Potential measurement error from vessel reflex and multiple light paths in dual-wavelength retinal oximetry.

PURPOSE: This study aims to characterize the dependence of measured retinal arterial and venous saturation on vessel diameter and central reflex in retinal oximetry, with an ultimate goal of identifying potential causes and suggesting approaches to improve measurement accuracy. METHODS: In 10 subjects, oxygen saturation, vessel diameter and optical density are obtained using Oxymap Analyzer software without diameter correction. Diameter dependence of saturation is characterized using linear regression between measured values of saturation and diameter. Occurrences of negative values of vessel optical densities (ODs) associated with central vessel reflex are acquired from Oxymap Analyzer. A conceptual model is used to calculate the ratio of optical densities (ODRs) according to retinal reflectance properties and single and double-pass light transmission across fixed path lengths. Model-predicted values are compared with measured oximetry values at different vessel diameters. RESULTS: Venous saturation shows an inverse relationship with vessel diameter (D) across subjects, with a mean slope of -0.180 (SE = 0.022) %/µm (20 < D < 180 µm) and a more rapid saturation increase at small vessel diameters reaching to over 80%. Arterial saturation yields smaller positive and negative slopes in individual subjects, with an average of -0.007 (SE = 0.021) %/µm (20 < D < 200 µm) across all subjects. Measurements where vessel brightness exceeds that of the retinal background result in negative values of optical density, causing an artifactual increase in saturation. Optimization of model reflectance values produces a good fit of the conceptual model to measured ODRs. CONCLUSION: Measurement artefacts in retinal oximetry are caused by strong central vessel reflections, and apparent diameter sensitivity may result from single and double-pass transmission in vessels. Improvement in correction for vessel diameter is indicated for arteries however further study is necessary for venous corrections.

Real-time dynamic single-molecule protein sequencing on an integrated semiconductor device.

Studies of the proteome would benefit greatly from methods to directly sequence and digitally quantify proteins and detect posttranslational modifications with single-molecule sensitivity. Here, we demonstrate single-molecule protein sequencing using a dynamic approach in which single peptides are probed in real time by a mixture of dye-labeled N-terminal amino acid recognizers and simultaneously cleaved by aminopeptidases. We annotate amino acids and identify the peptide sequence by measuring fluorescence intensity, lifetime, and binding kinetics on an integrated semiconductor chip. Our results demonstrate the kinetic principles that allow recognizers to identify multiple amino acids in an information-rich manner that enables discrimination of single amino acid substitutions and posttranslational modifications. With further development, we anticipate that this approach will offer a sensitive, scalable, and accessible platform for single-molecule proteomic studies and applications.

Topical Review: Studies of Ocular Function and Disease Using Hyperspectral Imaging.

SIGNIFICANCE: Advances in imaging technology over the last two decades have produced significant innovations in medical imaging. Hyperspectral imaging (HSI) is one of these innovations, enabling powerful new imaging tools for clinical use and greater understanding of tissue optical properties and mechanisms underlying eye disease.Hyperspectral imaging is an important and rapidly growing area in medical imaging, making possible the concurrent collection of spectroscopic and spatial information that is usually obtained from separate optical recordings. In this review, we describe several mainstream techniques used in HSI, along with noteworthy advances in optical technology that enabled modern HSI techniques. Presented also are recent applications of HSI for basic and applied eye research, which include a novel method for assessing dry eye syndrome, clinical slit-lamp examination of corneal injury, measurement of blood oxygen saturation in retinal disease, molecular changes in macular degeneration, and detection of early stages of Alzheimer disease. The review also highlights work resulting from integration of HSI with other imaging tools such as optical coherence tomography and autofluorescence microscopy and discusses the adaptation of HSI for clinical work where eye motion is present. Here, we present the background and main findings from each of these reports along with specific references for additional details.

Effect of Molecular Weight of Methylphenylsiloxy-Containing Vinyl-Functionalized Terpolysiloxanes on Their UV-Activated Crosslinking by Hydrosilylation and Mechanical Properties of Crosslinked Elastomers.

