Which of the following conditions causes the ciliary muscles to lose their function?

Cycloplegia is a condition characterized by the paralysis of the ciliary muscles, which are responsible for controlling the shape of the lens in the eye. When these muscles become paralyzed, the eye's ability to focus on near objects is impaired. This loss of function is crucial in understanding the mechanics of vision and the overall effects on accommodation—the process by which the eye changes optical power to maintain a clear image of an object as its distance varies.

In contrast, the other conditions listed are related to different issues affecting the eye but do not directly impact the function of the ciliary muscles. For instance, blepharitis refers to inflammation of the eyelid margins, while astigmatism is an irregular shape of the cornea that leads to blurred vision. Entropion involves the inward turning of the eyelid, which can cause lashes to rub against the eye, but does not affect the ciliary muscles directly. Therefore, recognizing cycloplegia as the condition affecting ciliary muscle function highlights its physiological role in vision.