Sources of error in clinical measurement of the amplitude of accommodation.

Measurement of the amplitude of accommodation is established as a procedure in a routine optometric eye examination. However, clinical methods of measurement of this basic optical function have several sources of error. They are numerous and diverse, and include depth of focus, reaction time, instrument design, specification of the measurement end-point, specification of the reference point of measurement, measurement conditions, consideration of refractive error, and psychological factors. Several of these sources of inaccuracy are composed of multiple sub-sources, and many of the sub-sources influence the common methods of measurement of amplitude of accommodation. Consideration of these sources of measurement error casts doubt on the reliability of the results of measurement, on the validity of established normative values that have been produced using these methods, and on the value of reports of the results of surgery designed to restore accommodation. Clinicians can reduce the effects of some of the sources of error by modifying techniques of measurement with existing methods, but a new method may further improve accuracy.

Identification and quantitation of human amniotic fluid components using capillary zone electrophoresis.

A capillary electrophoresis method was used to measure albumin, immunoglobulin G (IgG), transferrin, and uric acid in 230 amniotic fluid (AF) samples collected at 15.15+/-0.06 weeks gestation. Species were quantified by external calibration using thiamine as internal standard. All major components were detected within 10 min. Migration time reproducibility was 3.0% relative standard deviation (RSD) and normalized peak areas were 12% RSD or better at 190 nm from 81 measurements of a pooled AF sample. The separation profile was not affected by 10h of storage at room temperature or by 10 freeze-thaw cycles, suggesting that frozen AF samples are suitable for protein biomarker studies.

A Review of Depth of Focus in Measurement of the Amplitude of Accommodation.

The aim of this review is to investigate the role of depth of focus (DoF) as a potential confounding variable in the measurement of the amplitude of accommodation (AoA). The role of DoF in human vision is briefly summarised, and it is noted that the prevalent method of measuring AoA is the push-up method. Factors influencing the effect of DoF on the push-up and other methods of measuring AoA are reviewed in detail. DoF is shown to add substantial measurement error in the routine assessment of accommodation when the AoA is measured by methods involving subjective judgement of an object's clarity. Reliable compensation for this source of error is not realistically possible because of the complexity of the aetiology of DoF, and its inter-individual and intra-individual variation. The method of measurement also influences the extent of the error. It is concluded that methods of measurement of AoA that exclude DoF should be preferred.

Accurate myoglobin oxygen saturation by optical spectroscopy measured in blood-perfused rat muscle.

Optical spectra were acquired from myoglobin and hemoglobin solutions and from the tibialis anterior muscle of Sprague-Dawley rats in the visible region (515 to 660 nm). Validation studies were performed on the in vitro spectra to demonstrate that partial least squares analysis of second-derivative spectra yields accurate measurements of myoglobin saturation in the presence of varying hemoglobin concentrations and saturations. When hemoglobin concentrations were varied between 0.25 and 4 times that of myoglobin, myoglobin saturations were measured with a root mean squared error (RMSE) of 4.9% (n = 56) over the full range from 0 to 1. Myoglobin saturations were also shown to be largely unaffected by hemoglobin saturation. RMSE values of only 1.7% (n = 77) were found when hemoglobin saturations were varied independently from myoglobin saturations. These in vitro validation studies represent the most complete and rigorous done to date using partial least squares analysis on myoglobin and hemoglobin spectra. Analysis of reflectance spectra from the rat hind limb yielded accurate measures of volume-averaged myoglobin fractional saturation in the presence of hemoglobin in vivo. Hemodilution showed that myoglobin fractional saturation measurements in the rat leg are not sensitive to changes in hematocrit, thereby confirming the results from solutions in vitro. Decreases in optical density of 11.3 +/- 3.0% (n = 3) were achieved while myoglobin saturation decreased by only 3.1 +/- 3.8%. Myoglobin saturation was significantly increased when the fraction of inspired O(2) was increased, showing that manipulations of myoglobin saturation are detectable and that myoglobin is not fully saturated in resting muscle. Together, these in vitro and in vivo studies show that cellular oxygenation derived from myoglobin fractional saturation can be measured accurately with little cross-talk from hemoglobin in the visible wavelength region, thereby extending optical spectroscopic studies of cellular and vascular oxygenation beyond the near-infrared regions previously studied.

