Let their eyes be darkened (skotisthētōsan hoi ophthalmoi autōn). First aorist passive imperative of skotizō, to darken. A terrible imprecation.
That they may not see (tou mē blepein). Repeated from Rom 11:8.
Bow down (sunkampson). First aorist active imperative of sunkamptō, old verb, to bend together as of captives whose backs (nōton, another old word, only here in N.T.) were bent under burdens. Only here in N.T.