Vitreous Fluorophotometry Research Articles

Protocols for the vitreous fluorophotometry examination: A general plan

The parameters of vitreous fluorophotometry differ when fluorescein is administered by intravenous and by oral routes. Differences also exist for “normals” and patients with known chorio-retinal pathology. Four protocols are presented for fluorophotometry in normals and diseased individuals by both intravenous and oral routes.

In vivo evaluation of signal loss due to lens opacity

We have shown that by using the information available in a standard scan, one can estimate the loss of fluorescence signal at the anterior vitreous. The proposed method is restricted to lenses without cataracts, which is not a serious limitation because vitreous fluorophotometry is not performed on cataractous lenses. The procedure is easily implemented and requires only the use of an instrument with good axial resolution and reliable alignment with the ocular optical axis.

Outward transport of fluorescein from the vitreous in normal human subjects.

Vitreous fluorophotometry was performed on eight normal subjects to compare the outward and inward permeabilities of fluorescein into the vitreous. The results indicate that diffusion alone does not account for the outward flow of fluorescein in the vitreous. The possible underlying factors and significance of these findings are discussed.

Vitreous fluorophotometry studies in aphakia.

Vitreous fluorophotometry was performed on 63 patients undergoing cataract extraction. Pre- and postoperative studies demonstrated that this procedure always induces alterations in the blood-aqueous barrier. A correlation was found between the degree of this alteration and the frequency of cystoid macular edema.

Configuration of the normal vitreous fluorophotometry recording: Symbols

Findings during fluorophotometry studies of the normal human vitreous are described. The major landmarks are presented and a system of significant fluorophotometric variables is proposed. Use of this approach should optimize the evaluation of fluorophotometry data and maximize the information obtained concerning the status of the blood retinal barrier.

Algorithm for the correction of artifacts.

The sources of vitreous fluorophotometry artifacts are described. An algorithm to define this "spread function" is presented. The use of improved instrumentation and compensation for this artifact by data processing of the "correction" algorithm can improve the results of vitreous fluorophotometry. This algorithm was carried out in 40 eyes and was found to have an error of 0.7 mg/ml at 3 mm from the choroid-retina.

Vitreous fluorophotometry recordings in posterior segment disease.

The results of vitreous fluorophotometry in a variety of retinal and systemic diseases are described, particularly in photoreceptor and retinal pigment epithelium dystrophies, in Best dystrophy, in choriocapillaris atrophy, in choroidemia and in inflammatory conditions, and in cystoid aphakic and non-aphakic macular edema. The patterns involved in breakdown of the blood-retinal barrier are defined for various diseases, and an attempt is made to characterize each disease type by a fluorophotometric "profile."

Pharmacokinetic interpretation of kinetic vitreous fluorophotometry

A refined mathematical model for interpretation of the data on fluorescein kinetics across the blood-vitreous barrier is presented. This model is better adapted to the geometry of the human eye and thus yields superior results.

Studies on fluorescein concentration in the plasma

Preliminary studies on fluorescein kinetics in the plasma of humans were performed by fluorophotometry and spectrophotometry. Noninsulin diabetics (type II) were similar to normal individuals. Insulin-dependent diabetics (type I), however, had lower plasma concentrations of fluorescein than the other two groups. No significant differences were found in protein binding among normal volunters and patients with diabetes types I and II. The best time interval for measurement appeared to be 60 min after the intravenous injection. The possible reasons for these results are discussed, and the importance of these findings to vitreous fluorophotometry is outlined.

Factors affecting vitreous fluorescence.

A variety of mechanical (intensity of the light source, the width and the angle of the exciting source) and physiological factors (retinal pigmentation, vitreous fluorescence) and many systemic factors affect the results of vitreous fluorophotometry. These factors are discussed with respect to identifying those that are inconsequential and those that are significant. Methods to compensate for the important factors are described.