Ultrasonic frequency analysis for estimating pH in albumin-rich biofluids.

Ultrasound is known as a non-invasive imaging modality capable of propagating through highly scattering media such as tissue, blood, and other biological fluids, yet currently provides little chemical information. We have developed a straightforward and rapid methodology for estimating pH in albumin-rich biofluids based on analysis of ultrasonic frequencies. Albumin is the most abundant protein in serum and undergoes conformational changes with pH. It was shown that when ultrasound propagated through albumin solutions, the attenuation of collected ultrasound signals increased with pH. By measuring the ultrasound frequency spectra at several albumin concentrations and pH values, the pH of the solutions could be determined by multilinear regression. Differences in absolute protein content contributed to signal differences in the frequency profiles and were minimized through normalization of each spectrum by the sum of all its frequency intensities. This strategy was applied to human serum samples from multiple donors, for which a multilinear regression model was developed with a coefficient of determination (R(2)) of 0.93 and a standard error of estimate (SEE) of 0.08 pH units. The use of albumin as a pH indicator opens the doors for estimations in other albumin-rich media, such as amniotic fluid and cerebrospinal fluid.

Sources of error in clinical measurement of the amplitude of accommodation / Fuentes de error en la medición clínica de la amplitud de acomodación

Measurement of the amplitude of accommodation is established as a procedure in a routine optometric eye examination. However, clinical methods of measurement of this basic optical function have several sources of error. They are numerous and diverse, and include depth of focus, reaction time, instrument design, specification of the measurement end-point, specification of the reference point of measurement, measurement conditions, consideration of refractive error, and psychological factors. Several of these sources of inaccuracy are composed of multiple sub-sources, and many of the sub-sources influence the common methods of measurement of amplitude of accommodation. Consideration of these sources of measurement error casts doubt on the reliability of the results of measurement, on the validity of established normative values that have been produced using these methods, and on the value of reports of the results of surgery designed to restore accommodation. Clinicians can reduce the effects of some of the sources of error by modifying techniques of measurement with existing methods, but a new method may further improve accuracy

La medición de la amplitud de acomodación se ha establecido como un procedimiento del examen optométrico ocular rutinario. Sin embargo, los métodos clínicos de medición de esta función óptica básica tienen diversas fuentes de error. Estas son numerosas y diversas, e incluyen profundidad de foco, tiempo de reacción, diseño del instrumento, especificación del punto final de la medición, especificación del punto de referencia de la medición, condiciones de la medición, consideración del error refractivo, y factores psicológicos. Algunas de estas fuentes de imprecisión se componen de múltiples sub-fuentes, muchas de las cuales influyen en los métodos comunes de medición de la amplitud de acomodación. La consideración de estas fuentes de error en la medición plantea dudas sobre la fiabilidad de los resultados de dicha medición, la validez de los valores normativos establecidos que se han producido utilizando estos métodos, y el valor de los informes sobre resultados de la cirugía diseñada para restablecer la acomodación. Los clínicos pueden reducir los efectos de algunas de las fuentes de error, modificando las técnicas de medición con ayuda de los métodos existentes, aunque el desarrollo de un nuevo método podría mejorar la precisión

Prediction of gestational diabetes mellitus based on an analysis of amniotic fluid by capillary electrophoresis.

AIM: To detect gestational diabetes mellitus biomarkers in human amniotic fluid collected for age-related genetic testing using capillary electrophoresis and a sophisticated data analysis methodology. MATERIALS & METHODS: Amniotic fluid samples were separated by capillary electrophoresis. Samples were classified using a genetic algorithm with Bayesian benefit function. The best model maximized the sensitivity and specificity and employed a leave-one-out cross-validation strategy. RESULTS: Gestational diabetes mellitus (GDM; n = 14) was distinguished from non-GDM (n = 95) with 86% sensitivity and 99% specificity using two wavelets. These wavelets were located in the unresolved protein region and on the edge of the maternally derived albumin peak. CONCLUSION: GDM is a maternal pathology; however, it was shown that it alters the biochemical profile of amniotic fluid. Testing for GDM is normally carried out at 24-28 weeks, but changes can be detected at 15 weeks gestation, suggesting that GDM onset occurs early in gestation.

