Translation:These are the glasses I gave you.
When the direct object ("les lunettes" here) appears before the auxiliary verb ("ai"), if the auxiliary verb is avoir, then the participle must agree with the number and gender of the direct object (feminine, plural in this case).
On the other hand, if the auxiliary verb is être the participle must agree with the subject.
"The past participle of avoir verbs that are preceded by a direct object must agree with the direct object"
les lunettes (fem. plural) --> données
Interesting. You believe that insisting on relying on established established conventions and standards can not in any way be classified as prescriptivist
That seems like an example of prescribing what English words should mean and how they should be used.
But I take your point and will amend my comment to read:
But when learning the rules of a foreign language, it is the established conventions and standards that you have to focus on.
Glasses " Spectacles" marked wrong, does the word not exist in American vocab.?