Characterization of the early stages of diabetic retinopathy by vitreous fluorophotometry

Characterization of the early stages of diabetic retinopathy by vitreous fluorophotometry

Characterization of the early stages of diabetic retinopathy by vitreous fluorophotometry.

We compared insulin-dependent diabetic patients with minimal (16 eyes of 9 patients) or no retinopathy (45 eyes of 27 patients) to normal volunteers (20 eyes of 12 subjects) using a commercial vitreous fluorophotometer and different procedures for artifact correction. The influence of background autofluorescence was minimized through the use of a software program that subtracted a fluorophotometric scan obtained before administration of fluorescein from that obtained after its injection. We also compared two programs designed to minimize the contribution of the chorioretinal peak spread function to the readings in the vitreous. The fluorescein concentration in the posterior vitreous was then averaged within two different regions. We then assessed the influence of these data-processing methods on the spread of the results of the different groups. The clinical study showed that only the posterior vitreous concentration of fluorescein is relevant in the evaluation of the blood-retinal barrier. However, since there is a gradient of fluorescein concentration in the posterior vitreous, one needs a scanning device so that one can measure at a precise location in front of the retina. The posterior vitreous concentration of fluorescein was significantly increased in diabetic subjects with one or no aneurysms as compared with normals. Moreover, the eyes with minimal retinopathy, as judged by the presence of microaneurysms, had higher values than those without retinopathy. The clear differences among these three groups were not present when the midvitreous values were used.(ABSTRACT TRUNCATED AT 250 WORDS)

Early Diagnosis of So‐Called Late Complications in Type 1 Diabetic Children

AbstractPrevention of late complications is the main problem in type 1 diabetes of childhood. Longitudinal studies of subjects diagnosed before puberty demonstrated significant prevalence of retinopathy, nephropathy and neuropathy after 10‐ 15 years, correlated with the duration of diabetes. Proliferative retinopathy is rarely observed in children with diabetes of less than 5 years duration but vitreous fluorophotometry has shown abnormalities of retinal vessels in asymptomatic patients. In early diabetes glomerular permeability can be tested by radioimmunoassay of microalbuminuria; values above 30 mcg/min are a good predictor of later clinical proteinuria. The development of overt neuropathy is extremely variable and it may not be present even after many years of poorly controlled diabetes.Vitreous fluorophotometric abnormalities, basal and post‐exercise microalbuminuria and reduction of nerve conduction velocity have been proven to be reversible with intensive therapy. When secalled “late” complications are diagnosed early, careful and intensive therapy to maintain metabolic equilibrium near normal is called for.

Steroid effect on capillary permeability in gram-negative septic shock. Evaluation by vitreous fluorophotometry.

The purpose of this study was to use vitreous fluorophotometry to evaluate the effects of glucocorticoids on capillary permeability during gram-negative septic shock. Twelve preconditioned mongrel dogs were cannulated with arterial lines and Swan-Ganz catheters for complete hemodynamic monitoring. All 12 dogs were injected with fluorescein and live Escherichia coli intravenously. Six of the 12 dogs were administered methylprednisolone at set intervals after the initiation of the E coli infusion. Vitreous fluorophotometric recordings were taken hourly. Leakage of fluorescein into the extravascular space occurred in both groups, up to several hours after E coli infusion. However, in the steroid group, the capillary permeability decreased and stabilized following the initial increase in permeability. We conclude that steroids, when administered during the development of gram-negative septic shock, may modify capillary permeability changes.

Vitreous fluorophotometry in patients with cone-rod dystrophy.

Eight patients with cone-rod dystrophy were examined by means of vitreous fluorophotometry. The data in three patients with an early stage of retinitis pigmentosa (rod-cone dystrophy) served for comparison. In contrast with the abnormal findings on vitreous fluorophotometry in patients with an early stage of retinitis pigmentosa the value of vitreous fluorophotometry in cone-rod dystrophy was within the normal range in all patients except the two with advanced stages of this disease. Our results suggest that, although both diseases are based on diffuse dystrophy of photoreceptors, and the final stages of the two diseases may show several similar features, the process of breakdown of the blood retinal barrier differs greatly in the two diseases.

