Electric field can be a viable method in controlling various combustion properties. Comparing to traditional actuators, an application of electric field requires very small power consumption. Especially, alternating current (AC) has received attention recently, since it could modulate flames appreciably even for the cases when direct current (DC) has minimal effects. In this study, the effect of AC electric fields on small coflow diffusion flames is focused with applications of various laser diagnostic techniques. Flow characteristics of baseline diffusion flames, which corresponds to stationary small coflow diffusion flames when electric field is not applied, were firstly investigated with a particular focus on the flow field in near-nozzle region with the buoyancy force exerted on fuels due to density differences among fuel, ambient air, and burnt gas. The result showed that the buoyancy force exerted on the fuel as well as on burnt gas significantly distorted the near-nozzle flow-fields. In the fuels with densities heavier than air, recirculation zones were formed very close to the nozzle exit. Nozzle heating effect influenced this near-nozzle flow-field particularly among lighter fuels. Numerical simulations were also conducted and the results showed that a fuel inlet boundary condition with a fully developed velocity profile for cases with long fuel tubes should be specified inside the fuel tube to obtain satisfactory agreement in both the flow and temperature fields with those from experiment. With sub-critical AC applied to the baseline flames, particle image velocimetry (PIV), light scattering, laser-induced incandescence (LII), and laser-induced fluores- cence (LIF) techniques were adopted to identify the flow field and the structures of OH, polycyclic aromatic hydrocarbons (PAHs), soot zone. Under certain AC condi- tions of applied voltage and frequency, the distribution of PAHs and the flow field near the nozzle exit were drastically altered from the baseline case, leading to the formation of toroidal vortices. Increased residence time and heat recirculation inside the vortex resulted in appreciable formation of PAHs and soot near the nozzle exit. Decreased residence time along the jet axis through flow acceleration by the vortex led to a reduction in the soot volume fraction in the downstream sooting zone. Electromagnetic force generated by AC was proposed as a viable mechanism for the formation of the toroidal vortex. By varying applied AC in a wide range of frequency and voltage, several insta- bility modes were observed, including flicking flames, partial pinch-off of flames, and spinning flames. High speed imaging together with Mie scattering techniques were combined to reveal the flame dynamics as well as the flow structure inside the flames. Original steady toroidal vortices triggered by AC were noted to exhibit axisymmetric axial instability in the flicking and partial pinch-off modes and non-axisymmetric azimuthal instability in the spinning mode. Electrical measurements were also conducted simultaneously to identify the voltage, current, and electrical power responses. Integrated power was noted to be sensitive to indicate subtle variation of flames properties and to the occurrence of axial instability. Under low frequency AC forcing with electrical conditions not generating toroidal vortices, responses of flames were further investigated. Several nonlinear flame responses, including frequency doubling and tripling phenomena, were identified. Spectral analysis revealed that such nonlinear responses were attributed to the combined effects of triggering buoyancy-induced oscillation of the flame as well as the Lorenz force generated by applying AC. Phase delay behaviors between the applied voltage and the heat release rate (or flame size) were also studied to explore the potential of applying AC in controlling flame instability. It was found that the phase delay had large variations for AC frequency smaller than 80 Hz and became saturated at over 80 Hz, which has been explained based on the interaction between the buoyancy and ionic wind. Electrical measurement showed the power consumed by the AC was smaller than 0.01% of the heat release rate from the flame. To improve the understanding on the electric current resulting from applying electric field on flames, a simplified one-dimensional model was developed in that the reaction zone was modeled as a thin ionized layer. Model governing equations were derived from species equations by implementing mobility differences depending on the type of charged particles, especially between ions and electrons. The result showed that the sub-saturated current along with field intensity was significantly influenced by the polarity of DC due to the combined effect of non-equal mobility of charged particles as well as the position of the ionized layer in a gap relative to two electrodes. Experiments with quasi-one-dimensional flames under DC were conducted to substantiate the model and measured currents agreed qualitatively well with the model predictions.

