Final answer:
Dacryocystorhinostomy (DCR) surgery creates a new pathway for tear drainage to treat dacryocystitis, an inflammation of the lacrimal sac caused by a blocked nasolacrimal duct.
Step-by-step explanation:
The principal of dacryocystorhinostomy (DCR) surgery is to create a new pathway for tear drainage when there is an obstruction in the nasolacrimal duct. This is often necessary in cases of dacryocystitis, which is the inflammation of the lacrimal sac. This inflammation is commonly associated with a blockage of the nasolacrimal duct, leading to tear accumulation and infection. The DCR surgery bypasses the blocked nasolacrimal duct by directly connecting the lacrimal sac to the nasal cavity, thus restoring normal tear drainage.