A 23-year-old woman is noticed to have irregular pupils on routine examination. She has 1 large pupil, which has minimal response to light stimulation, but it does respond to accommodation. The eye movements are normal and she experiences no double vision.For the above patient with a pupillary abnormality, select the most likely diagnosis.

**Core Concept**
Tonic pupils, also known as Holmes-Adie syndrome, is a rare neurological disorder characterized by a dilated pupil with a poor or absent light reflex but a preserved or exaggerated near reflex. This condition is often associated with a denervation supersensitivity of the iris sphincter muscle.

**Why the Correct Answer is Right**
The patient's presentation of a large pupil with minimal response to light stimulation but a response to accommodation is consistent with Holmes-Adie syndrome. The condition arises due to a degeneration of the postganglionic parasympathetic fibers supplying the iris sphincter muscle, leading to a loss of light reflex. However, the near reflex is preserved due to the involvement of the ciliary ganglion, which also controls accommodation. The preserved near reflex is a key distinguishing feature of Holmes-Adie syndrome.

**Why Each Wrong Option is Incorrect**
**Option A:** Essential anisocoria typically presents with a fixed and dilated pupil in the affected eye, but both pupils have a normal response to light and accommodation. This condition does not involve a significant impairment of the near reflex.

**Option B:** Horner syndrome is characterized by a constricted pupil, ptosis, and anhidrosis due to a disruption in the sympathetic pathway supplying the eye. This condition does not match the patient's presentation of a dilated pupil.

**Option D:** Argyll Robertson pupils are characterized by small, irregular pupils that constrict with accommodation but not with light. This condition is often associated with neurosyphilis and does not match the patient's presentation of a large, dilated pupil.

**Clinical Pearl / High-Yield Fact**
Holmes-Adie syndrome is often associated with other neurological symptoms, such as tremors, ataxia, and sensory disturbances. It is essential to remember that the condition is typically unilateral, and the affected pupil may have a delayed or absent reaction to light, but a preserved or exaggerated near reflex.

**✓ Correct Answer: C. tonic pupils (Holmes-Adie syndrome)**

✓ Correct Answer: C. tonic pupils (Holmes-Adie syndrome)