Why my cat has dilated pupils

Did you notice that your feline's eyes look different? Do you see that your cat has round and large pupils? It is normal that when changing your appearance you ask yourself " why my cat has dilated pupils? " especially if it has been a change that is becoming chronic, that is, they have stayed that way and by themselves do not return to their original form.

If you have observed this in your feline friend, we advise you to take it to the veterinarian so that he can check it well and give you a diagnosis, since it can be something mild or something more serious and that requires treatment soon. Remember that the veterinarian is the only one who can make the diagnosis and prescribe a treatment. Apart, from we provide basic information on everything related to the pupils of cats and we tell you what can be the causes of dilated pupils in cats, as well as the asymmetry in these.

How are the pupils of cats

In any animal, the movement of the eye when the pupils contract or become small is known as pupillary miosis, but when the pupils dilate or get larger it is called mydriasis of the pupil . These are normal movements in the eyes, as this regulates the entry of light to see properly, so if there is a lot of light the pupils become smaller or narrower and if there is little, they open or dilate to capture the maximum possible light.

In the case of cats, the system to capture the light in the eyes to see is the same, but it is added that they have a tissue called tapetum lucidum, like many other animals of total or partially nocturnal life (dogs, deer, rabbits, etc.), which allows them to retain more light and be able to see perfectly in the dark. Thus, by low light of the moon or a lighthouse that reaches the eyes of these animals at night is enough for them to see very well, because this tissue reflects light, as a mirror effect, illuminating more and facilitating vision night Here we tell you more about How nocturnal animals can see in the dark.

In addition, something that has always caught the eyes of cats is the shape of the pupils because in normal state they are vertical, whether they are straight or elliptical.

Meaning of the shape of the pupils of cats

As we have mentioned, the normal thing is to see a cat with eyes with thin and vertical pupils, but these can change shape according to the amount of light they perceive or according to a variety of stimuli that reach them or affect the eyes. So, this is the basic meaning of the shape of the pupils of cats:

  • Vertical straight pupil: is its contracted form, the smallest possible, and occurs when there is excessive light in the environment, so that the pupil regulates its entry into the eye to continue to see well and so the cat is not dazzled or blind
  • Vertical elliptical pupil: this is its most usual form, so it is at a midpoint between dilation and contraction. This occurs when the lighting is adequate for the eye structure of the cat and does not need more or less light.
  • Round pupil: in this case, the pupil of the cat is fully dilated or enlarged and occurs when there is very little light or practically none. The pupil opens to the maximum in an effort to capture as much light as possible from the environment, even if it is small.

In addition, we recommend this other article where we have How to see cats.

Why my cat has dilated pupils: main causes

These are the common causes that cause dilation of the pupils in cats, among which there are causes by emotions, which are natural reactions to a stimulus, and causes that are physical problems:

Emotions that cause pupil dilation in cats

When animals, including domestic felines, feel a strong emotion, they undergo several changes at the physical level in response. These reactions, which include enlarged and round pupils, can occur in both good and bad emotions, such as:

  • Fear.
  • Aggressiveness.
  • Stress.
  • Anxiety.
  • Excitement and agitation.
  • Satisfaction.
  • Relaxation.

In the case of positive emotions this reaction is due to a general relaxation, but in situations of negative emotions, it is a reaction that prepares the body to survive producing a state of alertness and sharpening the senses, so although Let's call them negative, they can be considered good and necessary for the living being.

Physical problems that cause dilated pupils in cats

  • Brain damage that causes symmetric arreactive mydriasis.
  • lumps, masses, abscesses, tumors or neoplasms in the eye area or after it.
  • Neurophthalmological problems that affect the sympathetic nervous system.
  • Various ocular problems, such as glaucoma and uveitis.
  • Hypertension.
  • Renal insufficiency.
  • FIV or Feline leukemia virus.
  • Poisoning.

Thus, when a cat has round pupils it can be a symptom of any of these diseases or conditions. The enlarged pupils are one of the symptoms of FIV, but there are many more that can warn that something is not right in the health of the feline. In this other article on How to treat feline leukemia you can learn more about the symptoms of this disease.

Regarding poisoning, it will depend totally on the type of poison or toxin that the pupils dilate or contract, apart from presenting other symptoms. If you observe this sign in your cat, keep in mind that this is a possible cause and requires immediate attention.

In addition, hypertension causes, among other things, that the pupils are enlarged and there are diseases and conditions, such as kidney failure in cats, whose symptoms include hypertension and, derived from it, the enlargement of the pupils.

Next, we explain the other physical causes of dilated pupils in cats, because they are more complex and specific and deserve a more detailed explanation.

Dilated pupils due to brain damage in cats: symmetric arreactive mydriasis

Brain damage, such as trauma to the head or face, can have several symptoms, but one of the most recognizable is a pupil disorder called symmetric arreactive mydriasis . In this disorder both pupils are affected and dilate, becoming large and round, and remain paralyzed in this state, being unable to return to their normal form even when too much light reaches them.

For example, when there is a victim in a traffic accident, the emergency health personnel first check whether or not there is a reaction in the pupils using a flashlight, and in this way, it is possible to know if there is a probability of brain damage. This happens exactly the same with all animals, including cats. Therefore, if you have dilated pupils and you know or think you may have had an accident, one way to know if it is possible or not to have brain damage is to focus it with direct light on each eye; If there is a normal reaction of the pupils, even a slight one, it is unlikely that there is any damage to the brain, but if there is no answer, it may have said damage to the brain. Anyway, in such case it is necessary to take it urgently to the veterinarian .

Dilated pupils in cats due to lumps

Another of the causes that answer your question " why my cat has dilated pupils? ", Is that in the eye area or just behind it the animal has some lump or tissue increase that presses the eyeball or the nerve ocular and that this gives several symptoms, among which it is possible the dilation of the pupil of the eye affected by said pressure.

It may be a lump in the brain or eye and the types of lumps of new tissue or neoplasms in cats and in these parts of your body are:

  • Benign neoplasms.
  • Tumor neoplasms.
  • Malignant or cancerous neoplasms.
  • Abscesses

Abscesses, benign and malignant growths and tumors in the brain and eyes can modify the structure and physiology of the eye, to the point of changing its appearance seen from the outside or changing its operation and even leaving one pupil smaller or bigger than the other. So if your cat has a larger or larger pupil than the other, this is a possible cause. It could also happen in both eyes, but it would mean that the lump is centered or in an area of ​​the brain that controls the reactions of the pupils or that the animal has two masses that affect each eye, which is less likely but not impossible.

Why my cat has one larger pupil than the other: anisocoria

If you notice that your cat has a larger pupil than the other, this is a symptom that is known as anisocoria and means that the pupils have asymmetry or are unequal . It can be presented in a temporary way in situations in which the eyes can receive different lighting, but when it becomes a symptom that lasts a certain time or is chronic, then it is a physical problem. It can be due to a variety of causes related to physical problems, but never for emotional reasons alone, since before reactions by emotions both eyes react equally and in this situation one of the two eyes does not perceive the physical and emotional stimuli well and can not react with normality because its structure or physiology does not work correctly.

One of the health problems manifested by this symptom called anisocoria or pupils of different sizes is Horner's syndrome . In this health problem, which occurs in a variety of animals (including cats and also humans), one of the pupils contracts (miosis) becoming very small, while the other pupil remains in a normal state, so that next to the other may seem bigger or good, it can expand normally if the animal feels some strong emotion (fear, stress, excitement) or if there is very little light and be increased while the other is contracted and immobile.

Horner syndrome in cats

It is a neurophthalmological disease and is caused by an alteration or affectation of the sympathetic nervous system. It is the part of the nervous system that regulates the body against external stimuli and is responsible, among other things, for alerting and preparing for action in order to survive, for example by increasing the heart rate, accelerating breathing and dilating the bronchi, sharpening the ear and sharpening the view through the dilation of the pupils . Therefore, when there is damage to the sympathetic nervous system, the nerve impulses are no longer transmitted and the muscles and functions of the different organs are no longer controlled in order to respond to the stimuli. With this syndrome, this happens at the level of the nerves of the face and eyes and usually happens only on one side, so a very visible symptom of this syndrome is that a pupil does not react, is always the same size and remains small .

Thus, among the symptoms of Horner syndrome in cats is the contracted pupil, seeing the one next to normal size or larger, drooping eyelids and prolapse of the nictitating membrane or third eyelid, among others.

There are a variety of possible causes of Horner syndrome in cats, which can often be of idiopathic origin, which means that the underlying cause is unknown, and some of the most common causes are trauma, tumors or neoplasms and abscesses behind the eyeball, infarcts, severe otitis, cervical injuries and injuries in the middle ear.

Dilated pupils in cats due to eye problems

This symptom can be due to merely eye problems. The two most common problems of this type are glaucoma and uveitis, although these conditions do not always include this part of the rounded and enlarged eye as a symptom, that is, a cat can have uveitis without having a large pupil.

Other symptoms of uveitis are ocular hypertension, a lot of sensitivity in the eye area, a lot of tearing and discomfort due to light, among others. Also, glaucoma also has other signs such as a whitish tissue in the eye, eye rimmed by the edges, vision problems that you can detect because the cat becomes more clumsy and more, like the ones we told you in this other article about the Symptoms of glaucoma in cats.

Bibliography
  • LOWENSTEIN, O. (1954). Alternating contraction anisocoria: a pupillary syndrome of the previous midbrain. AMA Archives of Neurology & Psychiatry, 72 (6), 742-757.
  • DESSAL, F. Neurological manifestations of systemic diseases in cats . Gattos Felino Clinical Center.
  • TAMI, G. What is hidden behind a cat's eye . Affinity Petcare.