Le contrôle de la production des particules de suies est aujourd'hui un enjeu industriel majeur en raison de leur impact néfaste tant sur le climat que sur la santé humaine et de leur forte contribution aux transferts radiatifs. Pour mieux comprendre et contrôler la production de ces polluants dans les foyers industriels, il est primordial d’améliorer nos connaissances à ce sujet dans un brûleur turbulent. L’objectif de cette thèse est donc de mettre en place des diagnostics optiques pour l’étude des flammes suitées turbulentes et pour caractérise la production de suies dans une nouvelle configuration de combustion prémélangée,confinée, swirlée turbulente académique tout en se rapprochant des configurations industrielles. Une première configuration expérimentale laminaire est donc considérée afin de valider la mise en place de la technique d’Incandescence Induite par Laser (LII) pour mesurer la fraction volumique de suies fv. Il s’agit d’un brûleur conçu à l’université de Yale qui permet la stabilisation d’une flamme laminaire de diffusion éthylène/air. Ce brûleur a été largement étudié dans la littérature nous permettant ainsi de comparer nos mesures aux résultats de différentes équipes internationales. La calibration du signal LII avec la technique MAE (Modulated Absorption Emission) a été effectuée via une collaboration avec l’UPMC, permettant de mesurer quantitativement fv et de comparer les techniques MAE et LII. Le brûleur a ensuite été équipé d’un haut-parleur afin de moduler l’écoulement et de pouvoir étudier les effets d’une perturbation contrôlée sur la production de suies, se rapprochant ainsi des phénomènes instationnaires caractéristiques des écoulements turbulents. Enfin, les effets d’élargissement de la nappe laser sur les résultats de la LII sont examinés afin de pouvoir appliquer ce diagnostic optique dans une configuration turbulente innovante caractérisée par de grandes dimensions. Ce brûleur (EM2Soot) a été développé pour mesurer la production de suies dans une flamme turbulente swirlée riche confinée prémélangée. Il permet de quantifier indépendamment les effets de la richesse, de la puissance et de l’environnement thermique sur la production de suies. Un point de fonctionnement représentatif a alors été étudié et, en parallèle avec la LII, les techniques de vélocimétrie par images de particules (PIV), et de mesure de température des parois par phosphorescence induite par laser (LIP) ont été employées afin de caractériser l’effet de la turbulence sur la production des suies et d’établir une base de données pour la validation de futures simulations numériques. Enfin, la géométrie du brûleur a été modifiée permettant une stabilisation différente de la flamme (en forme d’un V). Un nouveau point de fonctionnement a alors été étudié afin de mettre en évidence le rôle de la géométrie de l’injecteur sur la stabilisation de la flamme et, par conséquent, la production totale de suies. / The control of soot particles production represents today a major industrial issue because of their harmful impact on both the climate and the human health and their strong contribution to the radiative transfers. To better understand and control the production of these polluting emissions, it is essential to improve our knowledge on this subject in a turbulent burner. The objective of this Ph.D. is to set up optical diagnostics for the study of turbulent flames and to experimentally characterize soot production in a new academic turbulent premixed combustion configuration while approaching industrial configurations, generally confined and swirled flows. For this, a laminar experimental configuration is first considered to validate the implementation of the Laser Induced Incandescence (LII) technique to measure the soot volume fraction fv. This burner designed at Yale University allows the stabilization of a laminar ethylene/air diffusion flame. This burner has been widely studied in the literature, so that it is possible to compare the quality of our measurements with the results of different international teams. Through collaborations with the UPMC, we calibrated the LII signal with the MAE (Modulated Absorption Emission) technique, making it possible to quantitatively measure fv and to compare the MAE and LII techniques. Finally, the burner was equipped with a loudspeaker to modulate the flow and to study the effects of a controlled perturbation on the soot production, thus approaching the unsteady phenomena characteristics of turbulent flows. Finally, the effects of the enlargement of the laser sheet on LII results were also investigated in order to be able to apply this diagnostic technique in an innovative large turbulent configuration. This experimental configuration, called EM2Soot, was developed to measure the production of soot in a turbulent swirled rich confined premixed ethylene/air flame. This burner makes it possible to independently quantify the effects of the equivalence ratio, the total flame power and the thermal environment on the total soot production. A representative operating point was then characterized, in parallel with LII measurements, Particle Image Velocimetry (PIV) and Laser Induced Phosphorescence (LIP) techniques have been employed in order to characterize the effect of the turbulence on soot production and to establish a database for the validation of future numerical simulations. Finally, the geometry of the burner has been modified allowing a different stabilization of the flame (V flame shape). A new operating point is then studied in order to highlight the role of the injector geometry on the stabilization of the flame and, consequently, on the total soot production.

