Visual accommodation plays a critical role in one's visual perception and activities of daily living. The age-related accommodation loss poses a greater risk to older adults' safety and independence. Although extensive effort has been made to study the effects of aging on accommodation, the relationship between aging and the dynamic aspects of accommodation is still unknown. Furthermore, since light is the carrier of external stimuli for accommodation, it is of value to assess the influences of light on the age-related accommodation loss. Therefore, a study was conducted to investigate the age-related dynamic accommodative characteristics under various conditions of the intensity and chromaticity of light. To ascertain the effects of aging, ten individuals from each of three age groups (i.e., younger group: 20 to 29 years old, middle-aged group: 40 to 49 years old, and older group: 60 to 69 years old) were recruited, and their dynamic accommodation responses were examined. Laboratory experiments were designed to measure accommodation in a simulated condition where a person must alternate from viewing outside to reading the dashboard while driving. It was hypothesized that the advancing of age will lead to the deterioration of one's dynamic accommodative performance, and light of different intensities and chromaticities will interact with the effects of aging on accommodation. The results of the study supported the above hypotheses. It was found that the advancing of age, the decrease of light intensity, and the change of light chromaticity all led to the alteration of one's dynamic accommodative performance. The present study concluded with a biomechanical and neural model elaborating the mechanism of an accommodation process within the scope of the study. / Ph. D.

Neste trabalho descreve-se o desenvolvimento e a construção de um instrumento eletro-óptico que analisa o processo de inibir a acomodação ocular utilizado nos exames refrativos dinâmicos. Nesses exames, devido a não utilização de drogas para dilatar e paralisar a pupila e o cristalino, pode haver variações no poder dióptrico ocular, o que torna o exame ineficaz e ineficiente. Isto é evitado se o equipamento analisador possuir um sistema de inibição. O projeto do instrumento foi dividido em 2 etapas. A primeira etapa foi dedicada à simulação óptica do instrumento eletro-óptico, pelo método do Traçado de Raios, e de um sistema aferidor. Na segunda etapa, construiu-se a eletrônica de controle e as peças mecânicas do conjunto (instrumento eletro-óptico e sistema aferidor). Após o desenvolvimento do protótipo do instrumento, foram realizados testes de avaliação através da análise de imagens feita pelo aferidor. O instrumento eletro-óptico foi desenvolvido para ser utilizado num analisador de frente de ondas, que utiliza uma das técnicas mais recentes e eficientes aplicada nos exames refrativos oftalmológicos. / In this work it is described the development and construction of an electro-optical instrument It analyzes the process of inhibiting ocular accommodation used in the dynamic refractive exams. Due to no use of drugs to dilate and paralyze the pupil and the crystalline lens, variations in the ocular dioptric power can occur, becoming those exams ineffective and inefficient. This is avoided if the analyzer equipment possess an inhibition system. The project of the instrument was divided in 2 stages. The first stage was dedicated to the optical simulation of electro-optical instrument, by the Ray Tracing Method, and of the system inspector. In the second stage, the control electronics and the mechanical parts (electro-optical and system inspector) was built. After the development of the prototype of the instrument, evaluation tests were accomplished through the analysis of images done by the inspector. The electro-optical instrument was developed to be used in an analyzer of front of waves, using one of the most recent and efficient techniques applied in the ophthalmologic refractive exams.

