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Fluorescence-mediated photoplethysmography (FM-PPG) is the first routine clinical methodology by which to quantifiably measure tissue blood perfusion in absolute terms (mL blood/sec ∗ mm 2 tissue). The FM-PPG methodology has been described in detail previously in this journal (MVR 114, 2017, 92-100), along with initial proof-of-concept measurements of blood perfusion in both ocular and forearm skin tissues. The motivation for the current study was to investigate whether FM-PPG can be used readily and routinely under realistic clinical conditions. The vehicle for doing this was to measure medial foot capillary blood flow, i.e., tissue perfusion, in 7 normal subjects, mean = 6.76 ± 2.29 E-005 mL/(sec ∙ mm 2 ), and lesion-free areas of 8 type-2 diabetic patients with skin ulceration, mean = 4.67 + 3.15 E-005 mL/(sec ∙ mm 2 ). Thus, perfusion in the diabetics was found to be moderately lower than that in the normal control subjects. Earlier skin perfusion measurements in medial forearms of 4 normal subjects, mean = 2.64 + 0.22 E-005 mL/(sec ∙ mm 2 ), were lower than both the normal and diabetic foot perfusion measurements. Variability in the heartbeat-to-heartbeat blood perfusion pulses in the skin capillaries, defined as the ratio of the standard deviation among beat-to-beat pulses divided by the mean perfusion of those pulses, was determined for each subject. Average variability in foot skin was 21% in the diabetic population, versus 16% for normal subjects; and it was 18% in forearm skin. We conclude that absolute quantitative FM-PPG measurement of skin blood perfusion at the level of nutritive capillaries is feasible routinely under clinical conditions, allowing for quantitative measurement of skin tissue blood perfusion in absolute terms., (Copyright © 2018 Elsevier Inc. All rights reserved.)

Fluorescence-mediated photoplethysmography (FM-PPG) was developed to facilitate determination of tissue microvascular (capillary) blood perfusion, requiring intra-venous injection of a small bolus (~0.33mL) of dye (25mg/mL ICG) and acquisition of high-speed angiogram images (>15images/s). The methodology is applicable to microvascular capillary beds of tissues that can be optically imaged, directly or laparoscopically. Proof of concept of the methodology and feasibility of its implementation are demonstrated in human forearm skin and in the choroid of a monkey eye, determined to have blood perfusion rates on the order of 1e-5mL/(s·mm 2 ) and 10e-5mL/(s·mm 2 ), respectively. Ability to obtain absolute quantified tissue perfusion data ultimately can provide the means by which to characterize blood flow information at the nutritive capillary-vessel level in an objective and universally understood manner, in much the same sense that body temperature or blood pressure are., (Copyright © 2017 Elsevier Inc. All rights reserved.)

A clinical method for characterizing the state of micro-vasculature vasomotion is demonstrated, based on observing in capillaries the dynamics of autologously re-injected erythrocytes containing ICG dye. Since a manifestation of vasomotion is transient erythrocyte pausing, vasomotion state within a field of capillaries is characterized by an histogram plot of the number of paused erythrocytes as a function of pause duration during a fixed period of observation, then the ratio of long-pausing to short-pausing erythrocytes was calculated. The method was first applied to the posterior pole retinal vasculatures of anesthetized-monkey eyes, and normal vasomotion state during air-breathing was compared to the state induced by O 2 -breathing, known to cause mild arteriolar vasoconstriction in the mature eye. Subsequently, the effects of other antagonists to normal arteriolarvasotonia state (long-standing experimentally-induced ocular hypertension and branch-vein occlusion, as well as tissue edema) were similarly characterized and the results compared to those obtained during baseline air-breathing. The feasibility of applying the histogram characterization of vasomotion state to human eyes and skin was also preliminarily explored., (Copyright © 2017 Elsevier Inc. All rights reserved.)

This technical note describes a modification to a fundus camera that permits simultaneous recording of pattern electroretinograms (pERGs) and pattern visual evoked potentials (pVEPs). The modification consists of placing an organic light-emitting diode (OLED) in the split-viewer pathway of a fundus camera, in a plane conjugate to the subject's pupil. In this way, a focused image of the OLED can be delivered to a precisely known location on the retina. The advantage of using an OLED is that it can achieve high luminance while maintaining high contrast, and with minimal degradation over time. This system is particularly useful for animal studies, especially when precise retinal positioning is required.

