While working outside in Antarctica it is very important that everyone wears sunglasses and/or goggles to protect our eyes from a condition known as Snow Blindness. Snow blindness is caused by the high about of solar or light radiation reflecting off of the ice. The ice in Antarctica can reflect up to 90% of the solar radiation hitting the surface. The amount of solar radiation that is reflected by a surface is known as albedo. You may have heard someone on a hot day say the asphalt in a parking lot is “so hot you could fry an egg on it!” That is because asphalt actually absorbs solar radiation, which causes it to heat up, and only reflects about 5-10%.
Think of snow blindness like getting a sunburn in your eye that is painful and negatively affects your vision. It usually improves within a day or two, but if not treated can cause permanent vision issues.
Heather Harris and Emma Weitzner in the field sporting their sunglasses
Weddell seals, nor any other polar organisms, wear sunglasses; so how are Weddell seals’ eyes protected from this solar radiation reflection?
First, let us take an up-close look at a Weddell seal eye.
Up-close view of a Weddell seal eye
Photo credit: Patrick Robinson, MMPA Permit # 17411
I find the detail in this image amazing! As you can see the iris is very muscular, this is important because the iris controls the size of the pupil, which controls the amount of light that reaches the retina. The human eye works similarly if you look into a mirror with the lights on then turn the lights off you can watch your pupil grown and if you turn the light on your pupil will get smaller again.
A study conducted on an northern elephant seal, a fellow deep-diving seal, found that the “pupil area varied within an extremely wide range, from a giant area of 422 mm2 in dark-adapted conditions (approximately 23 mm in diameter) to a pinhole opening of 0.9 mm2 in light-adapted conditions” (Mass, YA, & Supin, 2007) That is almost equivalent going from the size of a nickel, a little over 21 mm in diameter to the period at the end of this sentence, 1 mm in diameter.
Did you know? Weddell seals eyes have a similar structure to dogs and cats that make their eyes seem to glow in the dark. Continue reading my journals to understand how.
Mass, A. M., YA, A., & Supin. (2007, May 21). Adaptive features of aquatic mammals' eye - Mass - 2007 - The Anatomical Record - Wiley Online Library. Retrieved from https://onlinelibrary.wiley.com/doi/pdf/10.1002/ar.20529
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