Experienced and professional animal trainer provide their insights in answering this question :
A. Bring him to the vet as soon as possible. Eyes and brains are usually considered emergencies because they can deteriorate so fast. This problem could be either one.

How to Identify Common Pet Problems ?

Our sources include academic articles, blog posts, and personal essays from experienced pet care professionals :

There are several potential causes of an altered pupil size in dogs, including inflammation in the frontal region of the eye, increased pressure in the eye, diseases that are focused in the iris tissue itself, a poorly developed iris, scar tissue build up in the eye, medications, and cancer.
In conclusion, anisocoria in dogs is a condition in which the pupils of one or both eyes are different sizes. While usually harmless, it is important to have any changes in pupil size evaluated by a veterinarian as they may be indicative of an underlying medical condition that needs to be treated.
Your pup can get red eyes for various reasons, including an injury, a foreign object in the eye, allergies, and a host of eye conditions like glaucoma, conjunctivitis, and dry eye. If your dog has red eyes, you can take care of some issues at home, while others need to be addressed at a veterinary clinic.
The pupils of an individual are usually very symmetrical in appearance. In certain instances the pupils may vary in size. Occasionally, differing pupil size is inherited and there is no underlying disorder. Varying pupil size may also be due to infection, tumors, disease or trauma.
What causes uneven pupils? Slight differences between the two pupils may be present in up to 20 percent of people. This is called “physiologic anisocoria” and is normal. In these cases, there are no other symptoms and both of the person`s pupils react to changes in light.
What is anisocoria? Anisocoria is the medical term for when one of your pupils is bigger than the other. The pupil is the black center of your eyes that expands and contracts to help you see in different amounts of light. It naturally changes size without you noticing or controlling it.
Simple anisocoria

This is a benign condition that causes the pupils to differ in size, usually by up to one millimeter in diameter, without affecting the pupils` response to light. This condition can be intermittent or constant, and may even go away on its own without medical intervention.

Dog pupils are round. The pupils should be the same size and should constrict to a pinpoint when a bright light is shined in the eye. The pupil is a hole in the center of the iris. The lens is behind the pupil but is not seen when healthy, as it is clear.
There are types of diseases that can cause a change in eye color. Cataracts are a common cause, mainly in dogs and can cause changes either because of congenital reasons or because of diabetes. “Other changes of eye color can be due to conditions of the cornea or infections of the iris,” she said.
It is important to make a visit to the veterinarian if you notice redness of the eye persisting for longer than 24 hours. There are many different causes of red eyes in dogs and can be as simple as allergies, or more serious such as glaucoma.
Dilated pupils can occur with any type of anxiety, but are most common during periods of intense anxiety that occur in the following conditions: Panic Disorder/Panic Attacks. PTSD. Phobias.
A coloboma is a defect in the iris of the eye. It can appear as a black notch of varying depth at the edge of the pupil, giving the pupil an irregular shape. Coloboma may be associated with hereditary conditions, trauma to the eye, or eye surgery.
Asymmetrical eyes are common and often not cause for concern. A person may have one eye bigger than the other due to genetics, age, and lifestyle factors, among other causes. In rare cases, having asymmetrical eyes may indicate an underlying medical condition. Most of the time, however, this is not a cause for concern.
Anisocoria is a relatively common eye condition that is characterized by “unequal pupil sizes”. Pharmacologic Anisocoria is caused by certain medications, such as atropine, nasal vasoconstrictors, or clonidine, that may be taken for other health conditions.
Concussion of the brain may cause unequal pupils if the injury affects certain areas of the brain. Additionally, when the skull comes to a sudden stop, the brain can not only be injured on the side that has been impacted, but on the opposite side as well, as the brain bounces back.
Your doctor`s recommended treatment plan will depend on the underlying cause of your anisocoria. For example, if an infection is the cause, your doctor might prescribe antibiotic or antiviral eye drops. If you have an abnormal growth, such as a brain tumor, your doctor might recommend surgery to remove it.
While not a life-threatening condition in itself, anisocoria is a symptom that may be indicative of a serious or irreversible condition. Anisocoria refers to pupil asymmetry, or when the two pupils of the eyes in a dog are different sizes.
Physiologic anisocoria is pupils that are naturally different in size. No disorder is present. About 20% of people have this lifelong condition, which is considered a normal variation. In such people, both pupils react normally to light and darkness and there are no symptoms.
Warning signs of an ophthalmic problem include squinting and discomfort exhibited by rubbing at the eyes. Some types of eye pain (for example from high pressure) can cause lethargy and decreased appetite. Redness, tearing or excessive discharge, cloudiness or vision loss are also signs something is wrong.
Eye examinations can reveal signs that are suggestive of bacterial, viral or other systemic infections, as well as cancer, hypertension and diabetes. Dr. Catherine Nunnery, DVM, DACVO, a veterinary ophthalmologist based in Gaithersburg, Md., fielded our questions about some of the most common eye issues in canines.
All puppies have blue (or bluish) eyes when they first open them. But by the time they`re about 16 weeks old, their eyes change to their true color—typically brown. So, if you`ve got a young, blue-eyed pup at home now, keep in mind their eye color may change.
Mature Eye Coloration