Early prediction of macrosomia based on an analysis of second trimester amniotic fluid by capillary electrophoresis.

AIM: To identify, using capillary electrophoresis and chemometrics, early biomarkers in human amniotic fluid of large-for-gestational-age (LGA) infants. MATERIALS & METHODS: Second trimester amniotic fluid samples, obtained from mothers undergoing age-related amniocentesis, were analyzed by capillary electrophoresis. Electropherogram data were aligned using correlation-optimized warping. A genetic algorithm using a Bayesian evaluation function and a leave-one-out cross-validation strategy for two birth outcomes: appropriate-for-gestational-age (AGA) versus LGA infants. RESULTS: LGA (n = 23) was differentiated from AGA (n = 86) with a sensitivity of 100% and a specificity of 98% using only two wavelets. The first wavelet is associated with albumin and the second wavelet with an unknown small molecule. CONCLUSION: The approach developed herein allows LGA fetuses to be metabolically distinguished from AGA fetuses early in pregnancy and indicates that the birth of a LGA infant is already associated with an altered biochemical profile by the second trimester.

Determination of volume fractions in multicomponent mixtures using ultrasound frequency analysis.

Controlling the composition of mixtures is critical for quality control in a wide variety of applications. There is a need for rapid, on-site measurements to optimize processes in real time. Ultrasound easily penetrates opaque samples and containers, yet currently provides minimal chemical information. We have developed a general approach to determine the volume fraction of a liquid in mixtures with multiple components. Ultrasound waves propagating through a medium undergo distortion processes that are characteristic of the chemical bonding composition. The distortion of the waveform can be measured in the ultrasound frequency profile. An ultrasound pulse-through configuration with matching 5 MHz transducers was used to analyze mixtures of water, methanol, and ethanol. Multilinear regression analysis was used to determine the volume fraction of all components in a series of mixtures. Using this technique, volume fractions were determined simultaneously with correlation coefficients (r(2)) greater than 0.98 in two-component mixtures. Determination of volume fractions in three-component mixtures ranging from 65-100% water also showed correlation coefficients of 0.91 for methanol and 0.94 for ethanol. This technique is attractive for process monitoring due to the short measurement time and the simple methodology that excludes sample pretreatment.

Simultaneous determination of alcohol and carbohydrate content in commercial beverages by ultrasound frequency analysis.

Controlling the composition of commercial beverages is critical for quality control. Rapid on-line measurements would allow optimization in real time. We have developed a methodology to monitor the volume fraction of ethanol and the carbohydrate concentrations in liquid mixtures using ultrasound frequency analysis. Characteristic distortion to ultrasound waves propagating through liquids is induced by the specific chemical composition of the mixture. The distortion induced by the hydrogen bonding between water, ethanol, and sucrose can be monitored in the frequency domain using 5 MHz wideband ultrasonic transducers. Multilinear regression was used to quantify both ethanol and sucrose over a wide range of concentrations with correlation coefficients (r(2)) greater than 0.98. Calibrations based on prepared solutions were then used to estimate the ethanol volume and carbohydrate concentration in 22 commercial beverages ranging from sodas to distilled alcohols. Results indicate that the ethanol and carbohydrates could be estimated with a 3.18% and 0.032 g/mL error, respectively. Further, by focusing the analysis over a limited range, the error could be reduced to 0.81% ethanol. This technique demonstrates a strong potential for rapid, in situ monitoring of beverage production, which excludes sample extraction and pretreatment.

Ultrasonic frequency analysis of antibody-linked hydrogel biosensors for rapid point of care testing.