Neste trabalho descreve-se o desenvolvimento e a construção de um instrumento eletro-óptico que analisa o processo de inibir a acomodação ocular utilizado nos exames refrativos dinâmicos. Nesses exames, devido a não utilização de drogas para dilatar e paralisar a pupila e o cristalino, pode haver variações no poder dióptrico ocular, o que torna o exame ineficaz e ineficiente. Isto é evitado se o equipamento analisador possuir um sistema de inibição. O projeto do instrumento foi dividido em 2 etapas. A primeira etapa foi dedicada à simulação óptica do instrumento eletro-óptico, pelo método do Traçado de Raios, e de um sistema aferidor. Na segunda etapa, construiu-se a eletrônica de controle e as peças mecânicas do conjunto (instrumento eletro-óptico e sistema aferidor). Após o desenvolvimento do protótipo do instrumento, foram realizados testes de avaliação através da análise de imagens feita pelo aferidor. O instrumento eletro-óptico foi desenvolvido para ser utilizado num analisador de frente de ondas, que utiliza uma das técnicas mais recentes e eficientes aplicada nos exames refrativos oftalmológicos. / In this work it is described the development and construction of an electro-optical instrument It analyzes the process of inhibiting ocular accommodation used in the dynamic refractive exams. Due to no use of drugs to dilate and paralyze the pupil and the crystalline lens, variations in the ocular dioptric power can occur, becoming those exams ineffective and inefficient. This is avoided if the analyzer equipment possess an inhibition system. The project of the instrument was divided in 2 stages. The first stage was dedicated to the optical simulation of electro-optical instrument, by the Ray Tracing Method, and of the system inspector. In the second stage, the control electronics and the mechanical parts (electro-optical and system inspector) was built. After the development of the prototype of the instrument, evaluation tests were accomplished through the analysis of images done by the inspector. The electro-optical instrument was developed to be used in an analyzer of front of waves, using one of the most recent and efficient techniques applied in the ophthalmologic refractive exams.

Although the static measure of accommodation is well documented, the dynamic aspect of the resting state (dark focus) of accommodation is still unknown. Previous studies suggest that refractive error is minimal at the intermediate resting point of accommodation — i.e., at the dark focus distances. Additionally, aging is closely linked to increased refractive error. In order to assess the effects of age on dark focus distance and its utility in enhancing the visual information transfer rate, two experiments were conducted under nighttime condition (scotopic vision) in a laboratory setting. A total of forty participants with normal vision or corrected to normal vision were recruited from four different age groups (younger: 26.9±5.0 years; middle-aged: 50.7±4.8 years; young-old: 64.6±2.8 years; and old-old: 79.8±6.1 years). Each age group included ten participants. In Experiment I, the accommodative status of dark focus at the fovea was assessed objectively using the modified autorefractor, a newly developed method to continuously monitor the accommodation process. The mean dark focus distances for younger, middle-aged, young-old, and old-old adults were 64.5±6.6, 73.4±20.6, 84.4±29, and 92.1±33.4 cm, respectively. There was a significant difference between the dark focus distances among different age groups. Post-hoc analysis indicated that there were statistically significant differences among young and old-old, young and young-old, and middle-aged and old-old age groups. In Experiment II, the information transfer rate was determined while viewing a target at three different distances: 52 cm, 73 cm (current recommended reading distances) and the individual's dark focus. A set of randomized alphabet characters were presented on a visual display with a luminance level of 20 cd/m2 and ambient illumination level of 4 lux. To assess the information transfer rate, participants were asked to read a set of characters aloud with their fastest rate for three seconds. Three measurements of information transfer rate at each viewing distance at random were made. Results obtained from each viewing distance were collected and averaged. The results showed that the mean visual information transfer rate for younger, middle-aged, young-old, and old-old adults were 14.27±1.43, 10.58±2.25, 9.35±2.13, and 7.73±2.36 bits/sec, respectively. There were statistically significant differences at α < 0.05 in means and standard deviations of visual information transfer rate in young and old-old, young and young-old, young and middle-aged, and middle-aged and old-old age groups. The mean visual information transfer rate at 52 cm, 73 cm and individual dark focus were 11.08±3.10, 10.14±2.97, and 10.22±3.42 bits/sec, respectively. There were statistically significant differences at α < 0.05 in means and standard deviations of visual information transfer rate at different viewing distances at 52 cm and 73 cm, and 52 cm and individual's dark focus. However, there were no statistically significant differences in the interaction between age and viewing distance (F = 1.6818, P = 0.1378) on the amount of visual information transfer rate. In summary, the visual information transfer rate was not greater when presenting visual stimulus at the individual's dark focus as compared with two fixed recommended viewing distances (52 cm and 73 cm). The greatest amount of visual information gained was at 52 cm. Actual and potential applications of this study including specifications for designs were also discussed. / Ph. D.

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