No description available.

No description available.

Call number: LD2668 .T4 1937 A805 / Master of Science

Handedness is the most obvious expression of lateralized behaviour in humans. However, there is only limited knowledge about other forms of lateralized behaviour, e.g. preferential use of an eye and whether these may correlate with handedness. Thus to investigate this, 100 subjects (50 males and 50 females) between 11 and 80 years of age were assessed for their eye preference, eye dominance, visual acuity, and handedness. Eye preference was assessed by performing four different monocular tasks, eye dominance by performing the binocular Dolman test, visual acuity was assessed with a Snellen chart and handedness was surveyed using the Edinburgh Handedness Inventory. Regarding eye preference, the right eye was preferred by 69% of the subjects. 90 % of the subjects were consistent for their preferred eye across all four tasks. 66% of the subjects had a dominant right eye, 33% had left eye dominance and 1% could not be assessed using the Dolman test. 56% of the subjects differed in their visual acuity between both eyes, while 43% had the same visual acuity in both of their eyes. 86% of the subjects were right-handed while 4% were left handed and 10% were ambidextrous. Significant correlations were found between visual acuity and eye preference and between visual acuity and eye dominance. The study also found a positive correlation between handedness and eye preference. These results support the notion that there is a weak correlation between the different aspects of lateralized behaviour in humans.

Simulated images can provide insight into the performance of optical systems, especially those with complicated features. Many modern solutions for presbyopia and cataracts feature sophisticated power geometries or diffractive elements. Some intraocular lenses (IOLs) arrive at multifocality through the use of a diffractive surface and multifocal contact lenses have a radially varying power profile. These type of elements induce simultaneous vision as well as affecting vision much differently than a monofocal ophthalmic appliance. With myriad multifocal ophthalmics available on the market it is difficult to compare or assess performance in ways that effect wearers of such appliances. Here we present software and algorithmic metrics that can be used to qualitatively and quantitatively compare ophthalmic element performance, with specific examples of bifocal intraocular lenses (IOLs) and multifocal contact lenses. We anticipate this study, methods, and results to serve as a starting point for more complex models of vision and visual acuity in a setting where modeling is advantageous. Generating simulated images of real- scene scenarios is useful for patients in assessing vision quality with a certain appliance. Visual acuity estimation can serve as an important tool for manufacturing and design of ophthalmic appliances.

No description available.

Thesis advisor: Daniel Kirschner / Thesis advisor: Caroly Shumway / Species-specific differences in visual acuity have been demonstrated across species of cichlids differing in social and habitat complexity. What is the role of plasticity? A visual acuity assay on two species of fish reared in different habitat and social complexity was used to study brain plasticity in Xenotilapia flavipinnis and Asprotilapia leptura juveniles. The X. flavipinnis lives in sandy habitats and schools as juveniles. These fry were raised in an impoverished social environment in one case and an enriched habitat environment in another. The A. leptura lives in rocky habitats naturally. These fry were raised in an impoverished habitat environment. All conditions were compared to control groups with natural social and habitat conditions. I found that a change in social complexity had a plastic effect on visual acuity but a change in habitat complexity in both cases did not. / Thesis (BS) — Boston College, 2006. / Submitted to: Boston College. College of Arts and Sciences. / Discipline: Biology. / Discipline: College Honors Program.