Effects of molecular weight of methylphenyl-containing vinylsiloxy-functionalized terpolysiloxanes on their UV-activated crosslinking by hydrosilylation at room temperature in air, shelf life stability of "all-in-one" pastes prepared from them for additive manufacturing, and mechanical properties of the resulting crosslinked elastomers, are investigated. It is found that while rheology of pastes containing base polymers, trimethylsilylated silica fillers, and thixotropic additives is not significantly affected by the base polymer molecular weight but is dominated by the filler concentration, the pastes based on higher molecular weight polymers exhibit faster crosslinking (corresponding to higher catalyst turnover numbers) and their crosslinked elastomers show transient strain-induced crystallization. The latter appears in networks from terpolymers with degrees of polymerization (DP) of 240 and above (corresponding to about one half of the critical polydimethylsiloxane chain length for entanglement formation of DP = 460), within the temperature range of -80 to -30 °C, characteristic for polydimethylsiloxane melting transition. It is believed that this is the first time an observation of this chain length effect is reported for polysiloxane elastomers and that the properties reported herein can be expected to have major implications on the application potential of these polymers in both additive manufacturing and performance of their elastomers at sub-ambient temperatures.

In Vivo Assessment of Retinal Biomarkers by Hyperspectral Imaging: Early Detection of Alzheimer's Disease.

A noninvasive and cost-effective means to detect preclinical Alzheimer's disease (AD) and monitor disease progression would be invaluable. The retina is a developmental extension of the brain and has been viewed as a window to evaluate AD-related pathology. Cross-sectional studies have shown structural changes in the retina of AD patients that include thinning of the retinal nerve-fiber layer and changes in retinal vasculature. However, such changes do not manifest in early stages of the disease nor are they specific biomarkers for AD. Described herein is the utilization of our retinal hyperspectral imaging (rHSI) technique as a biomarker for identification of AD-related early pathological changes in the retina. Specifically, this account concerns the translation of our rHSI technique from animal models to human AD subjects. The underlying principle is Rayleigh light scattering, which is expected from low-order Aß aggregates present in early pathology. Recruitment was restricted to AD subjects (N = 19) and age-matched controls, with no family history of AD (N = 16). To limit the influence of skin pigmentation, subjects were restricted to those with skin pigmentation values of 2-3 on the Fitzpatrick scale. The largest spectral deviation from control subjects, rHSI signature, was obtained at the MCI stage with MMSE scores ⩾22, suggesting higher sensitivity of this technique in early disease stages. The rHSI signature observed is unaffected by eye pathologies such as glaucoma and cataract. Age of the subjects minimally influenced the spectral signatures. The rHSI technique shows promise for detection of preclinical AD; it is conducted in a truly noninvasive manner, without application of an exogenous label, and is thus potentially suitable for population screening.

Development/verification of methods for measurement of exhaled breath and environmental e-vapor product aerosol.

Concerns have been raised about the potential health effects of potential bystander exposure to exhaled aerosols from e-vapor products (EVPs). An exhaled breath collection system (EBS) was developed and analytical methods were verified for collection and analysis of exhaled breath from users of EVPs. Analytical methods were adapted and verified for collection of environmental air samples during EVP use in an exposure chamber. Analysis of constituents in exhaled breath focused on nicotine, propylene glycol, and glycerin (because these are reported as the major constituents in EVPs) and selected carbonyl compounds (acetaldehyde, acrolein, and formaldehyde). Analysis of environmental samples included nicotine, propylene glycol, glycerin, 12 volatile organic compounds (VOCs), 15 carbonyl compounds and 4 metals. The EBS and analytical methods used were found to be suitable for collection and analysis of the target constituents in exhaled breath. Environmental sampling for background levels of VOCs and carbonyl compounds found only acetone, acetaldehyde, benzene, ethylbenzene, formaldehyde, isoprene, methyl ethyl ketone, hexaldehyde, propionaldehyde, and toluene above the limit of quantification in some samples. None of the targeted metals were detected. Background levels of VOCs and carbonyl compounds were consistent with levels previously reported for ambient air.

Cerium oxide nanoparticles: a 'radical' approach to neurodegenerative disease treatment.

