Accommodation lags are higher in myopia than in emmetropia:Measurement methods and metrics matter

Purpose: To determine whether accommodative errors in emmetropes and myopes are systematically different, and the effect of using different instruments and metrics. Methods: Seventy-six adults aged 18–27 years comprising 24 emmetropes (spherical equivalent refraction of the dominant eye +0.04 ± 0.03 D) and 52 myopes (−2.73 ± 0.22 D) were included. Accommodation responses were measured with a Grand Seiko WAM-5500 and a Hartmann–Shack Complete Ophthalmic Analysis System aberrometer, using pupil plane (Zernike and Seidel refraction) and retinal image plane (neural sharpness—NS; and visual Strehl ratio for modulation transfer function—VSMTF) metrics at 40, 33 and 25 cm. Accommodation stimuli were presented to the corrected dominant eye, and responses, referenced to the corneal plane, were determined in the fellow eye. Linear mixed-effects models were used to determine influence of the refractive group, the measurement method, accommodation stimulus, age, race, parental myopia, gender and binocular measures of heterophoria, accommodative convergence/accommodation and convergence accommodation/convergence ratios. Results: Lags of accommodation were affected significantly by the measurement method (p < 0.001), the refractive group (p = 0.003), near heterophoria (p = 0.002) and accommodative stimulus (p < 0.05), with significant interactions between some of these variables. Overall, emmetropes had smaller lags of accommodation than myopes with respective means ± standard errors of 0.31 ± 0.08 D and 0.61 ± 0.06 D (p = 0.003). Lags were largest for the Grand Seiko and Zernike defocus, intermediate for NS and VSMTF, and least for Seidel defocus. Conclusions: The mean lag of accommodation in emmetropes is approximately equal to the previously reported depth of focus. Myopes had larger (double) lags than emmetropes. Differences between methods and instruments could be as great as 0.50 D, and this must be considered when comparing studies and outcomes. Accommodative lag increased with the accommodation stimulus, but only for methods using a fixed small pupil diameter.</p

Engineering data compendium. Human perception and performance. User's guide

The concept underlying the Engineering Data Compendium was the product of a research and development program (Integrated Perceptual Information for Designers project) aimed at facilitating the application of basic research findings in human performance to the design and military crew systems. The principal objective was to develop a workable strategy for: (1) identifying and distilling information of potential value to system design from the existing research literature, and (2) presenting this technical information in a way that would aid its accessibility, interpretability, and applicability by systems designers. The present four volumes of the Engineering Data Compendium represent the first implementation of this strategy. This is the first volume, the User's Guide, containing a description of the program and instructions for its use

Characterizing the Linguistic Chameleon: Personal and Social Correlates of Linguistic Style Accommodation

© 2016 International Communication Association Linguistic style accommodation between conversationalists is associated with positive social outcomes. We examine social power and personality as factors driving the occurrence of linguistic style accommodation, and the social outcomes of accommodation. Social power was manipulated to create 144 face-to-face dyadic interactions between individuals of high versus low power and 64 neutral power interactions. Particular configurations of personality traits (high self-monitoring, Machiavellianism and leadership, and low self-consciousness, impression management and agreeableness), combined with a low-power role, led to an increased likelihood of linguistic style accommodation. Further, greater accommodation by low-power individuals positively influenced perceptions of subjective rapport and attractiveness. We propose individual differences interact with social context to influence the conditions under which nonconscious communication accommodation occurs

The Chromatic Aberration of the Eye and its Importance in the Modern World

The human eye has various aberrations that distort the image formed on the retina. Monochromatic aberrations are the distortions present at a single wavelength and chromatic aberrations are wavelength dependent. Longitudinal chromatic aberration (LCA) describes the difference in defocus at different wavelengths. The LCA of the human eye is approximately 2 dioptres (D) across the visible spectrum. Normally we are unaware of these distortions, however, they do play an important role in our vision. The aim of this thesis was to investigate the importance of these aberrations in the context of the modern world. The illuminant spectra that we are exposed to today are quite different from 100 years ago. Because LCA results in a difference in defocus with wavelength this means that the amount of defocus blur in the retinal image will change depending on the spectrum of light. In this thesis findings are reported indicating that there are certain illuminant spectra for which the chromatic fringes due to LCA were more visible. We also investigated how people accommodated to spectra made up of two distinct narrowband LEDs. The findings suggest that people do not accommodate optimally to these spectra. There is also increasing interest in blurring stimuli realistically. This is partly with the emergence of virtual reality, so that 3D scenes appear as realistic as possible, but also has more clinical applications in trialling the effects of different corrective lenses on vision before the lenses are made (or inserted in the case of intraocular lenses). We investigated the importance of including monochromatic aberrations when rendering out of focus stimuli. It seems that monochromatic aberrations do make the stimuli appear more realistic, however, they did not have a significant impact on visual acuity

