Effects of Light on the Choroid and Pupil

Study Overview
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Brief Summary
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Monochromatic light creates longitudinal chromatic aberration, with short wavelength blue light forming a focal point in front of the retina and long wavelength red light forming a focal point behind the retina. The investigators hypothesize that such chromatic aberrations, induced by exposure to red or blue LED lights, will cause the choroid behind the retina to respond to bring the image into focus by modulating its thickness, either thickening in the case of blue light or thinning in the case of red light. The magnitude and direction of this response is difficult to predict as previous studies have shown opposite findings in non-human primates and rodents. Furthermore, the investigators hypothesize that exposure to red or blue light will induce changes in how the pupil responds to light, because the cells in the eye that are involved in pupil control are most sensitive to blue light.

Detailed Description
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Ambient light exposure is associated with choroid thickness and eye growth. The spectral composition of light, which has been shown to play a role in eye growth, can differentially regulate changes in choroid thickness by forming a focal point either in front of the retina in the case of short wavelength blue light or behind the retina in the case of long wavelength red light. In addition, melatonin suppression and the pupil light response, specifically, that driven by the intrinsically photosensitive retinal ganglion cells (ipRGCs), are most sensitive to short wavelength blue light. Therefore, the role of the wavelength of light on eye growth may involve ipRGC activity. As such, it is relevant to determine whether exposure to monochromatic light will alter choroidal thickness, ipRGC activity and melatonin levels. The purpose of this study is to compare the short-term changes in choroid thickness, melatonin concentration, and the ipRGC-driven pupillary light response following one hour of light therapy with either short wavelength blue light or long wavelength red light. It has previously been shown that a one week period of daily morning light therapy produces a short term increase in choroid thickness throughout the day. Therefore, the investigators hypothesize that one hour of morning light therapy with short wavelength blue light will result in different effects in the changes in choroid thickness, melatonin levels, and the ipRGC-driven pupillary light response compared to one hour of morning light therapy with long wavelength red light.

Official Title
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Effects of Narrowband and Broadband Light on Choroidal Thickness and Melanopsin-driven Pupil Response

Conditions
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Emmetropia, Myopia

Intervention / Treatment
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* Other: White Light therapy
* Other: Blue light therapy
* Other: Red light therapy
* Other: Darkness


Participation Criteria
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Eligibility Criteria
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Inclusion Criteria: ages 18-64 must be able to comply with the experimental protocol, including collecting saliva and being present for the experiment in the lab on four separate occasions. must be willing to abstain from the use of sleep aids 12 hours prior to and for the duration of the study. must also be willing to abstain from alcohol and caffeinated beverages (coffee, espresso, energy drinks) or foods enriched with caffeine, such as power bars, the morning of and during each of the four experimental sessions. Exclusion Criteria: age < 18 or >64 years old not willing to collect a saliva sample or be present in the lab on four separate occasions. ocular disease that may affect retinal light levels and function (e.g. glaucoma, significant cataract, etc.) use of prescription or over-the-counter medications known to affect sleep and cortisol levels.

Ages Eligible for Study
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Minimum Age: 18 Years

Sexes Eligible for Study
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All

Accepts Healthy Volunteers
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Accepts Healthy Volunteers

Study Plan
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How is the study designed?
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Design Details

Primary Purpose: Basic Science
Allocation: Randomized
Intervention Model: Crossover Assignment
Interventional Model Description: All subjects will participate in four conditions on separate days
Masking: None (Open Label)


Arms and Interventions

| Participant Group/Arm | Intervention/Treatment |
| --- | --- |
| Experimental: Light exposure broadband<br>Participants will be exposed to indoor levels of light that appear colorless for one hour | Other: White Light therapy<br>* Participants will be exposed to broadband light for one hour<br>|
| Experimental: Light exposure long wavelength<br>Participants will be exposed to indoor levels of light that appear red for one hour | Other: Red light therapy<br>* Participants will be exposed to re light for one hour<br>|
| Experimental: Light exposure short wavelength<br>Participants will be exposed to indoor levels of light that appear blue for one hour | Other: Blue light therapy<br>* Participants will be exposed to blue light for one hour<br>|
| Experimental: Light exposure darkness<br>Participants will be exposed to darkness for one hour | Other: Darkness<br>* Participants will be in complete darkness for one hour<br>|

What is the study measuring?
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Primary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Choroidal Thickness | The choroid will be imaged with OCT to determine choroidal thickness | one hour | 
| Pupil response | The pupil response will be measured before and after one hour to see if exposure to light affects the diameter | one hour |