Laser photocoagulation of the feeder vessels of age-related macula degeneration-related choroidal neovascularization (CNV) membranes is a compelling treatment modality, one important reason being that the treatment site is removed from the fovea in cases of sub- or juxtafoveal CNV. To enhance the energy absorption in a target feeder vessel, an indocyanine green dye bolus is injected intravenously, and the 805 nm wavelength diode laser beam is applied when the dye bolus transits the feeder vessel; this tends to reduce concomitant damage to adjacent tissue. A 3D theoretical simulation, using the Pennes bioheat equation, was performed to study the temperature distribution in the choroidal feeder vessel and its vicinity during laser photocoagulation. The results indicate that temperature elevation in the target feeder vessel increases by 20% in dye-enhanced photocoagulation, compared to just photocoagulation alone. The dye bolus not only increases the laser energy absorption in the feeder vessel but also shifts the epicenter of maximum temperature away from the sensitive sensory retina and retinal pigment epithelial layers and toward the feeder vessel. Two dominant factors in temperature elevation of the feeder vessel are location of the feeder vessel and blood flow velocity through it. Feeder vessel temperature elevation becomes smaller as distance between it and the choriocapillaris layer increases. The cooling effect of blood flow through the feeder vessel can reduce the temperature elevation by up to 21% of the maximum that could be produced. Calculations were also performed to examine the effect of the size of the laser spot. To achieve the same temperature elevation in the feeder vessel when the laser spot diameter is doubled, the laser power level has to be increased by only 60%. In addition, our results have suggested that more studies are needed to measure the constants in the Arrhenius integral for assessing thermal damage in various tissues.

Indocyanine green (ICG) dye angiography has been used by ophthalmologists for routine examination of the choroidal vasculature in human eyes for more than 20 years. In this study, a new approach is developed to extract information from ICG dye angiograms about blood velocity distribution in the choriocapillaris and its feeding blood vessels. ICG dye fluorescence intensity rise and decay curves are constructed for each pixel location in each image of the choriocapillaris in an ICG angiogram. It is shown that at each instant of time the magnitude of the local instantaneous dye velocity in the choriocapillaris is proportional to both the slope of the ICG dye fluorescence intensity curve and the dye concentration. This approach leads to determination of the absolute value of blood velocity in the choriocapillaris, assuming an appropriate scaling, or conversion factor can be determined. It also enables comparison of velocities in different regions of the choriocapillaris, since the conversion factor is independent of the vessel location. The computer algorithm developed in this study can be used in clinical applications for diagnostic purposes and for assessment of the efficacy of laser therapy in human eyes.

Diabetes mellitus develops spontaneously in middle-aged, obese rhesus monkeys, thus making them a good model for examining the effects of co-morbid factors on the development of end-organ damage. Changes in structure and function in the eyes of one monkey who spontaneously developed type 2 diabetes are reported here. This animal had concomitant hypertension, high levels of triglycerides and serum cholesterol, and a low fraction of high-density lipoprotein. The eyes showed intraretinal hemorrhages and large areas of retinal capillary nonperfusion. Indo-cyanin green (ICG) angiography revealed a large area of non- or poorly perfused choriocapillaris in one eye, and immunohistochemistry showed loss of viable choriocapillaries in this region. Both basal laminar deposits and hard drusen were present on areas of Bruch's membrane adjacent to nonviable choriocapillaris. Blood flow via the nasal posterior ciliary arteries to this section of choroid was not detectable by color duplex Doppler ultrasound, indicating contribution of extraocular vascular disease to ischemia in this eye. There was a severe decline in number of photoreceptor inner and outer segments, and corresponding reductions in the multifocal electroretinogram (ERG), in the areas of choriocapillaris loss. The ganzfeld ERG indicated loss in both inner and outer retinal function. Much of the ganglion cell layer was absent throughout the retina, possibly reflecting the effect of diabetes as well as chronic open angle glaucoma; the latter diagnosis supported by elevated intraocular pressures and excavated optic disks. In summary, high resolution, enzyme histochemical and histopathological analyses of a diabetic hypertensive monkey retina and choroid after serial functional in vivo analyses have demonstrated the relationship between vascular dysfunction and visual function loss. Choroidal vascular dysfunction in both large and small vessels was associated with age-related macular degeneration-like changes in Bruch's membrane and photoreceptor degeneration.