However, the process occurs slowly and doesn`t happen overnight. It often takes nine to 12 weeks, starting from this point, for a puppy`s eye color to settle in and “stay.” The permanent eye color change can even happen as late as 16 weeks in age.

The first cause is exhaustion. If your dog is having trouble falling asleep at night or staying asleep throughout the night, this could cause your dog`s eyes to dry out and redden in irritation and discomfort.

Relevant Questions and Answers :

the most relevant questions and answers related to your specific issue

Q. How do I get my dog to stop chewing on things? I kennel her when I leave for a few hours, but I can’t go to the mailbox without her eating something.
ANSWER : A. If she’s young, then this is just normal puppy behavior. Don’t worry about it. The thing about puppies is, they explore using their mouths. If your puppy grabs a coat hanger, or a slipper, you should roll up a newspaper, and smack yourself on the head with it for leaving those things out.. your puppy is going to explore things, that’s normal! It is 100% up to YOU to keep those things away from your puppy when your puppy is unsupervised… even for just a moment.

Remember to never scold your puppy for grabbing these things. They are just curious little cuties, and they don’t chew things up to bother us.. Dogs do not have intentional thought, so they aren’t ever doing anything ON PURPOSE to us.. The most important thing you can do when your puppy is chewing something you don’t want her to be chewing is TRADE her the inappropriate item with a toy of hers, so she understands “no honey, that isn’t what puppies chew on… THIS is what puppies chew on!” and then begin playing with her using her toy to show her that TOYS ARE FUN.. Way more fun than a boring ol’ coat hanger.

Another helpful thing you can do is have two bags of toys. In each bag is many different kinds of toys. Lots of chew toys, lots of soft squeaky toys, lots of rope-type toys, a bunch of balls.. All kinds of things! For one week you have bag#1’s toys out for your puppy to play with.. At the end of the one week, you collect those toys, and you bring out bag#2! The toys will be more interesting/feel like new to your puppy, which will in-turn, make her chew less inappropriate things. Her toys are too fun to care about that dumb Wii-mote that you left laying around.

Hope this helps!

Q. I have 6 month old puppy this morning his pupils were two different sizes. And now his right eye is red. What do I do ?
ANSWER : A. Bring him to the vet as soon as possible. Eyes and brains are usually considered emergencies because they can deteriorate so fast. This problem could be either one.

