Final answer:
Upon observing underaction in Ductions testing, it is key to ask if there is diplopia because misalignment of the eyes, leading to double vision, may indicate internuclear ophthalmoplegia or other conditions affecting eye muscle coordination.
Step-by-step explanation:
If UA (underaction) is observed after Ductions testing, one should ask if there is diplopia. Ductions testing involves tracking eye movement by having the patient follow the tip of a pen through their visual field. The key purpose of this test is to assess the eye's conjugate movements and related nerve function. A failure in these movements, such as the inability of one eye to abduct while the other adducts, could result in internuclear ophthalmoplegia, which often presents as diplopia or double vision. This symptom occurs when the eyes are misaligned, focusing on different stimuli. It is important to ask about diplopia because it is not limited to malfunction of the lateral rectus muscle; any extraocular muscle weakness can lead to lack of eye movement coordination and double vision.
Diplopia can also be a symptom of other visual field deficits, such as bilateral hemianopia, where there is loss of lateral peripheral vision without losing superior or inferior peripheral fields. This condition typically arises not from problems within the visual system itself but perhaps due to a pituitary gland growth pressing against the optic chiasm, affecting the signal transmission yet sparing axons projecting to the same side of the brain.