Purpose: To review and update techniques of posterior segment ophthalmic fundus imaging., Design: Literature review and collective experience of the authors., Methods: This perspective includes sections on digital imaging, fundus autofluorescence, ultrasonography, angiography, and optical coherence tomography (OCT) -ophthalmoscopy written by leading clinicians and researchers in these areas., Results: Digital angiography has become the new standard in the ophthalmic community based upon improved technology which has enhanced resolution, processing time, and ease of image duplication, manipulation, and transmission. A relatively new imaging technique, fundus autofluorescence, highlights lipofuscin deposits and improves our understanding of the metabolic status of the retinal pigment epithelium. Diagnostic ultrasonography continues to be a major adjunct to ocular evaluation where advances now allow for exceptional versatility and portability. High speed angiographic techniques provide detailed visualization of choroidal perfusion which improves our understanding of both normal and pathologic vascular phenomenon. Advances in high-resolution OCT currently under development promise an even more detailed fundus representation. The integration of the scanning laser ophthalmoscope and OCT has produced a dynamic new instrument, the OCT ophthalmoscope, which simultaneously images the fundus in numerous ways with point to point correlation., Conclusions: Ophthalmic imaging technology has revolutionized fundus examination. Currently available systems have contributed significantly to our understanding of the pathophysiology and treatment of various retinal diseases. Future advances promise near histologic resolution of retinal structures as well as real-time image manipulation and instantaneous transmission world-wide.

Purpose: Anterior ischemic optic neuropathy (AION) is caused by sudden loss of vascular supply to retinal ganglion cell (RGC) axons in the anterior portion of the optic nerve and is a major cause of optic nerve dysfunction. There has been no easily obtainable animal model of this disorder. The current study was conducted to design a novel model of rodent AION (rAION), to enable more detailed study of this disease., Methods: A novel rodent photoembolic stroke model was developed that is directly analogous to human AION. Using histologic, electrophysiological, molecular- and cell biological methods, the early changes associated with isolated RGC axonal ischemia were characterized., Results: Functional (electrophysiological) changes occurred in RGCs within 1 day after rAION, with a loss of visual evoked potential (VEP) amplitude that persisted in the long term. The retinal gene expression pattern rapidly changed after rAION induction, with an early (<1 day) initial induction of c-Fos mRNA, and loss of RGC-specific gene expression. RGC-specific protein expression declined 2 days after detectable mRNA level changes, and immunostaining suggested that multiple retinal layers react to isolated RGC axonal ischemia., Conclusions: rAION rapidly results in electrophysiological and histologic changes similar to clinical AION, with reactive responses in primary and supporting neuronal cell layers. The rAION model can enable a detailed analysis of the individual retinal and optic nerve changes that occur after optic nerve stroke, which may be useful in determining possible therapeutic interventions for this disorder.

Purpose: To optimize the method of treating choroidal neovascularization (CNV) associated with age-related macular degeneration (AMD)., Design: Experimental study and interventional case series., Methods: The parameters associated with locating and then photocoagulating CNV feeder vessels were identified and optimized using published data and data derived from modeling the choroidal vasculature. Based on these optimized parameters, a prototype diagnostic/treatment system was designed that captures high-speed indocyanine green (ICG) angiogram images and facilitates analysis of the images by enhancing visualization of dye movement through CNV feeder vessels (FVs). The system also permits precise aiming and delivery of 810- nm wavelength photocoagulation laser energy to target FVs on a real-time ICG angiogram image of the choroidal vasculature. Target FVs are tracked by a joy-stick controlled laser aiming beam until an intravenously-injected high-concentration ICG dye bolus is observed to enter the target vessel, at which time the laser is fired. Proof of principle of the combined diagnosis/treatment system design for performing dye-enhanced photocoagulation (DEP) in the clinical setting and determination of the minimum DEP laser energy needed to close CNV FVs was made in 11 AMD patients requiring treatment of CNV, but for whom other treatment was not appropriate., Results: Using ICG-DEP, CNV feeder vessels were closed with single pulse laser energy, delivering as little as 0.6 to 1.8 J of energy to the fundus, producing no visible change in the fundus. Successful FV closure was usually indicated immediately by presence of incarcerated ICG dye in the vessel adjacent to the burn site. The prototype system proved relatively easy to operate. After acquiring and interpreting diagnostic angiograms and repositioning a patient in front of the device, feeder vessel DEP and treatment evaluation required 15 to 20 minutes., Conclusions: Indocyanine green dye-enhanced photocoagulation of CNV feeder vessels, facilitated by use of a device that permits real-time visualization of the choroidal circulation while aiming the treatment laser beam, appears to minimize the amount of energy applied to the fundus and the volume of fundus tissue affected by treatment, compared with other treatment modalities. The combination diagnosis/treatment device should be useful in optimizing FV treatment and in refining and evaluating the efficacy of DEP in future clinical trials.

