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The increasing prevalence of myopia over the past few decades and its association with potential ocular complications make myopia an important research topic. The present work is concerned with the structural and functional characteristics of a group of myopic and emmetropic individuals. The technical experiments in this work investigated firstly the effect of instrument alignment on peripheral refraction measurements and revealed that the corneal vertex was an acceptable alignment position of the Shin-Nippon NVision-K 5001 autorefractor, allowing consistent alignment with other instruments used in this research. Secondly, spectacles could be used to provide comparable vision to contact lenses in the visual performance studies. In the main experimental parts of this work, visual performance and multiple aspects of ocular structure were assessed across a wide range of eccentricities along the horizontal and vertical meridians within the same eyes. The structural properties of the myopic eye were measured through central and peripheral autorefraction, and through cornea to retina dimensions using non-contact biometry. In addition, the central and peripheral resolution acuities of myopic and emmetropic eyes for high and low contrast levels were investigated. Our structural and functional measurements revealed relatively prolate myopic eyes with reduced high contrast resolution acuity, compared to emmetropic eyes. Moreover, multiple regression analyses were performed at the fovea and outermost retinal eccentricities common to all core experiments but revealed no strong relationship between the structure and function of the myopic eye. Finally, regarding asymmetry, the nasal and superior retinae were found to be longer and to perform better in comparison to the temporal and superior retinae respectively.

The increasing prevalence of myopia over the past few decades and its association with potential ocular complications make myopia an important research topic. The present work is concerned with the structural and functional characteristics of a group of myopic and emmetropic individuals. The technical experiments in this work investigated firstly the effect of instrument alignment on peripheral refraction measurements and revealed that the corneal vertex was an acceptable alignment position of the Shin-Nippon NVision-K 5001 autorefractor, allowing consistent alignment with other instruments used in this research. Secondly, spectacles could be used to provide comparable vision to contact lenses in the visual performance studies. In the main experimental parts of this work, visual performance and multiple aspects of ocular structure were assessed across a wide range of eccentricities along the horizontal and vertical meridians within the same eyes. The structural properties of the myopic eye were measured through central and peripheral autorefraction, and through cornea to retina dimensions using non-contact biometry. In addition, the central and peripheral resolution acuities of myopic and emmetropic eyes for high and low contrast levels were investigated. Our structural and functional measurements revealed relatively prolate myopic eyes with reduced high contrast resolution acuity, compared to emmetropic eyes. Moreover, multiple regression analyses were performed at the fovea and outermost retinal eccentricities common to all core experiments but revealed no strong relationship between the structure and function of the myopic eye. Finally, regarding asymmetry, the nasal and superior retinae were found to be longer and to perform better in comparison to the temporal and superior retinae respectively.

For purposes of this thesis, live visual performance is defined as the accompaniment of music using projected or televised visual stimuli to achieve a supplemental interpretation of the music to tell its 'story' in a visual way. In my research I have found that, while complex narrative in a song can be conveyed through various means, the attention span of those listening and watching in a club setting is not conducive for patrons to sit down and engage in watching the visuals for a protracted period of time. Most patrons are dancing and socializing and do not choose to watch the video to derive complex meaning or context. My research has shown that, while introducing complex visual storylines may be the ultimate goal for a live visual performance in a studio or orchestral setting, the best way to convey an artist's message in a club environment is through the use of repetitive symbols and visuals that move according to the beats of the music, light up the darkened atmosphere, and/or create a social metronome. This thesis presents the process by which the visual symbols were created and then chosen for specific, targeted performances and discusses the results of patron surveys that assess their initial responses to the accompanying live visual performance.

