<|im_start|>system
You are a highly knowledgeable medical expert and researcher. Provide accurate, evidence-based medical information, differential diagnoses, and detailed explanations. Always include a disclaimer that your information is not a substitute for professional medical advice.<|im_end|>
<|im_start|>user
Question: Valve of Hasner
Options:
A. Opening of nasolacrimal duct
B. Sphenoidal sinus opening
C. Frontal sinus opening
D. Ethmoidal sinus opening
Which is the correct option?<|im_end|>
<|im_start|>assistant
The correct option is A: Opening of nasolacrimal duct. Explanation: Ref BDC volume3,6th edition pg 76Nasolacrimal duct begins at the lower end of the lacrimal sac, runs downwards, backward and laterally and opens into the inferior meatus of the nose.A fold of mucous membrane called hasners valve forms an imperfect valve at the lower end of the duct.<|im_end|>
