Biomicroscopy of the tear film: the tear film of the pekingese dog

Abstract

Polarised light biomicroscopy was used to examine the normal pre-corneal tear film in 21 eyes of 12 pekingese dogs. The purpose of the study was to examine the influence of excessive exophthalmos on the pre-corneal tear film in the dog. The majority of the animals were found to have high levels of ocular surface contamination by particulate material and plaques of viscous mucus. Other abnormalities included surface lipid with an abnormal granular (three dogs) or 'curdled' (two dogs) appearance; excessive thinning of the lipid layer of the tear film; and the presence of dark globular structures in two dogs, which were presumed to be abnormal meibomian lipid. Break up of the tear film was observed in one dog. Grossly, a thread of viscous mucus was frequently observed along the margin of the lower eyelid. It is postulated that this thread forms because of the excessively exophthalmic conformation of the breed, which prevents the normal access of effete mucus and entrapped debris to the lower conjunctival fornix. The combination of the above factors in the pekingese is suggested as the mechanism whereby the tear film has a reduced stability, thus enhancing the risk from factors more usually considered to initiate corneal ulceration in the breed. The possible adverse effects of lid splitting for the mass removal of distichiae in exophthalmic dogs is discussed.

Pharmacokinetics of topically applied ciprofloxacin in tears of mesocephalic and brachycephalic dogs

“…Because of the increased corneal surface area exposed and the thinner lipid layer in the tear film of brachycephalics, 19 it was suspected that the tear film concentration of ciprofloxacin differed between brachycephalic and mesocephalic dogs. While the tear film concentration of ciprofloxacin was higher in the brachycephalics at all but one time‐point (1 h), this difference was not significant.…”

“…Dogs have tremendous variability in facial anatomy, with the greatest variation seen between the brachycephalic dogs and the mesocephalic or dolicocephalic breeds. Brachycephalic breeds have shallow orbits, excessive prominence of the globe, decreased corneal sensitivity, and reduced tear film stability 18,19 . Many brachycephalic dogs also have lagophthalmos, trichiasis, and distichiasis.…”

Canine keratoconjunctivitis sicca: disease trends in a review of 229 cases

“…Both the CKCS and shih‐tzus have exophthalmic conformation. Exophthalmia in the Pekingese has been associated with poor corneal sensitivity and accumulation of more surface debris than eyes with average conformation and sensitivity, which could contribute to the formation of ulcers (Carrington and others 1987, 1989). Corneal aesthesiometry was not conducted in any of the cases in the present study.…”

Effect of topical naltrexone 0.3% on corneal sensitivity and tear parameters in normal brachycephalic dogs

“…Brachycephalic dogs are predisposed to developing chronic keratitis leading to corneal pigmentation, vascularization, and ulceration . In mild cases, these conditions may lead to obscured vision and in advanced cases can result in severe ocular disease that may require corneal surgery or enucleation.…”

“…Conformational factors such as lagophthalmos, medial entropion, and trichiasis are all likely contributing factors, but do not always explain the keratitis detected in brachycephalics. Brachycephalic dogs have also been shown to have decreased corneal sensitivity and tear film abnormalities . Sensory nerves and normal sensation of the cornea and conjunctiva regulate lacrimal gland fluid secretion and secretion of the conjunctival goblet cells, both of which are crucial to the normal tear film .…”