Evidence of Medieval(?) Reading-Glasses (Midweek Miscellany 5)

Source

I spotted this about ten years ago, but only got a good photograph a few weeks ago:

MS 9, fols. 6v-7r
Courtesy of the Watkinson Library, Trinity College (Hartford, CT)

(Enhanced detail)

Something precisely similar has been found at the Harry Ransom Center, Texas.

EDIT 16 Nov. 2015:
I recently found an amusing image of Conrad I of Salzburg using such a pair of glasses, in a manuscrupt in the Kupferstichkabinett, Berlin: