Which symptom is associated with prostaglandin agonists?

Prostaglandin agonists are primarily used in the treatment of glaucoma and are known for their ability to lower intraocular pressure. One of the unique and significant side effects associated with prostaglandin agonists is the potential for permanent changes in eye color. This occurs particularly because these medications increase the amount of melanin in the iris, leading to a darkening of the eye color, especially in individuals with lighter-colored eyes. This effect is not just temporary but can be permanent as the changes in the pigmentation of the iris continue as long as the medication is used.

The other options, while potentially related to eye conditions or treatments, do not directly relate to the specific and notable side effect of eye color change that is characteristic of prostaglandin agonists.