RESUMEN

BACKGROUND AND OBJECTIVE: Proof of concept for the first system of noninvasive human retinal vessel and tissue oxygenation measurement in axial and radial directions. MATERIALS AND METHODS: A confocal imaging system capable of calculating and mapping relative retinal blood oxygenation in radial and axial directions from three eyes of two healthy subjects was built. The relationship between oxygenation and retinal depth in vivo was analyzed to illustrate application of this novel system. RESULTS: The system shows capacity for measuring oxygenation along retinal depth for the first time. (1) Arteriovenous oxygenation difference decreases with blood vessel diameter. (2) Artery-tissue oxygenation difference is greater than vein-tissue oxygenation difference in the same region. (3) Intravascular-extravascular oxygenation difference decreases with blood vessel diameter. (4) Oxygenation data reported with a 95% CI are as follows: A1 91.5% ± 18.2%, V1 32.8% ± 18.6%, A2 97.3% ± 17.8%, V2 64.4% ± 11.2%, A3 73.2% ± 19.1%, V3 52.9% ± 15.3%, and Tissue 56.6% ± 00.4%. CONCLUSION: This article demonstrates proof of concept for retinal oxygenation calculation in radial and axial dimensions for the first time. Initial results provide biological validity to this method. Future aims include further characterization of this system's results in healthy subjects and subsequent comparison of oxygenation between diseased and healthy retinae. [Ophthalmic Surg Lasers Imaging Retina. 2022;53:275-283.].

Asunto(s)

Asunto(s)

RESUMEN

PURPOSE: To determine the retinal oxygen saturation trend with onset of diabetes and increasing severity of diabetic retinopathy by comparing diabetic groups with and without retinopathy to controls. METHODS: A fundus camera-based dual-wavelength snapshot oximeter imaged retinas of healthy subjects and patients with and without diabetic retinopathy. The images were analyzed to determine oxygen saturation in major retinal arteries and veins, which is inversely proportional to optical density ratio. RESULTS: Control retinal oxygen saturation (n = 14) in arteries was 92.3 ± 4.2% and in veins, 57.2 ± 6.0%. Retinal oxygen saturation for diabetic patients with no signs of diabetic retinopathy (NDR, n = 45) in arteries was 96.3 ± 8.6% (P = 0.662) and in veins, 58.7 ± 7.5% (P = 0.998). Retinal oxygen saturation for diabetics with mild to moderate nonproliferative diabetic retinopathy (NPDR, n = 23) in arteries was 97.7 ± 5.8% (P = 0.590) and in veins, 61.1 ± 7.6% (P = 0.658). Retinal oxygen saturation for diabetics with severe NPDR (n = 12) in arteries was 102 ± 10.2% (P = 0.023) and in veins, 66.8 ± 8.4% (P < 0.001). Retinal oxygen saturation for patients with proliferative diabetic retinopathy (PDR, n = 13) in arteries was 103.6 ± 8.7% (P = 0.003) and in veins, 66.6 ± 10.2% (P = 0.026). Retinal oxygen saturation for all diabetics with retinopathy combined (all DR, n = 48) in arteries was 100.4 ± 7.6% (P = 0.004) and in veins, 64.2 ± 8.4% (P = 0.007). CONCLUSIONS: A trend of increasing retinal oxygen saturation was found from controls to NDR group to increasing levels of diabetic retinopathy, though significance was only reached for the comparison of controls to severe-NPDR, PDR, and all-DR groups.

Asunto(s)

RESUMEN

PURPOSE: Hypoxia of the retina and optic nerve head (ONH) is believed to be pivotal in the development of ocular vascular disorders, including diabetic macular edema (DME). Glucocorticoids are among the most effective agents for the treatment of back of the eye diseases. However, this class of compounds is highly liable to increase intraocular pressure (IOP) and does not improve ocular perfusion or tissue oxygenation. Nitric oxide (NO) has vasodilating properties and lowers IOP in experimental models and humans, suggesting that its properties might complement those of glucocorticoids. NCX 434 is an NO-donating triamcinolone acetonide (TA) that is less likely to increase IOP while targeting both the vascular and inflammatory components of DME. METHODS: NCX 434 was studied in vitro with respect to its NO-releasing properties in isolated methoxamine-precontracted rabbit aortic rings and glucocorticoid-like activity in recombinant human glucocorticoid receptors. IOP and oxygen saturation in the ONH and overlaying arteries and veins were studied in the anesthetized cynomolgus monkey. Measurements were taken using, respectively, an applanation tonometer and a hyperspectral imaging system before and 7, 14, 21, 31 and 41 days after the intravitreal injection of NCX 434 (5.8 mg/eye) or TA equimolar doses (4.0 mg/eye). RESULTS: NCX 434 inhibited (3)H-dexamethasone-specific binding (IC(50)=34±5 nM) on human glucocorticoid receptors and elicited NO-dependent aortic ring relaxation (EC(50) of 0.5±0.1 µM, E(max) 98.9%). In monkey eyes, NCX 434 enhanced, whereas TA did not, oxygen saturation in various ONH areas (*P<0.05 vs. basal), decreased it in veins, and did not affect it in the overlaying arteries. Neither NCX 434 nor TA altered IOP significantly at all time points. However, at 31 days post-treatment TA appeared to start increasing IOP (Δ(IOP)=+3.31±0.51 mmHg, 30.8%, over baseline, NS). CONCLUSIONS: NCX 434 enhances ocular tissue oxygenation. This feature appears to depend on its NO-donating properties; thus, the compound deserves to be further investigated for the treatment of DME and other ocular disorders with impaired ocular perfusion.