Computational fluid dynamics (CFD) modeling and analysis were used in three projects: solar CO2 conversion modeling, improved coal combustion modeling using STAR-CD, and premixed combustion modeling. Each project is described below. The solar CO2 conversion modeling project involved CFD simulations of a prototype solar CO2 converter that uses sunlight to dissociate CO2 into CO and O2. Modeling was used to predict the performance of this prototype converter using three CFD software packages, and involved predicting the flow, heat transfer, and chemical kinetics. Accuracy was determined by comparison of model predictions and experimental data. Parametric modeling studies were performed in order to better understand converter performance and limitations. Modeling analysis led to proposed operational and design changes meant to improve converter performance. Modeling was performed to quantify the effects of proposed design modifications and operational adjustments. Modeling was also used to study the effects of pressure, some geometric design changes, and changing from pure CO2 to a CO2/He mixture. The insights gained from these modeling studies have played a key role in improving the performance of this process. The second project involved the implementation of advanced coal models into STAR-CD, a commercial CFD program. These coal models were originally developed for PCGC-3, a code developed at Brigham Young University. This project involved modifying modern PCGC-3 coal combustion and gasification models so that they could be incorporated into STAR-CD. Models implemented included a coal set-up subroutine, and coal reactions models for devolatilization, char oxidation, and vaporization. Each implemented model was tested to verify its accuracy by comparison of model predictions with experimental data. All implemented coal submodels were validated by comparison between overall modeling predictions and experimental data. These implemented coal models increased the capability of STAR-CD to model coal combustion and gasification systems. The third project was to assemble previously obtained experimental data on lean, premixed natural gas combustion. Velocity, temperature, and species concentration measurements were previously taken throughout a laboratory-scale gas turbine combustor using advanced laser diagnostics. However, these data were taken by different investigators at BYU over the course of 10 years, and the data were scattered through several publications, theses, and dissertations. This third project was to compile these data into a central location for analysis and distribution. This data set is excellent for validation of any comprehensive combustion model, and is now accessible to the public.

Quantitative Planar Laser Induced Fluorescence (QPLIF) is developed as a diagnostic technique and then applied to a prototype Jaguar optical internal combustion engine. QPLIF derives quantitative, two-dimensional, spatially-resolved measurements of fuel concentration. This work reports the first demonstration of a fully-fractionated surrogate fuel which exhibits all the characteristics of a typical gasoline. This 'pseudo' fuel, developed in association with Shell UK, is blended to accept a fluorescent tracer which may track one of the light, middle or heavy fractions of the fuel, each of different volatility. The traditional weaknesses of PLIF for quantitative measurements are addressed by use of a fired in-situ calibration method, which maps the quantum efficiency of the tracer and concurrently corrects for window fouling and exhaust gas residuals (EGR). Fuel distributions are presented with an estimated super-pixel accuracy of 10% at different operating conditions, and then compared to the computational fluid dynamics (CFD) predictions of an in-house Jaguar model. Fuel/Air Ratios by Laser Induced thermal Gratings (FARLIG) is developed theoretically, and results of validation experiments conducted in a laboratory setting are reported. FARLIG conceptually enables the measurement of fuel concentration, oxygen concentration and temperature within a spatially-localised probe volume. Uniquely, the technique exploits the dominant influence of molecular oxygen on non-radiative quenching processes in an aromatic tracer molecule. The changing character of a model quenching mechanism potentially allows the oxygen concentration in the measurement volume to be derived. Absolute signal strength is used to determine fuel concentration, while the oscillation period of the signal provides a precise measurement of temperature (~0.3% uncertainty), with accuracy limited by knowledge of the gas composition.

L’étude expérimentale des processus physico-chimiques de la combustion nécessite de disposer de diagnostics non-intrusifs. Le présent manuscrit reporte le développement du diagnostic laser de mesure de température DRASC (Diffusion Raman anti-Stokes Cohérente) en régime d’impulsions laser femtoseconde pour lequel la configuration à sonde à dérive de fréquence (CPP) a permis d’effectuer des mesures instantanées de température à 1kHz. Un travail à la fois théorique, numérique et expérimental a permis d’extraire la température des spectres DRASC instantanés acquis dans des mélanges air/argon (300-600K) et en flamme prémélangée CH4/Air avec une précision de l’ordre de 1% à 2100 K. La validité de ces résultats est obtenues par des confrontations numérique/expérimental pour différentes grandeurs d’influence. Cette étude permettra dans un proche futur d’appliquer le diagnostic DRASC fs CPP dans des flammes turbulentes représentatives d’écoulements réels observés en combustion aéronautique. / The experimental study of the physico-chemical processes of combustion requires the use of non-intrusive diagnostics. This manuscript reports the development of the CARS (Coherent Anti-Stokes Raman Scattering)) laser diagnostic in the femtosecond pulse regime for which the Chirped Pulse Probe (CPP) configuration enabled instantaneous measurements of temperature at 1kHz. A theoretical, numerical and experimental study allowed highlighting the possibility to measure temperature from the data processing of instantaneous DRASC spectra acquired in air/argon mixtures (300-600K) and in premixed flame CH4/Air with an accuracy of 1% at 2100 K. Validity of these results was obtained from numerical/experimental confrontations for different scalar parameters configurations. This study would enable in the near future the application of the CPP fs CARS diagnostic in turbulent flames representative of real flows observed in aeronautical combustion.

