Problem in the eye, the nerves to the eye and brain are primary causes of dilation. Infections of the eye or abscesses behind the eye (are the eyes bulging?), brain swelling due to trauma or infection, eating raw fish (has an enzyme that destroys thiamine) or on a mostly milk diet (deficient in taurine) are possible causes. Glaucoma is also, but it is rare in kittens.
Are there any other signs besides dilatation? Are the eyes red, goopy, squinting? These can be seen in infections with the respiratory viruses in kittens.
Poisoning (antifreeze) is another possible cause.
Rabies is another possible cause and I sincerely hope this is not the case. Is the mother still alive and healthy? If so, that's good. If not, was she sick when you last saw her?
It would be good if you could take the kitten to your vet. Dehydration and bacterial infections are fairly common in kittens.
Let me know if you have follow up questions.
Veterinarian
30 years as owner of a mobile practice treating dogs, cats, horses and other pets.