Asunto(s)

RESUMEN

This paper presents an automated method to identify arteries and veins in dual-wavelength retinal fundus images recorded at 570 and 600 nm. Dual-wavelength imaging provides both structural and functional features that can be exploited for identification. The processing begins with automated tracing of the vessels from the 570-nm image. The 600-nm image is registered to this image, and structural and functional features are computed for each vessel segment. We use the relative strength of the vessel central reflex as the structural feature. The central reflex phenomenon, caused by light reflection from vessel surfaces that are parallel to the incident light, is especially pronounced at longer wavelengths for arteries compared to veins. We use a dual-Gaussian to model the cross-sectional intensity profile of vessels. The model parameters are estimated using a robust M-estimator, and the relative strength of the central reflex is computed from these parameters. The functional feature exploits the fact that arterial blood is more oxygenated relative to that in veins. This motivates use of the ratio of the vessel optical densities (ODs) from images at oxygen-sensitive and oxygen-insensitive wavelengths (ODR = OD600/OD570) as a functional indicator. Finally, the structural and functional features are combined in a classifier to identify the type of the vessel. We experimented with four different classifiers and the best result was given by a support vector machine (SVM) classifier. With the SVM classifier, the proposed algorithm achieved true positive rates of 97% for the arteries and 90% for the veins, when applied to a set of 251 vessel segments obtained from 25 dual wavelength images. The ability to identify the vessel type is useful in applications such as automated retinal vessel oximetry and automated analysis of vascular changes without manual intervention.

Asunto(s)

RESUMEN

PURPOSE: A method is presented for the calculation and visualization of percent blood oxygen saturation from specific tissue structures in hyperspectral images of the optic nerve head (ONH). METHODS: Trans-pupillary images of the primate optic nerve head and overlying retinal blood vessels were obtained with a hyperspectral imaging (HSI) system attached to a fundus camera. Images were recorded during normal blood flow and after partially interrupting flow to the ONH and retinal circulation by elevation of the intraocular pressure (IOP) from 10 mmHg to 55 mmHg in steps. Percent oxygen saturation was calculated from groups of pixels associated with separate tissue structures, using a linear least-squares curve fit of the recorded hemoglobin spectrum to reference spectra obtained from fully oxygenated and deoxygenated red cell suspensions. Color maps of saturation were obtained from a new algorithm that enables comparison of oxygen saturation from large vessels and tissue areas in hyperspectral images. RESULTS: Percent saturation in retinal vessels and from the average over ONH structures (IOP = 10 mmHg) was (mean +/- SE): artery 81.8 +/- 0.4%, vein 42.6 +/- 0.9%, average ONH 68.3 +/- 0.4%. Raising IOP from 10 mmHg to 55 mmHg for 5 min caused blood oxygen saturation to decrease (mean +/- SE): artery 46.1 +/- 6.2%, vein 36.1 +/- 1.6%, average ONH 41.9 +/- 1.6%. The temporal cup showed the highest saturation at low and high IOP (77.3 +/- 1.0% and 60.1 +/- 4.0%) and the least reduction in saturation at high IOP (22.3%) compared with that of the average ONH (38.6%). A linear relationship was found between saturation indices obtained from the algorithm and percent saturation values obtained by spectral curve fits to calibrated red cell samples. CONCLUSIONS: Percent oxygen saturation was determined from hyperspectral images of the ONH tissue and retinal vessels overlying the ONH at normal and elevated IOP. Pressure elevation was shown to reduce blood oxygen saturation in vessels and ONH structures, with the smallest reduction in the ONH observed in the temporal cup. IOP-induced saturation changes were visualized in color maps using an algorithm that follows saturation-dependent changes in the blood spectrum and blood volume differences across tissue. Reduced arterial saturation at high IOP may have resulted from a flow-dependent mechanism.