As afecções que acometem a via óptica anterior podem acarretar perda de fibras das células ganglionares retinianas, gerando alterações na camada de fibras nervosas da retina (CFNR). O objetivo deste trabalho foi o de comparar a capacidade da tomografia de coerência óptica (OCT-1), do OCT 3 (Stratus OCT) e do polarímetro de varredura a laser (GDx) em diferenciar olhos normais de olhos com atrofia em banda do nervo óptico e hemianopsia temporal, assim como, comparar o desempenho de tais tecnologias entre si. Foram estudados 37 indivíduos num total de 46 olhos divididos igualmente em dois grupos. O Stratus OCT, o OCT 1 e o GDx se mostraram capazes de identificar corretamente a redução global (average) da espessura da CFNR dos indivíduos com AB comparados com uma população normal. Observamos uma melhora progressiva das sensibilidades/especificidades e das AROC, com o desempenho melhor do OCT1 sobre o GDx e do Stratus OCT sobre o OCT 1 / Most diseases that affect the optic pathways present clinically with loss of one or more visual functions.When optic pathway injuries involve the anterior visual pathways they may cause loss of the retinal nerve fiber layer (RNFL) and "band atrophy" (BA). The purpose of this study was therefore to compare the ability of the optical coherence tomography (OCT) 1, the OCT 3 (Stratus OCT) and the scanning laser polarimetry (GDx) to differentiate normal eyes from eyes with BA of the optic nerve and temporal hemianopsia. Thirty-seven individuals in a total of 46 eyes divided equally in two groups were studied. Each one of the parameters, except the values from the nasal quadrant measured by the GDx, showed statistically significant difference when we compare normal patients with the BA group. The study also showed a gradual improvement of the sensibilities/specificities and of the AROC, with a better performance of the OCT1 compared to GDx and of the Stratus OCT compared to the OCT 1

Alterações no aspecto do disco óptico e da camada de fibras nervosas da retina (CFN) freqüentemente precedem o aparecimento de defeitos de campo visual no glaucoma, o que faz com que a avaliação destas estruturas seja essencial para o diagnóstico precoce e prevenção da perda visual nesta doença. A polarimetria de varredura a laser (GDx VCC), a oftalmoscopia confocal de varredura a laser (HRT II [Heidelberg Retina Tomograph]) e a tomografia de coerência óptica (Stratus OCT) são tecnologias que permitem a avaliação objetiva e quantitativa do disco óptico e da CFN. No presente estudo, estas tecnologias foram comparadas em sua habilidade para diferenciar pacientes glaucomatosos de indivíduos normais. Pacientes com glaucoma foram selecionados com base na presença de defeitos reprodutíveis de campo visual na perimetria acromática automatizada (glaucoma perimétrico), ou com base na evidência documentada de progressão do dano glaucomatoso ao disco óptico, sem presença de defeitos de campo visual (glaucoma pré-perimétrico). Indivíduos normais apresentaram campos visuais e exame clínico dentro da normalidade. Todos os indivíduos foram submetidos a exames com o GDx VCC, HRT II, Stratus OCT e campo visual dentro de um período de três meses. Diversas medidas foram utilizadas para avaliação da acurácia diagnóstica, incluindo áreas sob as curvas receiver operating characteristic (AROC), sensibilidades para especificidades fixas, e razões de probabilidade. Modelos estatísticos foram utilizados para avaliação da influência da severidade do glaucoma e tamanho do disco óptico na performance diagnóstica dos diferentes instrumentos. Um olho de cada indivíduo foi utilizado para análise. Dos 258 sujeitos inicialmente avaliados, 33 (13%) foram posteriormente excluídos por apresentarem imagens de baixa qualidade em pelo menos um dos aparelhos, restando 225 indivíduos (133 glaucomatosos e 92 normais) para análise. Na comparação entre os parâmetros de cada instrumento com maiores valores de AROC, o parâmetro do GDx VCC, Nerve Fiber Indicator (NFI; AROC = 0,91), e o parâmetro do Stratus OCT, Espessura Média (AROC = 0,90), apresentaram áreas sob as curvas ROC significativamente superiores à do parâmetro do HRT II, função discriminante de Bathija (AROC = 0,84). A severidade do defeito de campo visual exerceu influência significativa sob a acurácia diagnóstica dos três instrumentos, com melhora no poder diagnóstico em casos mais avançados da doença. Para o GDx VCC e Stratus OCT, o aumento no tamanho do disco óptico foi associado à diminuição na sensibilidade para detecção do glaucoma; enquanto que, para o HRT II, diminuição no tamanho do disco óptico foi associada à diminuição na sensibilidade. Razões de probabilidade para resultados anormais nas xxv