Vitreous fluorophotometry in rats with streptozocin-induced diabetes.

Vitreous fluorophotometry (VF) has been used to study the blood-retinal barrier in rats with streptozocin-induced diabetes. Subsequent investigations have shown that many variables other than diabetes influence VF values. With the use of a commercially available fluorophotometer, we assessed VF measurements in diabetic rats while simultaneously measuring other variables, including plasma fluorescein level, free plasma fluorescein level, and blood pH. Mean total plasma fluorescein concentration, mean free plasma fluorescein concentration, and mean midvitreous fluorescein concentration were significantly decreased in diabetic animals. The mean ratio of midvitreous fluorescein concentration to total plasma fluorescein concentration was significantly increased in diabetic animals. In comparison with nondiabetic animals, the diabetic animals showed no significant difference in blood pH or mean ratio of free plasma fluorescein concentration to total plasma fluorescein concentration. Our findings confirm an early derangement of the blood-retinal barrier in diabetic rats.

Effect of vitreous detachment on vitreous fluorophotometry.

Twenty eyes of 17 normal subjects with or without posterior vitreous detachment (PVD) were examined to investigate the influence of various types of PVD on vitreous fluorophotometric readings. Biomicroscopic examinations of the vitreous body were performed with an El Bayadi - Kajiura preset lens, and the findings were classified according to the extent of vitreous detachment and the position of the posterior hyaloid membrane when the eye was stationary. Equivalent fluorescein concentration profiles along various directions in the vitreous cavity were obtained with vitreous fluorophotometry. The degree of PVD significantly affected the measurements. Close to the retina, fluorescein concentrations were significantly higher when the subhyaloid space was sampled than when the vitreous gel was sampled. Our findings have implications for vitreous fluorophotometric assessment of the permeability of the blood-retinal barrier.

Transport of fluorescein in the ocular posterior segment in retinitis pigmentosa.

The function of the blood-retinal barrier was assessed by vitreous fluorophotometry in 12 patients with various genetic types of retinitis pigmentosa and in 11 normal subjects. The measurements were corrected to minimize the effect of artifacts. We evaluated the inward penetration of fluorescein sodium across the blood-retinal barrier and determined the outward permeability coefficient for fluorescein by interpreting the data with a pharmacokinetic computer model. Patients with retinitis pigmentosa had increased inward permeability and decreased outward permeability to fluorescein in comparison with values of normal subjects.

Breakdown of the blood-retinal barriers and cystoid macular edema

After reviewing the definition, incidence and main etiologic factors of cystoid macular edema (CME) the authors analyze the structural and physiologic characteristics of the macular area, including the blood-retinal barriers, and the basic concepts of retinal edema. Personal observations on three different groups of diseases associated with CME, retinitis pigmentosa, pars planitis and aphakia, are presented. CME evaluation was made by slit-lamp microscopy, fluorescein angiography and vitreous fluorophotometry. In the situations examined, the main factors involved in CME formation appear to be a marked increase in blood-retinal-barrier permeability and alterations in retinal tissue compliance.

Photometric oculometry. I. An analysis of the optical principles in slit-lamp fluorophotometry.

The optical principles of slit-lamp fluorophotometry are analysed by aid of a mathematical model of the optical system. The analysis forms the theoretical basis for a slit-lamp technique called photometric oculometry, which makes possible an estimation of intraocular axial distances and axial length. The technique is based on a calculation--by aid of a mathematical model of the eye--of the ratio between intraocular movement of the slit-lamp focal plane and corresponding movement of the slit-lamp. Intraocular axial distances can be calculated by aid of this ratio and a direct measurement of the slit-lamp movement when the focal plane is moved in the optical axis from retina to cornea. These items are prerequisites for a quantitative determination of the blood-retinal barrier permeability to fluorescein during vitreous fluorophotometry.