Purpose: To report clinical observations consistent with conclusions from a previous theoretical investigation indicating that photocoagulation of choroidal neovascularization (CNV) efferent vessels can be, in some instances, an effective treatment., Design: Interventional case series., Methods: In five eyes with age-related macular degeneration (five patients with mean age +/- SD of 65 +/- 11 years, range 55-79 years) requiring treatment of CNV. In each case, the appropriate treatment was location and photocoagulation of the CNV efferent vessels, since the afferent vessels were not identifiable or were located beneath the fovea. Targeted vessels were determined to be draining vessels by analysis of pretreatment high-speed indocyanine green (ICG) angiograms, and successful vessel closure by photocoagulation was demonstrated by posttreatment ICG angiograms. The eyes subsequently were followed from 2 to 12 months., Results: After photocoagulation of efferent vessels, CNV-related retinal edema was significantly reduced or resolved within 1 to 4 days. Visual acuity became stabilized in three eyes and improved in two eyes. In a few days, metamorphopsia disappeared in four of the eyes and was stable for a period longer than the duration of the associated efferent vessel closure. Initial efferent vessel closure by photocoagulation persisted on average for 7 to 15 days, after which additional treatment was required. It is significant that in no case did hemorrhage result from the photocoagulation treatment., Conclusions: These observations are consistent with the earlier theoretical study prediction that photocoagulation of efferent CNV vessels can be effective in reducing CNV-associated edema. That no hemorrhage was induced by photocoagulation is consistent with the theoretical concept that there appears to be no direct hydrostatic connection between the CNV and its afferent vessels. Rather, that connection appears to be a functional one made through the choriocapillaris, which may dissipate excess CNV hydrostatic pressure produced by occlusion of a draining vessel. However, this finding is not intended to be a recommendation to attempt CNV efferent vessel photocoagulation.

Purpose: To investigate the relationship between choriocapillaris blood flow and blood flow through an overlying choroidal neovascularization, as it relates to photocoagulation-induced changes in the choriocapillaris circulation., Methods: A theoretical model that simulates the blood flow in the choriocapillaris and choroidal neovascularization of the human eye was developed, based on histologically determined vascular geometry and experimentally measured blood pressure gradients. The choriocapillaris blood pressure and blood flow were examined before and after simulated photocoagulation of various Sattler layer vessels entering the choriocapillaris in the vicinity of the choroidal neovascularization. (The Sattler layer is the inner layer of medium-sized choroidal vessels that includes both arterioles and venules that supply the choriocapillaris.), Results: The theoretical model showed that both partial and complete occlusion of either Sattler arteriole or venous vessels in the vicinity of the capillary-like vessels connecting a choroidal neovascularization to the underlying choriocapillaris results in significant choroidal neovascularization blood flow reduction. These theoretical results are similar to clinically observed changes induced by laser photocoagulation of feeder vessels. (In this discussion, the term "feeder vessels" refers to those vessels in an indocyanine green angiogram image that appear to supply blood to a choroidal neovascularization; these vessels appear to be Sattler layer vessels, rather than the histologically demonstrated short, capillary-like vessels that form choriocapillaris-choroidal neovascularization communications.), Conclusions: Reduction of choriocapillaris blood flow underlying a choroidal neovascularization may be sufficient to reduce the blood flow rate in the choroidal neovascularization and thereby reduce the associated retinal edema. The results also suggest that reduction of choriocapillaris blood flow may be the common hemodynamic event associated with the successful application of several currently practiced methods of choroidal neovascularization treatment, including feeder vessel photocoagulation, photodynamic therapy, transpupillary thermotherapy, and prophylactic drusen photocoagulation. Ultimately, this model may be useful in determining optimal placement of laser photocoagulation burns to achieve a desirable perturbation in choroidal blood flow distribution and thereby reduce choroidal neovascularization blood flow to the extent necessary to obliterate associated retinal edema.

Purpose: To demonstrate an indocyanine green (ICG) angiography-based clinical method for characterizing choroidal blood flow and for detecting changes in choroidal circulation patterns, and by use of that method, to demonstrate that pentoxifylline affects choroidal blood flow., Methods: High-speed ICG angiography was performed in rhesus monkeys before and after intravenous administration of pentoxifylline or saline (which served as a control) while monitoring blood pressure and heart rate. From these data, three-dimensional surface maps indicating the instantaneous relative distribution of choroidal blood flow during the peak of intra-ocular pressure pulse systole in a 30 degrees field, centered on the macula, were generated to characterize the state of the choroidal circulation at various times during the experiments., Results: Comparisons of the 3-dimentional surface maps consistently indicated an increase in sub-macular choroidal blood flow occurring within 5 to 10 minutes post-pentoxifylline injection, with a gradual return to baseline level 20-40 minutes later. Injection of equal volumes of saline produced no changes in choroidal blood flow., Conclusions: Posterior-pole choroidal blood flow can be characterized as by a three-dimensional surface representing the instantaneous relative distribution of choroidal blood flow during the peak of intra-ocular pressure pulse systole. Pentoxifylline does, at least transiently, increase sub-macular choroidal blood flow.

Purpose: To report a model of choroidal neovascularization feeder vessels that reconciles current histologic, angiographic, and clinical data, and to report experimental studies that investigate the potential of indocyanine-green-dye-enhanced photocoagulation to improve feeder-vessel treatment., Methods: A model of choroidal neovascularization feeder vessels was conceived to account for current histologic and angiographic data. Based on that model, experimental studies of the efficacy of indocyanine green-dye-enhanced photocoagulation were performed, using pigmented rabbit eyes as a model system. A Zeiss fundus camera was modified to permit visualization of choroidal blood flow by high-speed indocyanine green angiography and to permit simultaneous delivery of 810-nm-wavelength diode laser photocoagulation pulses to specific choroidal vascular targets during indocyanine green-dye bolus transit., Results: Choroidal neovascularization feeder vessels appear to originate in the Sattler layer (that is, that portion of the choroidal vasculature consisting of medium-diameter vessels) and enter the choriocapillaris in close proximity to the small capillary-like vessels that penetrate Bruch membrane and communicate with the choroidal neovascularization. The rabbit eye experiments demonstrated that the presence of high indocyanine green dye concentration in circulating blood enhances uptake of near-infrared laser energy (three eyes); injection of sequential indocyanine green dye boluses results in gradually decreased efficiency of dye-enhanced photocoagulation (two eyes); and by application of laser energy during the initial transit of small-volume, high-concentration indocyanine green dye boluses, dye-enhanced photocoagulation of large diameter choroidal arteries can be accomplished with relatively little concomitant retinal tissue damage (three eyes)., Conclusions: Although future trials will be necessary to substantiate these initial findings in the clinical arena, it appears that the efficiency of choroidal neovascularization feeder-vessel photocoagulation may be enhanced, while minimizing concomitant damage to overlying retinal tissue, by delivery of 810-nm wavelength laser energy immediately upon arrival of a high-concentration indocyanine green dye bolus in a targeted feeder vessel. However, molecules of dye adhering to vessel walls or lying in tissue interstitial spaces appear to divert laser energy from the photocoagulation process, so efficiency of indocyanine green dye-enhanced photocoagulation gradually diminishes as the number of injected dye boluses increases.

