Can a doctor tell if i have contacts on or not?

You don't have to be a medical doctor to see if someone is wearing contacts. They are visible to anyone who notices.

If they examine your eyes, yes.

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Your question belongs in Health>Optical as it's currently in Yahoo Products>Yahoo Mail>Calendar and Contacts and not applicable to this subcategory (and thus decreases your chances of getting many useful answers).

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If the doctor is looking closely at your eyes they can tell. If you are at the doctor for something unrelated such as an ingrown toe nail, they most likely wouldn't be able to say if you're wearing contacts or not.

Yes, doctors are trained to assess from head to toe.

I would sure hope so.  Anyone should be able to tell that if they look at your eyes.