Final answer:
The corneal reflex is used to assess the sensory function of the trigeminal nerve, and is tested by stimulating the cornea, causing a blink response.
Step-by-step explanation:
The reflex that is used to assess the sensory function of the trigeminal nerve is the corneal reflex. This reflex involves the stimulation of the cornea, which could be by a tactile stimulus like a gentle touch or by bright light, leading to blinking. The sensory component of the corneal reflex is carried through the trigeminal nerve. If there's a need to test this reflex, a practitioner might use an air puff or a cotton-tipped applicator to gently touch the cornea, and observe the reflex blinking motion of the eyelids.