The Lacrimal System

Question 1

List the layers of the tear film and identify what structure produce each layer

Question 2

What is the most common cause of quantitative KCS in dogs?

Answer 2

Immune mediated destruction of the lacrimal gland

Question 3

What is quantitative KCS?

Answer 3

inflammation of the cornea and conjunctiva secondary to dryness caused by impaired lacrimal gland function and decreased tear flow (aqueous deficiency)

Question 4

What is qualitative KCS?

Answer 4

Inflammation of the cornea and conjunctiva secondary to inadequate production of mucin or lipid components of the precorneal tear film

Question 5

What is neurogenic KCS

Answer 5

Inflammation of the cornea and conjunctiva secondary to dryness caused by loss of PNS innervation to the lacrimal glands and ipsilateral nasal mucosa

Question 6

The oily layer of the tear film is produced by _________

Answer 6

Meibomian glands

Question 7

The aqueous layer of the tear film is produced by _________

Answer 7

lacrimal and 3rd eyelid glands

Question 8

The mucin layer of the tear film is produced by _________

Answer 8

Conjunctival goblet cells

Question 9

What is parotid duct transposition?

Answer 9

• Duct of the parotid salivary gland is surgically relocated to the lower conjunctival fornix, allowing saliva to replace tear deficiency
• surgical procedure for KCS that is refractory to medical therapy

Question 10

What are the 3 layers of the tear film, from outer to innermost?

Answer 10

1. Lipid layer
2. Aqueous layer
3. Mucinous layer

Question 11

What structures of the eye are responsible for the aqueous layer of the tear film?

Answer 11

• Lacrimal gland
• 3rd eyelid gland

Question 12

What are causes of quantitative KCS in dogs?

Answer 12

1. Immune mediated lacrimal gland destruction (most common)
2. Excision of 3rd eyelid
3. Parasympathetic nerve lesions
4. Canine distemper

Question 13

What diagnostic test should be performed in patients with suspect KCS?

Answer 13

Schirmer tear test

Question 14

What layer of the tear film is affected to result in quantitative KCS?

Answer 14

Aqueous deficiency

Question 15

How does the tear film compensate for an aqueous deficiency in cases of quantitative KCS?

Answer 15

Mucin layer starts to produce mucus to compensate for decreased aqueous tears, results in bacteria proliferation and mucopurulent discharge

Question 16

What is the drug of choice for treatment of KCS?

Answer 16

Cyclosporine life long

(T cell inhibitor, helps immune system, stimulates tear production, anti-inflammatory properties)

(tacrolimus if refractory to cyclosporine)

Question 17

What is the pathophysiology behind neurogenic KCS?

Answer 17

loss of PNS innervation to the lacrimal gland and ipsilateral nostril

Question 18

What are the possible causes of neurogenic KCS?

Answer 18

• Trauma, severe otitis interna, neoplasia, idiopathic

Question 19

How do patients with neurogenic KCS typically present?

Answer 19

• Older dogs, often unilateral
• Unilateral Xeromycteria / dry nose

Question 20

What is the treatment protocol for patients with neurogenic KCS?

Answer 20

• Pilocarpine (stimulates PNS)

**beware SLUDD signs, narrow therapeutic index

Question 21

What is the surgical treatment option available for correction of KCS?

Answer 21

Parotid duct transposition

(moves parotid salivary gland to conjunctival fornix, saliva replaces deficient tears)

beware of high pH with saliva, can cause mineral deposits… treat with EDTA

Question 22

What diagnostic test should be performed to confirm a mucin layer disorder?

Answer 22

• Tear film break up time - abnormal if < 20 seconds
• Schirmer tear test will be normal bc aqueous layer unaffected

(Example of qualitative KCS)