The Truth About Dog's Vision

I recently had a very interesting conversation with a veterinarian whose specialty is ophthalmology.  He's been practicing veterinary medicine for decades, and was open to my myriad of questions regarding the vision of animals.  I wanted to dispel rumor against myth, and he offered me some great information.

The largest myth to debunk is that dog's are color blind.  What determines how we see shape, movement, color, etc. live in the cones and rods in our eyes.  Dogs have both.  They have less cones, which see color.  He told me that the only color dogs are unable to see is red.  He said the same goes for cats.  Birds have way more of both, and can see ultra violet light, in addition to already having impeccable vision.

We always assume our dogs and cats have greater vision than us, and this is also not entirely true.  While optimal vision for us is 20/20 vision, dogs have 20/70.  This means all dogs are technically near-sighted.  He explained that if I were to hang a seeing eye chart up, the dog would see that largest letter as being blurry.  The difference, is that they retain that 20/70 vision in the darkness, unlike we who nearly go blind.  So all things added up, perhaps their vision is better overall, but not in the light.  He added that cats are virtually technically blind.  Their vision would be more like 2200.  When met with a disbeliever, he rolled a cotton ball in front of an eyeless cat, who quickly stomped the ball with it's paw.  They rely on their other senses to make those amazing feats of hunting and agility.

The other myth I sought to debunk was that of dog's being able to watch television.  I'd heard people in the past make claims that dogs cannot see anything other than 3 dimensional images.  He explained to me that while a human has 1 nerve for each 1 retinal cell, dogs have more like 1 nerve per 5 retinal cells.  This means that dogs, for lack of a better explanation, see slower.  It takes longer for those complex images generated from your television to make sense.  He explained that while dogs can indeed watch TV, the images likely appear to have lines running through them, as they are unable to receive all the information as fast as we do.  He said the same is true for cats.  While they can see the TV has images, he still insists that the dogs are likely paying more attention to the sounds from the TV than the images.

When I think of seeing talented dogs ability to retrieve very specific toys of varying colors, this all makes sense.  Without some grasp of color, it'd be hard to ask them to bring back 1 stuffed toy that looks very much like the other, if we assume to take out the ability to see color.  I'm also reminded of an episode of The Dog Whisperer where a woman insisted her dog loved to watch his show.  While he wasn't truly seeing clear images of other dogs, he was still responding to all those fun barking sounds he was hearing!

As far as "seeing slower", I can imagine how a dog owner of a super agile breed may feel it doesn't add up.  They catch frisbees mid-air, as if they can slow down time themselves!  It all comes down to the amazing orchestra of senses they use for their day to day lives.  Smell, sound, feel..  this is why we see so many visually impaired pets fairing so well when vision is diminished!

-by Shannon Murphy

Understanding "Cherry Eye"

The condition referred to as "Cherry Eye" gathers a lot of questions from dog owners.  More often than not, dog owners have heard of the condition but aren't really sure what is going on.  Great Pyrenees are not predisposed to this condition; Basset Hounds, Beagles, Boston Terriers, and Cocker Spaniels are sited as being prone. (Common Disease of Companion Animals, Alleice Summers)

We know that our dogs have a "third eyelid".  We see it when they awake from sleep, and sometimes it is exposed when our dog's are sick or dehydrated.  It protects the eye, and helps spread half of the fluid which keeps their eyes nice and moist. That eyelid (called the nictitating membrane) is embedded in a superficial gland.  The eye can position itself in such a way that it allows this gland to prolapse (poke out).

The part of their eye closest to their nose fills with the red, swollen membrane.. and it looks like a small "cherry".  It is most commonly associated with younger dogs, and there are other conditions found in older animals which can cause this appearance, such as growth of new tissues (a tumor) unrelated to cherry eye.

It's irritating to the dog, but not thought to be painful.  In addition to the swelling, they will probably have teary eyes.  Your veterinarian can make this diagnosis quite easily.  To treat this, your vet will surgically tack down that gland back where it should be.  Some dogs have the gland removed, but it is not advised unless there is a tumor present.  Without the gland, their eyes cannot effectively keep the eye moist and they will have chronic dry eye.  Surgery is important, because without your dog may injure the eye and compromise his vision.

