Function of tears
Tears provide nutrition, moisture, and protection for the cornea and are important in refraction and corneal healing.
Normal tear flow drainage
puncta (superior and inferior)canaliculi lacrimal sac naso-lacrimal duct nose or mouth
3 components in the pre corneal tear flim
mucin, aqueous, lipid
Mucin
secreted by goblet cells found in the conjunctiva. It is the innermost layer of tear film which smooths the corneal epithelial cells and binds hydrophilic aqueous tears to the lipophilic corneal epithelium.
Aqueous tears secreted by what
secreted by the orbital lacrimal gland (superior-temporal orbit; 70-75% of aqueous tears) and the gland of the nictitating membrane (GNM, 25-30% of aqueous tear production).
Function of aqueous tears
The aqueous tear layer keeps the cornea moist and nourished. This is the middle layer and the bulk of the tear film. Deficiency of aqueous tears = “dry eye” or KCS (keratoconjunctivitis sicca).
epiphora
may be the result of excessive tear production due to pain, deficiency of adequate lipid tear production, imperforate or obstructed lacrimal system, or wicking of tears by trichiasis.
Lipid layer secreted by what
the meibomian glands (tarsal glands) that line the inner eyelid margin.
function of the lipid layer
The lipid layer holds aqueous tears against cornea and keeps them from spilling over eyelids. They also prevent evaporation of tears that causes the sensation of ‘dry eye’ and provokes excessive aqueous tear production.
Imperforate puncta is
is a congenital defect that should be considered in a young dog with epiphora with a non-painful eye. The puncta is covered by conjunctival epithelium that fails to regress during development and prevents tears from entering the canaliculus. The surgical correction is a referral procedure
N-L obstruction is often caused by what
often due to a foreign body, tumor or dental disease
clinical signs of N-L obstruction
Epiphora is accompanied by copious mucopurulent discharge, often without obvious discomfort to the patient, and does not resolve with medical therapy.
Dacryocystitis
inflammation of the nasal-lacrimal system. This is usually associated with a foreign body or dental disease.
treatment of dacrocystitis
Specific treatment directed to the underlying cause is needed in addition to topical and possible therapy with antibiotics and anti-inflammatory medication.
Meibomian gland adenitis
inflammation of the meibomian glands, is often secondary to blepharitis, and associated with staph infection.
clinical signs of meibomian gland adenitits
It has a classic appearance of a “string of pearls” along the lid margin appearing as white nodules. When expressed, exudate is seen extruding from the gland openings.
Treatment for meibomian gland adenitis
Treatment for the adenitis is warm compresses to the eyelids and oral doxycycline. The blepharitis is commonly associated with food or other allergies in dogs and needs to be addressed. Dogs suffering from chronic allergies and blepharitis often develop meibomian gland atrophy and life-long tear ointment replacement is needed.
Normal STT
Dog = 15 – 25 mm/min. Cat = highly variable- can be near zero due to sympathetic tone from excitement Horse = highly variable and may be 10 to >30mm/min.
KCS in dogs vs cats
KCS is one of the most common causes of conjunctivitis in dogs, but is usually the result of conjunctivitis in cats. This is diagnosed by a STT below normal.
Nine causes of KCS
**1-Immune mediated- This may be associated with other immune-mediated diseases or occur alone.
2-Drug induced – Atropine, sulfas, etogesic, acetaminophen, anesthetics
3-Neurogenic – Loss of parasympathetic input (runs with CrN VII) and may be associated with otitis media; loss of sensation to cornea (Crn V)
4-Hormonal –DM (diabetes mellitus), hypothyroid, hypoestrogenism, HAC (hyperadrenocorticism),
5-Inflammatory –Lacrimal gland adenitis, chronic otitis (Crn VII/parasympathetic nerve damage), periodontitis
6-Removal of Gland of NM (nictitating membrane, third eyelid)
7-Viral – Distemper, herpes virus in cats (FHV 1)
8-Radiation therapy
9-Congenital alacrima (Yorkshire Terrier & Chihuahua)
KCS in cats is associated with
FHV
Dx of KCS in horses
A corneal ulcer in a horse without epiphora is strongly suggestive of KCS.
Treatment for KCS
immunosupporessives (tacrolimus, cyclosporin), natural tears, pilocarpine, topical abx, PDT
consideration RE pilocarpine
(parasympathomimetic) if neurogenic KCS is suspected. These patients may have a dry nose and possibly oral mucous membranes as well. It