Which cranial nerve weakness may lead to the most common causes of double vision?

Cranial nerve III, also known as the oculomotor nerve, is primarily responsible for the movement of most of the eye muscles, as well as controlling the size of the pupil and maintaining an open eyelid. Weakness in CN III can result in a range of problems, one of the most significant being double vision, as this nerve controls the majority of the eye's movements.

When CN III is impaired, it can lead to a variety of eye movement issues, including ptosis (drooping of the eyelid) and diplopia (double vision). The misalignment of the eyes, due to the inability of CN III to function properly, causes the brain to receive two different images, which leads to the perception of double vision.

While CN IV (trochlear nerve) and CN VI (abducens nerve) are also involved in eye movement and can indeed cause double vision if weakened, CN III is more commonly involved due to its extensive control over multiple muscles that direct eye movement. CN VIII deals with hearing and balance and does not contribute to eye movement, making it irrelevant in terms of causing double vision.