Clinical and pathological observations in English cocker spaniels with primary metabolic vitamin E deficiency and retinal pigment epithelial dystrophy.

Fifteen English cocker spaniels with confirmed vitamin E deficiency were examined physically, ophthalmologically and neurologically. Eleven of them had clinical signs of neurological dysfunction which included ataxia, proprioceptive deficits, abnormal spinal reflexes and muscle weakness. In the two dogs examined histopathologically there was central neuronal fibre degeneration with prominent neuroaxonal dystrophy, particularly within the sensory relay nuclei of the brainstem, and one of the dogs had severe intestinal lipofuscinosis.

Vitamin E deficiency in dogs with retinal pigment epithelial dystrophy.

The role of vitamin E deficiency in the development of retinal pigment epithelial dystrophy was investigated in 11 cocker spaniels and four other dogs. The concentration of alpha-tocopherol was measured by high performance liquid chromatography in plasma samples obtained from the affected dogs and from 28 ophthalmoscopically normal, healthy control dogs. The mean (sd) plasma alpha-tocopherol concentration in the normal dogs was 20.2 (7.1) microg/ml, compared with 1.14 (0.67) microg/ml in the 11 affected cocker spaniels. The difference between the two groups remained highly significant when the alpha-tocopherol concentrations were expressed relative to the concentrations of the plasma lipids cholesterol and triglycerides. Low plasma concentrations of alpha-tocopherol were observed in the four affected dogs of other breeds, but the finding was not so consistent. The plasma lipid concentrations were normal in the affected dogs. The deficiency of alpha-tocopherol in the affected dogs appeared to be primary, because there was no clinical, biochemical or pathological evidence of underlying disease, or any indication of a dietary deficiency which might have contributed to the low concentrations of alpha-tocopherol.

Collie eye anomaly in the Lancashire heeler.

An ocular disease ophthalmoscopically identical to collie eye anomaly (CEA) is described in the Lancashire heeler breed of terrier. Survey work completed in 1996 demonstrated a significant incidence of 13.7 per cent. The clinical findings together with initial pedigree analysis support the accepted view that, in the traditionally affected breeds, CEA is a true pleiomorph which segregates as a recessive Mendelian trait. Alternative hypothesis speculates that the several lesions ascribed to CEA may occur as separate congenital disease entities, each with its own mode of inheritance. However, the combination of bilateral chloroidal hypoplasia, papillary or peripapillary coloboma and neuroretinal non-attachment in a non-collie breed tends to confirm that these three lesions are indeed individual parts of the one disease. The established appearance of CEA outwith the collie breeds dictates that the nomenclature for this disease is now somewhat inappropriate and that an alternative name should be considered. It is suggested that the term 'congenital posterior segment anomaly' could be adopted.

Technique of lateral canthoplasty for the correction of macropalpebral fissure in the dog.

The various clinical anomalies associated with macropalpebral fissure in the dog can be relatively successfully addressed by a reduction in functional eyelid length and stabilisation of the lateral canthus. In this new technique the basic principles of the Kuhnt-Szymanowski lateral canthoplasty have been extended to include an additional shortening of the upper eyelid obtained by a triangular split thickness resection. Results in a series of 22 patients have demonstrated significant clinical improvement throughout, with optimum positioning of the modified palpebral fissures being achieved in five of these patients by the additional and subsequent resection of redundant forehead skin.

The cytoskeletal intermediate filaments of canine retinal pigment epithelial cells in vivo and in vitro.

The cytoskeletal intermediate filament characteristics of normal, freshly isolated and subcultured canine retinal pigment epithelial (RPE) cells were studied using immunocytochemistry and immunoblotting techniques. Commercially available primary antibodies recognising a broad range of cytokeratins and vimentin were selected. Cytokeratin reactivity was a constant feature of all canine RPE cells. The main cytokeratins expressed by cultured RPE cells included 8, 18 and 19. This finding is consistent with the published findings of work carried out in other mammalian species including man. Freshly isolated RPE cells stained positively with broad-spectrum antibodies to cytokeratins but generally did not stain with antibodies specific to cytokeratins 18 or 19 and did not stain with antibodies to vimentin, or stained only very weakly. After a short time in culture however, cells demonstrated intense positive staining for vimentin. This study demonstrated that cytokeratin immunoreactivity (in conjunction with vimentin immunoreactivity in vitro) is a useful and consistent marker for canine RPE cells.

