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Equine Special Senses - Horse Anatomy (view source)
Revision as of 16:38, 22 November 2012
, 16:38, 22 November 2012→Lacrimal Apparatus
*Flushes away foreign body material.
*Flushes away foreign body material.
*Maintains an optically smooth corneal surface so that light can pass freely into the cornea.
*Maintains an optically smooth corneal surface so that light can pass freely into the cornea.
The '''pre-corneal tear film''' is made up of three major constituents:
The '''pre-corneal tear film''' is made up of three major constituents:
*Aqueous layer: in the middle, performs the primary functions of the tear film. The '''lacrimal gland''', '''superficial gland of the nicitating membrane''' and, '''Hardenian gland''' and '''accessory lacrimal glands''' in the conjunctiva contribute to its formation. Evaluate this layer with the Shirmir Tear Test.
*Aqueous layer: in the middle, performs the primary functions of the tear film. The '''lacrimal gland''', '''superficial gland of the nicitating membrane''' and, '''Hardenian gland''' and '''accessory lacrimal glands''' in the conjunctiva contribute to its formation. Evaluate this layer with the Shirmir Tear Test.
*Mucin: is the inner layer which sticks the aqueous phase to the corneal epithelium. It is produced by conjunctival goblet cells, mainly in the '''conjunctival fornixes'''. Evaluate with fluorescein breakup time.
*Mucin: is the inner layer which sticks the aqueous phase to the corneal epithelium. It is produced by conjunctival goblet cells, mainly in the '''conjunctival fornixes'''. Evaluate with fluorescein breakup time.
The '''nasolacrimal drainage system''' functions to eliminate the used tear film and any excessive tears. Malfunction of the nasolacrimal apparatus results in tear overflow (epiphora), which may cause a cosmetic/dermatological problem of the medial periocular region. Precorneal tear film accumulates along the palpebral margin of each eyelid. '''Lacrimal puncta''' at the '''medial canthus''' of each eyelid are essentially holes which lead to '''canaliculi'''. Where the caniculi meet to drain into the nasolacrimal duct there is a slight dilatation known as the '''lacrimal sac'''. Blinking moves the fluid towards the medial canthus, most of the aqueous phase evaporates, the rest is drained by the nasolacrimal system. When ''orbicularis occuli'' muscle contracts, the eyelids close. The lacimal sac is within the muscle structure, so when the muscles contract during blinking they act like a pump to empty the lacrimal sac. When the blink is released, the muscle relaxes and the lacrimal sac opens; it sucks fluid down the canaliculi by capillary action. The fluid is then drained down the '''nasolacrimal duct''' to exit at the '''nasal punctum/nasal ostium''' in the '''nasal vesibule''' and out through the '''external nares'''.
==Ear==
==Ear==