Analyte quantification in highly scattering media such as tissue, blood, and other biological fluids is challenging using conventional spectroscopic methods. Ultrasound easily penetrates these opaque samples, yet currently provides little chemical information. We have developed a general approach for creating hydrogel biosensors based on antibody-linked cellulose polymers. Target recognition induces changes to the sensor stiffness and size, which is accompanied by characteristic changes to a measured ultrasonic frequency profile. Using this technique, nM sensitivity for acetaminophen is demonstrated in a series of biofluids including whole blood, blood plasma, saliva, and urine. Likewise, this methodology is attractive for point of care diagnostics due to the short measurement time, simple methodology which excludes pretreatment of samples, and has minimal chemical or buffer requirements.

Ultrasonic quantification using smart hydrogel sensors.

Analyte quantification in samples with extensive matrix effects can be challenging using conventional analytical techniques. Ultrasound has been shown to easily penetrate samples that can be difficult to measure optically or electrochemically, though it provides little chemical information. Recent ultrasound contrast agents provide highly localized contrast within a sample based on concentration. We have developed a general approach for creating smart biosensors based on molecularly imprinted hydrogel polymers that recognize and bind a target analyte, changing ultrasonic properties with analyte concentration. Multilinear analyte calibration in hydrogel solutions provided quantification of the chosen analyte, theophylline, from 8.4 µM to 6.1 mM with a high degree of linearity (correlation coefficient exceeding 0.99). Simultaneous quantification of both theophylline and of an interfering species, caffeine, was also carried out, providing an avenue for simultaneous analyte analysis with one smart biosensor that can be dispersed and remotely detected.

Fetal exposure to altered amniotic fluid glucose, insulin, and insulin-like growth factor-binding protein 1 occurs before screening for gestational diabetes mellitus.

OBJECTIVE: We explored the possibility that perturbations in amniotic fluid glucose, insulin, and insulin-like growth factor-binding protein 1(IGFBP1) and/or metabolic acids exist before routine screening for GDM. RESEARCH DESIGN AND METHODS: We selected consenting mother-infant pairs (n = 408) who met our inclusion criteria (singleton pregnancy, no genetic abnormalities, and no preexisting diabetes) and for whom sufficient amniotic fluid and appropriate medical information were available. We compared birth outcomes and second trimester amniotic fluid glucose, insulin, IGFBP1 concentrations, and amniotic fluid lactic, ß-hydroxybutyric, and uric acids of mothers with gestational diabetes mellitus (GDM) (n = 52) with those of mothers with no diagnosis of GDM at >24 weeks (n = 356). RESULTS: Higher amniotic fluid glucose, lactic acid, uric acid, and insulin and lower IGFBP1 concentrations were present by 15.1 ± 0.1 weeks in mothers in whom GDM was subsequently diagnosed. However, logistic regression showed that second trimester amniotic fluid glucose, but not insulin, IGFBP1, or metabolic acids was associated with an increased odds ratio (1.2 [95% CI 1.052-1.338]) for diagnosis of GDM at 24-28 weeks. In addition, probability contour maps that accounted for nonlinear relationships among the dynamically changing amniotic fluid constituents showed an increased risk for GDM with elevated second trimester amniotic fluid glucose in combination with either elevated amniotic fluid insulin or low amniotic fluid IGFBP1 CONCLUSIONS: Fetuses are exposed to increased amniotic fluid glucose before 15 weeks of gestation, suggesting that metabolic perturbations are underway before diagnosis and that earlier screening and intervention may be warranted.

Use of near-infrared spectroscopic analysis of second trimester amniotic fluid to assess preterm births.