Purpose: Indocyanine green (ICG) angiograms of each of five patients with retinal pigment epithelium (RPE) detachments were made using first a Topcon fundus camera and then a Heidelberg scanning laser ophthalmoscope (SLO); for each patient, both types of angiograms were obtained on the same day. In each case, the serous fluid appeared bright throughout the fundus camera studies and dark throughout the SLO studies. This study sought to explain the disparity in the appearance of the lesions in the two kinds of images and to determine whether there was dye in the serous fluid., Methods: Simple model eyes were constructed to demonstrate the effects of Mie light scatter and integrating sphere behavior of the sclera on ICG image formation by the fundus camera and SLO optics. Analysis was made of both the clinical angiograms and model eye images to structure an explanation for the disparate RPE detachment angiographic images., Results: Indocyanine green fluorescent light from choroidal vessels adjacent to the lesions and scattered by the turbid serous fluid accounted for the lesion brightness seen in the fundus camera images. The models confirmed that SLOs suppress scattered light., Conclusions: The apparent fluorescence of serous fluid beneath RPE detachments in fundus camera early-phase ICG angiogram images is not attributable to the presence of dye; rather, it appears to be attributable to serous fluid light scatter of fluorescent light arising from adjacent fluorescent structures. This light scatter is a consequence of the fundus camera illumination and recording optics and is not present in SLO-generated images. The necessity of understanding such phenomena as absorption, diffraction, polarization, and scatter of light and routinely applying them to ICG angiogram interpretation is underscored when it is shown that they offer simple explanations for unusual or unexpected angiographic results, as in the case of the patients with RPE detachment discussed here.

Purpose: To investigate variability of choriocapillaris blood flow patterns., Methods: After the intravenous injection of indocyanine green, angiograms were recorded at 30 images per second in rhesus monkey eyes using a fundus camera equipped with a pulsed laser diode light source, synchronized with a gated (5 msec), intensified charge-coupled device, or CCD, video camera. Images of choriocapillaris filling alone were extracted. Plastic corrosion casts were made of two of the monkey's choroidal vasculatures for subsequent scanning electron microscopy examination., Results: Pulsed laser indocyanine green fluorescence excitation produced better definition of choriocapillaris filling than had been achieved using continuous illumination. No correlation was found between the choriocapillaris plexus architecture revealed by the plastic corrosion casts and the observed choriocapillaris lobular filling. Overall posterior pole choriocapillaris dye-filling patterns were relatively stable for periods of days, but they changed gradually for periods of weeks. Localized minor pattern changes occurred on a much shorter time scale. Choriocapillaris filling patterns were altered by acutely elevating intraocular pressure, by O2 and CO2 breathing, and by argon laser retinal photocoagulation of adjacent areas., Conclusions: Choriocapillaris filling patterns appear to be determined by the network of perfusion pressure gradients that exist among the interspersed feeding arterioles and draining venules connected to the choriocapillaris plexus. Changes in intraocular pressure and in blood PO2 and PCO2 levels can produce marked changes in the distribution of choriocapillaris blood flow. Retinal laser photocoagulation of adjacent fundus areas alters choriocapillaris blood flow to the extent that the altered flow might be an important factor in the beneficial results attributed to retinal laser treatment.

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 male rhesus macaque was found to have what appeared to be numerous platelet-fibrin emboli in retinal vessels in the perimacular area. Indocyanine green (ICG) dye fluorescence and fluorescein angiograms of the fundus demonstrated leakage of fluorescein, but not ICG, from the involved arterioles. Histopathologic changes in the eyes included occlusion of retinal and choroidal vessels with platelet-fibrin emboli, inner retinal ischemia, ischemic injury to the parafoveal capillary bed distally to occlusion of precapillary arterioles, and retinal exudate limited to the regions of capillary damage. Differential leakage of fluorescein may be explained by the difference in binding affinities of the 2 dyes to blood protein: 20% to 40% of the circulating fluorescein is unbound, and 98% of ICG is bound to serum albumin. Simultaneously or serially performed angiograms with fluorescent probes of different sizes might be used to obtain a qualitative measure of vascular integrity in persons with embolism, diabetic retinopathy, sickle cell retinopathy, vasculitis, and other disorders known to produce focal retinal and choroidal vascular occlusion.