A Numerical Exploration of the Crystalline Lens: from Presbyopia to Cataracts and Intraocular Lenses

Esta tesis aborda, de forma numérica, la resolución de tres problemas relacionados con el cristalino. En primer lugar, se ha construido un modelo de elementos finitos del cristalino humano para abordar la simulación de la acomodación, gracias a la incorporación de la contracción muscular del músculo ciliar. El modelo se ha validado con resultados experimentales comparando con Ramasubramanian & Glasser, 2015. Con el mismo modelo, se ha estudiado como afecta el cambio de las propiedades mecánicas de los tejidos del cristalino en la pérdida de amplitud de la acomodación con la edad para entender si la rigidización de los tejidos juega un papel importante en la presbicia. La conclusión principal del estudio numérico ha sido que las propiedades mecánicas y tensiones iniciales de la cápsula del cristalino proporciona la fuerza necesaria para acomodar, es decir, cambiar su curvatura para enfocar de cerca. Especificamente, el ratio de rígidez entre el núcleo y el cristalino gobierna cómo el cristalino cambia de forma. Con la edad, se produce una rigidización del núcleo, y el incremento de la relación entre ambas rigideces (núcleo y corteza) podría ser el principal responsable de la pérdida de la amplitud de acomodación con la edad. En segundo lugar, se ha estudiado la estabilidad biomecánica de diferentes diseños de lentes intraoculares (IOL). Las IOLs sustituyen las funciones del cristalino en pacientes con cataratas, es por ello necesario garantizar su estabilidad en el interior del saco para garantizar una visión adecuada. Entre los aspectos estudiados destaca la caracterización mecánica de los materiales acrílicos con los que se fabrican las lentes. Para ello, se han combinado ensayos uniaxiales con ensayos de indentación. Éstos últimos se han utilizado para caracterizar la respuesta visco-elástica del material. El definir la respuesta del material mediante modelos visco hiperelásticos es necesario para posteriormente analizar la estabilidad de la IOL mediante elementos finitos. Este análisis se ha defino a dos niveles, en un primer nivel se analiza la estabilidad de la IOL simulando el ensayo establecido en la norma ISO 11979-3:2012. Esta norma es de obligado cumplimiento para los fabricantes antes de introducir un nuevo diseño en el mercado. Se ha realizado un estudio estadístico para estudiar el efecto de la geometría de los hápticos tipo C-loop en la estabilidad mecánica de la IOL, obteniendo que el entronque, la unión entre el háptico y la lente, es el parámetro más influyente. Para validar la metodología numérica, se fabricaron varios diseños y se analizaron experimentalmente para comparar los resultados correspondientes con biomarcadores mecánicos (desplazamiento axial, rotación y la inclinación de la IOL) que están relacionados con la calidad visual resultante de la IOL. En un segundo nivel, se ha simulado la respuesta de la IOL en el interior del saco capsular, estudiando la influencia de diferentes parámetros del paciente, como geometría y propiedades mecánicas del saco. También se ha analizado la influencia de parámetros de la cirugía de la catarata, como es el diámetro y posición de la capsulorexis. En este último nivel, se ha estudiado tanto la respuesta instantánea, es decir, tras la cirugía, como a largo plazo, cuando sucede la huella de fusión (fusion footprint) entre la cápsula y la IOL. Para que los modelos computacionales sean de ayuda a los cirujanos o puedan servir en tiempo real, se ha planteado una metodología basada en inteligencia artificial. En este caso la base de datos de partida corresponde a modelos numéricos altamente fiables y con ellos, se genera datos con los que se entrena la red neuronal. En esta tesis, se estudia la estabilidad de la IOL en función del diámetro de compresión del paciente y la edad, que a su vez influye en las propiedades mecánicas del saco. Por último, se ha evaluado experimentalmente la influencia del material de la IOL (hidrófobo o hidrofílico) y su geometría durante la inyección de la IOL en el saco, registrando la fuerza de inyección que debe realizar el cirujano. De cara a evitar complicaciones (se dañe la IOL o el tejido corneal) durante la cirugía, es conveniente que la fuerza a ejercer sea baja. Se ha comprobado que su valor está fuertemente influenciado por el material de la lente.¿Por qué el cristalino es de vital importancia?El cristalino es el responsable tanto del cambio dinámico de la potencia refractiva del ojo a través del mecanismo de acomodación como de la corrección de las aberraciones de la córnea. El cambio óptico dinámico es consecuencia de un cambio geométrico del cristalino. Sin embargo, a medida que el cristalino envejece, disminuye este cambio óptico dinámico y se opacifica, lo que da lugar a las dos patologías comúnmente asociadas al envejecimiento como es, la presbicia y las cataratas. Por este motivo, en esta tesis doctoral se ha profundizado en el estudio mecánico del cristalino y tras su sustitución mediante una lente intraocular artificial durante la cirugía de catarata. La metodología establecida pueden ayudar en un futuro tanto al diseño de nuevos implantes como a los oftalmólogos a seleccionar la IOL adecuada a cada paciente para mejora su calidad visual.This thesis addresses three different case studies related to the crystalline lens. Firstly, the mechanical causes of the loss of accommodation amplitude with age, called presbyopia, were analysed through the finite element method. A high-fidelity simulation of the mechanism of accommodation including the contraction of the ciliary muscle was developed. This allowed us to analyse accommodation in depth, showing that although the lens capsule provides the force to accommodate, the stiffness ratio between the lens cortex and lens nucleus could have a higher effect on how the lens changes its shape. Secondly, the biomechanical stability of intraocular lenses (IOLs) was analysed. IOLs are essential for post-cataract patients as they substitute the functions of the crystalline lens. In this thesis, a wide variety of solutions were addressed: from the visco- and hyper-elasticity characterisation of IOL acrylic materials from depth sensing indentation and uniaxial tests to the simulation of the IOL biomechanical stability inside the capsular bag. We also performed a high-fidelity simulation of the IOL compression standards tests required by the IOLs to be commercialised and the results obtained were compared with clinical data. Lastly, we developed a patient-specific methodology to customise the IOL haptic design. Most of the numerical methology developed is intended to be used in the IOL pre-design phase to avoid costs and time. Thirdly, the IOL delivery during cataract surgery according to haptic and material design and injector characteristics was experimentally studied to avoid any possibility of IOL and eye damage. Apart from the injector size, the IOL material was the most influential parameter in the force exerted in IOL delivery. Why is the crystalline lens of vital importance? The crystalline lens is the responsible for both the dynamic change of the refractive power of the eye through the mechanism of accommodation and the correction of cornea aberrations. The dynamic optical change is consequence of change of the lens shape. However, as the lens ages over time, it decreases this dynamic optical change and becomes cloudy, what leads to the two most common lens-related pathologies, presbyopia and cataracts. Therefore, it is of utmost importance to study the lens mechanics and all issues related to the artificial intraocular lens that substitutes the lens during cataract surgery.<br /

