Which action requires contraction of the orbital portion of the orbicularis oculi?

The contraction of the orbital portion of the orbicularis oculi muscle is specifically associated with forced eyelid closure. This muscle is responsible for both voluntary and involuntary eyelid movements, but its orbital portion plays a crucial role in providing a strong, forceful closure of the eyelids.

During actions that require a significant or strong closure, such as squinting into bright light or during a protective reflex, this portion of the muscle contracts more vigorously to ensure the eyelids come together tightly. This action helps protect the eye from potential threats, bright lights, or irritants by shielding the cornea and limiting exposure.

In contrast, spontaneous blinking and the menace reflex rely more on the muscle's palpebral portion, which is responsible for gentle, rhythmic movements of the eyelids. The dazzle reflex, which is a response to bright light, also does not require the same level of contraction from the orbital portion as forced eyelid closure does.

Thus, the requirement for strong contraction of the orbital portion specifically identifies forced eyelid closure as the correct action associated with this muscle function.