Dorsal midbrain damage can result in midsized pupils with poor light response and preserved near response. Such responses occur when the lesion spares the more ventrally located fibers of the near reflex pathway. Associated findings include bilateral eyelid retraction (Collier sign), vertical gaze palsy, accommodative paresis, and convergence-retraction nystagmus (Parinaud syndrome; see Chapter 8, Fig 8-5).
Table 10-3 Causes of Light–Near Pupil Dissociation
Argyll Robertson pupil occurs in patients with tertiary syphilis involving the CNS. Affected patients have small pupils (<2 mm in diameter) that are often irregular. The pupils do not react to light, but the near response and subsequent redilation are normal and brisk. These characteristics distinguish Argyll Robertson pupils from bilateral chronic tonic pupils (which may also result from neurosyphilis). In addition, iris atrophy frequently occurs, portions of the iris transilluminate, and dilation is poor after instillation of mydriatic eyedrops.
Argyll Robertson–like pupils are observed in widespread autonomic neuropathies such as bilateral tonic pupils (chronic), diabetes mellitus, and chronic alcoholism, as well as in encephalitis and after panretinal photocoagulation. Serologic tests for syphilis should be considered in the evaluation of patients with bilateral pupillary light–near dissociation with miosis.
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.