Retinal pigment epithelial dystrophy in Briard dogs.

The eyes of normal Briard dogs, Briards affected with inherited retinal pigment epithelial dystrophy (RPED) and a range of normal crossbred and beagle dogs were examined and the histopathology of RPED in the Briard was compared with the histopathological features of ageing in the normal canine retina. RPED was characterised by the accumulation of auto-fluorescent lipofuscin-like inclusions in the retinal pigment epithelium (RPE), which initially involved only non-pigmented RPE cells overlying the tapetum but subsequently spread to all pigmented RPE cells. Secondary neuro-retinal degeneration was characterised by a gradual loss of the outer nuclear layer and the subsequent atrophy and degeneration of the inner retina. The loss of primary photoreceptors in the peripheral retina was accompanied by the migration of photoreceptor nuclei and appeared to resemble severe changes due to ageing. Intra-vitreal radiolabelled leucine was used to examine the rate of turnover of the outer segments of the rods in some Briards, but no significant variations were found. The activity of acid phosphatase in RPE was assayed in vitro and showed comparable regional variations in Briard and crossbred dogs. The results suggest that RPED in the Briard is unlikely to be due either to an increased rate of turnover of rod outer segments (and thus an increased phagocytic load) or to a primary insufficiency of lysosomal enzyme.

Hypercholesterolaemia in briards in the United Kingdom.

Elevated fasting plasma cholesterol concentrations were identified in clinically healthy briards. Biochemical investigations revealed no other major abnormalities. Plasma lipoprotein electrophoresis demonstrated a marked increase in the intensity of the alpha 2 band (compared with control dogs) which was reduced by dextran sulphate-magnesium chloride or sodium phosphotungstate-magnesium chloride precipitation of apo B and apo E containing lipoproteins in the plasma. The study has identified a hyperlipidaemia in briards characterised by increased cholesterol but normal triglyceride concentrations. The absence of obvious metabolic changes associated with secondary hypercholesterolaemia, suggests the breed may have a primary abnormality in cholesterol metabolism. The increased density of the precipitable lipoprotein which migrates to the alpha 2 band suggests that the hypercholesterolaemia may be due to an abnormal accumulation of high density lipoprotein (HDL) possibly HDLc. The possibility that abnormality in lipid metabolism might play a role in the development of retinal pigment epithelial dystrophy in briards is currently being investigated.

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

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.

Biomicroscopy of the tear film: aqueous and lipid tear substitutes in the normal and abnormal eye.

Polarised light biomicroscopy was used to assess the behaviour and interactions of two polymer-containing preparations of artificial tears, and two lipid-containing ointments, with the normal and abnormal pre-corneal tear film. The preparations were used topically in six normal dogs, and three dogs with keratoconjunctivitis sicca. A transient morphological alteration of the surface lipid layer of the tear film was commonly observed after the use of polymer solutions. The ointments spread as a continuous or semi-continuous layer over the normal, or polymer-supplemented, aqueous tears. Further applications of artificial tears produced only a temporary disruption of this layer. In dogs with keratoconjunctivitis sicca, thickening of the lipid layer of the tear film was observed for over 20 hours after the administration of ointment. These observations are discussed in relation to the prospects for the improved medical treatment of keratoconjunctivitis sicca by the use of polymer-containing solutions and ointments in combination.

Aqueous drainage in the dog.

The anatomical features of the iridocorneal angle and its associated structures are described and their role in the drainage of aqueous in the dog discussed. Anterior segment material from 126 dogs of various ages and many breeds was examined by light and electron microscopy, the results confirming that the elements of bulk aqueous drainage in this species are essentially the same as those of the primate eye. In particular, the demonstration of an avascular aqueous plexus lined with a vacuolating endothelium as an analogue of the primate Schlemm's canal has indicated that the theory of capillary drainage of aqueous is no longer tenable for the dog.