Optical versus video see-through mead-mounted displays in medical visualization

We compare two technological approaches to augmented reality for 3-D medical visualization: optical and video see-through devices. We provide a context to discuss the technology by reviewing several medical applications of augmented-reality research efforts driven by real needs in the medical field, both in the United States and in Europe. We then discuss the issues for each approach, optical versus video, from both a technology and human-factor point of view. Finally, we point to potentially promising future developments of such devices including eye tracking and multifocus planes capabilities, as well as hybrid optical/video technology

Optical aberrations in ametropic eyes and their change with corneal refractive surgery

In this thesis the laser ray tracing (LRT) technique for measurement of ocular aberrations has been implemented, validated and applied, in conjunction with complementary techniques, to the study of ocular aberrations in human eyes. In particular, we studied optical aberrations in myopic and hyperopic eyes and the optical changes induced by refractive surgery for myopia and hyperopia. We have studied the impact of the optimisation of some experimental parameters on the estimation of the wave aberration. We demonstrated that although the polarisation state and wavelength of the illumination light affected the intensity patterns of the images obtained using reflectometric aberrometry (LRT and Hartmann Shack sensor), these changes did not affect the estimation of aberrations. We also showed that the difference in the defocus term (focus shift) due to the use of different wavelengths is in agreement with the Longitudinal Chromatic Aberration of the Indiana Chromatic Eye Model for average normal eyes, although intersubject variability is not negligible. In addition, we studied experimentally the influence of the geometrical distribution and density of the pupil sampling on the estimation of aberrations using artificial and normal human eyes, and performed numerical simulations to extend our results to "abnormal"eyes. We found that the spatial distribution of the samples can be more important than the number of samples, for both our measured as well as our simulated "abnormal" eyes. Experimentally, we did not find large differences across patterns except, as expected, for undersampled patterns. We found that hyperopic eyes tended to have more positive asphericity and greater total and corneal spherical aberrati on than myopic eyes, as well as greater 3rd and higher order aberrations. Although we found no significant differences between groups in terms of internal aberrations, internal spherical aberration showed a significant age-related shift toward less negative values in the hyperopic group. We also assessed the impact of the LASIK corneal surgery, a popular surgical technique for correction of refractive errors, on the optical quality for both myopic and hyperopic standard techniques. Third and higher order ocular and an terior corneal aberrations increased with the surgery. Ocular and corneal spherical aberration changed towards more positive values with myopic LASIK, and towards more negative values with hyperopic LASIK. Changes in internal spherical aberration were of opposite sign than those induced in corneal spherical aberration. Changes induced by hyperopic LASIK were larger than those induced by myopic LASIK for a similar attempted correction

Correcciones para la presbicia : implicaciones ópticas, perceptuales y adaptativas

Tesis de la Universidad Complutense de Madrid, Facultad de Óptica y Optometría, leída el 18-05-2016Presbyopia is the physiological inability of the crystalline lens to accommodate for objects at near distance. While accommodative lenses are the ideal solutions for presbyopia, current optical solutions rely on providing an acceptable quality of vision at near and far distances. Optimization of the optical solutions rely on better understanding of how the visual system copes with the visual quality produced by the various optical solutions. The aim of this thesis is to study optical, visual and perceptual performance of different presbyopic corrections such as alternating vision, monovision and simultaneous vision, and to study the effect of adaptation on perceptual performances. Methods: We measured and corrected ocular aberrations using custom developed adaptive optics setup, used images blurred by real aberrations of different orientation and/or magnitude and measured the internal code for blur in eyes with long term differences in blur magnitude or orientation using a classification-image like technique. We later used numerically convolved images of different far/near energy and different near additions to study the short term adaptation to pure simultaneous vision using single stimulus detection and scoring tasks...La presbicia es la incapacidad del cristalino para enfocar objetos cercanos. Mientras que las lentes acomodativas son una buena solución para la presbicia, las soluciones más actuales se basan en una corrección aceptable de la visión cercana y lejana simultáneamente. La optimización de estas soluciones pasa por comprender cómo reacciona el sistema a las diferentes correcciones ópticas. El objetivo de esta tesis es el estudio óptico, visual y perceptual de diferentes correcciones a la presbicia como la visión alternante, la mono visión y la visión simultánea, y el estudio del efecto dela adaptación desde el punto de vista perceptual. MétodosSe han medido y corregido las aberraciones oculares mediante un sistema de óptica adaptativa de construcción propia y se han usado imágenes desenfocadas con aberraciones reales con diferentes magnitudes y/u orientaciones para medir el código interno de emborronamiento en los ojos para los diferentes desenfoques y orientaciones mediante métodos de clasificación de imágenes. Posteriormente se han usado imágenes convolucionadas numéricamente con diferentes proporciones en las energías del enfoque cercano o lejano y con diferentes adiciones para estudiar laadaptación a corto plazo en la visión simultánea pura a través de la detección y valoración de estímulos individuales...Fac. de Óptica y OptometríaTRUEunpu