What Do Cloudy Eyes Mean?

There can be a lot of questions and confusion out there regarding the changes we see in our dog's eyes, especially as they age.  I've noticed a tendency for dog owners to assume their dog has cataracts, when in fact there are other causes for that cloudy look that concerns us.

To dispel the myth that cloudy eyes is caused only by cataracts or glaucoma, let me introduce you to a condition called senile nuclear (lenticular) sclerosis.  Sounds scary.. it isn't.  It is a very normal change in the eyes of many animals as they age.  As the cells in their eyes grow older, the cells can become dehydrated and the cells begin to overlap each other.  The light reflecting off of those older cells looks differently, and it appears cloudy.  The eye may appear grey or opaque.  The good news, is that on the whole their vision is maintained!  I think often we see this cloudy look emerging, and we say "Oh, he's going blind".  There can always be other medical conditions at play, but if it's simply nuclear sclerosis, this may not be true.  (Your cats can have this happen also.)

Cataracts, however, do cause blindness.  Your veterinarian will determine which condition your dog has.  While often an inherited disease, it can also be caused by diabetes, trauma, electric shock, hypocalcemia (lacking calcium) and vitamin deficiencies, to name a few.  Cataracts are removed by surgery, and of course we address and treat any underlying conditions which may have caused them.

There are many conditions which affect the eye, and the above picture isn't meant to be diagnostic.  On the whole, it's important for owners to be aware that some changes in the eye can be normal due to aging!

Don't Overlook Teary Eyes

We've encountered several Pyrs who seemed to be prone to teary eyes.  While this can be a simple response to a superficial irritation, there are other conditions that should be ruled out.  Some breeds are predisposed naturally to runny eyes, or "epiphora", and this includes Poodles, Lhasa apso, and Maltese Terriers.  Breeds with excessive nasal folds like Pugs, Pekinese, Bull Dogs, and Persian cats are also prone.

The condition we've encountered with our rescued Pyrs is something called Entropion.  Chows, Shar-peis, St. Bernards, and Bull Dogs are all predisposed to this.  With the hundreds of Pyrs who came through the rescue, I can personally recall about maybe 5 Pyrs with Entropion.  What happens, is that the top eyelid (dogs only have eyelashes on the top) curls under and the hairs scratch their eye's surface, thusly the tearing.  Untreated, it can scratch the corneal surface to a degree which may cause damaged vision or even blindness if left long enough.  Some young pups can be born with this, and end up outgrowing it in a short period of time; it would hardly be noticed. 

While usually congenital, it can be acquired through trauma or introduction of a foreign body.  This can also result in "pink eye" (conjunctivitis) and other conditions.  It can be treated with anti-inflammatories and/or anti-biotics.  In it's congenital form, surgery is usually required to fix it.  Think of it as an "eye lift". It's not a serious procedure, but it's not cheap.  It is, however, necessary to ensure your dog's eye is not damaged.  Recovery from the surgery is minimal. Visualizing if the eyelid is curled under is easy, in my experience.  You can easily take a close look and determine it.  I'd be willing to bet, though, that less severe cases of Entropion may be harder to spot and you'll definitely want to ask your vet if you see tearing.

Conversely, there is the opposite of this condition called Ectropion which impacts the bottom eyelid versus the top, and the lid is everted.  Also congenital, this dog may not be able to properly keep their eye moisturized while blinking and can get chronic dry eye.  This condition is common in loose-skinned dogs; we think of Bassets, Hounds... that "droopy eyed" look.  If not congenital, some dogs can acquire it from fatigue of facial muscles (hunting dogs) or due to paralysis from damaging a facial nerve.  Often this condition doesn't need any treatment.  In cases where the health of the eye is compromised, surgery may be needed to replace the lid against the eye.

So while sometimes tearing can be normal, there are other things which may be the culprit.  Always be concerned about bilateral tearing, and any time the tearing is cloudy or mucousy.  Always have your vet check out your dog's eyes to determine if their tearing is normal, to rule out any infections or eye conditions.

Ectropian

Entropian