Q. I have a 6 yr, old, neutered, male tabby cat. His left eye is dilated and his right eye is normal. No recent meds. He is eating and acting normal.
ANSWER : A. You’re describing something called “anisocoria”, which means unequal pupil sizes. Sometimes as cats age their iris (the colored part of the eye) atropies and we’ll see one pupil take on a slightly different shape or appearance. But there are some concerning problems that can cause anisocoria, including certain inflammatory diseases, diseases of the neurologic system (brain or nerves controlling pupil size) and exposure to some drugs (unlikely in this case since you mentioned that he hasn’t been given any drugs).

I’m glad that he seems normal otherwise, but see a vet so that the eyes can be examined and you can make sure this is not a serious condition.

Q. One eye is more red than the other. Last night he was pawing at it,today, he isn’t. Should I bring him to the vet?
ANSWER : A. Sounds possible that he had some irritation to the eye that is at least not itchy anymore. You can do either, having it checked now to confirm mild irritation, potentially due to debris or a topical irritant to the eye; or you can flush the eye with sterile saline eye wash (over the counter) using care not to poke or prod the eye and see if the irritation goes away on its own within the next 24 hrs. It has shown improvement already it appears, however if it is not cleared up and your pet seems irritated by it AT ALL, then it should be looked at by a vet and tested for a possible corneal scratch or ulcer. These can cause redness of the eye, eye discharge and pawing at the face. They are usually treated by prescription only topical eye antibiotic ointment and generally do very well after treatment.

Read Full Q/A … : Eye Problems in Cats

Q. My 6 year old male neutered cat has suddenly developed an eye problem where one pupil is enlarged and covers the eye and the other one is pinpoint siz
ANSWER : A. This phenomenon is called Anisocoria (inequality of pupil size). There are several different causes of this including glaucoma, anterior uveitis, cancer of the eye, old age change, etc.
To help pinpoint what could be causing your pets condition I would recommend a thorough eye exam. Your vet may need to refer your pet out to an opthalmologist if any abnormalities are seen that need further treatment.

Q. Weak, discharge from eyes, swelling on right eye, does not want to open eyes. What is wrong?
ANSWER : A. If the discharge from the eye is green or yellow in color, it can indicate a secondary infection. Swollen eyes can be caused by a number of things ranging from allergies to infections, to injury to the eye itself or surrounding areas.

It is best to have your pet’s eye examined by your local vet. They will most likely wish to place a stain in the eye that can check for damage such as cuts or scratches. An ointment can then be given to help reduce inflammation, pain and take care of infection.

Until you can get to the vet, be sure to not let your pet scratch or paw at their eye as this can make things worse. You can also use a warm wet washcloth to gently remove any debris and allow the eye to open some, providing relief. However, if symptoms worsen, or the swelling travels to the face, head or neck, it may indicate a serious allergic reaction which should be treated immediately.

Q. Is it okay to leave your dog alone on the house for over8 hrs? Will it harm him to not be able to go to the bathroom for that long?
ANSWER : A. It depends on the age of the dog. Most adult dogs need potty breaks after 6 hours. If it’s a puppy no it should not be left that long especially if it’s in a crate. No dog should be left in a crate for more than 6 hours. One month old puppy should only be in a crate for one hour. A two month two hours, ect ect until 6 hours which is the cut off for all ages.

Q. My puppy is urinating a lot. And the lady I gave one of the puppies to said she thinks her puppy has diabetes could my puppy have it to
ANSWER : A. It is not likely that either one of these puppies has diabetes. It is very uncommon for a puppy that young to have diabetes. If your puppy is straining to urinate or is urinating very small amounts frequently and cannot seem to wait for very long between urination, he may have a urinary tract infection. It is quite possible that your puppy is completely normal. I would suggest an exam with your veterinarian and discuss the behavior with them. They may suggest a urinalysis. Your puppy should be going to the vet at 3 week intervals for vaccinations at this age, so you can discuss it when he has his next set of vaccines. The other person with the other puppy should also be taking hers to a vet for proper immunizations and she should also discuss her concerns with her vet.