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Nighttime intersection crashes account for nearly half of all the intersection crashes, making them a major traffic safety concern. Although providing lighting at intersections has proven to be a successful countermeasure against these crashes, existing approaches to designing lighting at intersections are overly simplified. Current standards are based on recommending lighting levels, but do not account for the role of human vision or vehicle headlamps or the numerous pedestrian-vehicle conflict locations at intersections. For effective intersection lighting design, empirical evidence is required regarding the effects of lighting configuration (part of the intersection illuminated) and lighting levels on nighttime visibility. This research effort had three goals. The first was to identify an intersection lighting design that results in the best nighttime visibility. The second goal was to determine the effect of illuminance on visual performance at intersections. The third goal was to understand the relationships between object luminance, contrast, and visibility. To achieve these goals, three specific configurations were used, that illuminated the intersection approach (Approach), intersection box (Box), and both the intersection approach and box (Both). Each lighting configuration was evaluated under five levels of illumination. Visibility was assessed both objectively (visual performance) and subjectively (perceptions of visibility and glare). Illuminating the intersection box led to superior visual performance, higher perceived visibility, and lower perceived glare. For this same configuration, plateaus in visual performance and perceived visibility occurred between 8 and 12 lux illuminance levels. A photometric analysis revealed that the Box lighting configuration rendered targets in sufficient positive and negative contrasts to result in higher nighttime visibility. Negatively contrast targets aided visual performance, while for targets rendered in positive contrast visual performance was dependent on the magnitude of the contrast. The relationship between pedestrian contrast and perceived pedestrian visibility was more complex, as pedestrians were often rendered in multiple contrast polarities. These results indicate that Box illumination is an effective strategy to enhance nighttime visual performance and perceptions of visibility while reducing glare, and which may be an energy efficient solution as it requires fewer luminaires. / Ph. D.

The main aim of this thesis is to evaluate the effect of meridional blur, using refractive induced astigmatism, on visual performance at far and close distances. Visual performance was evaluated using letter discrimination tasks at distance and near (visual acuity, VA) and a reading task at near on subjects with pharmacologically blocked (young) or absent accommodation (presbyopic and pseudophakic). The effect of astigmatism was tested using positive cylindrical lenses oriented at 180 and 90 degrees, these simulating with- (WTR) and against-the-rule (ATR) astigmatism. Other refractive status were also evaluated, namely, in-focus and spherical defocus. The visual performance data were correlated with biometric measurements (pupil size, anterior chamber depth (ACD), corneal and ocular aberrations, corneal multifocality, patient age, axial length). Further, the functionality of meridional blur was evaluated for alphabets in addition to the standard Roman alphabet using a VA task. The results confirm that myopic astigmatism contributes to a better visual performance at closer distances, with ATR astigmatism providing higher performance for reading tasks compared to other forms of astigmatism. Anatomical factors such as pupil size, corneal multifocality and ACD were significantly correlated visual performance, while other ocular characteristics were not. Ray tracing modelling using wavefront data was a moderate predictor of VA and reading acuity. The results of the effect of meridional blur orientation on alphabets other than the Roman alphabet, suggest that visual performance is dependent on the interaction between blur orientation and letter's spatial characteristics. In conclusion, pseudoaccommodation is a multifactorial phenomenon with pupil size being the major contributor for the improvement in visual performance. Against-the-rule shows advantages over WTR astigmatism, by providing higher reading performance, however extending the present and previous findings for clinical application will require further investigation on the effect of meridional blur in common and socio-culturally adapted tasks.

