The saying "the eyes are the window to the soul" has a medical application as well. From a medical perspective we should also say "the eyes are the window to our health" considering the many notions we can deduce from simply looking into the eyes of another person or an animal. Because most dog eyes are brown, looking into the pupil may be a bit challenging at times, but it's good to get acquainted with how those pupils look like normally so that we can identify signs of trouble promptly and refer to our veterinarians. So today, let's learn more about a dog's pupil, what it does, how it works and things to watch for.
Introducing Your Dog's Pupil
Hello, it's your dog's pupil talking! Yes, to simply put it, I am that black circle that you find in the middle of your dog's eye. Well, to tell you the truth, I am not really black. That's just an optical illusion!
In reality, I am a black hole and appear black because of the presence of special light absorbing pigments located in the interior portions of the eye.
I can be of different shapes and sizes based on the species you are looking at. For instance, in goats and horses, I am oval, in cats I am a thin vertical slit, but in dogs and humans I tend to be round.
I am an Adjustable Opening
For sake of comparison, you can compare your dog's eyes to a camera that takes pictures of the world and sends those images to your dog's brain through the optic nerve.
When it comes to me though, you can think of me as an adjustable opening. The iris (the colored part of the eye) acts as a camera's shutter and basically regulates how much light should enter and reach me. The amount of light that reaches me therefore elicits the iris to change my size.
When it's dark, the iris muscle contracts so to enlarge me so to allow more light into the dog's eye so he can see. When it's bright instead, the iris muscle expands so to constrict me so to allow less light into the dog's eye. My size is therefore controlled by two groups of smooth muscles of the dog's iris: the iris sphincter muscle and the iris dilator muscle. These two muscle basically work in opposition. Pretty neat no?
Did you know? The technical term for when I constrict is "miosis" (allowing less light in) whereas, the technical term for when I dilate is "mydriasis" (allowing more light in).
I Act as An "Eye-Opener"
On top of shrinking and dilating in response to light, I also react to certain stimuli and situations. For instance, if the dog sees something scary, I may dilate too. There's yet no proof to back up why I do so, but experts theorize that it's part of a survival tactic.
Basically, I dilate so to allow more light to enter the eyes so that the dog's brain can process information quicker when every second counts. I therefore act as an "eye-opener" so to say, so to help the dog take in more visual information about his surroundings in such a critical time.
According to Scientific American, the autonomic nervous system responsible for the fight and flight response is what triggers me to dilate when under stress, whereas the parasympathetic system, responsible for "rest and digest" functions, causes me to constrict.
When Things Go Wrong
When I am working properly, I will dilate and constrict based on the amount of light entering the eyes, but when things go wrong I may stop from properly responding to light.
In some cases, I might not look good from the get-go and you can notice abnormalities in my size. This is one of the main reasons why veterinarians often check a dog's eyes as part of the physical exam and check my dilation or constriction in different lighting situations as a diagnostic tool.
Anisocoria, is the medical term for when the pupil in a dog's eye is different from the other. Basically, in this case, I am bigger in one eye compared to the other.
According to veterinary ophthalmologist Caryn E. Plummer, anisocoria may be indicative of some type of ocular or neurological disorder. However, not always this is detectable from onset; it may be necessary to shine a light in the dog's eyes and watch how I respond both in bright and dim lights. This should be done by a vet, or even better, a veterinary ophthalmologist specially trained in evaluating eyes.
Just consider that there are many conditions that may cause anisocoria in dogs such as an eye injury, inflammation somewhere within the eye, Horner's syndrome, glaucoma, uveitis, exposure to toxins, head concussions and even cancer. Also, a very important important piece of information needed is uncovering which pupil is the abnormal one. Is it the dilated one or the constricted one?
"If anisocoria occurs suddenly, you should consider this an emergency situation and seek veterinary care immediately to lessen the chance that your dog's vision will be permanently affected."~ Dr. Cheryl Yuill, VCA Animal Hospital
Sometimes, I may also appear dilated in both eyes. When I no longer constrict in response to light this is often a sign that the dog's eyes are no longer capable of recognizing light on the back of the eye causing blindness. Several conditions can cause this, such as blood clotting problems, infections, high blood pressure or a mass around the area of the optic nerve, explains Dr. Christian K.
Other times, I may appear constricted in both eyes. Dog owners describe their dogs as having "pinpoint' pupils. This can be due to exposure to chemicals such as pesticides, exposure to certain medications such as opioid drugs or benzodiazepines, or traumatic brain injury affecting the front of the brain stem, explains veterinarian Dr. Altman.
In some cases, abnormalities in my shape can be due to congenital eye problems affecting me or the surrounding iris such as persistent pupillary membranes in dogs, coloboma, iris hypoplasia or sunburst pupils.
As seen, I am very important when it comes to your dog's vision and by looking at me, vets can even sort out medical problems. If you notice anything odd with me and the surrounding eye, please see your vet sooner than later. A "wait and see" approach could cost your dog's vision and even affect his health, so keep an "eye" on me and report changes to your vet promptly! Yours truly,
Your Dog's Pupil
Disclaimer: this article is not meant to be used as a substitute for professional veterinary advice. If your dog has signs of eye problems, please see your vet promptly to protect your dog's vision.