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 25-28 September, 2018 | Singapore
normal tear production but a sufficiently dysfunctional tear delivery system (due to conjunctivitis-induced compression of the lacrimal gland ductules) to (likely reversibly) reduce his STT-1 result. I do not routinely use STT-2 (STT following topical anesthesia) or STT-3 (STT following or during a noxious stimuli) in canine patients but am beginning to appreciate their value in cats.
Despite the utility of the STT, there are many other potentially underused tests that are of value – particularly in those patients who are unresponsive to topically applied CsA. I like to use an assessment of blink rate and effectiveness. It amazes me – especially in many brachycephalic breeds how poorly and infrequently they blink. Unless they have a remarkably increased tearfilm stability to compensate for this, one must assume that they have greater evaporative losses than dolichocephalic dogs. Perhaps these are patients who would benefit from a medial canthoplasty. Our best clinical test of tear film stability in vivo appears to be
the tear film breakup time (TFBUT). Although patient compliance sometimes makes this test difficult, I believe that it provides highly valuable information in select patients. As we learn more about this test, we would do well to pay attention to what the physicians have known for some time about performing this test very consistently especially with regards timing relative to the rest of the exam, amount of fluorescein applied. I think that the specially prepared Dry Eye Test (DET) strips by Amcon Labs (www.dryeyetest.com) are worth considering. The normal range has not been established using sufficiently large population of normal dogs of various skull shapes, but most manuscripts to date report mean ± SD values of around 20 ± 5 seconds.
In patients where the clinical exam suggests it may
be informative, I consider culture and sensitivity
and cytology of expressed mebum and/or an eyelid (meibomian gland) and/or conjunctival biopsy. If I am interested primarily in the conjunctiva (and especially
the goblet cells) I simply do a snip biopsy of the fornicial conjunctiva under topical anesthesia. In patients where
I am more interested in the entire qualitative tear film
unit I do a full-thickness punch biopsy from dermis to conjunctiva through an affected area of the eyelid. If there is marginal disease, I consider a wedge biopsy. In all cases, I work with our in-house ocular pathologist to ensure goblet cell density (GCD) is reported. These are typically calculated (and reported) as a percentage of the non-goblet conjunctival epithelial cells. Like TFBUT, the number of normal dogs which have been sampled and assessed in a uniform manner is insufficient to permit
the statement yet of a true reference range, and there
is much variation in GCD according to site sampled; however the GCD of the palpebral/forniceal sites (which are the most readily sampled) are typically reported to be around 20-30%. The periodic acid Schiff (PAS) staining technique can greatly facilitate counts.
An often overlooked but critical component of the exam of some dry-eye patients is assessment of corneal sensitivity (or corneal touch threshold – CTT) using the Cochet-Bonnet aesthesiometer. If we recall the critical role of the trigeminal nerve in sensing ocular surface dryness, reflex and basal tearing, reflex and basal blinking, and carriage of the parasympathetic fibers of lacrimation as well as trophic factors for the ocular surface, it is difficult to underrate the importance of normal function of this nerve to the lacrimal unit.
It is involved in the afferent and efferent arm of tear production and delivery, and in tear distribution and retention via normal lid position and blinking.
In all cases, the ocular surface should be stained with vital dyes. It is critical to recall that these stain the corneal epithelium (rose bengal or lissamine green) or subepithelial collage n (fluorescein) of both conjunctiva and cornea and the entire visible ocular surface should be examined following stain application.
Recalling the DAMNIT list facilitates an efficient but directed examination of the body systems and signs sometimes associated with those less common causes of KCS are essential. I include a thorough history directed at the known causes, followed by examination for associated systemic diseases, a thorough assessment of cranial nerve function, especially palpebral and corneal reflexes, and careful evaluation of upper, lower, and third eyelids. This must include assessment of their position
in relationship to the cornea, and appearance of eyelid margins, cilia, and the meibomian glands and orifices. Globe retropulsion and jaw opening, “slipping” the oral mucous membranes, and assessment of the nares for dryness is also essential – sometimes in association with an otic exam. Culture and sensitivity, along with cytology is unnecessary as microbial overgrowth is secondary and typically responds as soon as tear production is improved.
TREATMENT
My five main treatment goals:
· Always diagnose and treat the underlying cause if possible. (This is especially important in patients unresponsive to CsA)
· Minimize further tear loss and maximize tear distribu- tion
· Stimulate of tear production (CsA irrespective of cause)
· Supplement the tear film in a manner that considers which of the components is inadequate
· Treat or prevent secondary infection
Underlying causes
Thorough attention to the “DAMNIT” list, a careful assessment of history and clinical signs, and appropriate diagnostic testing will facilitate recognition of any underlying cause, expedite appropriate treatment, and improve prognosis for full return of secretory function.
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43RD WORLD SMALL ANIMAL VETERINARY ASSOCIATION CONGRESS AND 9TH FASAVA CONGRESS







































































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