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By day, your dog’s eyes may be a stunning hue of chestnut or sky blue. However, in dim light, his eyes may cast a ghoulish green glow, a diluted blue shade or even a beautiful purple hue.
For answers, we contacted two leading veterinary ophthalmologists: Dr. Cynthia Powell, at Colorado State University, and Dr. Bill Miller, of the Animal Ophthalmology Clinic in Memphis, Tenn.
In the dark, canine eyes react to exposure to light differently than human eyes because dogs (along with cats and many other animals) possess a light-reflecting surface known as the tapetum lucidum, located between the optic nerve and the retina. It operates like a mirror, reflecting the light and allowing the rods and cones another opportunity to pick up the limited amount of light available at night, Dr. Powell explains.
“This is an adaptive feature in animals who tend to be hunters at dawn and dusk,” Dr. Miller says. “The eyes of these animals are geared for low-light vision. They include dogs, cats, cattle, deer, horses and ferrets. However, humans and primates do not have the tapetum lucidum — and neither do squirrels because they are more active during the day — because their retinas are designed for brighter light vision.”
The specific glow color varies by animal and the amount of zinc or riboflavin present in special pigment cells within the tapetum lucidum. “Zinc is a metal, and riboflavin is an amino acid, and both act as reflective agents,” Dr. Powell says. “Depending on how densely packed these cells are with zinc or riboflavin, the glow color can vary from animal to animal and breed to breed.”
The animal’s age, as well as the color of his coat and eyes, can also influence this luminescence, also known as eyeshine. “Age can change reflectivity as the lenses become denser," Dr. Powell says. "It decreases the animal’s ability to reflect light back out of the eye.”
Dr. Miller notes that most dogs are born with blue to purple tapetums, but the color shifts by 16 weeks of age. “It’s not a hard and fast rule, but adult yellow Labradors tend to have light yellow-colored tapetums and black labs tend to have deeper yellow or green-colored tapetums,” he says.
Dogs with white coats and blue eyes can give off a red-eye effect in dark settings. The red-eye look is due to blood vessels in the eyes that reflect when exposed to light. “Among my favorites are Miniature Schnauzers," Dr. Powell says. "Their eyes tend to glow a beautiful turquoise color.”
As for tips on reducing that ghoulish glow when using a camera flash, Dr. Powell has two suggestions: “Try to take a photo looking more into the bottom of your dog’s eye and not have his eyes looking up, or take two quick shots using the flash, which causes the pupils to restrict. Flash first to make the pupils small, and then quickly take another photo."
Plus: For more tips on avoiding eyeshine when taking pet photos, check out 5 Tips for Perfect Holiday Card Pet Snapshots.
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