Impact of Dark Chocolate on Visual Performance
Condition: Dietary Supplementation
Study type: Interventional

Summary: 
      The purpose is to conduct a randomized, single-masked crossover study to determine if acute
      consumption of a commercially available, highly palatable dark chocolate bar can improve
      visual performance. Vision testing will include multiple measures of contrast and color
      perception, reaction time, effects of distraction on visual performance during simulated
      hands-free phone calls, simulated marksmanship, as well as multiple, objective
      electro-diagnostic tests including standard and color visual-evoked potentials and various
      types of electro-retinograms to assess visual pathway function.
    

Detailed description: 
      Consumption of dark chocolate has been associated with improved blood flow, cardiovascular
      function, slowing of degenerative aging processes, as well as enhanced mood and cognitive
      performance. Dark chocolate is rich in cocoa flavanols which have both antioxidant effects to
      prevent and impede degenerative disease and as well as more immediate effects on local and
      cerebral blood flow. One study demonstrated an improvement in contrast sensitivity (CS) which
      is the visual ability to detect low contrast targets. Hence dark chocolate may enhance vision
      during critical task performance in military and law enforcement settings as well as
      every-day tasks such as driving. Whereas it is assumed that visual enhancements from dark
      chocolate derive from increased cerebral and/or retinal blood flow, direct measurements are
      lacking. Prior research demonstrated that hands free phone communication (verbal distraction)
      can delay reaction time and impair CS. Hence in this study our purpose is to determine if
      acute consumption of dark chocolate impacts: CS and reaction time with and without verbal
      distraction, measures of high and low contrast vision as well as color vision, and bjective
      electrophysiological measures of retinal, optic nerve and cortical function. In prior studies
      of acute effects of dark chocolate on cognition and CS, the dark chocolate was consumed
      90-120 minutes prior to testing. In this study the investigators are using a somewhat larger
      dose and beginning electrophysiological testing after consumption with color and CS testing
      approximately 1 hour and 30 minutes afterconsumption. The investigators believe this will
      capture possible more immediate blood flow changes in retina and cortex based on
      electrophysiological measures and CS and cognitive changes later in the session.

      A total of 30 subjects will be recruited from UIW and RSO students, staff, faculty and
      patients. The age range will be 18 to 65 years and the investigators will attempt to include
      comparable numbers of male and female participants. Inclusion criteria include visual acuity
      of at least 20/20 in each eye with no evidence of ocular, systemic or neurologic disease or
      ocular trauma. Based on prior research using repeated-measures designs, a difference of 0.1
      log CS is considered significant and the estimated standard deviation is 0.13 log units.
      Hence the effect size = (mean difference)/SD = 0.1/0.13 = 0.76. The estimated minimum number
      of subjects to achieve significance at the 5% level with a power of 80%: (1/effect size)2 x
      16 = (1/0.76)2 x 16 = 28 subjects.(8,9). Hence 30 subjects will be recruited to account for
      subject attrition during the course of the study. Prior to obtaining written informed
      consent, each subject will be briefed on the nature of the study by one or more members of
      the research team. Subjects will be informed that they will be evaluated with standard vision
      tests one hour after consuming a chocolate bar to assess its effects on performance. The dark
      chocolate and milk chocolate bars to be used are commercially available from Trader Joe's and
      have comparable ingredients and nutrients except for the higher percentage (72%) of cacao
      dark chocolate in the experimental bar while the control bar contains 31% milk chocolate
      cocao solids which are not associated with acute beneficial effects on performance. As stated
      in the informed consent document, subjects will be asked if they have allergies to any of the
      ingredients contained in the chocolate bars, and will be excluded from participating if they
      answer affirmatively. As noted above, any subjects with ocular, systemic or neurologic
      disease, including diabetes and hypoglycemia, will not be allowed to participate in the
      study.