A technique for chronic implantation of a device for long-term continuous, quantitative monitoring of intraocular pressure (IOP) in experimental animals is presented. The methodology employed is straight forward and should be easily duplicated for experimental investigations where such monitoring might be useful. Continuous IOP data recorded from the device implanted in a conscious adult rhesus monkey are compared with continuous IOP data reported by other investigators.

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.

Electroretinographic (ERG) transient responses elicited in monkeys by abrupt changes in the periodicity of a rapidly intermittent (suprafusion) luminance stimulus were studied experimentally, and analyzed and interpreted through a theory of dynamic retinal responses. The suprafusion ERG transients are confirmed to behave in accord with theoretical expectation, as elemental responses (retinal Green's functions). By aid of the theory the ERG wave-forms can be reduced to two significant elements. One element, accounting for approximately two-thirds of the total ERG variance, is strictly linear, and correlates well with simultaneously evoked cortical (VEP) transients which were previously related to suprafusion perception in humans. The other element, comprising approximately one-third the ERG transient, is a rectification, with properties indicating that it may arise from a specific layer of retinal neurons (amacrine cells); on this assumption the theory demonstrates that high-frequency nonlinear ERG flicker can isolate activities proximal and distal to the rectifying (amacrine) layer. Thus, the hypothesis of an amacrine origin for the rectifying element entails the possibility that suprafusion ERG studies could accomplish in vivo "dissection" of the human retina.

The sensory retina of the eye is nourished by two essentially separate blood circulations. The more superficial of these, the retinal circulation, is easily evaluated by direct visualization or routine fluorescein angiography. However, the underlying choroidal circulation, which is attributed with maintenance of the outer layers of the retina is not easily visualized due to the pigment epithelial layer and choroidal pigment. Fluorescence and infrared absorption angiographic techniques using indocyanine green (ICG) dye, which can be used to evaluate the choroidal circulation routinely, are described in this paper. A method is also described which can provide these angiograms simultaneously with standard fluorescein fluorescence angiograms of the retina. Finally, a comparison of all three types of angiograms is made. Limitations to the resolution of fundus details in angiograms imposed by optics of the fundus camera, photographic films, and optics and anatomy of the eye are examined.

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.

Simultaneously recorded visual-evoked responses and electroretinograms are reported for a transient response produced by an abrupt change in the frequency of a light modulated above fusion. A principal components analysis was made of the recorded waveforms, and results of this analysis and their possible significance to clinical electrophysiology are discussed.

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.

In vivo observations of the immature beagle puppy retina indicates that in general O2-breathing induces vasoconstriction whereas CO2 or CO2 combined with O2 induces vasodilation. It was the goal of this study to determine whether a specific correlation could be found between this pattern of vascular response to changes in blood gas content and production of prostaglandins in the eye. Prostaglandin production by puppy choroidal and retinal tissues and platelets exposed in vitro to these gas combinations was such that it appears platelet-derived thromboxane could have a significant influence in determining retinal vasotonia.

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.

Aspirin administration, at a dosage producing plasma levels within the human therapeutic range, caused marked inhibition of production of both vascular prostacyclin (a vasodilator) and platelet thromboxane (a vasoconstrictor) in beagle puppies. In addition, aspirin-treated, oxygen-exposed puppies developed retinopathy of significantly greater severity than their unmedicated, oxygen-exposed littermates. Direct ophthalmoscopic observations indicated that whereas sustained oxygen breathing produced retinal vasoconstriction in unmedicated puppies, retinal vessels of aspirin-treated littermates became more dilated or remained unchanged. It is postulated that retinal vasoconstriction may be a normal physiologic mechanism to protect the immature retina from damaging effects of high blood oxygen levels; i.e., it may be a protective rather than a pathologic process in response to hyperoxia. Many vascular anomalies which characterize the human disease were present in the retinas of the puppies. Several of the most severely affected puppies treated with aspirin even displayed grade III cicatricial retinopathy (falciform retinal fold). Thus, a major criticism of the retrolental fibroplasia animal model has been addressed by producing cicatricial retrolental fibroplasia in puppies, and the confidence with which results from experimental animal studies might be extrapolated to the clinical situation is thereby strengthened.

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.