203 research outputs found

    Temporal multiplexing with adaptive optics for simultaneous vision.

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    We present and test a methodology for generating simultaneous vision with a deformable mirror that changed shape at 50 Hz between two vergences: 0 D (far vision) and -2.5 D (near vision). Different bifocal designs, including toric and combinations of spherical aberration, were simulated and assessed objectively. We found that typical corneal aberrations of a 60-year-old subject changes the shape of objective through-focus curves of a perfect bifocal lens. This methodology can be used to investigate subjective visual performance for different multifocal contact or intraocular lens designs

    Home or hospital as the place of end-of-life care and death: A grounded theory study of parents' decision-making

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    BACKGROUND: While several studies have examined 'what' families want with regard to the place of a child's end-of-life care and death, few have explored 'how' parents reach a decision. AIMS: (1) to develop a model explaining how parents of a child with a life-threatening illness in Greece decide about the place of end-of-life care and death; (2) to identify the factors affecting decision-making; (3) to consider the implications for clinical practice. DESIGN: Grounded theory study of bereaved parents using semi-structured open-ended interviews following Strauss and Corbin's principles of data collection and analysis. SETTING/PARTICIPANTS: Semi-structured interviews with 36 bereaved parents of 22 children who died at home (n = 9) or in a paediatric hospital (n = 13) in Athens, Greece. RESULTS: (1) Decisions regarding place of care and death were reached in one of four ways: consensus, accommodation, imposition of professional decisions on parents or imposition of parents' decisions without including professionals. (2) Six factors were identified as affecting decisions: awareness of dying, perceived parental caregiving competence, perceived professional competence, parents' view of symptom management, timing of decision-making, and being a 'good parent'. (3) Decisions were clear-cut or shifting. Few parents did not engage in decisions. CONCLUSION: Parents' decisions about place of end-of-life care and death are affected by personal, interpersonal, timing and disease-related factors. Parents are best supported in decision-making when information is presented clearly and honestly with recognition of what acting as 'good parents' means to them, and opportunities to enhance their caregiving competence to care for their child at home, if they choose so

    Objective assessment of the effect of pupil size upon the power distribution of multifocal contact lenses.

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    AIM: To analytically assess the effect of pupil size upon the refractive power distributions of different designs of multifocal contact lenses. METHODS: Two multifocal contact lenses of center-near design and one multifocal contact lens of center-distance design were used in this study. Their power profiles were measured using the NIMO TR1504 device (LAMBDA-X, Belgium). Based on their power profiles, the power distribution was assessed as a function of pupil size. For the high addition lenses, the resulting refractive power as a function of viewing distance (far, intermediate, and near) and pupil size was also analyzed. RESULTS: The power distribution of the lenses was affected by pupil size differently. One of the lenses showed a significant spread in refractive power distribution, from about -3 D to 0 D. Generally, the power distribution of the lenses expanded as the pupil diameter became greater. The surface of the lens dedicated for each distance varied substantially with the design of the lens. CONCLUSION: In an experimental basis, our results show how the lenses power distribution is affected by the pupil size and underlined the necessity of careful evaluation of the patient's visual needs and the optical properties of a multifocal contact lens for achieving the optimal visual outcome

    Amplitude, Latency, and Peak Velocity in Accommodation and Disaccommodation Dynamics.

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    The aim of this work was to ascertain whether there are differences in amplitude, latency, and peak velocity of accommodation and disaccommodation responses when different analysis strategies are used to compute them, such as fitting different functions to the responses or for smoothing them prior to computing the parameters. Accommodation and disaccommodation responses from four subjects to pulse changes in demand were recorded by means of aberrometry. Three different strategies were followed to analyze such responses: fitting an exponential function to the experimental data; fitting a Boltzmann sigmoid function to the data; and smoothing the data. Amplitude, latency, and peak velocity of the responses were extracted. Significant differences were found between the peak velocity in accommodation computed by fitting an exponential function and smoothing the experimental data (mean difference 2.36 D/s). Regarding disaccommodation, significant differences were found between latency and peak velocity, calculated with the two same strategies (mean difference of 0.15 s and -3.56 D/s, resp.). The strategy used to analyze accommodation and disaccommodation responses seems to affect the parameters that describe accommodation and disaccommodation dynamics. These results highlight the importance of choosing the most adequate analysis strategy in each individual to obtain the parameters that characterize accommodation and disaccommodation dynamics
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