Purpose: There is little agreement on the age at which visual acuity (VA) and contrast sensitivity (CS) become adult-like. The ultimate purpose of this thesis was to determine whether VA and CS are adult-like at the age of 6-8 or 9-12 years by using both objective and subjective methods in the same individuals. The objective method (sweep visually evoked potentials [sVEP]) has many parameters that may affect the measurement of VA or CS and previously these had not been studied systematically, especially in children. Therefore, a second purpose was to study the effects of these parameters on VA and contrast thresholds and to determine the parameters that give the most repeatable measurements and the greatest number of viable readings in children, to be compared to previous data obtained in adults. Methods: The effect of five criteria (C0-C4) for choosing the endpoint for the regression line fitting and three luminance levels (25, 50, and 100 cd/m2) on the sVEP VA and contrast thresholds (at 1 and 8 cpd) was investigated in six 6-8 year old children. Additionally, the effect of these parameters on the number of viable readings obtained from five active electrodes was investigated. C0 was derived from the sVEP software (PowerDiva), C1 used the best fit by eye to determine the range over which the regression line was fitted, C2 used the data point between signal peak and the last data point with an SNR ≥ 1, C3 was similar to C2 but was defined so that the threshold should be within the sweep range, and C4 was similar to C2 except that the SNR should not fall below one at any point within the range used for the regression line fitting. The effects of two electrode placements, three temporal frequencies (6, 7.5, and 10 Hz), sweep direction (low to high and high to low), presence or absence of a fixation target, three stimulus areas (6, 4, and 2° for VA and 15, 10, and 6° for contrast thresholds) and three sweep durations (10, 15, and 20 sec) on VA and contrast thresholds (at 1, 4, or 8 cpd) measured with sVEP were also investigated in six 6-8 year-old children and six adults with normal vision. Additionally, the effect of these parameters on the number of viable readings obtained from five active electrodes was investigated. The sVEP parameters that were found to give the best threshold measurements were employed in a cross sectional study of the development of VA and CS. In this study the objective sVEP technique and two psychophysical techniques were used. The psychophysical techniques were comprised of a two-alternative forced choice (2AFC) staircase for measuring VA and contrast thresholds and signal detection theory (SDT) for measuring contrast threshold. Crowded and uncrowded logMAR VA were also measured with a Bailey-Lovie logMAR chart. The study included three age groups (6-8, 9-12 year olds and adults). The criterion employed by each age group as indicated by the SDT was compared. Results: There was a significant effect of the criterion for choosing the endpoint for the regression line fitting (p < 0.05) on all the measures and a significant effect of luminance (p = 0.036) on contrast threshold at 1 cpd. Criterion C2 (in which the range for the regression line fit was defined to include all the data between the signal peak and the last data point [furthest from the peak] with an SNR ≥ 1) consistently gave more viable readings and better thresholds (i.e. higher VA and lower contrast thresholds) than the other criteria. Also C2 was the best criterion in terms of repeatability in children, and repeatability and validity in adults (Yadav et al., 2009). The luminance of 25 cd/m2 gave higher contrast thresholds than 50 or 100 cd/m2. There was a significant effect of temporal frequency on the number of viable readings for VA (p < 0.0001) and for contrast thresholds (p = 0.0001), with more viable readings at 7.5 Hz than at either 6 or 10 Hz. The adults gave more readings with the fixation target than without it (p = 0.04) for contrast threshold at 1 cpd. The smallest stimulus area used gave rise to fewer viable readings in both adults and children (p = 0.022 for VA and 0.0001 for contrast threshold). The other parameters (electrode placement, sweep direction and sweep duration) did not result in significant differences. There was a significant effect of age on crowded (p = 0.0001) and uncrowded (p < 0.0001) VA. The 6-8 year olds gave poorer VA than the 9-12 year olds or adults for both crowded and uncrowded VA. For the grating VA (sVEP and 2AFC staircase) there was a significant effect of age (p = 0.002). The 6-8 year olds had poorer VA than the 9-12 year olds or adults. For contrast threshold at 1 cpd, a significant effect of age was found for the 2AFC (p = 0.008) and SDT (p = 0.0003). The 6-8 year olds gave poorer contrast thresholds than adults with each procedure. For contrast thresholds at 8 cpd, there was a significant effect of age with the 2AFC staircase (p = 0.036). The 6-8 year olds gave poorer contrast thresholds than the 9-12 year olds. For SDT, there was a significant effect of age on criterion (p < 0.05), with adults being more likely to say “no” in the yes-no SDT procedure than both the 6-8 year olds and the 9-12 year olds for contrast threshold at 1 cpd. Adults were also more likely to say “no” than the 9-12 year olds for contrast thresholds at 8 cpd. Conclusions: This thesis has shown that VA and CS are not adult-like until the age of 9-12 years by these measures and that children do show differences in criterion compared to adults in psychophysical testing. This difference in criterion indicates the use of SDT or force-choice procedures to avoid this problem in any psychophysical developmental study. It has also shown that criterion for choosing the endpoint for the regression line fitting in the sVEP technique has the greatest effect on VA and contrast thresholds measurements and viable readings, while the other sVEP parameters have little effect on the thresholds.