Accommodation : clinical and theoretical investigations

Background: Accommodative insufficiency (AI) is a relatively common visual anomaly in children and young adults with an estimated prevalence of about 5%. Patients with AI usually suffer from blur, headaches and asthenopia associated with near work. The two most important treatment regimes for AI are plus lens reading additions (PLRA) and orthoptic exercises with the aim of normalising the accommodative system. The stimulus for the accommodative system is blur, which is an even-error signal, i.e., the blur gives the magnitude of the accommodation, but lacks the directional information; therefore, it is dependent on other cues to know if the accommodation needs to be increased or reduced. The main directional cues for the accommodative system are thought to be chromatic aberration (CA) and spherical aberration (SA). Recently there has been a large interest in the use of contact lenses to correct aberrations in order to create an improved image quality or create a near addition. Aims: The purpose was to evaluate the outcome of AI treatment, to investigate the effect on accommodation response when manipulating the directional cues to accommodation and to study the effect on accommodation when using a multifocal contact lens. Material and Methods: 46 children between 7-18 years of age, diagnosed with AI were dissipating in study I and II where they were treated with PLRA (+1.00 or +2.00D) or orthoptic exercise. In study III and IV, a normal group of 40 subjects were included (age 21 to 35) and 5 AI patients (age 10 to 18). They had their aberration and accommodation measured with and without accommodative cues present, and also with a multifocal contact lens which gives a near reading addition. Results: The result showed that there was no significant difference between the two treatment methods for AI patients. Further, there was a significant difference between the PLRA given, which indicates that the PLRA should not be of the higher strength. The accommodative response was not affected when the accommodative cues was eliminated or decreased. The multifocal contact lens was not able to relax the accommodation in young normal subjects and neither on AI subjects. Discussion: Results of our study and others have shown that vision therapy (PLRA and/or orthoptic exercises) can improve the time characteristic and magnitude of accommodation response with a persistent result. The PLRA of +1.00D is preferred to allow comfortable vision at near and at the same time exercise and stimulated the accommodative system rather than completely relieved. The SA and CA were showed to not be a strong directional cue for the accommodation which indicates that there are other cues more important for directional information. Since the multifocal contact lens was not able to relax the accommodation for neither of the subjects it is therefore unlikely that subjects with AI can be effectively treated with such lens. Conclusion: Based of the finding in the studies I would like to recommend that AI subjects can be treated with either +1.00D reading addition or orthoptic exercise, however, multifocal contact lenses should not be used for the treatment purpose of AI subjects

