What's your diagnosis? It's not Horner. The left eye does respond to light, but in a well lit room it takes about half an hour before it's reached the proper size. The right eye is normal. I'll post the correct answer in a few days!
Correct answer: Yes, it's Holmes-Adie syndrome. Due to ciliary ganglion degeneration, the pupil is constantly dilated (usually unilateral). The pupil will respond to light properly, but only after about 30 minutes in a well-lit room. Accomodation, on the other hand, is normal.