of the retinal vasculogenic processes in dual perspective. The technique has permitted observation of the stages in angioblast differentiation and the apparent importance of glycosaminoglycan-rich cell-free spaces in this process. Perhaps the most important observation is that initial vessel formation occurs by coalescence of angioblasts after differentiation in situ.

Adenosine Triphosphatases↗
PubMed1985

Ten years experience with choroidal angiography using indocyanine green dye: a new routine examination or an epilogue?

The choroidal circulation can be studied by an angiographic technique which utilizes near-infrared light wavelengths and a biocompatible dye, indocyanine green (CardiogreenR). Near-infrared light is less absorbed than visible light by the pigment epithelium and the macular xanthophyll, and indocyanine green (ICG) dye doesn't leak from the choriocapillaris as sodium fluorescein dye typically does. Due to the high rate of choroidal blood flow, a fundus camera adapted with special filters and a continuous light source was used in order to make angiograms at the rate of 10 per second. Our experience at the Wilmer Institute and the Eye Clinic at St. Gallen includes 180 choroidal angiograms of normal volunteers and approximately 500 choroidal angiograms of patients with several fundus diseases, mainly senile macular degeneration, diabetic retinopathy and choroidal tumors. Although many of our results are preliminary, we present them to demonstrate the potential applications of this method in ophthalmology. Some factors which may have inhibited an extensive propagation of clinical choroidal angiography in the past are also discussed.

Aged↗
PubMed1985

Postnatal retinal vascular development of the puppy.

Retinal vascular development during the first three postnatal weeks was studied in 63 purebred beagle puppies. Use of a positive enzyme histochemical reaction for adenosine triphosphatase in the nuclei and nucleoli of vascular cells made visualization of the retinal vasculature possible. Animals were killed by decapitation. Thus, artifacts resulting from use of anesthetics or tracer substances were avoided. In general, this study demonstrates important similarities between canine and human retinal vascular development, and this gives further reason to use of the puppy retina as a superior model for studying retrolental fibroplasia pathogenesis. This staining technique demonstrates undifferentiated cells in the avascular retina that appear to be vascular precursors or angioblasts. Primordial vessels form by organization of differentiating angioblasts that exist in peripheral retinal cystic spaces at birth, or by addition of fully differentiated endothelium; they form unlike neovascularization. Müller cell processes appear to provide a structural matrix throughout the avascular puppy retina on which differentiated angioblasts organize into a vascular network. Arteries develop in beds of primordial capillaries lying near the leading edge of the developing vasculature. This precedes vein formation which occurs through a process involving coalescence of embryonic capillaries which themselves were derived from primordial capillaries. Preliminary examination of eight mongrel kitten retinas prepared by this method clearly indicates that the puppy retina is much more completely vascularized at birth than that of the newborn kitten. Moreover, the rate of postnatal retinal vascularization is significantly faster in the kitten. The kitten vasculature does appear to form by the organization of angioblasts as in the puppy, but kitten angioblasts have a different appearance from those in the puppy.

Adenosine Triphosphatases↗
PubMed1985

Foreign body granulomas in normal ovaries.

In 100 consecutive cases in which grossly normal ovaries were removed at the time of pelvic surgery, 9% were found to contain crystalline foreign particles. An additional 9% contained cortical granulomas. In four of six cases, computer-assisted x-ray analysis of the crystalline foreign particles was successful and revealed magnesium and silicon.

Adult↗
PubMed1978

The effect of blood on ocular fundus reflectance and determination of some optical properties of retinal blood vessels.

Light reflected from 50 micrometer diameter spots on the fundi of two adult rhesus monkeys was measured as a function of wavelength in 10 nm jumps from 400 to 900 nm. The areas measured were a retinal artery and vein, areas of the disk, macula, and retina devoid of visible blood vessels, and the foveola. The eyes of the two monkeys were then exsanguinated, the blood vessels were filled with normal saline, and reflectances of the same spots on the fundi were again measured. The pairs of reflectance curves were compared and demonstrated that blood is not the major determinant of the characteristic shapes of the retinal tissue spectral reflectance curves. From the pre-exsanguination and postexsanguination data, the isolated retinal artery and vein wall reflectances were determined to be 0.020 and 0.009, respectively, their transmittances 0.837 and 0,977, and the fractions of light absorbed by them 0.143 and 0.014, respectively, in the visible spectral region below 500 nm.

Animals↗
PubMed1977

Electroretinographic changes and choroidal defects in a case of central retinal artery occlusion.

A 62-year-old white woman with hypertensive diabetes had central retinal artery occlusion of her right eye. Serial electroretinographic (ERG) studies demonstrated reversible changes in the scotopic components but permanent reduction of the photopic b-wave. Serial simultaneous fluorescein and indocyanine green angiographic studies demonstrated a perfusion defect in the choroid involving part of the macula which subsided after reopening the retinal circulation. Differential hypoxic susceptibility of the ERG photopic and scotopic b-waves was demonstrated, and changes in the patient's retinal tissue oxygenation were postulated on the basis of retinal and choroidal angiographic studies performed during and after central retinal artery occlusion to account for the observed changes in serial ERGS.

Adaptation, Ocular↗
PubMed1977

Reflection of light by small areas of the ocular fundus.

Light reflected from 50 micrometer spots on the fundi of two rhesus monkeys and three human volunteers was measured as a function of wavelength in 10 nm. jumps from 400 to 900 nm. The areas measured were a retinal artery and vein, areas of the disk, macula, and retina devoid of visible blood vessels, and the fovea.

Adult↗