classificações finais de cada instrumento foram associadas a grandes efeitos de mudança na probabilidade pós-teste em relação à probabilidade préteste, sugerindo que o encontro de um resultado anormal em qualquer um destes testes, durante a avaliação de um paciente com suspeita de glaucoma, tem impacto significativo em aumentar a probabilidade de que a doença esteja presente. Além disso, os resultados obtidos na avaliação de pacientes com glaucoma pré-perimétrico sugerem que todos os três instrumentos sejam capazes de detectar alterações estruturais precoces no glaucoma, antes do aparecimento de defeitos de campo visual na perimetria acromática / Changes in the structural appearance of the optic nerve head (ONH) and retinal nerve fiber layer (RNFL) have been reported to precede the development of visual field loss in glaucoma. Detection of ONH and RNFL damage is therefore crucial for early diagnosis of glaucoma and prevention of functional loss from the disease. Scanning laser polarimetry (GDx VCC), confocal scanning laser ophthalmoscopy (HRT II [Heidelberg Retina Tomograph]) and optical coherence tomography (Stratus OCT) are different technologies capable of providing objective and quantitative information related to these structures. The purpose of the present study was to compare, in a single population, the diagnostic abilities of these technologies in the discrimination of glaucomatous patients from healthy subjects. Glaucoma patients were selected based on the presence of repeatable visual field defects, as identified by standard automated perimetry (perimetric glaucoma), or documented evidence of progressive damage to the optic disc, in the absence of detectable visual field loss (preperimetric glaucoma). Normal subjects had normal visual fields and normal clinical examination. All subjects underwent imaging with the GDx VCC, HRT II and Stratus OCT within a 3-month period. Several measures were used for evaluation of diagnostic accuracy, including the area under the receiver operating characteristic curve (AROC), sensitivities at fixed specifities, and likelihood ratios. Statistical models were used to evaluate the influence of glaucoma severity and optic disc size on the diagnostic performance of the different instruments. One eye of each individual was randomly selected for statistical analysis. From an initial group of 258 eligible subjects, 33 (13%) had images of unacceptable quality, leaving 133 glaucoma patients and 92 healthy subjects for further analysis. In the comparison of the parameters with highest values of AROC from each instrument, the GDx VCC Nerve Fiber Indicator (AROC = 0.91) and the Stratus OCT Average Thickness (AROC = 0.90) perfomed significanlty better than the HRT II Bathija discriminant function (AROC = 0.84). For all instruments, the diagnostic accuracy increased with increasing severity of visual field defects. For the GDx VCC and Stratus OCT parameters, an increase in the size of the optic disc was related to a decrease in the sensitivity for glaucoma detection. An opposite effect was observed with the HRT II: a decrease in the size of the optic disc was related to a decrease in the sensitivity for glaucoma diagnosis. Abnormal results for each of the instruments were associated with strong positive likelihood ratios, indicating a large change from prestest to posttest probability of glaucoma. These results suggest that the finding of an abnormal result in any of these tests, when assessing a patient suspect of having glaucoma, would substantially raise the probability of disease. Results of the evaluation of patients with preperimetric glaucoma also suggest that all three instruments are able to detect early glaucomatous structural damage in the absence of visual field loss

Objetivos: Analisar o potencial da oftalmoscopia confocal de varredura a laser, através do Heidelberg Retina Tomograph (HRT), para predizer o risco de progressão em pacientes com suspeita de glaucoma. Comparar os resultados obtidos com o índice de probabilidade de glaucoma (GPS) do HRT aos resultados da análise de regressão de Moorfields (ARM), dos parâmetros morfométricos e da avaliação das fotografias estereoscópicas. Métodos: Uma coorte foi selecionada com 223 pacientes com suspeita de glaucoma, que foram seguidos por um período médio de 64,9 ± 37,3 meses. A suspeita de glaucoma baseou-se na aparência do disco óptico e/ou na pressão intraocular elevada (> 21 mmHg). Todos os participantes apresentavam dois exames de campo visual normais ao entrar no estudo. Conceituou-se progressão como o desenvolvimento de um defeito confirmado de campo visual ou deterioração do disco óptico na avaliação seriada das estereofotografias. A