O estudo da acuidade Vernier (VRN) revela a capacidade do sistema visual humano em detectar deslocamentos espaciais de poucos arcos de segundos, menores que a distância entre dois cones foveais adjacentes. Tal fato desperta interesse teórico sobre o tema, além de futuras aplicações na área clínica. A acuidade VRN pode ser medida tanto psicofisicamente quanto eletrofisiologicamente. Para a detecção de quebras de colinearidade (acuidade VRN), alguns autores hipotetizam que as células ganglionares (CGs) M da retina provêem sinal adequado da retina ao córtex, e dão suporte ao desempenho psicofísico da tarefa VRN. Em condições de estímulos semelhantes, as células ganglionares magnocelulares (M) em primatas parecem ter precisão espacial com razão sinal-ruído mais alta do que as células parvocelulares (P) . A dependência ao contraste (C) das células M na precisão espacial, frequência espacial, frequência temporal e velocidade do estímulo é mais similar ao desempenho psicofísico em humanos do que comparados aos dados das células P (Rüttiger et al., 2002; Sun et al., 2004). Nós utilizamos o Potencial Provocado Cortical Visual de Varredura (sVEP) para avaliar esta hipótese no nível de processamento intermediário entre as respostas de célula única na retina e a detecção psicofísica. Nós medimos os limiares corticais VRN em função do contraste (14 participantes, média de 28,21 ± 2,8) e lacunas (9 participantes, média de 29,7 ± 5,9). As quebras verticais VRN na colinearidade foram introduzidas em uma grade de onda quadrada horizontal. O estímulo VRN alternou entre um estado alinhado (grades sem quebras) e desalinhado (grades com quebras) a 6 Hz. Durante cada uma das 10 tentativas, o deslocamento aumentou em passos logarítmicos iguais de 0,5 a 7,5. O limiar VRN foi definido no momento do deslocamento em que a extrapolação linear da média vetorial das respostas em 1F atinge zero uV. Os contrastes testados foram: 4, 8, 16, 32, 64, 80%. Os resultados mostram que (1) aos limiares VRN em Log, medidos com sVEP, com o C em Log, diminuíram de forma linear (com uma inclinação de -0,5), similiares às células ganglionares M mas não P (Sun et al., 2004) e próximo às medidas psicofísicas (Sun et al., 2004; Wehrhahn e Westheimer, 1990); (2) Para C 16% obtivemos limiares de hiperacuidade (menor que 1 arcmin). Em altos contrastes a média do limiar foi de 0,37(erro padrão de 0,06 unidades logarítmicas); (3) Os limiares para o 2F tiveram uma dependência para o contraste diferente, com poucos efeitos para contraste abaixo de 16%. (4) As inclinações das linhas de extrapolação dos sVEP para o 1F1 foram 2 a 3 vezes maiores que as inclinações para 2F; (5) No protocolo controle, deslocamentos bidirecionais e simétricos geraram somente respostas no 2F. Os resultados 3 a 5 implicam que os componentes 1F e 2F derivam de neurônios distintos e fundamentam que respostas no 2F refletem respostas de movimento cortical simétrico. A dependência dos limiares de contraste do sVEP VRN (1F) é similiar aos estudos prévios psicofísicos (Sun et al., 2004; Wehrhahn e Westheimer, 1990), e repete a dependência ao contraste das células M (Sun et al., 2004). Estes resultados fundamentam a hipótese que o córtex extrai informações da posição relativa com precisão de hiperacuidade dos sinais advindos das células M / The human visual system is able to detect spatial displacements of a few arcsec, much smaller than the distance between two adjacent foveal cones. Hyperacuity tasks such as Vernier (VRN) have both theoretical importance as well as clinical application. VRN can be measured psychophysically and with sVEP. Some authors hypothesize that M ganglion cells provide the retinal signal to cortex adequate to support Vernier performance. Under stimulus conditions analogous to detection of Vernier offsets, primate magnocellular (M) ganglion cells appear to have more precise spatial localization (with higher Signal to Noise Ratio) than parvocellular (P) cells, and the dependence of M cell spatial precision on contrast (C), spatial frequency, temporal frequency and stimulus velocity is more similar to human psychophysical performance than comparable data from P cells (Ruttiger et al, 2002; Sun et al., 2003, 2004) (Rüttiger et al., 2002; Sun et al., 2004). We measured the C-dependence of cortical VRN thresholds (thd) using the Sweep VEP (sVEP) to help evaluate this hypothesis at a processing level intermediate between single-cell retinal responses and psychophysical detection. We measured Vernier thds using sVEP as function of constrast (12 young adults, age means 28.21 yrs ± 2.8) and Gaps (9 participants, 29.7 ± 5.9) with normal vision. Vertical VRN breaks in colinearity were introduced to a horizontal squarewave grating. The VRN stimulus alternated between aligned (grating w/o breaks) and misaligned (w/breaks) states at 6 (or 10) Hz. During each of ten, 10-s trials, displacement (D) was increased in equal logarithmic steps from 0.5 to 7.5. Vernier thd was defined as the D at which the rising slope of the vector averaged 1F response extrapolated to zero V. The Cs tested were: 4, 8, 16, 32, 64, 80%. We Found: (1) Log Vernier thd measuered with sVEP decreased linearly with log C similar to M- (but not P-) ganglion cells (Sun et al., 2004) with a slope of -0.5, close to that measured psychophysically (Rüttiger et al., 2002; Sun et al., 2004); (2) For C 16% , thds were true hyperacuities (less than 1). At high C, mean thd was 0.37(S.E = 0.06 log units); (3) Thds for 2F had a different C dependence, with little effect of C below 16 %. Thds for 2F were < 1F thds below 16 % C, but were 1F thds beyond 16 %; (4) The slopes of the sVEP extrapolation lines for 1F were 2-3 times > 2F slopes; (5) In a control protocol, symmetric, bidirectional displacements only generated 2F responses. Results 3-5 imply that the 1F and 2F components derive from distinct neurons, and support the notion that 2F responses reflect symmetric cortical motion responses. The C-dependence of sVEP Vernier (1F) thresholds is similar to prior psychophysics (Sun et al., 2004; Wehrhahn e Westheimer, 1990), and recapitulates Mcell C-dependence (Sun et al., 2004). This results support the hypothesis that cortex extracts relative position information with hyperacuity precision preferentially from M cell signals