The main aim of this thesis is to evaluate the effect of meridional blur, using refractive induced astigmatism, on visual performance at far and close distances. Visual performance was evaluated using letter discrimination tasks at distance and near (visual acuity, VA) and a reading task at near on subjects with pharmacologically blocked (young) or absent accommodation (presbyopic and pseudophakic). The effect of astigmatism was tested using positive cylindrical lenses oriented at 180 and 90 degrees, these simulating with- (WTR) and against-the-rule (ATR) astigmatism. Other refractive status were also evaluated, namely, in-focus and spherical defocus. The visual performance data were correlated with biometric measurements (pupil size, anterior chamber depth (ACD), corneal and ocular aberrations, corneal multifocality, patient age, axial length). Further, the functionality of meridional blur was evaluated for alphabets in addition to the standard Roman alphabet using a VA task. The results confirm that myopic astigmatism contributes to a better visual performance at closer distances, with ATR astigmatism providing higher performance for reading tasks compared to other forms of astigmatism. Anatomical factors such as pupil size, corneal multifocality and ACD were significantly correlated visual performance, while other ocular characteristics were not. Ray tracing modelling using wavefront data was a moderate predictor of VA and reading acuity. The results of the effect of meridional blur orientation on alphabets other than the Roman alphabet, suggest that visual performance is dependent on the interaction between blur orientation and letter¿s spatial characteristics. In conclusion, pseudoaccommodation is a multifactorial phenomenon with pupil size being the major contributor for the improvement in visual performance. Against-the-rule shows advantages over WTR astigmatism, by providing higher reading performance, however extending the present and previous findings for clinical application will require further investigation on the effect of meridional blur in common and socio-culturally adapted tasks. / Bradford School of Optometry and Vision Sciences

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Sport has become a very competitive business and focus has been placed on reaching ones full potential. Visual involvement in a sport varies according to environmental demands associated with that sport. These environmental demands are matched by a task specific motor response. The primary aim of this study was to determine if visual skills training programmes could produce beneficial performance results for cricket and soccer players. In order to measure the athletic ability of a cricket and soccer player it is important not only to measure the hardware visual skills of the player, but also the player’s hand-eye co-ordination ability and software visual skills. Thus, aspects of the nervous system such as perceptual motor co-ordination, reaction time and anticipation ability should also be measured to get an indication of the player’s performance ability. In this study highly skilled cricket players and highly skilled soccer academy players, who were actively participating at a provincial level of competition, served as subjects. Due to professional reasons, the soccer academy players had to withdraw from this study. The provincial cricket players continued for the duration of the programme. Thus, due to the abovementioned the aim of this study was two fold, to determine whether statistically significant differences exist between the pre and post-training measurements of cricket players on several visual skills tests and secondly to determine whether statistically significant differences exist between the pre-training measurements of cricket and soccer players on the various visual skills measurements. The data of the variables tested were coded in computer format and statistically evaluated. Since the sample is relatively small non-parametric statistics were used to analyse the data. Two different Non-parametric t-tests were used: the Wilcoxon test is the distribution-free analogue of the t-test for related samples and the Mann-Whitney test is the distribution-free alternative to the independent samples t-test and was used for testing the differences between the means of the cricket players and the soccer players. After the initial testing the cricket players participated in an eight-week visual skill and performance skills programme for 60 minutes a day, once a week. The programme included sports vision activities, speed and agility activities and ball skills activities. Hereafter a retest was done. The pre-training and post-training values of the cricket players were recorded and significance of difference was determined by using the Wilcoxon signed-ranks test. The experimental research revealed that the visual skills programme did have a significant influence on most of the tested variables (ball handling skills, co-ordination, visual awareness, eye tracking skills, accuracy, peripheral awareness, pro-action – reaction skills and visual concentration). For some variables that were tested on the experimental group (the cricket players) improvements were found, which indicates that the improvements can be ascribed to the visual skills programme. The results indicated that more than half of the variables tested improved. It can thus be concluded that the hypothesis that was set for this paper has been proven right. Statistics indicated that there was an increase in most of the variables tested (ball handling skills, co-ordination, visual awareness, eye tracking skills, accuracy, peripheral awareness, proaction – reaction skills and visual concentration), which prove then that visual skills training will result in an increase in the players’ visual fields resulting to an increase in the visual skills on and off the cricket fields. Visual skills training programmes are beneficial to competitive sports performance. Copyright / Dissertation (MA)--University of Pretoria, 2009. / Biokinetics, Sport and Leisure Sciences / unrestricted