Asunto(s)

RESUMEN

We present an automated method to perform accurate, rapid, and objective measurement of the blood oxygen saturation over each segment of the retinal vascular hierarchy from dual-wavelength fundus images. Its speed and automation (2 s per entire image versus 20 s per segment for manual methods) enables detailed level-by-level measurements over wider areas. An automated tracing algorithm is used to estimate vessel centerlines, thickness, directions, and locations of landmarks such as bifurcations and crossover points. The hierarchical structure of the vascular network is recovered from the trace fragments and landmarks by a novel algorithm. Optical densities (OD) are measured from vascular segments using the minimum reflected intensities inside and outside the vessel. The OD ratio (ODR=OD600/OD570) bears an inverse relationship to systemic HbO2 saturation (SO2). The sensitivity for detecting saturation change when breathing air versus pure oxygen was calculated from the measurements made on six subjects and was found to be 0.0226 ODR units, which is in good agreement with previous manual measurements by the dual-wavelength technique, indicating the validity of the automation. A fully automated system for retinal vessel oximetry would prove useful to achieve early assessments of risk for progression of disease conditions associated with oxygen utilization.

Asunto(s)

RESUMEN

PURPOSE: To evaluate a hyperspectral imaging technique for monitoring relative spatial changes in retinal oxygen saturation. METHODS: The optic nerve head (ONH) and overlying vessels in cynomolgus monkey eyes were imaged with a fundus camera attached to a hyperspectral imaging system. Images were acquired with inspiration of room air and pure oxygen and at controlled intraocular pressures (IOP) of 15 mm Hg (normal) and 60 mm Hg (sustained for up to 5 minutes). Changes in relative blood oxygen saturation in the vessels and ONH were assessed from reflectance spectra. Saturation maps were derived from contributions of oxygenated and deoxygenated hemoglobin spectral signatures extracted from hyperspectral images. The results obtained with hyperspectral imaging were compared with known experimental outcomes. RESULTS: Pure oxygen markedly increased oxygen saturation in veins. Increases in arteries and the ONH were smaller. The results obtained with hyperspectral image analysis agreed with known changes in oxygen saturation from breathing experiments. Raising IOP reduced saturation in all structures and resulted in profound desaturation of arteries. During sustained high IOP, a rebound in saturation was observed in the ONH. Spatial maps clearly showed the saturation changes in arteries, veins, and surrounding tissues. CONCLUSIONS: Hyperspectral imaging can be adapted to measure and map relative oxygen saturation in retinal structures and the ONH in nonhuman primate eyes.

Asunto(s)

RESUMEN

BACKGROUND AND OBJECTIVE: The goal of this study was to quantify retinal hemodynamics using the freeze-frame technique for determining volumetric retinal blood flow. MATERIALS AND METHODS: Leukocytes and erythrocytes were removed from the circulation of rats, stained with fluorescent dyes, returned to the animals' circulation, and excited to fluorescence using the scanning laser ophthalmoscope. The retinal circulation was videotaped and viewed frame-by-frame to count the total number of visible stained cells passing through the field of view during a known period of time while excluding repeated appearances of cells in multiple frames. The total number of cells visualized, in conjunction with cell density data collected in a coincident in vitro study, was used to calculate in vivo volumetric blood flow for both cell types. RESULTS: Measurements of volumetric blood flow based on fluorescent leukocytes (34.2 +/- 5.9 nL/sec [mean +/- standard deviation]; n = 30 rats) and fluorescent erythrocytes (35.1 +/- 6.1 nL/sec; n = 30 rats) were not significantly different, indicating that the freeze-frame technique provides a blood flow measurement independent of cell type. Repeated blood flow measurements obtained from an individual rat over time showed little difference (P < .0001), demonstrating the reproducibility of the technique. CONCLUSIONS: The freeze-frame technique offers a promising method for calculating volumetric blood flow independent of individual cell velocity, size, or type.

Asunto(s)

RESUMEN

OBJECTIVE: To investigate the use of the photosensitizer hypocrellin A as a photodynamic agent to occlude the choriocapillaris in the eyes of pigmented rabbits. METHODS: Hypocrellin A (500 microg/kg) incorporated into liposomes was injected intravenously in pigmented rabbits. Ten to 15 minutes later, the retinas were irradiated with a dye laser (spot size, 2 mm; 10-60 mW; 10-60 seconds; fluences 3.2 to 95.5 J/cm2) at two wavelengths: yellow (568 nm) and red (647 nm). Fluorescein angiography was performed 2 and 24 hours later. Parallel controls were irradiated without a photosensitizer. Histology was performed immediately after the 24-hour angiogram. observed 24 hours after PDT in eyes subjected to yellow laser irradiation at 20 mW for 60 seconds (fluence, 38.2 J/cm2) and at higher powers for lesser durations: 30 mW for 40 seconds (fluence, 38.2 J/cm2), 40 mW for 20 seconds (fluence, 25.4 J/cm2), and 50 and 60 mW for 10 seconds (fluences, 15.9 and 19.1 J/cm2, respectively). Light microscopy showed occlusion of the choriocapillaris in all eyes with angiographic responses. Control eyes and eyes irradiated with the red laser revealed no angiographic or histologic changes. CONCLUSION: Photodynamic therapy using liposomal hypocrellin A and the yellow laser of 568 nm was effective in occluding the choriocapillaris of pigmented rabbits.

Asunto(s)