SALES, R. Achados da acuidade visual estática e dinâmica em pacientes com disfunção vestibular. 106f. Tese (Doutorado) da Faculdade de Medicina de Ribeirão Preto-USP. Ribeirão Preto-SP, 2013. Para a obtenção da visão nítida é necessário que a imagem permaneça estável na retina, mesmo com a movimentação cefálica. As pessoas que sofrem de labirintopatias são mais sensíveis a efeitos visuais, podendo apresentar os sintomas de tontura, enjoo e oscilopsia durante a movimentação cefálica. Esse fato ocorre devido ao conflito sensorial entre o sistema vestibular e visual. O presente estudo objetivou verificar a variação da acuidade visual estática e dinâmica em pacientes com disfunção vestibular. Foram selecionados pacientes de ambos os sexos, com idade entre 14 e 88 anos de idade submetidos ao exame de vetoeletronistagmografia entre os anos de 2009 e 2011. Esses pacientes também foram submetidos ao exame de acuidade visual estática e dinâmica. Na acuidade visual dinâmica, foram pré-determinadas frequências de 0.5, 1.0, 1.5 e 2.0 Hertz para a movimentação cefálica. Os resultados mostraram maior decréscimo da acuidade visual estática e dinâmica entre os pacientes com labirintopatias bilaterais se comparadas com as unilaterais e o grupo controle. Além disso, o aumento da frequência produziu decréscimo da acuidade visual em todos os grupos e a posição da movimentação cefálica na vertical mostrou maior sensibilidade se comparada à horizontal. Pôde-se concluir que os pacientes com labirintopatias apresentaram decréscimo da acuidade visual estática e dinâmica, principalmente nas frequências mais altas e com a movimentação cefálica na posição vertical, sendo esses exames importantes para auxiliar no diagnóstico e monitoramento das labirintopatias. Palavras-chave: Acuidade visual; Sistema vestibular / For obtaining an accurate image is necessary that remains stable on the retina, even with head movement. People suffering from labyrinthopathy are more sensitive to visual effects, and may have symptoms of dizziness, nausea and oscillopsia during head movement. This fact occurs because the sensory conflict between visual and vestibular system. The present study aimed to determine the variation of static and dynamic visual acuity in patients with vestibular dysfunction. Selected patients were of both gender, aged between 14 and 88 years old who underwent examination vetoeletronistagmografia between the years 2009 and 2011 at the home Institution. The patients were subjected to tests of visual acuity static and dynamic. In dynamic visual acuity, were predetermined frequencies of 0.5, 1.0, 1.5 and 2.0 Hz for the patient\'s head movement. The results showed a greater decrease in static and dynamic visual acuity among patients with bilateral labyrinthopathy compared with the unilateral and control groups. In addition, the frequency increase produced decreased visual acuity in all groups and the position of head movement in the vertical showed a higher sensitivity compared to the horizontal. It was concluded that patients with labyrinthopathy showed a decrease of static and dynamic visual acuity, especially at higher frequencies and with head movement in a vertical position, and these important tests to assist in diagnosis and monitoring of the labyrinthopathy. Keywords: Visual acuity; Vestibular system