associação entre os resultados do HRT na época do início do acompanhamento e a progressão para glaucoma foi investigada através de modelos de regressão do tipo Cox. Usou-se o C-index para a comparação entre os modelos com os diversos parâmetros do HRT, isolados ou ajustados para os outros já conhecidos fatores de risco para progressão (idade, espessura corneana, pressão intraocular e pattern standard deviation PSD). Resultados: No período do estudo, 46 pacientes (21%) apresentaram progressão. Na análise multivariada, o GPS, a ARM e diversos parâmetros morfométricos foram preditivos para progressão, assim como a avaliação subjetiva das estereofotografias. Cada GPS 0,1 maior foi associado com um aumento de 23% no risco de progressão (C-index de 0,69). Os resultados anormais nas classificações finais do GPS e da ARM foram associados a aumentos de 3 e 2 vezes no risco de progressão, respectivamente (C-indexes de 0,70 e 0,68, respectivamente). O parâmetro com o melhor C-index foi a área seccional tranversa da camada de fibras nervosas (0,72). Uma área 0,3 mm2 menor foi associada a um risco 62% maior de progressão. A comparação do valor preditivo entre os modelos com o GPS e com a avaliação subjetiva das estereofotografias foi similar (C-indexes de 0,69 e 0,68, respectivamente). Conclusão: Nesse estudo observamos que as análises objetivas do disco óptico e da região peripapilar obtidas com o HRT contribuíram na avaliação do risco de progressão em pacientes com suspeita de glaucoma. O GPS mostrou-se tão eficaz quanto os parâmetros morfométricos e a análise de regressão de Moorfields, e a comparação do desempenho dos modelos contendo a avaliação subjetiva das estereofotografias e aqueles contendo a avaliação objetiva pelo GPS não mostrou diferenças significativas / Purpose: To evaluate the ability of baseline confocal scanning laser ophthalmoscopy, using the Heidelberg Retina Tomograph (HRT), in predicting the development of progression in patients suspected of having glaucoma. In addition, the study also aimed to compare the predictive abilities of the glaucoma probability score (GPS) with those of the Moorfields regression analysis (MRA) and stereometric parameters, and to compare the performance of the HRT with that of subjective evaluation of optic disc stereophotographs. Methods: This longitudinal study included a cohort of 223 eyes suspected of having glaucoma, which were followed for an average of 64.9 ± 37.3 months. Included suspects had a suspicious appearance of the optic disc and/or elevated intraocular pressure, but normal visual fields. Progression was defined as the development of either repeatable abnormal visual fields or glaucomatous structural deterioration in the appearance of the optic disc during the study period. The association between baseline HRT parameters and progression was investigated by Cox regression models. The comparison between models with HRT parameters, individually or combined with other known risk factors (age, central corneal thickness, pattern standard deviation and intraocular pressure), performed by comparing their C-indexes. Results: Forty-six (21%) eyes converted during the study period. In multivariable models, the GPS, the MRA, and the stereometric parameters were all predictive of progression. A GPS 0.1 larger was associated with an increase of 23% in the risk of progression (C-index of 0.69). Abnormal final classifications for the GPS or the MRA were associated with a three-fold and two-fold increase in the risk of progression, respectively (with C-indexes of 0.70 and 0.68, respectively). The parameter with the best C-index was the nerve fiber layer cross-sectional area (0.72). An area 0.3 mm2 smaller was associated with a 62% higher risk of an individual progress. The comparison between models with the HRT parameters and those with the subjective stereophotograph evaluation had similar results (C-indexes of 0.69 and 0.68, respectively). Conclusion: In this study, we were able to show that the objective structural assessment of the optic disc and peripapillary area obtained with the HRT was significantly predictive for progression in suspected individuals. The GPS was as predictive as the other HRT parameters, and no significant differences were observed between models with the GPS and those with the subjective assessment of the stereophotographs.

