OPTHALMOLOGY
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- - Cavalier King Charles Spaniel
- - Chihuahua
- - English bulldog
- - English Cocker Spaniel
- - English springer spaniel
- - Lhasa apso
- - Miniature schnauzer
- - Pekingese
- - Pug
- - Samoyed
- - Shih Tzu
- - West highland white terrier
- - Yorkshire terrier
Idiopathic
Debilitated and dehydrated animals
Trauma
Drug-induced – this is important to takeinto
account when testing STT
- - Sulphonamides
- - Atropine
- - General anaesthesia
- - Topical anaesthesia
- - Etodolac
The latter may occur due to increased aqueous tear
production in an attempt to compensate for a loss of
mucin. Mucins are required to hydrate, lubricate and
protect the ocular surface. Additionally they provide
an “anchor” for the aqueous portion of the tear film to
the hydrophobic ocular epithelium.
A reduced Tear Film Break Up Time (TBUT) test is used
to assess for a qualitative defect in tear production.
• Apply 1 drop of fluorescein stain to the eye,
holding the eyelids open.
• Under cobalt-blue illumination, examine the
cornea. Note how many seconds it takes for dark
spots to appear as the tear film “breaks up” the
fluorescein layer.
• A normal TBUT is approximately 20 seconds
in dogs and 17 seconds in cats. Animals with
quantitative deficiencies often have a TBUT of <
5 seconds, which indicates an unstable tear film.
Alternatively, a conjunctival biopsy and histopathology
can be done to quantify the goblet cell density.
Lipid deficiency
QUANTITATIVE DISORDERS
Aqueous Deficiency
Most cases will fit into this category. Deficiency of the
aqueous portion of the tear film is more commonly
seen in dogs than cats or horses, and leads to the
typical KCS we see.
The aqueous portion of the tear film is produced by
the lacrimal gland and the gland of the third eyelid.
Here, true quantitive KCS needs to be differentiated
from animals in which corneal drying is due to
increased tear film evaporation. Increased evaporation
occurs when the ability to blink is decreased due
to facial nerve disease, lagopthalmos (incomp