Thesis (M.Sc.)--Memorial University of Newfoundland, 2000. / Bibliography: leaves 45-57.

Purpose: There is little agreement on the age at which visual acuity (VA) and contrast sensitivity (CS) become adult-like. The ultimate purpose of this thesis was to determine whether VA and CS are adult-like at the age of 6-8 or 9-12 years by using both objective and subjective methods in the same individuals. The objective method (sweep visually evoked potentials [sVEP]) has many parameters that may affect the measurement of VA or CS and previously these had not been studied systematically, especially in children. Therefore, a second purpose was to study the effects of these parameters on VA and contrast thresholds and to determine the parameters that give the most repeatable measurements and the greatest number of viable readings in children, to be compared to previous data obtained in adults. Methods: The effect of five criteria (C0-C4) for choosing the endpoint for the regression line fitting and three luminance levels (25, 50, and 100 cd/m2) on the sVEP VA and contrast thresholds (at 1 and 8 cpd) was investigated in six 6-8 year old children. Additionally, the effect of these parameters on the number of viable readings obtained from five active electrodes was investigated. C0 was derived from the sVEP software (PowerDiva), C1 used the best fit by eye to determine the range over which the regression line was fitted, C2 used the data point between signal peak and the last data point with an SNR ≥ 1, C3 was similar to C2 but was defined so that the threshold should be within the sweep range, and C4 was similar to C2 except that the SNR should not fall below one at any point within the range used for the regression line fitting. The effects of two electrode placements, three temporal frequencies (6, 7.5, and 10 Hz), sweep direction (low to high and high to low), presence or absence of a fixation target, three stimulus areas (6, 4, and 2° for VA and 15, 10, and 6° for contrast thresholds) and three sweep durations (10, 15, and 20 sec) on VA and contrast thresholds (at 1, 4, or 8 cpd) measured with sVEP were also investigated in six 6-8 year-old children and six adults with normal vision. Additionally, the effect of these parameters on the number of viable readings obtained from five active electrodes was investigated. The sVEP parameters that were found to give the best threshold measurements were employed in a cross sectional study of the development of VA and CS. In this study the objective sVEP technique and two psychophysical techniques were used. The psychophysical techniques were comprised of a two-alternative forced choice (2AFC) staircase for measuring VA and contrast thresholds and signal detection theory (SDT) for measuring contrast threshold. Crowded and uncrowded logMAR VA were also measured with a Bailey-Lovie logMAR chart. The study included three age groups (6-8, 9-12 year olds and adults). The criterion employed by each age group as indicated by the SDT was compared. Results: There was a significant effect of the criterion for choosing the endpoint for the regression line fitting (p < 0.05) on all the measures and a significant effect of luminance (p = 0.036) on contrast threshold at 1 cpd. Criterion C2 (in which the range for the regression line fit was defined to include all the data between the signal peak and the last data point [furthest from the peak] with an SNR ≥ 1) consistently gave more viable readings and better thresholds (i.e. higher VA and lower contrast thresholds) than the other criteria. Also C2 was the best criterion in terms of repeatability in children, and repeatability and validity in adults (Yadav et al., 2009). The luminance of 25 cd/m2 gave higher contrast thresholds than 50 or 100 cd/m2. There was a significant effect of temporal frequency on the number of viable readings for VA (p < 0.0001) and for contrast thresholds (p = 0.0001), with more viable readings at 7.5 Hz than at either 6 or 10 Hz. The adults gave more readings with the fixation target than without it (p = 0.04) for contrast threshold at 1 cpd. The smallest stimulus area used gave rise to fewer viable readings in both adults and children (p = 0.022 for VA and 0.0001 for contrast threshold). The other parameters (electrode placement, sweep direction and sweep duration) did not result in significant differences. There was a significant effect of age on crowded (p = 0.0001) and uncrowded (p < 0.0001) VA. The 6-8 year olds gave poorer VA than the 9-12 year olds or adults for both crowded and uncrowded VA. For the grating VA (sVEP and 2AFC staircase) there was a significant effect of age (p = 0.002). The 6-8 year olds had poorer VA than the 9-12 year olds or adults. For contrast threshold at 1 cpd, a significant effect of age was found for the 2AFC (p = 0.008) and SDT (p = 0.0003). The 6-8 year olds gave poorer contrast thresholds than adults with each procedure. For contrast thresholds at 8 cpd, there was a significant effect of age with the 2AFC staircase (p = 0.036). The 6-8 year olds gave poorer contrast thresholds than the 9-12 year olds. For SDT, there was a significant effect of age on criterion (p < 0.05), with adults being more likely to say “no” in the yes-no SDT procedure than both the 6-8 year olds and the 9-12 year olds for contrast threshold at 1 cpd. Adults were also more likely to say “no” than the 9-12 year olds for contrast thresholds at 8 cpd. Conclusions: This thesis has shown that VA and CS are not adult-like until the age of 9-12 years by these measures and that children do show differences in criterion compared to adults in psychophysical testing. This difference in criterion indicates the use of SDT or force-choice procedures to avoid this problem in any psychophysical developmental study. It has also shown that criterion for choosing the endpoint for the regression line fitting in the sVEP technique has the greatest effect on VA and contrast thresholds measurements and viable readings, while the other sVEP parameters have little effect on the thresholds.