This pilot study investigated the possibility that metabolomic differences exist in second trimester of women delivering at term (≥37 weeks, n = 216) and preterm (≤35 weeks, n = 11). For this retrospective study, biobanked AF samples underwent near-infrared (NIR) spectral analysis using wavelengths from 700 to 1050 nm. Spectral data was compressed then optimized by multilinear regression to create a calibration model. The resultant model was able to classify term and preterm births based on differing AF metabolomic profiles with a sensitivity and specificity of 100%. When groups were classified using a prematurity index (PI), there was a statistical difference (P < 0.001) between the predicted preterm group (PI 0.77 ± 0.08) and the term group (PI 1.00 ± 0.02). In conclusion, the 2nd trimester AF samples showed distinct differences in metabolomic profiles between patients delivering preterm as compared to those at term in functional groups related to proteins, carbohydrates, fats, polyols, and water.

Near-infrared spectroscopy of blood plasma for diagnosis of sporadic Alzheimer's disease.

There are currently no accepted blood-based biomarkers of sporadic Alzheimer's disease (AD). Augmented oxidative stress has been implicated in both neural and peripheral AD tissues. In this study, we determined whether short-wavelength near-infrared (NIR) spectrophotometry of blood plasma differentiates mild sporadic AD from normal aging. NIR analysis was conducted on 75 microl plasma samples from 19 AD, 27 amnestic MCI, and 17 normal elderly control (NEC) persons using an optical fiber-coupled, holographic grating-based NIR spectrograph. Five spectral bands associated with heme, R-CH, R-OH, H2O, and R-NH functional groups were sensitive to oxidative modification in pre-clinical studies and were pre-selected to develop a logistic regression model for sample classification. This model differentiated AD from NEC samples with a sensitivity of 80% and specificity of 77%. Fifteen and twelve MCI patients were classified with the NEC and AD groups, respectively. The spectra were not influenced by age, gender, exposure to cholinesterase inhibitors or vitamin E, or sample storage time. The NIR data further implicate oxidative stress in the systemic pathophysiology of sporadic AD and differentiate mild (and possibly pre-clinical) AD from NEC individuals with moderate-high accuracy. The procedure is minimally-invasive, rapid, relatively-inexpensive, and may provide a useful biological marker of sporadic AD.

Noninvasive metabolomic profiling of embryo culture media using proton nuclear magnetic resonance correlates with reproductive potential of embryos in women undergoing in vitro fertilization.

OBJECTIVE: To identify biomarkers associated with reproductive outcome using proton nuclear magnetic resonance ((1)H NMR) metabolomic profiling of embryo culture media. DESIGN: Retrospective study. SETTING: An academic assisted reproductive technology (ART) program; a university research center. PATIENT(S): Women undergoing ART treatment. INTERVENTION(S): Spent media samples from embryos that resulted in pregnancy and delivery (n = 17) and samples (n = 17) from embryos that failed to implant were individually collected on day 3, and evaluated using (1)H NMR spectroscopy. The spectra obtained were quantified by integrating six biomarker signals in the aliphatic region after baseline subtraction. Using a multivariate analysis, a model that calculates a viability index for each spectrum was developed. Sensitivity and specificity of predicting pregnancy (described as implantation and delivery) were calculated. MAIN OUTCOME MEASURE(S): The (1)H NMR metabolomic profile of embryo culture media and embryo viability. RESULT(S): Glutamate concentrations determined by (1)H NMR were significantly higher in spent culture media of embryos that resulted in pregnancy and delivery compared to those that failed to implant. Similarly, viability indices calculated by (1)H NMR using the weighted coefficients of glutamate and alanine/lactate ratio quantities were higher for embryos that implanted and resulted in a delivery. Proton NMR spectroscopy predicted viability of individual embryos with a sensitivity of 88.2% and a specificity of 88.2%. CONCLUSION(S): Metabolomic profile of spent embryo culture media using (1)H NMR correlates with the reproductive potential of embryos.

Noninvasive metabolomic profiling of human embryo culture media using Raman spectroscopy predicts embryonic reproductive potential: a prospective blinded pilot study.