Despite advances in understanding the factors that cause many neurodegenerative diseases (NDs), no current therapies have yielded significant results. Cerium oxide nanoparticles (CeONPs) have recently emerged as therapeutics for the treatment of NDs due to their antioxidant properties. This report summarizes the recent findings regarding CeONPs in treatment of various NDs, including Alzheimer's disease, Parkinson's disease, multiple sclerosis, ischemic stroke and amyotrophic lateral sclerosis. Interest in CeONPs as a potential nanomedicine for NDs has increased due to: their ability to alter signaling pathways, small diameter allowing passage through the blood-brain barrier and scavenging of reactive oxygen species. Due to these properties, CeONPs could eventually revolutionize existing treatments for NDs.

Early Detection of Amyloidopathy in Alzheimer's Mice by Hyperspectral Endoscopy.

PURPOSE: To describe a spectral imaging system for small animal studies based on noninvasive endoscopy of the retina, and to present time-resolved spectral changes from live Alzheimer's mice prior to cognitive decline, corroborating our previous in vitro findings. METHODS: Topical endoscope fundus imaging was modified to use a machine vision camera and tunable wavelength system for acquiring monochromatic images across the visible to near-infrared spectral range. Alzheimer's APP/PS1 mice and age-matched, wild-type mice were imaged monthly from months 3 through 8 to assess changes in the fundus reflection spectrum. Optical changes were fit to Rayleigh light scatter models as measures of amyloid aggregation. RESULTS: Good quality spectral images of the central retina were obtained. Short-wavelength reflectance from Alzheimer's mice retinae showed significant reduction over time compared to wild-type mice. Optical changes were consistent with an increase in Rayleigh light scattering in neural retina due to soluble Aß1-42 aggregates. The changes in light scatter showed a monotonic increase in soluble amyloid aggregates over a 6-month period, with significant build up occurring at 7 months. CONCLUSIONS: Hyperspectral imaging technique can be brought inexpensively to the study of retinal changes caused by Alzheimer's disease progression in live small animals. A similar previous finding of reduction in the light reflection over a range of wavelengths in isolated Alzheimer's mice retinae, was reproducible in the living Alzheimer's mice. The technique presented here has a potential for development as an early Alzheimer's retinal diagnostic test in humans, which will support the treatment outcome.

Hyperspectral interferometry: Sizing microscale surface features in the pine bark beetle.

A new method of interferometry employing a Fabry-Perot etalon model was used to locate and size microscale features on the surface of the pine bark beetle. Oscillations in the reflected light spectrum, caused by self-interference of light reflecting from surfaces of foreleg setae and spores on the elytrum, were recorded using white light hyperspectral microscopy. By making the assumption that pairs of reflecting surfaces produce an etalon effect, the distance between surfaces could be determined from the oscillation frequency. Low frequencies of less than 0.08 nm(-1) were observed in the spectrum below 700 nm while higher frequencies generally occupied wavelengths from 600 to 850 nm. In many cases, two frequencies appeared separately or in combination across the spectrum. The etalon model gave a mean spore size of 3.04 ± 1.27 µm and a seta diameter of 5.44 ± 2.88 µm. The tapering near the setae tip was detected as a lowering of frequency. Spatial fringes were observed together with spectral oscillations from surfaces on the exoskeleton at higher magnification. These signals were consistent with embedded multi-layer reflecting surfaces. Possible applications for hyperspectral interferometry include medical imaging, detection of spore loads in insects and other fungal carriers, wafer surface and subsurface inspection, nanoscale materials, biological surface analysis, and spectroscopy calibration. This is, to our knowledge, the first report of oscillations directly observed by microscopy in the reflected light spectra from Coleoptera, and the first demonstration of broadband hyperspectral interferometry using microscopy that does not employ an internal interferometer.

Pathway to Retinal Oximetry.

Events and discoveries in oxygen monitoring over the past two centuries are presented as the background from which oximetry of the human retina evolved. Achievements and the people behind them are discussed, showing parallels between the work in tissue measurements and later in the eye. Developments in the two-wavelength technique for oxygen saturation measurements in retinal vessels are shown to exploit the forms of imaging technology available over time. The last section provides a short summary of the recent research in retinal diseases using vessel oximetry.

Clinical value of a patient-reported goal-attainment measure: the global development of self-assessment goal achievement (SAGA) questionnaire for patients with lower urinary tract symptoms.

