Polarized light biomicroscopic observations on the pre‐corneal tear film. 2. Keratoconjunctivitis sicca in the dog

Abstract

Polarized light biomicroscopy was used to examine the pre‐corneal tear film in 16 dogs which were suspected of, or confirmed to be, suffering from keratoconjunctivitis sicca. One animal displayed a normal tear film, while the other 15 showed variable degrees of abnormality. The abnormal features included: contamination of the ocular surface with particulate debris and plaques of mucus, discontinuity and excessive granularity of the surface lipid film, pronounced thinning of the aqueous phase, and breakup of the tear film. After parotid duct transposition, the tear film of some animals was almost indistinguishable from normal. However, in others the surface lipid layer was thinned, discontinuous, or virtual absent. Discontinuity of surface lipid was most obvious in animals with marked salivary epiphora, and was associated with a variable amount of crystalline concretion over the ocular surface. The clinical usefulness of polarized light biomicroscopy for the diagnosis, and subsequent monitoring, of keratoconjunctivitis sicca is discussed.

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

“…Changes in meibomian lipid composition have been reported in ocular surface disease (Shine and McCulley, 1997) and could affect complexation with mucins, thereby altering viscosity and (indirectly) tear film break-up time (Tiffany, 1995). In addition, a normal lipid layer frequently does not form over the tear film in KCS (Carrington et al, 1987b). This may reflect an increased complexation of meibomian secretions with ocular mucins in the dry eye.…”

“…# 1998 Academic Press Keratoconjunctivitis sicca (KCS, ' dry eye ') may be induced by nutritional, environmental, toxic, pharmacological, neuronal or hormonal changes and other factors including autoimmune disease such as rheumatoid arthritis McGill, 1985 ;Sansom and Barnett, 1985b ;Carrington et al, 1987b ;Nelson, 1996 ;Schein et al, 1997). The condition is common in humans (Caffery et al, 1996) and in dogs (Kaswan, Pappas and Wall, 1996) : certain breeds of dog being particularly prone to a condition similar to Sjogren's syndrome in man (Grauwels, 1979 ;Sansom and Barnett, 1985a ;Barnett and Sansom, 1985 ;1987 ;Carrington et al, 1987b).…”

“…The condition is common in humans (Caffery et al, 1996) and in dogs (Kaswan, Pappas and Wall, 1996) : certain breeds of dog being particularly prone to a condition similar to Sjogren's syndrome in man (Grauwels, 1979 ;Sansom and Barnett, 1985a ;Barnett and Sansom, 1985 ;1987 ;Carrington et al, 1987b). In such cases, there is commonly an immune-mediated destruction of lacrimal tissue (Kaswan and Salisbury, 1990), a decrease in conjunctival goblet cell density (Grauwels, 1979) and accumulation of copious quantities of abnormal viscous mucus (Sansom and Barnett, 1985a).…”

“…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.…”

“…It is clear from clinical observation, and biomicroscopic studies (Zaidman et al, 1985 ;Carrington et al, 1987b), that the physicochemical properties of ocular surface mucins are grossly abnormal in KCS. In particular, accumulations of tenacious mucus are often found over the inferior conjunctival fornix and cornea Sansom and Barnett, 1985a).…”