Pictured is the eye of a juvenile male fox squirrel. The organ had a mass of 1 ± 0.5 g, a height of 13.6 ± 0.5 mm, a width of 14.2 ± 0.5 mm, resulting in a diameter of about half that of the 25 mm human eye (Ndabahaliye, 2002). A tinted lens probably protect the retina from the bright sun. Assuming the shorter diameter eyeball translates into a shorter focal length and by using photographs to estimate the squirrel aperature to be less than 5 mm in bright light, compared to the human aperature of about 2.7 mm, I can estimate the ratio of light that would strike the squirrel's retina comparted to the human. The squirrel's retina would receive somewhere around 3 times more light then a human's if the squirrel had no pre-retinal absorbance.
Ndabahaliye , A. (2002). Diameter of a Human Eye. Physics Factbook. Retrieved April 23, 2009, from http://hypertextbook.com/facts/2002/AniciaNdabahaliye1.shtml. (Link)
United States, South Dakota,
Image Date: 2008APR18
Image Species: Sciurus niger rufiventer
(EXIF Info is accurate – stamped in UTC).
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