Toward Simulation-Based Training Validation Protocols: Exploring 3d Stereo with Incremental Rehearsal and Partial Occlusion to Instigate and Modulate Smooth Pursuit and Saccade Responses in Baseball Batting

“Keeping your eye on the ball” is a long-standing tenet in baseball batting. And yet, there are no protocols for objectively conditioning, measuring, and/or evaluating eye-on-ball coordination performance relative to baseball-pitch trajectories. Although video games and other virtual simulation technologies offer alternatives for training and obtaining objective measures, baseball batting instruction has relied on traditional eye-pitch coordination exercises with qualitative “face validation”, statistics of whole-task batting performance, and/or subjective batter-interrogation methods, rather than on direct, quantitative eye-movement performance evaluations. Further, protocols for validating transfer-of-training (ToT) for video games and other simulation-based training have not been established in general ― or for eye-movement training, specifically. An exploratory research study was conducted to consider the ecological and ToT validity of a part-task, virtual-fastball simulator implemented in 3D stereo along with a rotary pitching machine standing as proxy for the live-pitch referent. The virtual-fastball and live-pitch simulation couple was designed to facilitate objective eye-movement response measures to live and virtual stimuli. The objective measures 1) served to assess the ecological validity of virtual fastballs, 2) informed the characterization and comparison of eye-movement strategies employed by expert and novice batters, 3) enabled a treatment protocol relying on repurposed incremental-rehearsal and partial-occlusion methods intended to instigate and modulate strategic eye movements, and 4) revealed whether the simulation-based treatment resulted in positive (or negative) ToT in the real task. Results indicated that live fastballs consistently elicited different saccade onset time responses than virtual fastballs. Saccade onset times for live fastballs were consistent with catch-up saccades that follow the smooth-pursuit maximum velocity threshold of approximately 40-70˚/sec while saccade onset times for virtual fastballs lagged in the order of 13%. More experienced batters employed more deliberate and timely combinations of smooth pursuit and catch-up saccades than less experienced batters, enabling them to position their eye to meet the ball near the front edge of home plate. Smooth pursuit and saccade modulation from treatment was inconclusive from virtual-pitch pre- and post-treatment comparisons, but comparisons of live-pitch pre- and post-treatment indicate ToT improvements. Lagging saccade onset times from virtual-pitch suggest possible accommodative-vergence impairment due to accommodation-vergence conflict inherent to 3D stereo displays

Depth Perception in Humans and Animals

This thesis has been the product of three projects which are all related to depth perception, within the core discipline of vision science. The first project was collaborative work between the University of Durham and researchers at University of California, Berkeley. These included Prof. Martin S. Banks and Bill Sprague at U.C. Berkeley, and Dr. Jurgen Schmoll and Prof. Gordon Love at the University of Durham. This project built on previous research investigating the ocular adaptations in different land-dwelling vertebrate species. We found that we could strongly predict pupil shape based on the diel activity and trophic strategies of a species, and our simulations showed that multifocal pupils may extend depth of focus. The second project was also in collaboration with U.C. Berkeley; Prof. Martin S. Banks, and Paul Johnson, which involved a study into 3D displays and different approaches to reducing the vergence-accommodation conflict. Our results showed that a focus-correct adaptive system did assist in the vergence-accommodation conflict, but monovision was less efficacious and we believe this was due to a reduction in stereoacuity. The third project considered spherical aberration as a cue to the sign of defocus. We present simulations which show that the spatial frequency content of images on either side of focus differ, and suggest that this could, in principle, drive the accommodative process

Optometric extension program: 1991 bibliography of near lenses and vision training research

Optometric extension program: 1991 bibliography of near lenses and vision training researc