What physical finding is associated with "blind as a bat" in anticholinergic toxidrome?

The phrase "blind as a bat" is often used to describe the visual disturbances associated with anticholinergic toxicity, primarily characterized by dilated pupils, or mydriasis. Anticholinergic agents inhibit acetylcholine at muscarinic receptors, which leads to smooth muscle relaxation in the iris sphincter muscle, resulting in pupil dilation. This dilation can lead to blurred vision and difficulty focusing on nearby objects because the eyes cannot constrict appropriately in response to light.

In contrast, constricted pupils would indicate increased cholinergic activity rather than the effects of anticholinergic toxicity. A lack of pupillary response might suggest a more severe neurological compromise, while unequal pupil sizes, or anisocoria, can arise from multiple causes but are not specifically associated with the classic anticholinergic toxidrome. Thus, the association of dilated pupils with "blind as a bat" highlights the typical presentation of visual changes in anticholinergic toxicity.