Lacrimal System Flashcards
1
Q
What is Pre-corneal Tear Film
A
- Crucial for ocular surface health
- Numerous functions:
- lubrication between lids and ocular surface
- Aids corneal refraction
- Antimicrobial properties
- Primary corneal oxygen source
- Removal of debris through tear drainage
- Trilaminar
2
Q
What are the layers of the Pre-corneal tear film
A
- Lipid - Outermost layer
- produced by Meibian glands
- Stabilizes and prevents evaporation of the aqueous layer
- Aqueous - Intermediate layer
- produced by the orbital lacrimal gland & third eyelid gland
- Provides corneal nutrition
- Removes waste products
- Mucin - innermost layer
- Produced by conjunctival goblet cells
- Thickest layer
- Immunoglobulins (IgA)
- Interface of tear film with hydrophobic corneal epithelium
3
Q
Where/why are Aqueous tears produced?
A
- Basal Tears
- parasympathetics of CN VII
- Stimulated tears
- Ocular pain (corneal irritation)
- Emotion (humans)
- Contributing glands
- Orbital lacrimal gland 60-70%
- 3rd eyelid gland 30-40%
- Accessory glands
4
Q
Where does tear film drain?
A
- Puncta
- superior and inferior
- Canaliculi
- dorsal and ventral
- Lacrimal sac
- Nasolacrimal duct
- Nasal Punctum
- opening into the ventral lateral nasal meatus
- 50% of dogs also have openings into oral cavity
5
Q
What are the different types of tear film deficiencies?
A
- Quantitative - KCS
- Keratoconjunctivitis sicca
- Decreased aqueous tear production
- Qualitative
- Disorder of mucin or lipid tear components
- Causes tear film instability
- Result in desiccation and inflammation of the ocular surface
6
Q
What is Keratoconjunctivitis Sicca (KCS)
A
- Dry eye disease
- insufficient aqueous tears
- Normal STT 15-25 mm/min
- <10mm/min = KCS
- 10-15mm/min is marginal
- <10mm/min = KCS
- Common in dogs, ~1% affected
- numerous cases and breeds affected
- Rare in other species
7
Q
What are the clinical signs of KCS
A
- Conjunctival hyperemia
- Mucoid to mucopurulent discharge
- intermittent initially, persistent in severe cases
- Blepharospasm +/- blepharitis
- Dull, lackluster corneal surface
- Keratitis, corneal pigmentation and fibrosis
- Corneal ulceration
- Secondary bacterial conjunctivitis
8
Q
What causes KCS?
A
-
Immune-mediated
- lacrimal gland adenitis
- Most common
- breed predisposition
-
Infectious/inflammatory
- canine distemper virus
- Leishmaniasis
- Chronic blepharoconjunctivitis (e.g. FHV-1)
-
Trauma
- uncorrected nictitans gland prolapse
- Post-proptosis
- Traumatic or inflammatory orbital disease
-
Drugs
- Atropine, sedation or anesthetic drugs,
- Sulfas and the NSAID etodolac
- Atropine, sedation or anesthetic drugs,
-
Iatrogenic
- Removal of nicitans gland
- Radiation therapy
-
Systemic metabolic diseases
- Hypothyroidism
- Diabetes mellitus
- Cushing’s Disease
-
Congenital acinar hypoplasia (unilateral or bilateral)
- yorkies over-represented
- young puppies
- Neoplasia of Lacrimal gland or third eyelid gland
- Debilitation/Dehydration
- transient tear reduction
- Neurologic dysfunction
- CN V (Ophthalmic branch)
- neurotrophic KCS
- decreased corneal sensation ⇢ decreased tear production
- neurotrophic KCS
- CN VII (Facial nerve)
- Neurogenic KCS
- parasympathetic loss
- Ipsilateral dry nose
- Neurogenic KCS
- CN V (Ophthalmic branch)
9
Q
How is KCS diagnosed?
A
- Schirmer tear test (STT)
- Tear production should be increased (>25mm/min) with pain (i.e. corneal ulcer)
- Evaluate STT and clinical signs
10
Q
How is KCS treated?
A
- Tear stimulation - lacrostimulants
- Tear replacement - lacrimomimetics
- +/- supplemental therapy
- secondary bacterial infections
- Client education
- Must use medications as often as directed
- May take a month or more to see STT improvement
- Tear stimulant therapy is lifelong
- Parotid duct transposition surgery - referral option
11
Q
What lacrostimulants are available in vet med
A
- Cyclosporine A
- Optimmune® 0.2% ointment
- Compounded 1% or 2% drops or ointment
- Tacrolimus
- Compounded 0.02% or 0.03% formulations
- 10-100x more potent than CsA in vitro
- T cell inhibitors with anti-inflammatory, anti-pigment, and possibly anti-fibrotic effects
- Use BID for life
12
Q
When are Cholinergic agents used for KCS treatment?
A
- Pilocarpine
- Indicated in cases of neurogenic KCS resulting from parasympathetic denervation
- Dilute topical (0.125%, compounded) or very careful oral dosing
- Warn owners of side effects
- Salivation
- Lacrimation
- Urination
- Defecation
13
Q
What are Lacromomimetics?
A
- Tear replacements or substitutes
- Many OTC products
- choose one with increased viscosity - not ‘rewetting’ drops
- Use 4-6x daily +
- While rear production is decreased
- Ointments can be used before bedtime
14
Q
Why should ocular cleansing be done?
A
- Minimizes debris accumulation
- Use OTC eyewash/saline
- Important before lacrostimulant application
- ensure drug contacts ocular surface tissues
15
Q
When are Antibacterial medications used for KCS?
A
- For secondary bacterial infections or concurrent corneal ulcers (to prevent infection)
- Broad-spectrum topical antibiotic
- Triple antibiotic ophthalmic ointment preferred (NeopolyBac)
- TID to QID for 2-3 weeks
- Bacterial culture and sensitivity testing is warranted if purulent discharge persists
