Effects of Light on the Choroid and Pupil

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.

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.