Aerospace Medicine and Biology: A continuing bibliography with indexes, supplement 178

This bibliography lists 230 reports, articles, and other documents introduced into the NASA scientific and technical information system in February 1978

Characteristics of flight simulator visual systems

The physical parameters of the flight simulator visual system that characterize the system and determine its fidelity are identified and defined. The characteristics of visual simulation systems are discussed in terms of the basic categories of spatial, energy, and temporal properties corresponding to the three fundamental quantities of length, mass, and time. Each of these parameters are further addressed in relation to its effect, its appropriate units or descriptors, methods of measurement, and its use or importance to image quality

The Importance of Contrast Sensitivity, Color Vision, and Electrophysiological Testing In Clinical and Occupational Settings

Visual acuity (VA) is universally accepted as the gold standard metric for ocular vision and function. Contrast sensitivity (CS), color vision, and electrophysiological testing for clinical and occupational settings are warranted despite being deemed ancillary and minimally utilized by clinicians. These assessments provide essential information to subjectively and objectively quantify and obtain optimal functional vision. They are useful for baseline data and monitoring hereditary and progressive ocular conditions and cognitive function. The studies in this dissertation highlight the value of contrast sensitivity, color vision, and cone specific electrophysiological testing, as well as the novel metrics obtained with potential practical clinical applications for visual function and perception evaluation in patients in various settings. The first study aimed to design a clinically expedient method to combine color CS and color naming (CN) into a single, multi-metric test of color vision, the Color Contrast Naming Test (CCNT). This was accomplished by comparing and validating it with the standardized computerized Cone Contrast Test (CCT; Innova Systems, Inc.). Color vision deficient (CVD) and color vision normal (CVN) findings showed a strong correlation between the CCNT CS and the standard CCT. Furthermore, CCT CS showed distinct scores in 50% of CVDs, while the CCNT composite score (mean of CS and CN) showed distinct scores in 70% of CVDs, showing better potential discrimination of CVD color abilities. This novel metric has potential applications for identifying hereditary or progressive CVD severity and capabilities. The second study focused on electrophysiological diagnostics, specifically cone specific visual evoked potentials (VEPs), to objectively measure long-term neural adaptive responses to color-correcting lenses (CCLs). Dr. Werner and colleagues determined that extended wear (for 12 days) of color-correcting lenses improved red-green color perception in hereditary CVD even without wearing CCLs. Furthermore, Dr. Rabin and colleagues were able to objectively measure both immediate short-term (baseline, 4, 8, 12 days) and long-term (3, 6, 12 months) improvements of color perception status post-CCL removal with cone specific VEPs – something that has never been done before. The novel findings from both studies support the notion that neural adaptive changes can occur over short- and longer-term periods despite minimal daily wear time. More importantly, this further supports the value of suprathreshold cone VEPs to objectively assess color vision function in both clinical and occupational settings. Most dry eye studies use measures of tear quality and volume coupled with standard clinical tests such as high contrast visual acuity (VA), while fewer studies have investigated the effects of dry eyes on low contrast vision. The final study was designed to determine the impact of Meibomian Gland Dysfunction (MGD) dry eye on high and low-contrast vision, including both black/white (luminance) and cone specific color vision. A primary intent was to determine if these novel metrics improved following minimal meibomian gland (MG) expression. The computerized CCNT and CCT (cone and black/white) tests used in this study confirmed that minimal MG expression improved low contrast performance for long (L cone) and short (S cone) wavelength-sensitive cones. These improvements were most significant using throughput (CS/response time) and CCNT composite scores, both novel metrics for potential use in dry eye diagnosis, treatment, and management. Physical optics, including decreased destructive interference in the stroma, most detrimental with red light, and increased scattering by subtle epithelial, endothelial, and/or tear film defects, most detrimental for blue light, could each decrease retinal image contrast most evident with L and S cone CS. Contrast sensitivity, color vision, and cone specific electrophysiological testing are non-optimally and infrequently utilized in basic, clinical, applied, and translational research or occupational settings. These studies showed provocative results within their respective categories and confirmed their validity and importance for identifying and monitoring ocular conditions and neural adaptive or cognitive functions. Furthermore, novel metrics such as throughput and CCNT composite scores serve as potential tangible and practical visual function and perception assessment standards

