What are potential side effects of antihistamines related to the eyes?

The correct answer highlights that mydriasis (dilated pupils) and dry eye are potential side effects of antihistamines. Antihistamines work by blocking histamine receptors, which helps alleviate allergy symptoms. However, one of their anticholinergic effects can lead to pupil dilation. This occurs because antihistamines inhibit the activity of the parasympathetic nervous system, which is responsible for constricting the pupil. The resulting mydriasis can impact vision and is particularly relevant in certain contexts, such as driving or operating machinery.

Additionally, antihistamines can reduce tear production due to their drying effects on mucous membranes, leading to a sensation of dryness in the eyes. Dry eye can cause discomfort, blurred vision, and increased irritation, further complicating the user's experience.

In contrast, increased tear production would not be a side effect associated with antihistamines, as their drying properties typically reduce such secretions. Redness and itching are often symptoms that antihistamines aim to treat rather than side effects, and pupil constriction is contrary to the action of antihistamines, which may lead to dilation instead.