autistic 9 yr old eyes dialated in bright light??

My granddaughter's eyes stay dialated for long periods of time, what may cause this?  She acts fine, no other symptoms .

[Sally44]

I think you need to get it checked, so ask your GP for a referal to an orthopist that has experience of autistic spectrum disorders and sensory processing disorders.
My son did the same and he was tested positive for Irlen Syndrome.  Alot of children with autism and dyslexia have Irlen Syndrome and it can be helped/rectified by wearing Irlen lenses.  So it just involves wearing glasses with the lense tinted to rectify the light frequency that her eyes are not coping with.
The other disorder is a problem with Binocular Vision.  My son's eyes used to dilate in and out sometimes and just looked unusual to me.  To rectify this you just need to do daily exercises to make the eye muscles stronger so that the eyes work together to form one image.  If she doesn't have binocular vision her brain will only register visual information through one eye or she will be seeing double.  She will probably get frequent headaches and will also have difficulties with depth perception.
But the above are just my experiences, so you need her checked out by the appropriate professionals.