      A single-blinded crossover design will be used to assess possible effects of the dark or milk
      chocolate bars (72% cacao dark chocolate) on visual performance and visual
      electrophysiological signals. Double-blinding (experimenter unaware of the type of chocolate)
      is not tenable due to the difference in coloration and aroma of the two chocolate bars and
      not likely to be a significant source of variability given the objective nature of the visual
      performance measures. Subjects will be tested in two one-hour sessions separated by at least
      72 hours. Each subject will consume a different chocolate bar one-hour prior to testing with
      the order of bars (dark vs. milk chocolate) counter-balanced across subjects. Subjects will
      be asked to refrain from consuming coffee or caffeinated drinks on the day of testing and to
      consume the bar without milk or milk products which can lessen beneficial effects of dark
      chocolate. The subject will be presented the bar in its original wrapper but with the name
      masked by tape and she/he will be given a paper plate and napkins and asked to remove and
      return the wrapping to the research team member(s). The subject will be offered water during
      consumption of the bar which will take place in the research room. Insofar as many of the
      subjects will be in-house student volunteers, she/he will then remain in UIWRSO to study,
      work-study, finish clinical records, etc. for about 30 minutes. The patient will then undergo
      preliminary evaluation to prepare for the testing to commence at least 1 hour after chocolate
      bar consumption. This will include measurement of distant visual acuity followed by
      refraction to best visual acuity if the patient does not achieve 20/20 in each eye with their
      habitual correction. Hence the patient will either wear their habitual correction or lenses
      in a trial frame to achieve best vision during testing. The patient will then be prepped for
      electro-diagnostic testing including visual-evoked potentials (VEPs) and electro-retinograms
      (ERGs) which objectively assess visual cortical and retina/optic nerve function,
      respectively. VEPs will be recorded using the Diopsys® system. The subject is seated
      comfortably before a reversing checkerboard display. The back of the head, forehead and
      temple will be wiped clean using an FDA approved non-abrasive cleaner. High and low contrast
      VEPs will be recorded from the back of the head using disposable skin electrodes with
      reference and ground electrodes at the forehead and temple, respectively. Cone specific color
      VEPs10 will also be recorded using the Diagnosys, LLC system. All VEPs will be recorded
      binocularly and not be initiated until one-hour following consumption of the chocolate bar.
      The Diopsys® system will be used to record pattern ERGs (optic nerve function), flicker ERGs
      (cone function) and the photopic negative response (phNR; cone, bipolar cell and optic nerve
      function). Half of the subjects in control and experimental sessions will be tested with ERGs
      first and half with VEPs first to control for order effects. These FDA approved
      electro-diagnostic tests will be followed by letter chart measures of large and small CS
      (Precision Vision, Inc.). Each subject will then be tested with the Innova Systems, Inc.
      computer controlled Cone Contrast Test which assesses red, green and blue cone CS as well as
      large and small black/white letter CS using an adaptive staircase (like a hearing test) to
      determine the lowest visible contrast and overall response time. As described in our previous
      study,7 each subject will undergo computer-based CS testing with and without verbal
      distraction during testing with order counterbalanced across subjects. The verbal distraction
      will be broadcast on a hands-free blue-tooth device to simulate an incoming phone call
      consisting of scripted questions to assess memory and cognitive performance while completing
      the CS tasks. Following these tests, the subject will be asked to perform a brief (<10
      minute) Wii™ shooting game using the Wii™ zapper which is shaped like a small rifle-no
      training is necessary. Two-way repeated measures ANOVA will be used to assess CS across
      distraction and chocolate bar conditions and post-hoc paired t-tests conducted to identify
      specific differences. Within subject ANOVAs and post-hoc t-test comparisons also will be used
      to assess amplitude and latency parameters of VEPs and ERGs across dark and milk chocolate
      conditions.
    

Intervention name(s): Dark chocolate; Milk Chocolate
Intervention type(s): Dietary Supplement; Dietary Supplement
Intervention description(s): Trader Joe's 72% Cacao Dark Chocolate bar, 47g, 34g cacao, total flavanols: 316.3 mg.; Trader Joe's Crispy Rice Milk Chocolate bar: 40g, 12.4g milk chocolate cocoa; total flavanols: 40 mg.
Allocation: Randomized
Intervention model: Crossover Assignment
Intervention model description: Randomized, single-masked crossover study to assess potential effects of dark chocolate vs. milk chocolate on multiple aspects of visual function and performance.
Masking: Single (Participant)
Primary purpose: Basic Science