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This will be the final blog entry in our ‘colors’ series from Boston Mountain Eye Care.  After this we will be writing about anything and everything.  I am thinking a piece on blue light and its effect on the eye is appropriate next.  If you have any questions for the optometrist you would like answered in the blog, please use our ‘contact’ tab and ask us.  We might write a blog about it!  We have enjoyed learning about the way people see colors and sharing that with our readers.  I apologize for the delayed release of the final blog- it is difficult to sit down between eye exams and type these things out in a growing eye doctor’s office!  Let’s finish this series off and answer the question everyone has been wondering: what does my dog see???

There are three elements to vision that I will use to compare and contrast human vision to canine vision:

  1. Color Perception
  2. Brightness
  3. Visual Acuity

Color perception is the ability to differentiate between different wavelengths of light on the electromagnetic spectrum.  You can read in depth about this fascinating process of the eye and visual system here Color Perception.  Humans see many colors because they have three types of color responsive cells on the retina which create a wide range of color perception.  Humans are ‘trichromats” and have red, green and blue cones in their eye to perceive color.  Contrary to popular past wisdom, dogs DO see color … it’s just different than humans.  Dogs are ‘dichromats’ and only have yellow and blue cones in their eyes.  They see the world similar to a human who is red/green color blind!  They would fail the color vision portion of an eye exam!  Does a dog see a school bus as yellow?  YES.  Does a dog see a red fire hydrant as ‘red’?  NO.  It would appear yellow.  A green plant??  It’s yellow to a dog.  How about a red rose??  A dog would again see YELLOW.  Just like red/green color deficient humans, dogs do not perceive reds as red or greens as green.  When the color is somewhere between the two on the spectrum (like Cyan or Magenta) dogs see neutral gray.

Brightness is the perception of light elucidated by an illuminated target Brightness.  This is different than color- have you ever seen a dull, faded red contrasted to some freshly painted red paint?  This is an example of brightness.  Humans and dogs differentiate brightness equally well.  What does this mean for Fido?  While your dog might not be able to differentiate a red ball versus a green tennis ball based on color, your dog might be able to tell a difference between the two based on brightness.  The visual system is more than color!  This is how red/green color deficient people tell the difference between objects in their day to day lives as well.  Dogs are equally as good at perceiving brightness as humans.

Visual acuity is way to measure spatial acuity in a visual system Visual Acuity.  This is the classic 20/20 chart you see at the optometrist.  Your eye doctor measures your visual acuity during your eye exam using a Snellen chart.  There are other ways to measure this.  One way is by measuring the cycles per degree your eye can detect.  I will spare you the math … humans see around 55 cycles per degree as an average.  Dogs see about 8 cycles per degree on average.  A dog’s visual acuity is about 6 times worse than humans on average.

To sum things up: you see a bright red car that says “FAYETTEVILLE ARKANSAS” on the side.  Your dog sees a yellow car and can’t read the writing.  He can tell that the fire hydrant next to it is different because it is not as bright as the beautiful car.  Pretty simple, huh?  Who doesn’t love dogs!

Thank you for reading.  Look for our next blog entry to dive into the truth about blue light- is it bad for you?  Is this a big deal?  Where does it come from?  Can we prevent damage from blue light?  Until then … enjoy beautiful springtime in Fayetteville, AR.  I love this city!

-Dr. Ben


Dr. Benjamin Lynch
Boston Mountain Eye Care
350 E Sunbridge Drive | Fayetteville, AR | 72703
479.442.3838 |