Pupils and Accommodation
Fixed, dilated pupil
Few patients provoke more concern regarding a potentially life-threatening neurologic condition than those with headaches and a fixed, dilated pupil. The differential diagnosis can be narrowed to pharmacologic blockade, CN III palsy, and Adie tonic pupil. Pharmacologic blockade may occur because of inadvertent or purposeful application of mydriatic or cycloplegic eyedrops; it may also occur after touching the eyes with fingers contaminated through use of a scopolamine patch or touching certain plants that contain parasympatholytic chemicals.
The pilocarpine test distinguishes parasympathetic denervation from pharmacologic blockade. In pharmacologic blockade, 1% pilocarpine cannot overcome the receptor blockade, and the pupil remains large. Dilute pilocarpine will constrict a dilated pupil in a majority of patients with either a CN III palsy or Adie tonic pupil. See Chapter 10 for further discussion of pupillary abnormalities.
Changes in pupil size
Widely dilated pupils may be observed in young patients, most likely caused by increased levels of circulating catecholamines. A few patients are able to voluntarily dilate both pupils. Intermittent miosis occurs in spasm of the near reflex (discussed earlier), accompanied by esotropia and accommodation.
Changes in accommodation
Weakness or paralysis of accommodation sometimes occurs, primarily in children and young adults. Such patients may complain of an inability to read clearly even in the presence of an appropriate plus lens. If a patient with normal distance vision fails to read despite appropriate near-vision correction, a nonorganic condition is possible.
Spasm of accommodation can be observed with spasm of the near reflex. Patients may report blurred distance vision and often can produce 8–10 D of myopia. Refraction with and without cycloplegia during the period of spasm establishes the presence of the induced myopia.
Excerpted from BCSC 2020-2021 series: Section 5 - Neuro-Ophthalmology. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.