Questions:
1. What is a tadpole pupil?
2. What are 6 causes of light-near dissociation?
3. Where is the lesion in a patient with light-near dissociation due to Argyll Robertson pupils?
4. What is the mechanism of light-near dissociation due to Argyll Robertson pupils?
5. Where is the lesion in a patient with light-near dissociation due to Adie tonic pupil?
6. What is the mechanism of light-near dissociation due to Adie tonic pupil?
7. What is the mechanism of light-near dissociation due to aberrant regeneration of the 3rd nerve?
8. What is the mechanism of light-near dissociation due to severe vision loss?
9. What is the mechanism of light-near dissociation due to laser panretinal photocoagulation or cryotherapy?
10. Where is the lesion in a patient with light-near dissociation due to peripheral neuropathy?
11. What are paradoxical pupillary reactions?
12. What is spasm of convergence?
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Questions with answers:
1. What is a tadpole pupil?
Tadpole pupil is an irregular pupil that resembles a tadpole. It is a benign phenomenon that is spontaneously reversible. The pupil undergoes sectoral dilation lasting for a few minutes before returning to normal (segmental spasm of the iris dilator muscle). Tadpole pupil may occur multiple times for several days or a week and then disappear.
2. What are 6 causes of light-near dissociation?
a. Severe loss of afferent light input to both eyes (retina, optic nerves, chiasm)
b. Ocular surgery (laser panretinal photocoagulation, cryotherapy orbital surgery)
c. Adie tonic pupil
d. Argyll Robertson pupils
e. Aberrant regeneration of the 3rd nerve
f. Peripheral neuropathy
3. Where is the lesion in a patient with light-near dissociation due to Argyll Robertson pupils ?
Tectum of the midbrain (loss of pretectal light input to the Edinger–Westphal nucleus).
4. What is the mechanism of light-near dissociation due to Argyll Robertson pupils?
The distinction between the light-reflex and near-reflex pathways forms the basis for some forms of pupillary light-near dissociation (i.e., pupils that do not react to light but react to near stimuli) in which the dorsal midbrain and pretectal nuclei are damaged, but the near-reflex pathways and the Edinger–Westphal nuclei are spared. The condition is classically described in patients with tertiary syphilis, is common in diabetes, and may happen in encephalitis.
5. Where is the lesion in a patient with light-near dissociation due to Adie tonic pupil?
The ciliary ganglion.
6. What is the mechanism of light-near dissociation due to Adie tonic pupil?
Aberrant reinnervation of the iris sphincter by accommodative fibers.
7. What is the mechanism of light-near dissociation due to aberrant regeneration of the 3rd nerve?
Aberrant reinnervation of the iris sphincter by fibers meant for the extraocular muscles or the ciliary body.
8. What is the mechanism of light-near dissociation due to severe vision loss?
Damage to the retina or optic nerve results in a decreased light response, but the near response is normal.
9. What is the mechanism of light-near dissociation due to laser panretinal photocoagulation or cryotherapy?
Aberrant reinnervation of the iris sphincter following damage to the short posterior ciliary nerves.
10. Where is the lesion in a patient with light-near dissociation due to peripheral neuropathy?
There is axonal loss in the short posterior ciliary nerves.
11. What are paradoxical pupillary reactions?
Paradoxical pupillary constriction in dim illumination after exposure to light can be observed in children with severe congenital retinopathies, such as congenital stationary night blindness and congenital achromatopsia.
12. What is spasm of convergence
Spasm of the near triad (also known as spasm of convergence) is a disorder in which intermittent over action of all three components of the near triad: miosis, accommodation, and convergence. This disorder can mimic a unilateral or bilateral abduction deficit. The pupils constrict when the patient “attempts” to abduct each eye, confirming the voluntary convergence. Because the near triad is under voluntary control, this disorder is usually functional (nonorganic) and not related to an underlying lesion.
Explanation: “12.5 Other Pupillary Abnormalities
12.5.1 Tadpole Pupil
Tadpole pupil is an irregular pupil that resembles a tadpole (▶Fig. 12.44). It is a benign phenomenon that is spontaneously reversible. The pupil undergoes sectoral dilation lasting for a few minutes before returning to normal (segmental spasm of the iris dilator muscle). Tadpole pupil may occur multiple times for several days or a week and then disappear.
12.5.2 Midbrain Corectopia
Midbrain corectopia refers to eccentric or oval pupils occasionally seen in patients with rostral midbrain lesions.
12.5.3 Argyll Robertson Pupils
Argyll Robertson pupils are small (<2mm), irregular pupils (almost always bilateral). They are characterized by no reaction to light, normal near response (light-near dissociation), often iris atrophy and iris transillumination defects, and poor dilated with drops. The condition is classically described in patients with tertiary syphilis, is common in diabetes, and may happen in encephalitis.
12.5.4 Light-Near Dissociation
Light-near dissociation refers to pupils that do not react to light but react to near stimuli (▶Table 12.7).
12.5.5 Paradoxical Pupillary Reactions
Paradoxical pupillary constriction in dim illumination after exposure to light can be observed in children with severe congenital retinopathies, such as congenital stationary night blindness and congenital achromatopsia.
12.5.6 Benign Episodic Pupillary Mydriasis
Also known as springing pupil, benign episodic pupillary mydriasis usually occurs in young, healthy individuals. It lasts from a few minutes to a few hours and is sometimes associated with migraine-like headaches. The condition resolves spontaneously and is not associated with any underlying disorder.
12.5.7 Bilateral Mydriasis
Bilateral large pupils that do not react to light are observed during generalized tonic clonic seizures, although in rare cases unilateral ictal mydriasis or miosis may occur. In coma patients, this condition is often associated with brain death. Bilateral large pupils in an awake patient are usually physiologic (more obvious in dim light, or produced by increased adrenergic state in young patients who are anxious or in pain) or pharmacologic (such as after cocaine use). Bilateral and symmetrical tonic pupils are rare.
12.5.8 Spasm of the Near Triad (Spasm of Convergence)
Spasm of the near triad (also known as spasm of convergence) is a disorder in which intermittent overaction of all three components of the near triad – miosis, accommodation, and convergence – occur. This disorder can mimic a unilateral or bilateral abduction deficit. The pupils constrict when the patient “attempts” to abduct each eye, confirming the voluntary convergence (▶Fig. 12.45). Because the near triad is under voluntary control, this disorder is usually functional (nonorganic) and not related to an underlying lesion.
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Reference: 1. Neuro-ophthalmology Illustrated-2nd Edition. Biousse V and Newman NJ. 2012. Theme
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