What are the pupillary manifestations of atropine poisoning?

Atropine poisoning presents typical pupillary features, including mydriasis (pupil dilation), sluggish or absent light reflex, impaired accommodation reflex, altered pupil morphology, and bilateral symmetry. Detailed analysis is as follows:

1. Mydriasis: Normal pupil diameter ranges from 2 to 5 mm. After poisoning, the pupils markedly dilate, often exceeding 5 mm, and in severe cases may reach more than 8 mm. This occurs because atropine blocks M-cholinergic receptors on the pupillary sphincter muscle, causing relaxation of the sphincter while the dilator muscle remains continuously contracted, resulting in sustained pupil dilation.

2. Sluggish or absent light reflex: When light is shone into the eyes, the pupillary constriction response in poisoned individuals is significantly delayed—termed a sluggish light reflex. In severe poisoning, there is no pupillary constriction response at all upon light stimulation, indicating a complete absence of the light reflex.

3. Impaired accommodation reflex: Normally, when viewing near objects, the pupils constrict to adjust focus. After poisoning, this accommodation reflex becomes disrupted, so the pupils fail to constrict properly when focusing on nearby objects, leading to blurred vision and particular difficulty in clearly focusing on close items.

4. Altered pupil morphology: In some poisoned individuals, slight changes in pupil shape may occur, with pupils shifting from regular roundness to slightly irregular forms. However, such changes are usually subtle and require careful observation. These morphological alterations are related to uneven contraction of the pupillary sphincter muscle and have relatively lower clinical significance compared to mydriasis.

5. Bilateral symmetry: Pupillary changes caused by atropine poisoning typically occur bilaterally and simultaneously—that is, both pupils dilate together and exhibit equal reduction or loss of reflexes. This bilateral symmetry is an important distinguishing feature from conditions such as intracranial lesions, which often cause unilateral pupillary abnormalities.

These pupillary signs should be interpreted in conjunction with medication history and other clinical symptoms. Atropine should always be used strictly according to medical instructions, with careful dose control to avoid overdose and potential toxicity.