On the west front of Wells Cathedral is a statue with great helm (http://warfare2.netai.net/13/Wells_Cathedral_West_Front_Statues_123-124.htm) with a single broad eye-slit reinforced at the edges by an additional piece of metal which also runs down the front of the helmet. A war elephant scene in a bestiary, Harley MS 4751, has simillar great helms (http://warfare2.netai.net/13/Harley_MS_4751-f8-Elephant.htm). This has a similar compostion to a war elephant scene (http://warfare2.netai.net/13/Rochester_Bestiary-f11v-Elephant.htm) in the Rochester Bestiary (http://warfare2.netai.net/13/Rochester_Bestiary-1230AD.htm), but, the great helms in this have divided eye slits. The other knight statue on Wells Cathedral (http://warfare2.netai.net/13/Wells_Cathedral_West_Front_Statues_145.htm) also has a divided eye-slit on his great helm.
(http://forums.totalwar.org/vb/attachment.php?attachmentid=12987&d=1401605420)
Are there other primary sources for early great helms with a single eye-slit?
MIRROR SITE
Wells Cathedral statue with great helm (http://warfare.likamva.in/13/Wells_Cathedral_West_Front_Statues_123-124.htm)
War elephant scene in a bestiary, Harley MS 4751 (http://warfare.likamva.in/13/Harley_MS_4751-f8-Elephant.htm)
Druzhina
13th Century Illustrations of Costume & Soldiers (http://warfare2.netai.net/13C.htm)
Nice find.
Ditto !
Cheers - Phil