Dilated Pupils in Cats – Causes, Symptoms and Treatment

Causes of dilated pupils     How is the cause determined?     What is the treatment for dilated pupils?

dilated pupils in cat

The pupil is the black slit/circular shape you see in the middle of the cat’s iris (the coloured part). The role of the pupil is to control the amount of light entering the eye. It does this by dilating (becoming large) and constricting (becoming small/slit-like). So, in poor light, the pupil will be dilated, to let in as much available light as possible, when it’s bright, the pupil will be small, to reduce the amount of light entering the eye.

Emotions also play a role in the size of the pupils, when a cat is angry or aggravated the pupils constrict when it is happy or frightened, they dilate.

Pupils should be equal in size and when looked at with a bright light, they should both constrict quickly.

What are the causes of dilated pupils in cats?

We have already mentioned that the pupils dilate in low light and also during times of stress, anger or fear. In both situations, the pupils should constrict either when light increases or when the cat has calmed down. Permanently dilated pupils can be a symptom of an underlying problem. One or both pupils may be affected, when only one pupil is affected, the condition is known as anisocoria.

Some causes of dilated pupils include:

  • Feline dysautonomia (feline dilated pupil syndrome) – A dysfunction of the autonomic nervous system, a part of the nervous system which operates without conscious control
  • Insulinoma – Tumour of the pancreas which causes it to produce too much insulin.
  • Brain tumour.
  • Certain drugs and medications (ADD medications which contain amphetamine and methylphenidate, atropine eye drops) can have an effect on the functioning of the pupil.
  • Poisoning such as snake bite or tick bite.
  • Retinal detachment – High blood pressure is the most common cause of retinal detachment in cats,  taurine deficiency used to be a cause, but this is extremely rare now. Other causes include glaucoma, certain infections (histoplasmosis), certain poisons which can lead to bleeding behind the pupil, and eventually retinal detachment.
  • Head trauma.
  • Glaucoma – An increase in pressure within the eyeball.
  • High blood pressure – A condition in which blood is pumped through the arteries at a higher than normal force.

How is the cause diagnosed?

Your veterinarian will perform a complete physical examination and may need to perform some diagnostic tests to determine the cause. He will carefully examine the eyes and obtain a medical history from you, including how long the eye(s) have remained dilated and if there are any other symptoms you may have noticed, is the vision affected? He may need to run some diagnostic tests, including:

  • Baseline tests such as biochemical profile, complete blood count and urinalysis to check the overall health of your cat and evaluate the organs
  • Checking the blood pressure
  • Blood tests to check for diabetes
  • Ultrasound of the eyes to look for lesions
  • Ultrasound to evaluate the pancreas
  • CT scan to check for tumours or brain lesions
  • Tonometry to measure the pressure within the eye
  • Gonioscopy to evaluate the angle of the anterior chamber of the eye
  • Ophthalmoscopy to examin the rear of the eye where the optic nerve is located

How is the condition treated?

Treatment is aimed at addressing the underlying condition and may include:

  • If caught early, retinal detachment can be helped, but without immediate treatment, blindness will occur. It is a medical emergency.
  • Feline dysautonomiaFluids and nutritional support and managing symptoms.
  • Brain tumours – Surgery to remove or reduce the size of the tumour and/or chemotherapy or radiotherapy.
  • Glaucoma – Medications to bring down the intraocular pressure. Anti-inflammatory drugs may be prescribed if inflammation is the cause. Painkillers to relieve pain. If blindness has occurred, the eye may be surgically removed.
  • High blood pressure – Finding and treating the underlying cause as well as medications to help bring down blood pressure and a low sodium diet.
  • Insulinoma – If possible, surgical removal of the tumour otherwise medical management such as steroids to promote the formation of glucose and dietary management.
  • If medications or poisons are the cause, the condition may improve once the drugs/toxins are out of the system.
  • Head trauma treatment depends on the severity of the trauma, it will require hospitalisation and supportive care including fluid therapy, oxygen therapy, medications to control seizures and in some cases surgery.

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