AIMS: To discuss the importance of patients' treatment goals and perceived goal attainment to better address expectations in the treatment of lower urinary tract symptoms (LUTS), including overactive bladder (OAB). METHODS: The development of the Self-Assessment Goal Achievement (SAGA) questionnaire was driven by measurement principles from the field of qualitative and psychometric research adapted to elicit patients' treatment goals. At baseline, SAGA solicits individualized responses of patient's treatment expectations and goals, and at follow-up SAGA uses a goal-attainment scale (GAS) to document goal achievement. RESULTS: The SAGA questionnaire provides a basis for the patient and physician to discuss realistic treatment expectations and to measure the alignment between patients' expectations and treatment outcomes in terms of improvement in symptoms and impact on function. Therefore, incorporating the SAGA questionnaire into clinical trials may provide an additional dimension of treatment efficacy by incorporating data on treatment satisfaction from the patient's perspective. CONCLUSIONS: The SAGA questionnaire is a useful tool for patient-centered discussions about the treatment and management of LUTS, including OAB, and assisting physicians in tracking progress and managing patient expectations during therapy.

Retinal arterial and venous oxygen saturation is altered in diabetic patients.

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.

RCN4GSC Meeting Report: Initiating a Testbed for Managing Data at the Interface of Biodiversity and Genomics/Metagenomics, May 2011.

Following up on efforts from two earlier workshops, a meeting was convened in San Diego to (a) establish working connections between experts in the use of the Darwin Core and the GSC MIxS standards, (b) conduct mutual briefings to promote knowledge exchange and to increase the understanding of the two communities' approaches, constraints, community goals, subtleties, etc., (c) perform an element-by-element comparison of the two standards, assessing the compatibility and complementarity of the two approaches, (d) propose and consider possible use cases and test beds in which a joint annotation approach might be tried, to useful scientific effect, and (e) propose additional action items necessary to continue the development of this joint effort. Several focused working teams were identified to continue the work after the meeting ended.

Goal attainment scaling in patients with lower urinary tract symptoms: development and pilot testing of the Self-Assessment Goal Achievement (SAGA) questionnaire.

INTRODUCTION AND HYPOTHESIS: The Self-Assessment Goal Achievement (SAGA) questionnaire was developed to identify treatment goals and assess goal-achievement in patients with lower urinary tract symptoms (LUTS). METHODS: This study consisted of (1) gathering information on goal setting/attainment concepts, (2) goal elicitation (n = 41 patients with LUTS), (3) cognitive debriefing of draft questionnaire (n = 11), and (4) pilot testing (n = 104). RESULTS: SAGA consists of baseline (goal-assessment; ranking) and follow-up (goal-achievement) modules. In addition to goals most frequently mentioned, patients can list up to five open goals. Goals most commonly reported as "very important" in pilot testing included reducing urgency (72%), incontinence (65%), and nocturia (64%). Treatment goals spontaneously reported as "very important" were reducing incontinence (45%), nocturia (40%), and frequency (26%). CONCLUSIONS: SAGA may be used to identify treatment goals and assess goal-achievement in patients with LUTS in the clinic and for research (with additional validation). This information may promote patient-physician interaction and help patients establish realistic treatment goals, which may in turn improve treatment adherence and outcomes.

Glaucoma filtration surgery and retinal oxygen saturation.

PURPOSE: Glaucoma may involve disturbances in retinal oxygenation and blood flow. The purpose of this study was to measure the effect of glaucoma filtration surgery on retinal vessel oxygen saturation. METHODS: A noninvasive spectrophotometric retinal oximeter was used to measure hemoglobin oxygen saturation in retinal arterioles and venules before and after glaucoma filtration surgery. Twenty-five consecutive patients were recruited, and 19 had adequate image quality. Fourteen underwent trabeculectomy and five glaucoma tube surgery. Twelve had primary open-angle glaucoma and seven had exfoliative glaucoma. IOP decreased from 23 +/- 7 to 10 +/- 4 mm Hg (mean +/- SD, P = 0.0001). RESULTS: Oxygen saturation increased in retinal arterioles from 97% +/- 4% to 99% +/- 6% (n = 19; P = 0.046) after surgery and was unchanged in venules (63% +/- 5% before surgery and 64% +/- 6% after, P = 0.76). There were no significant changes in saturation in the fellow eyes (P > 0.60). The arteriovenous difference was 34% before and 36% after surgery (P = 0.35). CONCLUSIONS: Glaucoma filtration surgery had almost no effect on retinal vessel oxygen saturation.