Applications of ray tracing to a pseudophakic eye model

The calculation of IOL power using keratometry is adversely affected by recent corneal reshaping surgeries. This thesis investigates the application of ray tracing and general anterior corneal surface modeling, for the purpose of improving ophthalmic measurements and in particular, the estimation of IOL power. A new algorithm (based on a multi-step approach) for the recovery of the corneal height using videokeratography is presented. The method ensures a cubic recovery with continuous curvature; skew rays are treated in post-processing. The RMS height error is measured for three simulated (with two skewed) cornea. The total errors are 6.2 x 10⁻⁴ mm ignoring the skew ray error, and 1.7 x 10⁻⁴ mm accounting for it. The individual height errors are submicron in the latter case. The algorithm gives average errors of 2.5 x 10⁻⁴ mm for a set of calibration balls. The completion time is 2.3 s over all cases, using a standard desktop PC. A new method for the recovery of the internal ocular radii of curvature is investigated. The method is used to recover the posterior corneal radii (PII) and the anterior lens radii (PIII) given several anterior cornea models (PI) in simulation. The recovered surface powers are no more than 0.1 D(PII) and 0.006 D(PIII) in error of the true surface powers. A framework is then presented for modeling the effect of lens decenter and tilt on perceived image quality. The SQRI image quality metric is determined for a range of lens tilt and lens decenter values. These are compared with the statistical moments of the spot diagrams. The SQRI shows asymmetric degradation (with tilt for a particular decenter value) of imaging for a plane displaced -0.1 mm from best focus. For a plane displaced +0.1 mm from best focus, the SQRI is symmetric and improves regardless of the sign of tilt. The statistical moments suggest that skew does not necessarily imply poor imaging. Finally, the modeling methods developed are tested on two clinically measured eyes. Minimizing the spot size, predicts the spectacle prescription to 0.0 D(OS) and 0.1 D(OD) of the mean spherical equivalent. Adding prescribed lenses to the model eye, estimates best focus to 0.03 mm and 0.02 mm of the retinal plane; consistent with better than 6/6 VA measured for OS/OD. A VisTech VCTS 6500 contrast sensitivity chart is used to verify the eye model. A 75% match with theory is found for OS, a 50% match is found for OD

Benchmarking of mobile phone cameras

fi=vertaisarvioitu|en=peerReviewed

Use of Coherent Point Drift in computer vision applications

This thesis presents the novel use of Coherent Point Drift in improving the robustness of a number of computer vision applications. CPD approach includes two methods for registering two images - rigid and non-rigid point set approaches which are based on the transformation model used. The key characteristic of a rigid transformation is that the distance between points is preserved, which means it can be used in the presence of translation, rotation, and scaling. Non-rigid transformations - or affine transforms - provide the opportunity of registering under non-uniform scaling and skew. The idea is to move one point set coherently to align with the second point set. The CPD method finds both the non-rigid transformation and the correspondence distance between two point sets at the same time without having to use a-priori declaration of the transformation model used. The first part of this thesis is focused on speaker identification in video conferencing. A real-time, audio-coupled video based approach is presented, which focuses more on the video analysis side, rather than the audio analysis that is known to be prone to errors. CPD is effectively utilised for lip movement detection and a temporal face detection approach is used to minimise false positives if face detection algorithm fails to perform. The second part of the thesis is focused on multi-exposure and multi-focus image fusion with compensation for camera shake. Scale Invariant Feature Transforms (SIFT) are first used to detect keypoints in images being fused. Subsequently this point set is reduced to remove outliers, using RANSAC (RANdom Sample Consensus) and finally the point sets are registered using CPD with non-rigid transformations. The registered images are then fused with a Contourlet based image fusion algorithm that makes use of a novel alpha blending and filtering technique to minimise artefacts. The thesis evaluates the performance of the algorithm in comparison to a number of state-of-the-art approaches, including the key commercial products available in the market at present, showing significantly improved subjective quality in the fused images. The final part of the thesis presents a novel approach to Vehicle Make & Model Recognition in CCTV video footage. CPD is used to effectively remove skew of vehicles detected as CCTV cameras are not specifically configured for the VMMR task and may capture vehicles at different approaching angles. A LESH (Local Energy Shape Histogram) feature based approach is used for vehicle make and model recognition with the novelty that temporal processing is used to improve reliability. A number of further algorithms are used to maximise the reliability of the final outcome. Experimental results are provided to prove that the proposed system demonstrates an accuracy in excess of 95% when tested on real CCTV footage with no prior camera calibration

Aerospace medicine and biology: A continuing bibliography with indexes

This bibliography lists 161 reports, articles, and other documents introduced into the NASA scientific and technical information system in November, 1987