Lecture 7 2/10/25 Flashcards
What are the functions of the tear film?
-optics: transparency
-comfort: lubrication/moisture
-metabolism: providing nutrients/removing waste
-immune system: IgA/lysozyme/lactoferrin/WBCs
What are the characteristics of tear film breakdown?
-blinking allows tear film distribution/mixing
-takes 20-40 seconds for tear film to break up when blinking is prevented
-triggers sensory nerves
-25% of tear volume evaporates normally; takes 10 minutes for aqueous tears to evaporate completely
What are the layers of the tear film?
-inner layer consisting of aqueous + mucous layer
-outer layer consisting of lipid
What are the characteristics of the mucous layer of the tear film?
-helps the aqueous part of the tears adhere to the cornea
-acts as a surfactant to help aqueous tears spread across cornea and trap bacteria/particulate matter
-produced by goblet cells in the conjunctival fornix
-creates a buffer between the aqueous layer and the hydrophobic corneal epithelial cells
What are the characteristics of the aqueous layer of the tear film?
-secreted by the lacrimal glands and third eyelid
-composed of water, electrolytes, glucose, enzymes, proteins, and antibodies
-makes up majority of tear film
-maintains an optically uniform corneal surface
-helps to remove foreign matter from corneal surface
-aids in lubrication
-provides nutrients to avascular cornea
What are the characteristics of the lipid layer of the tear film?
-secreted by Meibomian glands
-floats on top of the fluid to prevent evaporation and create surface tension to prevent spillover
What is the anatomy/physiology of the nasolacrimal system?
-tear components are produced by the lacrimal gland, gland of the third eyelid, tarsal glands, and goblet cells
-blinking pushes the tears from lateral to medial so they can go down the puncta
-tears drain down the canaliculi, into the lacrimal sac, and down the nasolacrimal duct to exit the nose/pharynx
What is the innervation of the eyelids and nasolacrimal system?
-afferent innervation arises in cornea and conjunctiva from the ophthalmic division of the trigeminal nerve
-efferent innervation of the glands is autonomic
-parasympathetic increases tear production, sympathetic decreases tear production
What are the characteristics of the Schirmer tear test?
-quantifies reflex and basal tearing
-normal in dogs is 15-25 mm/min
-normal in cats is > 8 mm/min
-normal in horses is > 11 mm/min
Which diagnostic tests can be run in exotics?
-phenol red thread test
-endodontic paper point test
What is the Jones test?
-evaluation of the passage of fluid down the nasolacrimal duct
-often done using fluorescein stain
-not always reliable; patient could swallow fluid
What are the characteristics of the tear film break up test?
-uses fluorescein stain since it mixes with the aqueous layer
-evaluates tear stability
-normal is >20 seconds; patients with deficiency in lipid or mucin will have a short result
What are the characteristics of the lissamine green dye test?
-stains dead epithelial cells
-indicates unhealthy eye surface and tear film
What is the use of the rose bengal dye?
stains where there is an absence of mucin
What are the characteristics of nasolacrimal duct flushing?
-flushing with or without resistance indicates patency; diagnostic of functional obstruction
-flushing with resistance at first before flushing normally is suggestive of an obstructive substance that was flushed out
-not flushing is indicative of an anatomical obstruction
What is epiphora?
excessive flowing of tears onto the face
What is reflex secretion?
secretion of tears secondary to mechanical irritation from hair, foreign body, painful ocular diseases, or irritants
What are the diagnostics and treatment for reflex secretion?
-full ophthalmic evaluation
-Jones test; should be positive
-NLD should flush without resistance
-want to determine and treat primary cause
What are the characteristics of micropunctum?
-congenital defect in which the puncta are small
-diagnosed through magnified examination of puncta
-treatment includes topical anesthetic and enlarging the opening with a blade or punctal dilator; can leave alone if defect is minimal
what are the characteristics of imperforate punctum?
-congenital defect in which there are no puncta due to conjunctiva overlying the openings
-diagnosed through magnified examination of the medial canthus
-also diagnosed via Jones test; would be negative
-treatment is to create an opening in the area the puncta should be by removing conjunctiva; closure is prevented by treating with topic antibiotic/steroid multiple times a day for a week
What are the characteristics of cicatricial nasolacrimal obstruction?
-developed condition in which there is scarring of the nasolacrimal duct
-often secondary to feline herpesvirus 1 in cats and chronic dacryocystitis in other species
-treatment involves treating the underlying condition and creating a new duct surgically if defect is severe
What are the potential consequences of abnormal facial conformation?
-puncta are in a poor position to properly drain
-duct is kinked due to small skull or brachycephalic conformation
-tears can be wicked onto face due to medial trichiasis
What is dacryocystitis?
-primary infection or infection secondary to foreign body in the duct or lacrimal sac
-congenital lacrimal atresia
How is dacryocystitis diagnosed?
-presence of thick exudate at medial canthus
-negative Jones test
-negative NLD flushing; may dislodge a blockage
-culture of discharge from duct/puncta
-dacryocystorhinography
What is the treatment for dacryocystitis?
-attempt to flush duct
-topical antibiotic/steroid, systemic antibiotics, and NSAIDs for 6 weeks with flushes every 1-3 weeks for acute cases
-indwelling catheter for chronic cases
-surgery if secondary infection from foreign body
What is tear staining?
staining of the hair at the medial canthus
What are potential causes of tear staining?
-medial aberrant dermis
-abnormal lower punctum
-medial lower entropion
-abnormal conformation of skull leading to kinking of duct
-distichia or trichiasis causing reflex tearing
What are the characteristics of tear staining treatment?
-difficult to resolve
-not always clinically necessary to treat
-daily drying of the face may be sufficient
-treat underlying condition if malodorous or causing secondary bacterial/yeast skin infections
-can clip long hair/fur and use topical repellents
-oral antibiotic use NOT warranted
-stained hair will not unstain; must clip and have hair grow back
