The reasons why cats’ eye pupils are one large and one small:

1. Cat’s genetic genes: cause the pupils of the cat’s eyes to be one large and one small at birth.

2. Pupil atrophy caused by trauma: The cat needs to be taken to a regular ophthalmic pet hospital for examination and timely treatment.

3. Spasmodic pupillary syndrome: Infection with feline leukemia virus causes this condition, and may alternate between the eyes.

4. Oculomotor nerve palsy: It is divided into congenital oculomotor nerve palsy and acquired oculomotor nerve palsy.

5. Horner syndrome: also known as childhood cervical sympathetic palsy syndrome.