Starting from the notes added to the margins of some Greek manuscripts in the hand of John Kamateros, the patriarch of Constantinople, as confirmed by the ex libris in MS Ambr. M 66 sup., other manuscripts are recognised as belonging to the same scholar, who densely glossed them. In MS Vat. gr. 1594 (Corpus Ptolemaicum), his hand not only wrote scholia but also replaced calligraphically some lost folios. By observing the peculiarities of the handwriting, the Vatican manuscript can be seen as the middle point of an evolution of this hand, from a moderate orderliness and regularity to an increasingly fraught and disordered appearance. An examination of both handwriting and content of the notes added by this hand results in the list of 28 Greek codices that are described here.