VN April 2021

Vetnuus | April 2021 28 Regulars I Ophthalmology Column In the previous ophthalmology article that I submitted, we discussed the anatomy and physiology of the precorneal tearfilm [PTF]. We are now going to continue by looking at the often-misdiagnosed qualitative KCS, whichcanbedivided intodeficiencyof thePTFmucinaswell asdeficiency of PTF lipid. In this column we are focusing on mucin deficiency. This is a common condition seen in both cats and dogs. The underlying pathophysiology include decreased numbers of conjunctival goblet cells or alterations in the corneal and conjunctival epithelial cell glycocalyx. The alterations in the glycocalyx are caused by chronic inflammation. As mentioned earlier, this condition is often misdiagnosed as the patients have many of the signs of the mild keratoconjunctivitis sicca [KCS] except that the Schirmer tear test [STT] values are normal to higher than normal. The clinical signs of a mucin deficient KCS is that of low grade chronic conjunctivitis and or keratitis. Diagnosis An essential part of diagnosing a mucin deficiency is to determine the tearfilm breakup time [BUT]. This is an easy, valuable but underutilised diagnostic test. A deficiency of the mucin layer of the pre-corneal tear film will lead to instability of the precorneal tearfilm and therefore an abnormally short BUT. Normal BUT in dogs is > 20 seconds. In animals with a mucin deficiency (qualitative keratoconjunctivitis sicca), the BUT is often < 1 second. The test is performed by placing the patient in a darkened room. A drop of fluorescein is installed and the eyelids are blinked manually and then held open. Immediately a blue light is shone on the eye and the examiner starts counting in seconds the time until the tearfilmstartsbreakingup. At thefirst signof tear evaporation, ablackarea will appear within the green stain on the cornea, and the time is noted. The diagnosis can be further confirmed by performing a conjunctival biopsy. Decreased number of goblet cells will be seen histologically. Treatment: Tacrolimus / Cyclosporin may improve ocular mucins independent of an increase in the aqueous component of the tear film and are therefor recommended. A critical part of the treatment however is tear replacement solutions containing sodiumhyaluronate. Dr Izak Venter, Digital Veterinary Ophthalmology Services (DVOS) Keratoconjunctivitis sicca [Part 2] The firstmissionof DVOS is to create a platformfor the general practitioner veterinary surgeon to improve their ophthalmological knowledge and enable them to deal with ocular cases with more confidence. This will be done with online courses allowing participants to download course material that will include written notes as well as narrated PowerPoint presentations. The first small animal course comprises of 240 pages and the PowerPoint lectures are 20 hours in total excluding a guest lecture on SARDS. I shall also make surgical videos available covering some common surgical procedures. The course is CPD accredited with the South African Veterinary council for a total of 23 CPD points. The second mission is to provide a service to the practicing veterinarian offering specialist advice regarding problematic cases. More information regarding both of these aims are available on the website: www.dvos.co.za Figure 1. The appearance of the eye after fluorescein installation and the tearfilm starting to disintegrate.