Diss. Linköping : Univ., 2001.

Thesis (Ph. D.)--Ohio University, June, 1998. / Title from PDF t.p.

Thesis (Ph.D.). / Written for the Dept. of Ophthalmology, Neurology and Neurosurgery. Title from title page of PDF (viewed 2008/03/12). Includes bibliographical references.

Thesis (Ph. D.)--Carleton University, 2004. / Includes bibliographical references (p. 202-217). Also available in electronic format on the Internet.

Thesis (M.S.)--West Virginia University, 2008. / Title from document title page. Document formatted into pages; contains viii, 77 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 74-77).

A opacificação do cristalino presente ao nascimento ou nos primeiros meses de vida é denominada de Catarata Congênita (CC). As primeiras semanas de vida são importantes no desenvolvimento visual, já que há diferença significativa no desempenho visual de crianças que passaram pela cirurgia até seis semanas de vida (com melhor desempenho visual) em relação às crianças que realizaram a cirurgia após seis semanas de vida. Crianças que tiveram privação visual durante a primeira infância por catarata bilateral apresentam redução da visão espacial. O objetivo deste trabalho foi verificar o impacto na Função de Sensibilidade ao Contraste (FSC) em crianças de tratamento cirúrgico de Catarata Congênita, durante a fase de desenvolvimento visual. Foram avaliados três grupos: 11 crianças do grupo controle (média idade =6,83; DP=1,38), 9 crianças do grupo CC (média idade =6,87; DP=2,03) e 15 indivíduos adultos (média idade =27,63; DP=4,16). Foi utilizado o software Metropsis para avaliação da sensibilidade ao contraste de luminância de grade senoidal nas frequências espaciais de 0,2 cpg; 0,5 cpg; 1,0 cpg; 2,0 cpg; 4,2 cpg e 8,9 cpg e luminância média de 34,4 cd/m². Houve redução em toda a curva de sensibilidade ao contraste (SC) do grupo CC quando comparado ao grupo controle e não houve relação entre o tempo de privação e a redução da SC / The opacification of the lens present at birth is called Congenital Cataract (CC). The first weeks of life are important in visual development since there is not any significant difference in visual performance of children who had surgery within six weeks of life (with better visual performance) compared with children who underwent surgery after this period. Children who have visual deprivation during infancy due to bilateral cataracts have reduced spatial vision. The aim of this study was to assess the impact on Contrast Sensitivity Function (CSF) in children with Congenital Cataract surgery during the visual development age range. We evaluated three groups: 11 control children (mean age = 6.83, SD = 1.38), 9 children in the CC group (mean age = 6.87, SD = 2.03) and 15 adults (mean age = 27.63, SD = 4.16). Metropsis software was used to evaluate sensitivity to luminance contrast of the sinusoidal grating spatial frequencies of 0.2 cpd, 0.5 cpd, 1.0 cpd, 2.0 cpd, 4.2 cpd and 8.9 cpd with an average luminance of 34.4 cd / m². There was a reduction in the contrast sensitivity function (CSF) of the CC group compared to the control group and there was no correlation between the duration of deprivation and the impairment in the SC

The altitude at which oxygen supplementation should commence to be administered to aircrew in South Africa, flying in unpressurised aircraft is 12,000 feet. Above that altitude effects of reduced tissue oxygen content (hypoxia) become significant. Vision is particularly sensitive to hypoxia, and it was decided to test visual parameters at 12,000 feet to see if there were any subtle changes which might impair flight safety. It this were so, the level at which oxygen supplementation should commence would have to be lowered. The visual parameters to be assessed, all important in aviation, were colour vision, contrast sensitivity, and the presence of phorias (potential squints). 37 Healthy volunteers had these parameters assessed in an altitude chamber at ground level, 8,000 feet and 12,000 feet. Analysis of the results revealed no clinically significant degradation of vision at 12,000 feet, and it was concluded that the present altitude at which oxygen supplementation should begin (12,000 feet) is appropriate. It was advised that further testing should take place in subjects based at sea level. / Dissertation (MSc)--University of Pretoria, 2006. / School of Health Systems and Public Health (SHSPH) / Unrestricted