TAFRAOUTE, Morocco — Molly Thompson craned her neck so she could make out the man climbing the tower of red rock. Squinting into the desert sun, she tried to identify a crack he could grab on to or a ledge wide enough for his foot. The climber, struggling to keep his grip, was her husband, Jesse Dufton.

His left arm trembled from the effort. His foot probed for a more secure hold, but found nothing. “A little bit higher there should be a foothold,” Molly said into a headset.

When Jesse extended his foot again, it missed the tiny outcropping. He returned his foot to its original position and tiptoed on 3 millimeters of quartzite, 200 feet above the ground. He did not look down.

He did not look anywhere. Jesse has advanced rod-cone dystrophy. Put another way: He is completely blind.

And another: He is one of the world’s few elite blind rock-climbers. Jesse, 38, is a “trad climber,” which means he ascends bare rock faces without permanent bolts. Instead, he places removable metal anchors into cracks in the mountain and attaches his rope to them.

If he places those anchors poorly and falls, he could die. It is a sport in which one’s vision — the ability to spot minor fractures or grooves in the rock — is considered vital. Molly’s words were meant to conjure the smallest nooks from the darkness so that Jesse’s hands and feet could find them.

During his climb in Morocco, bits of debris came loose under his fingers, ricocheting down the mountain. Molly could he.