OBJECTIVE: To determine if metabolomic profiling of embryonic development was associated with implantation rates in IVF. DESIGN: Prospective blinded. SETTING: University-affiliated assisted reproductive technology program. PATIENT(S): Unselected assisted reproductive technology population. INTERVENTION(S): None. MAIN OUTCOME MEASURE(S): Raman-based biospectroscopic metabolomic profiling of spent culture media and delivery rates. RESULTS: Forty-one spent media samples from 19 patients with known reproductive potential (0 or 100% delivery rates of each embryo that implanted) were evaluated. Raman-based metabolomic profiling was used to calculate a viability index for each sample. On day 3, the spent media of embryos with proven reproductive potential (n = 33) demonstrated higher viability indices (0.875 +/- 0.12) than those that failed to implant (0.56 +/- 0.09). Similar findings were present in spent media from embryos transferred on day 5 (n = 8) (-0.40 +/- -0.21 vs. -0.81 +/- -0.08). Receiver operating characteristic curve analyses were used to select thresholds with the greatest ability to discriminate outcomes. Overall diagnostic accuracy for predicting delivery or a failed implantation was 80.5%. CONCLUSIONS: There is a clear relationship between the reproductive potential of human embryos and their modification of their culture media as detected by Raman biospectroscopy-based metabolomic profiling. This technology offers great potential for development as a tool to allow rapid noninvasive assessment of embryonic reproductive potential before transfer.

Second trimester amniotic fluid transferrin and uric acid predict infant birth outcomes.

OBJECTIVE: To establish whether second trimester amniotic fluid protein and/or uric acid concentrations were associated with and predictive of infant birth weight and/or gestational age. METHODS: Second trimester amniotic fluid samples (n = 230) in mothers undergoing age-related amniocentesis for genetic testing were collected and quantified using capillary zone electrophoresis (CZE) for albumin, IgG, transferrin and uric acid. Maternal characteristics (prepregnancy weight and height, parity, ethnicity, smoking status) and infant birth weight, gestational age and gender were obtained from questionnaires and maternal obstetrical chart review. RESULTS: Preterm infants had higher concentrations of second trimester amniotic fluid transferrin than term infants (P = 0.0215). Transferrin was negatively associated with length of gestation, whereas uric acid was positively associated with the gestational age in spontaneous vaginal delivery (SVD) infants. Uric acid was also a significant predictor of the infant birth weight in grams. CONCLUSION: Second trimester amniotic fluid transferrin and uric acid concentrations are related to subsequent birth outcomes and might emerge as biomarkers of early fetal development.

Spectroscopy of human plasma for diagnosis of idiopathic Parkinson's disease.

BACKGROUND: No established chemical biomarkers of idiopathic Parkinson's disease (PD) currently exist. Augmented oxidative stress (OS) has been implicated in both neural and peripheral PD tissues. METHODS: In this study, Raman scattering and near-infrared spectroscopy were used to detect and quantify oxidative substrate modifications in blood plasma samples from PD and normal elderly control (NEC) subjects. RESULTS: Hypothesis-driven preselection of OS-sensitive bandwidths distinguished PD from NEC subjects with approximately 75% sensitivity and specificity using both complementary spectroscopic techniques. CONCLUSION: Biospectroscopy of plasma may provide a rapid, minimally invasive and inexpensive chemical biomarker of idiopathic PD.

Power law analysis estimates of analyte concentration and particle size in highly scattering granular samples from photon time-of-flight measurements.

Optical measurements of particle size and composition in granular samples are difficult to make due to complex light scattering from particles. These multiple scattering events bias absorption estimates and complicate the calculation of scattering and absorption coefficients used to estimate sample properties. Time series data, such as chromatograms and photon time-of-flight (TOF) profiles, contain self-repeating (fractal) characteristics. Power law analysis of photon TOF profiles allows the determination of absorption coefficients and particle sizes in a single experiment. A correlation dimension algorithm was used on photon TOF data from scattering samples. MLR models were then obtained from correlation dimension plots for the estimation of sample properties. Estimates of particle sizes and absorption coefficients were shown to agree well with theoretical values when compared using independent validation sets. Results show close to a 3-fold and up to a 5-fold decrease in the errors of estimation of dye concentration and particle size, respectively, as compared to steady-state measurements. The power law approach provides a useful means of determining sample properties in highly scattering media.