O objetivo desse estudo foi comparar a habilidade da avaliação subjetiva do disco óptico e da camada de fibras nervosas (CFN) por oftalmologistas generalistas e por um glaucomatólogo com medidas objetivas pela tomografia de coerência óptica (Stratus OCT), oftalmoscopia confocal de varredura a laser (HRTIII), e a polarimetria de varredura a laser (GDxECC) para discriminar olhos glaucomatosos de olhos normais. 61 olhos glaucomatosos e 57 olhos normais de 118 indivíduos foram incluídos nesse estudo. Três oftalmologistas generalistas independentes e um glaucomatólogo avaliaram fotografias estereoscópicas do disco óptico. Curvas ROC (Receiver Operator Characteristic) foram construídas para cada técnica de imagem e a sensibilidade a uma especificidade fixa foi determinada. Comparações das áreas sob essas curvas (AROC) e a concordância (k) foram determinadas entre a graduação das fotografias estereoscópicas e o melhor parâmetro de cada exame de imagem computadorizado. O melhor parâmetro de cada técnica de imagem computadorizada (CFN temporal inferior do Stratus OCT = 0,92; área integrada vertical da topografia do disco óptico pelo Stratus OCT = 0,86; espessura macular do setor inferior externo fornecido pelo Stratus OCT = 0,82; NFI do GDxECC = 0,91; razão área E/D do HRT3 = 0,83) mostrou AROC maior do que a graduação das fotografias estereoscópicas por oftalmologistas generalistas (0,80) para separar olhos glaucomatosos de olhos normais. A graduação por glaucomatólogo forneceu AROC igual ou maior (0,92) do que o melhor parâmetro de exame computadorizado de imagem. A avaliação das fotografias estereoscópicas por glaucomatólogo mostrou melhor concordância com o melhor parâmetro de cada técnica de imagem quantitativa na classificação de olhos como glaucomatosos ou normais comparadas à avaliação de fotografias estereoscópicas por oftalmologistas generalistas. A combinação da avaliação subjetiva do disco óptico por oftalmologistas generalistas com parâmetros objetivos da CFN melhorou a identificação de olhos com glaucoma em uma proporção maior do que a combinação desses parâmetros objetivos com a avaliação do disco óptico por um glaucomatólogo (29,5% versus 19,7%, respectivamente). Os resultados sugerem que a habilidade diagnóstica de todos os exames de imagem computadorizados estudados mostrou melhor desempenho que a avaliação subjetiva do disco óptico por oftalmologistas generalistas, mas não por um glaucomatólogo. Medidas objetivas da CFN podem permitir um aperfeiçoamento na detecção de glaucoma quando combinados com a avaliação subjetiva do disco óptico por oftalmologistas generalistas ou por um glaucomatólogo. / The purpose of this study was to compare the ability of subjective assessment of optic nerve head and retinal nerve fiber layer by general ophthalmologists and by a glaucoma expert with objective measurements by optical coherence tomography (Stratus OCT, Carl Zeiss Meditec, Inc.), confocal scanning laser ophthalmoscope (HRT III; Heidelberg Engineering, Heidelberg, Germany), and scanning laser polarimetry (GDx ECC; Carl Zeiss Meditec, Inc., Dublin, CA) in discriminating glaucomatous and normal eyes. 61 glaucomatous and 57 normal eyes of 118 subjects were included in the study. Three independent general ophthalmologists and one glaucoma expert evaluated ONH stereophotographs. Receiver operating characteristic curves were constructed for each imaging technique and sensitivity at fixed specificity was estimated. Comparisons of areas under these curves (aROC) and agreement (k) were determined between stereophoto grading and best parameter from each technique. Best parameter from each technique showed larger aROC (StratusOCT RNFL = 0.92; StratusOCT ONH vertical integrated area = 0.86; StratusOCT macular thickness = 0.82; GDxECC = 0.91; HRT3 global cup-to-disc area ratio = 0.83) compared to stereophotograph grading by general ophthalmologists (0.80) in separating glaucomatous and normal eyes. Glaucoma expert stereophoto grading provided equal or larger aROC (0.92) than best parameter of each computerized imaging device. Stereophoto evaluated by a glaucoma expert showed better agreement with best parameter of each quantitative imaging technique in classifying eyes either as glaucomatous or normal compared to stereophoto grading by general ophthalmologists. The combination of subjective assessment of the optic disc by general ophthalmologists with RNFL objective parameters improved identification of glaucoma patients in a larger proportion than the combination of these objective parameters with subjective assessment of the optic disc by a glaucoma expert (29.5% versus 19.7%, respectively). The results suggests that the diagnostic ability of all imaging techniques showed better performance than subjective assessment of the ONH by general ophthalmologists, but not by a glaucoma expert. Objective RNFL measurements may provide improvement in glaucoma detection when combined with subjective assessment of the optic disc by general ophthalmologists or by a glaucoma expert.