Purpose and hypothesis: The purpose of this study was to optimize and standardize the following parameters of sweep Visually Evoked Potential (sVEP) in adults: criteria for fitting the regression line to estimate threshold, luminance, electrode placement, temporal frequency, sweep direction, presence of fixation target and stimulus area. The hypothesis is that the parameters chosen will have an impact on the measured visual acuity, contrast threshold and on the number of viable sVEP plots. Methods: The Power Diva software, Version 1.9 was used for this study. Five gold cup active electrodes, one reference electrode and one ground electrode were used to measure the Electroencephalography (EEG) signals. Six adult participants (aged 17 to 35 years), with corrected to normal visual acuity and no history of ocular disease took part in each experiment, except for the repeatability experiment in which 3 subjects participated. Four criteria for regression line fitting were compared. Psychophysical thresholds were used to validate the sVEP measures for the different criterion and repeatability of sVEP was estimated for 10 sessions. The effect of luminance (25 cd/m2, 50 cd/m2, 100 cd/m2), electrode placement (Power Diva and ISCEV), temporal frequency (6 Hz, 7.5 Hz, 10 Hz), sweep direction, fixation target and stimulus area were investigated. A repeated measure ANOVA statistical method was used to analyze the average threshold and the number of viable plots out of five active channels for all subjects. Results: Criterion 2 and 3 gave better visual acuity, higher contrast sensitivity, better repeatability and gave results that were closer to the psychophysical threshold than criterion 0 and 1. Luminance of 25 cd/m2 gave significantly fewer viable readings than 50 and 100 cd/m2 while measuring visual acuity (F = 5.11, df = 2, p = 0.0295). Temporal frequency of 7.5 Hz gave significantly more viable readings than 6 and 10 Hz while measuring visual acuity (F = 50.53, df = 2, p < 0.0001) and contrast threshold (F = 9.87, df = 2,p = 0.0043). There was a highly significant interaction of criterion with temporal frequency (F = 1536.98, df = 6, p < 0.0001) while measuring contrast threshold. There was a significant interaction of criterion with sweep direction (F = 4.26, df = 3, p = 0.0231) and for the number of readings (F = 3.75, df = 3, p = 0.0343) while measuring visual acuity. There was an interaction of criterion with sweep direction (F = 4.97, df = 3, p = 0.0136) while measuring contrast threshold at a spatial frequency of 1 cpd. There was a significant effect of fixation target (F = 7.64, df = 1, p = 0.0396) while measuring visual acuity. There was a significant effect of stimulus area (F = 11.78, df = 4, p < 0.0001) on the number of readings while measuring contrast threshold. Conclusion: The sVEP parameters chosen do have a significant effect on visual acuity, contrast threshold and on the number of viable readings. The following parameters are recommended in adults on the basis of results; Criterion 2 or 3 for fitting regression line (C2 - regression line fitted from the signal peak amplitude to the last data point with a signal to noise ratio (SNR) >1; C3 – similar to criterion 2, but the threshold should be within sweep range used), luminance of 50 or 100 cd/m2 , either Power Diva (PD) or International Society for Clinical Electrophysiology of Vision (ISCEV) electrode placement, temporal frequency of 7.5 Hz, either sweep direction, measurement with the central fixation target, larger stimulus area.