Faculty Bibliography

PURPOSE. There are conflicting views about the organization of the posterior pole choriocapillaris, particularly concerning blood flow through it, and there are difficulties associated with attempting to obtain such information using histologic techniques, sodium fluorescein angiography, or both. The present study uses a method of analysis based on high-speed angiograms to investigate posterior pole choroidal blood flow. METHOD. The analysis method employed is based on the premises that dye filling of the choriocapillaris is more rapid (because it is pulsatile) than dye filling of the underlying larger diameter vessels, and that fluorescence from these two overlapping layers is additive. The described analysis algorithm was applied to high-speed ICG fluorescence angiograms to emphasize information about choriocapillaris hemodynamics. RESULTS. The analysis method was demonstrated in rhesus monkeys, and results indicate that the posterior pole choriocapillaris does not behave as a homogeneous structure, consisting of discrete lobular segments. In general, the cycle of dye filling of the choriocapillaris begins in the macular area and progresses radially toward the periphery in a wavelike manner, the filling cycle beginning with and being completed during one cycle of the intraocular pressure pulse. CONCLUSIONS. It is possible to extract information related to choriocapillaris blood flow from high-speed ICG angiograms when a fairly well-defined dye bolus wavefront is present. Interpretation of the results suggests that the choriocapillaris lobules fill in a pulsatile manner, out of phase with each other, and may act thereby to dissipate the blood volume entering the choroid during each cardiac cycle in such a way that the retinal macular is not significantly displaced by expansion of the choroidal vascular volume. Depending upon the distribution of pressure gradients across a group of lobules, blood may flow from one lobule into or even through an adjacent one

Acute posterior multifocal placoid pigment epitheliopathy (APMPPE) is an idiopathic posterior segment inflammatory disorder of young adults. The pathophysiology is poorly understood, and debate persists as to whether it represents a primary pigment epithelial disorder or a choroidal vascular disease. Indocyanine green angiography was used to study choroidal blood flow in two patients with typical APMPPE. The authors demonstrate profound delayed choroidal filling in addition to extensive areas of choroidal vessel nonperfusion in the acute stage of this disease. Recovery of choroidal blood flow was evident during clinical resolution. Choroidal blood flow abnormalities are present in APMPPE and suggest that the clinical findings of this disease reflect a primary choroidal vascular disease

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

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

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

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

Both aluminum and calcium are present in many pelvic concretions that have traditionally been attributed to calcium and phosphorus alone. There is considerable variation in both the amount and the distribution of aluminum when it is present

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