Final answer:
When performing the direct light check, the DRE checks for pupil reaction to light and the accommodation reflex to assess the integrity of the oculomotor nerve and the optic nerve's functionality. Accommodation reflex involves the muscles of the eye and the lens changing shape to focus on nearer objects, while the pupillary light reflex tests the bilateral constriction of pupils.
Step-by-step explanation:
When shining the penlight directly into the subject's eye for the direct light check, the DRE also checks for pupil reaction to light and accommodation reflex. The assessment of the accommodation reflex involves observing the coordination of the ocular muscles and the shape change in the lens of the eye when visual stimuli move closer to the face, a process controlled by the parasympathetic fibers of the oculomotor nerve. This is crucial for maintaining focus on nearby objects.
Moreover, testing the pupillary light reflex, where shining light in one eye will elicit constriction of both pupils, helps determine whether there is any damage to the optic nerve or the oculomotor nerve. A normal response involves bilateral constriction. However, if only one pupil constricts, or if there is no response when light is shined into one eye, it could indicate damage to the optic or oculomotor nerve respectively.