The Lacrimal System

Question 1

Function of tears

Answer 1

Tears provide nutrition, moisture, and protection for the cornea and are important in refraction and corneal healing.

Question 2

Normal tear flow drainage

Answer 2

puncta (superior and inferior)canaliculi  lacrimal sac naso-lacrimal duct  nose or mouth

Question 3

3 components in the pre corneal tear flim

Answer 3

mucin, aqueous, lipid

Question 4

Mucin

Answer 4

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.

Question 5

Aqueous tears secreted by what

Answer 5

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).

Question 6

Function of aqueous tears

Answer 6

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).

Question 7

epiphora

Answer 7

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.

Question 8

Lipid layer secreted by what

Answer 8

the meibomian glands (tarsal glands) that line the inner eyelid margin.

Question 9

function of the lipid layer

Answer 9

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.

Question 10

Imperforate puncta is

Answer 10

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

Question 11

N-L obstruction is often caused by what

Answer 11

often due to a foreign body, tumor or dental disease

Question 12

clinical signs of N-L obstruction

Answer 12

Epiphora is accompanied by copious mucopurulent discharge, often without obvious discomfort to the patient, and does not resolve with medical therapy.

Question 13

Dacryocystitis

Answer 13

inflammation of the nasal-lacrimal system. This is usually associated with a foreign body or dental disease.

Question 14

treatment of dacrocystitis

Answer 14

Specific treatment directed to the underlying cause is needed in addition to topical and possible therapy with antibiotics and anti-inflammatory medication.

Question 15

Meibomian gland adenitis

Answer 15

inflammation of the meibomian glands, is often secondary to blepharitis, and associated with staph infection.

Question 16

clinical signs of meibomian gland adenitits

Answer 16

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.

Question 17

Treatment for meibomian gland adenitis

Answer 17

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.

Question 18

Normal STT

Answer 18

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.

Question 19

KCS in dogs vs cats

Answer 19

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.

Question 20

Nine causes of KCS

Answer 20

**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)

Question 21

KCS in cats is associated with

Answer 21

FHV

Question 22

Dx of KCS in horses

Answer 22

A corneal ulcer in a horse without epiphora is strongly suggestive of KCS.

Question 23

Treatment for KCS

Answer 23

immunosupporessives (tacrolimus, cyclosporin), natural tears, pilocarpine, topical abx, PDT

Question 24

consideration RE pilocarpine

Answer 24

(parasympathomimetic) if neurogenic KCS is suspected. These patients may have a dry nose and possibly oral mucous membranes as well. It