Oxygen saturation in human retinal vessels is higher in dark than in light.

PURPOSE: Animal studies have indicated that retinal oxygen consumption is greater in dark than light. In this study, oxygen saturation is measured in retinal vessels of healthy humans during dark and light. METHODS: The oximeter consists of a fundus camera, a beam splitter, a digital camera and software, which calculates hemoglobin oxygen saturation in the retinal vessels. In the first experiment, 18 healthy individuals underwent oximetry measurements after 30 minutes in the dark, followed by alternating 5-minute periods of white light (80 cd/m(2)) and dark. In the second experiment, 23 volunteers underwent oximetry measurements after 30 minutes in the dark, followed by light at 1, 10, and 100 cd/m(2). Three subjects were excluded from analysis in the first experiment and four in the second experiment because of poor image quality. RESULTS: In the first experiment, the arteriolar saturation decreased from 92% +/- 4% (n = 15; mean +/- SD) after 30 minutes in the dark to 89% +/- 5% after 5 minutes in the light (P = 0.008). Corresponding numbers for venules are 60% +/- 5% in the dark and 55% +/- 10% (P = 0.020) in the light. In the second experiment, the arteriolar saturation was 92% +/- 4% in the dark and 88% +/- 7% in 100 cd/m(2) light (n = 19, P = 0.012). The corresponding values for venules were 59% +/- 9% in the dark and 55% +/- 10% in 100 cd/m(2) light (P = 0.065). CONCLUSIONS: Oxygen saturation in retinal blood vessels is higher in dark than in 80 or 100 cd/m(2) light in human retinal arterioles and venules. The authors propose that this is a consequence of increased oxygen demand in the outer retina in the dark.

Improved detection of the central reflex in retinal vessels using a generalized dual-gaussian model and robust hypothesis testing.

This updates an earlier publication by the authors describing a robust framework for detecting vasculature in noisy retinal fundus images. We improved the handling of the "central reflex" phenomenon in which a vessel has a "hollow" appearance. This is particularly pronounced in dual-wavelength images acquired at 570 and 600 nm for retinal oximetry. It is prominent in the 600 nm images that are sensitive to the blood oxygen content. Improved segmentation of these vessels is needed to improve oximetry. We show that the use of a generalized dual-Gaussian model for the vessel intensity profile instead of the Gaussian yields a significant improvement. Our method can account for variations in the strength of the central reflex, the relative contrast, width, orientation, scale, and imaging noise. It also enables the classification of regular and central reflex vessels. The proposed method yielded a sensitivity of 72% compared to 38% by the algorithm of Can et al., and 60% by the robust detection based on a single-Gaussian model. The specificity for the methods were 95%, 97%, and 98%, respectively.

Use of hyperspectral imaging to distinguish normal, precancerous, and cancerous cells.

BACKGROUND: The objective of the current study was to test the hypothesis that the cytologic diagnosis of cancer cells can be enhanced by the technique of hyperspectral imaging (HSI). METHODS: As a proof of principle, HSI was employed to obtain hyperspectrum from a normal human fibroblast, as well as its telomerase-immortalized and SV40-transformed derivatives. Novel algorithms were developed to differentiate among these cell models based on spectral and spatial differences. Using the same technique with modified algorithms, the authors were able to differentiate among normal and precancerous (low-grade [LG] and high-grade [HG]) cervical cells and squamous cell carcinoma (SCC) on liquid-based Papanicolaou (Pap) test slides. RESULTS: The specificity for identifying normal fibroblast cell type based on spatial and spectral algorithms was 74.2%. The sensitivity for identifying telomerase-immortalized and SV40-transformed cells was 100% and 90.3%, respectively. The system identified normal cervical cells with a specificity of 95.8%. With regard to LG precancerous cells and HG precancerous cells, the sensitivity was 66.7% and 93.5%, respectively. The sensitivity detected for SCC was 98.6%. CONCLUSIONS: HSI can be utilized in prescreening liquid-based Pap test slides to improve efficiency in Pap test diagnoses with the goal of ultimately reducing the mortality from cervical cancer while reducing health care costs.

Automatic identification of retinal arteries and veins from dual-wavelength images using structural and functional features.

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.

Oxygen saturation in optic nerve head structures by hyperspectral image analysis.

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.