Cornea & external disease · practice question
[READINESS SEED] Why does obstruction of the inferior canaliculus commonly cause…
[READINESS SEED] Why does obstruction of the inferior canaliculus commonly cause epiphora even when the superior canaliculus stays patent?
Show the answer and explanationAnswer and explanation
Answer: A. One canaliculus suffices for basal drainage
A single canaliculus is generally adequate only for basal tear drainage and cannot cope with the larger volume of reflex lacrimation, so watering commonly follows inferior-canaliculus obstruction. The near-miss is claiming the superior canaliculus does not drain at all — both drain, in varying proportion.
Clinical pearl: Patients with one blocked canaliculus may be symptom-free at rest yet water in wind or cold, when reflex tearing exceeds the single remaining channel.