Predictability of sinusoidally moving stimuli does not improve the accuracy of the accommodative response.

Previous research work suggests that predictable target motion such as sinusoidal movement can be anticipated by the visual system, thereby improving the accommodative response. The validity of predictable motion for studying human dynamic accommodation is sometimes put into question. The aim of this work was to assess the effect of anticipation along with learning (and motivation, etc.) and fatigue (and boredom, loss of attention, etc.) on dynamic accommodation experiments from a practical perspective. Specifically, changes in amplitude and temporal phase lag were estimated within and between trials as 9 adult observers were instructed to focus on a stimulus that oscillated sinusoidally towards and away from the eye at specific temporal frequencies. On average, amplitude decreased whereas phase increased within trials. No evidence of anticipation or learning was observed either within or between trials. Fatigue consistently dominated anticipation and learning within the course of each trial. Even if the eye is equipped by a prediction operator as it is often assumed, fatigue confounds the results from dynamic accommodation experiments more than anticipation or learning.

Assessing the accommodation response after near visual tasks using different handheld electronic devices.

PURPOSE:: To assess the accommodation response after short reading periods using a tablet and a smartphone as well as determine potential differences in the accommodation response at various stimulus vergences using a Hartmann- Shack aberrometer. METHODS:: Eighteen healthy subjects with astigmatism of less than 1 D, corrected visual acuity of 20/20 or better, and normal findings in an ophthalmic examination were enrolled. Accommodation responses were obtained under three different conditions: accommodation system of the eye relaxed and visually stressed with a tablet and an smartphone for 10 min, at a distance of 0.25 m from the subject's eyes. Three measurements of accommodation response were monocularly acquired at stimulus vergences ranging from 0 to 4 D (1-D step). RESULTS:: No statistically significant differences were found in the accommodation responses among the conditions. A moderate but gradually increasing root mean square, coma-like aberration was found for every condition. Conversely, the spherical aberration decreased as stimulus vergences increased. These outcomes were identified in comparison to the one-to-one ideal accommodation response, implying that a certain lag value was present in all stimulus vergences different from 0 D. CONCLUSIONS:: The results support the hypothesis that the difference between the ideal and real accommodation responses is mainly attributed to parameters associated with the accommodation process, such as the near visual acuity, depth of focus, pupil diameter, and wavefront aberrations. The wavefront aberrations were dependent on the 3-mm pupil size selected in this study. The accommoda tion response was not dependent on the electronic device employed in each condition, and it was mainly associated with young age and level of amplitude of accommodation of the subjects.

The effect of aberrations on objectively assessed image quality and depth of focus.

The effects of aberrations on image quality and the objectively assessed depth of focus (DoF) were studied. Aberrometry data from 80 young subjects with a range of refractive errors was used for computing the visual Strehl ratio based on the optical transfer function (VSOTF), and then, through-focus simulations were performed in order to calculate the objective DoF (using two different relative thresholds of 50% and 80%; and two different pupil diameters) and the image quality (the peak VSOTF). Both lower order astigmatism and higher order aberration (HOA) terms up to the fifth radial order were considered. The results revealed that, of the HOAs, the comatic terms (third and fifth order) explained most of the variations of the DoF and the image quality in this population of subjects. Furthermore, computer simulations demonstrated that the removal of these terms also had a significant impact on both DoF and the peak VSOTF. Knowledge about the relationship between aberrations, DoF, image quality, and their interactions is essential in optical designs aiming to produce large values of DoF while maintaining an acceptable level of image quality. Comatic aberration terms appear to contribute strongly towards the configuration of both of these visually important parameters.

Assessing the accommodation response after near visual tasks using different handheld electronic devices / Avaliação da resposta de acomodação após tarefas visuais próximas usando diferentes dispositivos eletrônicos portáteis

ABSTRACT Purpose: To assess the accommodation response after short reading periods using a tablet and a smartphone as well as determine potential differences in the accommodation response at various stimulus vergences using a Hartmann- Shack aberrometer. Methods: Eighteen healthy subjects with astigmatism of less than 1 D, corrected visual acuity of 20/20 or better, and normal findings in an ophthalmic examination were enrolled. Accommodation responses were obtained under three different conditions: accommodation system of the eye relaxed and visually stressed with a tablet and an smartphone for 10 min, at a distance of 0.25 m from the subject's eyes. Three measurements of accommodation response were monocularly acquired at stimulus vergences ranging from 0 to 4 D (1-D step). Results: No statistically significant differences were found in the accommodation responses among the conditions. A moderate but gradually increasing root mean square, coma-like aberration was found for every condition. Conversely, the spherical aberration decreased as stimulus vergences increased. These outcomes were identified in comparison to the one-to-one ideal accommodation response, implying that a certain lag value was present in all stimulus vergences different from 0 D. Conclusions: The results support the hypothesis that the difference between the ideal and real accommodation responses is mainly attributed to parameters associated with the accommodation process, such as the near visual acuity, depth of focus, pupil diameter, and wavefront aberrations. The wavefront aberrations were dependent on the 3-mm pupil size selected in this study. The accommoda tion response was not dependent on the electronic device employed in each condition, and it was mainly associated with young age and level of amplitude of accommodation of the subjects.

RESUMO Objetivo: Avaliar a resposta de acomodação após períodos de leitura curtos usando um tablet e um smartphone, bem como para determinar potenciais diferenças na resposta de acomodação em estímulos de várias vergências com uma aberrômetro Hartmann-Shack. Método: Dezoito indivíduos saudáveis com astigmatismo inferior a 1 D, apresentando acuidade visual corrigida de 20/20 ou melhor com exame oftalmológico normal foram avaliados. As respostas acomodativas foram obtidas em três condições diferentes: sistema de acomodação com o olho relaxado, e visualmente estressado com um tablet e um smartphone por 10 min, a uma distância de 0,25 m dos olhos dos sujeitos. Três medidas de resposta acomodativa foram obtidas monocularmente com estímulos cujas vergências variaram de 0 a 4 D (intervalos de 1 D). Resultados: Não houve diferença estatisticamente significativa entre as respostas acomodativas em todas as condições. Foi observada moderada aberração do tipo coma com aumento progressivo para cada condição, enquanto houve diminuição da aberração esférica com o aumento das vergências do estímulo. Estes resultados foram identificados em comparação com a resposta acomodativa de um-para-um ideal, o que implica que um certo valor de desfasagem estava presente em todos os estímulos com vergências diferentes de 0 D. Conclusões: Os resultados apoiam a hipótese de que a diferença entre as respostas acomodativas ideal e real é atribuída principalmente a parâmetros tais como a acuidade visual para perto, profundidade de foco, diâmetro pupilar e aberrações de frente de onda, associados ao processo acomodativo. As aberrações de frente de onda foram dependentes do tamanho da pupila de 3 mm, selecionado neste estudo. A resposta acomodativa não foi dependente do dispositivo eletrônico empregue em cada condição e foi associada principalmente à idade jovem e ao nível da amplitude de acomodação dos sujeitos avaliados.