Polarized light biomicroscopic observations on the pre‐corneal tear film. 1. The normal tear film of the dog

Abstract

Polarized light biomicroscopy was used to examine the normal pre‐corneal tear film in 25 dogs. Blink rates were also determined. The normal range of surface morphology of the canine tear film was established. Three categories of surface patterning of the lipid layer of the tear film were identified. These were: (a) a wave‐like pattern, (b) a pattern of irregular islets, and (c) a pattern resembling the polished surface of granite. All three patterns may occur in the same eye. The inter‐blink thickness of the lipid layer of the pre‐corneal tear film varied between 0·013 μm (the minimum thickness discernable by this method) and over 0·581 μm (the maximum thickness at which coloured interference fringes are clearly defined) in localized areas. The mean total blink rate was 14·2/min. Overall, incomplete blinks constituted approximately 66 per cent of the total blink rate, but the ratio of complete to incomplete blinks varied considerably between animals. By dividing the dogs into thick and thin lipid layer groupings, it was possible to demonstrate a statistically greater rate of complete blinks (P < 0·05, Mann‐Whitney U test) in animals with a thinner lipid layer. The applicability of polarized light biomicroscopy to veterinary clinical ophthalmology is discussed.

Eye-Blink Behaviors in 71 Species of Primates

“…These studies confirmed that nocturnal animals blink much less frequently than diurnally active animals, blinking frequency being one-tenth lower in nocturnal versus diurnal mammals [13] and birds [35]. Carrington et al [36] reported that the mean ± SD blink rate in dogs is 14.5 ± 5.63 bpm, and approximately 66% of all blinks were incomplete. Note that interindividual differences are quite large in dogs [36], but much smaller in birds [35].…”

“…One series of studies investigated the dopamine hypothesis of blinking in animals [27]–[33]. Another series directly measured the blink rates in animals, including cows [34], birds [35], dogs [36], guinea pigs [37], rabbits [37], [38], and 31 mammalian species [13]. These studies confirmed that nocturnal animals blink much less frequently than diurnally active animals, blinking frequency being one-tenth lower in nocturnal versus diurnal mammals [13] and birds [35].…”

“…Carrington et al [36] reported that the mean ± SD blink rate in dogs is 14.5 ± 5.63 bpm, and approximately 66% of all blinks were incomplete. Note that interindividual differences are quite large in dogs [36], but much smaller in birds [35]. Mowrer reported a detailed description of the nictitating membrane (i.e., the third eyelid) of birds [39].…”

Biochemical Analysis of Ocular Surface Mucin Abnormalities in Dry Eye: The Canine Model

“…While this may be true in many cases, mucins are also essential to the stability and spreading of the tear film because they contribute to the surface energy of the ocular surface, optimise the surface tension of the aqueous phase, and reduce the overall surface tension of the film through interaction with surface lipids (Holly and Lemp, 1977 ;Carrington et al, 1987aCarrington et al, , 1987bTiffany, Winter and Bliss, 1989). In addition, their non-Newtonian rheological behaviour (Bron, 1985) makes them ideal lubricants during blinking.…”

Partial ligation of the transposed parotid duct at the level of the parotid gland for excessive salivary secretions

“…Transposition of the parotid duct is the surgical therapy of choice for treatment for keratoconjunctivitis sicca (KCS) cases that are refractory to medical therapy. Keratoconjunctivitis sicca is primarily a deficiency in the aqueous tear layer of the precorneal tear film, which may be the result of congenital, infectious, immune‐mediated, drug‐induced, iatrogenic, or neuropathic conditions with immune‐mediated being the most common cause 1–9 . Deficiency of tear components can lead to desiccation and inflammation of the conjunctiva and cornea, most often manifested by mucopurulent discharge 10 .…”