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  • Melanopsin is a photopigment allowing a small subset of retinal ganglion cells to absorb light energy directly and fire

    action potential with or without synaptic input form rods and

    cones. Intrinsic photo response of melanopsin-containing

    retinal ganglion cells (MGCs) provides sustained irradiance

    coding for non-visual photoperception functions including

    circadian photoentrainment and the pupillary light response.

    A sustained pupil constriction can be observed after the

    offset of a bright blue light stimulus. This post-illumination

    pupil response (PIPR) is produced by MGC, and can be

    measured by chromatic pupillometry. Measuring PIPR holds

    promise as a novel tool to assess MGC function. Current

    testing protocols use central-field stimulation and require a

    very bright light of long duration which can be difficult for

    some subjects. We test the hypothesis that a consistent

    PIPR can be induced with full-field blue light stimuli of

    shorter duration and lower intensity than with central-field

    stimulation.

    IntroductionIntroduction

    Apparatus:

    Full-field and central-field light stimulation were presented

    with a Colordome Ganzfeld bowl originally designed for

    ERG testing.

    Pupillary light response was monitored with a video based

    eye tracker at 60Hz.

    MethodsMethods

    Experimental Conditions (cont.):

    For each of the intensity and duration steps, a red flash was

    presented first followed by a blue flash 45 s after the offset of

    the red flash. Participants were provided with a short break at

    45 s after the offset of the blue flash to allow the pupil size to

    return to baseline and to prevent fatigue.

    Measurement and Data Analysis:

    Pupil size data were normalized to baseline calculated from

    the mean pupil size during a 1 s period before the onset of

    each stimulus.

    Primary Outcome Measure

    PIPR: mean of the normalized pupil size over a 20 s period

    from 10-30s after the offset of light stimuli (smaller number

    means greater pupil constriction).

    400 cd/m2, full-field blue stimulus induced significantly

    larger PIPR than central-field blue stimulus of the same

    intensity.

    PIPR to red flashes did not differ significantly full-field vs.

    central-field.

    No further increase in PIPR was observed when the

    duration increased from 400-1000 ms.

    400-1000 ms, 400 cd/m2 blue full-field stimuli induced

    significantly greater PIPR than 1000 ms blue central-field

    stimulus of the same duration.

    Full-field stimulation is more effective that central-field

    stimulation in inducing PIPR, suggesting that PIPR is a

    function of stimulus intensity, duration and area.

    This study is the first to demonstrate that saturating PIPR

    up to 30 seconds post illumination can be induced in vivo

    with a strong blue flash lasting only a few hundred

    milliseconds.

    This updated understanding of the relation between PIPR

    and stimulus intensity, duration and area will allow

    investigators to tailor their PIPR testing paradigm to target

    a specific research question, and greatly facilitate the

    development of a convenient and comfortable technique to

    assess MGCs function for emerging clinical use.

    shao-bo.lei@sickkids.ca

    ConclusionsConclusions

    Contact InformationContact Information

    FullFull--Field Field ChChroromamatictic Pupillometry in the Assessment of the PostPupillometry in the Assessment of the Post--Illumination Pupil ResponseIllumination Pupil Response

    Driven by MelanopsinDriven by Melanopsin--Containing Retinal Ganglion CellsContaining Retinal Ganglion Cells

    1Shaobo Lei, 1,2H.C. Goltz, 1M. Chandrakumar, 1,2,3A.M.F. Wong

    1Program in Neuroscience & Mental Health, Hospital for Sick Children; Department of Ophthalmology and Vision Sciences, 2University of Toronto & 3Hospital for Sick Children, Toronto Canada

    No.4110 - A0098

    Session: 413

    Participants:

    10 visually-normal adult subjects (mean age: 31 years,

    range 22 56), only right eyes were stimulated and

    recorded, left eyes were patched during recording.

    Experimental Conditions:

    Experiment 1 (intensity trials): After 10 min dark adaptation,

    PIPR was induced with alternating red (64010 nm) and

    blue (46717 nm), 1-second full-field stimuli of increasing

    intensity from 0.1 to 400 cd/m2 (11 steps) . For comparison

    with a previously published protocol, a 6090 central-field

    blue stimulus at 400 cd/m2 was also presented for 1 second.

    Experiment 2 (duration trials): 10 min dark adaptation, 100

    cd/m2 and 400 cd/m2, red and blue full-field stimulations of

    increasing duration from 4-1000 ms were presented

    alternately. 100 cd/m2 and 400 cd/m2 trials were conducted

    on different days.

    * Mean (n=10) normalized post-illumination pupil response (PIPR) tracings in response to 1 s stimulation of varying intensity from 10 visually-normal participants.

    PIPR to full-field blue stimulation increased monotonically

    with increasing stimulus intensity.

    Red light (internal reference) induced no or minimal PIPR

    at all intensity level.

    Results: Results: Experiment 1 (intensity Experiment 1 (intensity trials)trials)

    * Comparison of PIPR induced using 400 cd/m2 central-field stimuli (dashed line) vs 100-400 cd/m2 full-field stimuli (solid lines)

    PIPR in response to 400 cd/m2 increased as the duration of

    stimulus increased from 4-200 ms.

    * Mean PIPR to 100 cd/m2 and

    400 cd/m2 full-field stimulation

    of varying duration from 10

    visually-normal observers.

    Results: Results: Experiment 2 (duration trials)Experiment 2 (duration trials)

    * comparison of PIPR to full-field blue stimuli of 400 cd/m2 intensity of the 6 longest duration steps (100, 200, 400, 600, 800, and 1000 ms.

    *Authors have no commercial interest to disclose.

    Statistic Analysis

    One-way ANOVA with post hoc corrected for pairwise

    multiple comparisons using the TukeyKramer method.

    Full-Field vs. Central-field Stimulation

    * Intensity-response function of PIPR to full-field stimulation vs. PIPR to 1s, 400 cd/m2 central-field stimuli

    * Duration-response function of PIPR to full-field stimulation vs. PIPR to 1s, 400 cd/m2 central-field stimuli