ANATOMY AND PHYSIOLOGY
Tears are secreted from lacrimal glands. The lacrimal gland has two parts. The orbital and palpebral.The ducts originate from orbital part passes through palpebral part and empty into lateral part of superior fornix. Tears are also secreted by assesry larimal glands of krause and wolfring over conjuntiva. Tears move over external ocular surface and then drained from puncta. From here they enter canaliculi anf then enter into lacrimal sac, then nasolacrimal duct and finally into nose through opening under inferior turbinate of nose. The length of puncta is 2mm, of canalculi is 8mm, of lacrimal sac is 10mm and of nasolacrimal duct is 12 mm.
when eyes close the ampulla and canaliculi contract resisting reflex and lacrimal sac contracts pushing the tears down the nasolacrimal duct into the nose under the action of pretarsal orbicularis and lacrimal part of orbicularis oculi. when eyes open, the canaliculi and lacrimal sac expands creating a negative pressure pulling the tears from canaliculi into the lacrimal sac