Alterações no aspecto do disco óptico e da camada de fibras nervosas da retina (CFN) freqüentemente precedem o aparecimento de defeitos de campo visual no glaucoma, o que faz com que a avaliação destas estruturas seja essencial para o diagnóstico precoce e prevenção da perda visual nesta doença. A polarimetria de varredura a laser (GDx VCC), a oftalmoscopia confocal de varredura a laser (HRT II [Heidelberg Retina Tomograph]) e a tomografia de coerência óptica (Stratus OCT) são tecnologias que permitem a avaliação objetiva e quantitativa do disco óptico e da CFN. No presente estudo, estas tecnologias foram comparadas em sua habilidade para diferenciar pacientes glaucomatosos de indivíduos normais. Pacientes com glaucoma foram selecionados com base na presença de defeitos reprodutíveis de campo visual na perimetria acromática automatizada (glaucoma perimétrico), ou com base na evidência documentada de progressão do dano glaucomatoso ao disco óptico, sem presença de defeitos de campo visual (glaucoma pré-perimétrico). Indivíduos normais apresentaram campos visuais e exame clínico dentro da normalidade. Todos os indivíduos foram submetidos a exames com o GDx VCC, HRT II, Stratus OCT e campo visual dentro de um período de três meses. Diversas medidas foram utilizadas para avaliação da acurácia diagnóstica, incluindo áreas sob as curvas receiver operating characteristic (AROC), sensibilidades para especificidades fixas, e razões de probabilidade. Modelos estatísticos foram utilizados para avaliação da influência da severidade do glaucoma e tamanho do disco óptico na performance diagnóstica dos diferentes instrumentos. Um olho de cada indivíduo foi utilizado para análise. Dos 258 sujeitos inicialmente avaliados, 33 (13%) foram posteriormente excluídos por apresentarem imagens de baixa qualidade em pelo menos um dos aparelhos, restando 225 indivíduos (133 glaucomatosos e 92 normais) para análise. Na comparação entre os parâmetros de cada instrumento com maiores valores de AROC, o parâmetro do GDx VCC, Nerve Fiber Indicator (NFI; AROC = 0,91), e o parâmetro do Stratus OCT, Espessura Média (AROC = 0,90), apresentaram áreas sob as curvas ROC significativamente superiores à do parâmetro do HRT II, função discriminante de Bathija (AROC = 0,84). A severidade do defeito de campo visual exerceu influência significativa sob a acurácia diagnóstica dos três instrumentos, com melhora no poder diagnóstico em casos mais avançados da doença. Para o GDx VCC e Stratus OCT, o aumento no tamanho do disco óptico foi associado à diminuição na sensibilidade para detecção do glaucoma; enquanto que, para o HRT II, diminuição no tamanho do disco óptico foi associada à diminuição na sensibilidade. Razões de probabilidade para resultados anormais nas xxv classificações finais de cada instrumento foram associadas a grandes efeitos de mudança na probabilidade pós-teste em relação à probabilidade préteste, sugerindo que o encontro de um resultado anormal em qualquer um destes testes, durante a avaliação de um paciente com suspeita de glaucoma, tem impacto significativo em aumentar a probabilidade de que a doença esteja presente. Além disso, os resultados obtidos na avaliação de pacientes com glaucoma pré-perimétrico sugerem que todos os três instrumentos sejam capazes de detectar alterações estruturais precoces no glaucoma, antes do aparecimento de defeitos de campo visual na perimetria acromática / Changes in the structural appearance of the optic nerve head (ONH) and retinal nerve fiber layer (RNFL) have been reported to precede the development of visual field loss in glaucoma. Detection of ONH and RNFL damage is therefore crucial for early diagnosis of glaucoma and prevention of functional loss from the disease. Scanning laser polarimetry (GDx VCC), confocal scanning laser ophthalmoscopy (HRT II [Heidelberg Retina Tomograph]) and optical coherence tomography (Stratus OCT) are different technologies capable of providing objective and quantitative information related to these structures. The purpose of the present study was to compare, in a single population, the diagnostic abilities of these technologies in the discrimination of glaucomatous patients from healthy subjects. Glaucoma patients were selected based on the presence of repeatable visual field defects, as identified by standard automated perimetry (perimetric glaucoma), or documented evidence of progressive damage to the optic disc, in the absence of detectable visual field loss (preperimetric glaucoma). Normal subjects had normal visual fields and normal clinical examination. All subjects underwent imaging with the GDx VCC, HRT II and Stratus OCT within a 3-month period. Several measures were used for evaluation of diagnostic accuracy, including the area under the receiver operating characteristic curve (AROC), sensitivities at fixed specifities, and likelihood ratios. Statistical models were used to evaluate the influence of glaucoma severity and optic disc size on the diagnostic performance of the different instruments. One eye of each individual was randomly selected for statistical analysis. From an initial group of 258 eligible subjects, 33 (13%) had images of unacceptable quality, leaving 133 glaucoma patients and 92 healthy subjects for further analysis. In the comparison of the parameters with highest values of AROC from each instrument, the GDx VCC Nerve Fiber Indicator (AROC = 0.91) and the Stratus OCT Average Thickness (AROC = 0.90) perfomed significanlty better than the HRT II Bathija discriminant function (AROC = 0.84). For all instruments, the diagnostic accuracy increased with increasing severity of visual field defects. For the GDx VCC and Stratus OCT parameters, an increase in the size of the optic disc was related to a decrease in the sensitivity for glaucoma detection. An opposite effect was observed with the HRT II: a decrease in the size of the optic disc was related to a decrease in the sensitivity for glaucoma diagnosis. Abnormal results for each of the instruments were associated with strong positive likelihood ratios, indicating a large change from prestest to posttest probability of glaucoma. These results suggest that the finding of an abnormal result in any of these tests, when assessing a patient suspect of having glaucoma, would substantially raise the probability of disease. Results of the evaluation of patients with preperimetric glaucoma also suggest that all three instruments are able to detect early glaucomatous structural damage in the absence of visual field loss