This review paper provides a summary of the anatomy, physiology and pathology of the tear film: its production sites, composition and function, as well as the causes, clinical signs and treatment of keratoconjuncitivitis sicca in veterinary medicine. The paper focuses on reports of schirmer tear test in exotic and wildlife species, as well as reports of keratoconjunctivitis in these species. It is hypothesized that in some wildlife species, especially those of the Cervidae (deer) family, low baseline tear production values predispose the animals to keratoconjunctivitis, thus accounting for the high number of reports of this disease in wildlife ruminants.

The 102 dogs discussed in this report present 123 cases of recurrent corneal epithelial erosion arising from a suspected primary basement membrane abnormality. Eighty of the dogs were purebred and 22 were mixedbreed. The most common breeds were Boxers (33 cases), Yorkshire Terriers¹³⁾, German Shepherds⁷⁾, and Miniature Poodles⁴⁾. Ages ranged from 3,5 months to 14 years with an average of 6,7 years. Sixty-three were male and 39 female. Forty-nine right and 62 left eyes were affected, with 6 erosions bilateral. The most common presenting complaints were: a non healing corneal ulcers, lacrimation, and blepharospasm. Debridement using sterile cotton-tipped swabs and grid keratotomy with a 25 G needle were performed in all cases, and repeated, if not healed, 15 days later. In the second treatment session a soft contact lens (SCL) was also inserted. In 21 dogs debridement, grid keratotomy and application of the SCL were performed at the first examination. The corneal erosions that were not healed after thirty days by these therapies were then treated with superficial keratectomy. Sixty-eight erosions healed by the first treatment, 26 by the second, 21 by the direct application of the SCL, and in only 2 cases was a keratectomy performed. Six cases were lost to follow-up. The mean time of healing was 19 days.

We evaluated the effectiveness of a laser flare meter for objective assessment of aqueous flare, which results from increased protein in the anterior chamber and is associated with uveitis. Measurements were carried out in 100 normal canine eyes, 30 normal feline eyes, and 10 canine eyes diagnosed with unilateral uveitis based on clinical symptoms and findings. The flare values (pc/ms) (mean ± SD) were 4.60 ± 1.30 in the normal canine eyes, 6.14 ± 1.60 in the normal feline eyes, and 83.18 ± 3.20 in the canine eyes with uveitis. The flare value in canine eyes with uveitis was significantly higher than in normal canine eyes (p<0.01). No statistically significant difference was shown between the left and right normal canine or between the left and right normal canine or between the left and right normal feline eyes. Evaluation of normal canine eyes by age group showed a significantly higher flare value of 6.10 ± 1.22 in dogs aged ≥ 10 years (mean age, 12.9 years) versus 4.20 ± 0.99 in dogs aged ≤ 4 years (mean age, 2.1 years) (p<0.01). This suggests that aqueous flare increases with age. We found the laser flare meter to be very useful for objective and quantitative clinical evaluation of canine and feline aqueous flare.

A laser flare meter (FM-500, Kowa, Tokyo) can be used to measure protein concentrations in aqueous humor via use of a helium-neon laser. Experimentally, measurements are easier to obtain in eyes with a larger pupil size. In normal right eyes of 19 beagles, one drop of a mydriatic agent composed of 0.5% phenylephrine and 0.5% tropicamide (Mydrin P, Santen Pharmaceutical, Osaka) was administered. The left eyes were used as controls. Time course measurements were scheduled before and 0.5, 1, 2, 3 and 4 hours after the topical administration of the mydriatic agent. Pupil size was significantly increased after agent administration (Wilcoxon's rank sum test, p<0.01) and remained increased in size over the duration of the measurement period. The flare value was significantly lower 1 hour after drug administration as compared to the same measurement point for the control eyes, and remained lower throughout the rest of the measurement period (Wilcoxon's rank sum test, p<0.01). In this study, aqueous flare measurements obtained with a laser flare meter were easier to perform in mydriatic eyes as opposed to in non-mydriatic eyes due to the extension of the measurement area caused by the mydriasis. However statistically, the mydriasis significantly decreased the flare value. Hence the reliability of flare values obtained after the application of a mydriatic agent may be questionable in dogs.

A 4-month-old, intact male, Miniature Dachshund was referred to us for evaluation of congenital blindness. The dog had reduced pupillary light reflexes and defective vision. The electroretinograms were normal, but small optic disks were present in both eyes. The dam and a littermate of this dog exhibited similar signs in the left eye. The sire was normal. These dogs were being raised as pets, so that pathological examination and genetic tests could not be performed, but the ophthalmological findings suggested the presence of inherited optic nerve hypoplasia.

Ophthalmologic examination of a 14-month-old male beagle revealed that the right optic disc was atrophic and abnormal in color and the retina was supplied by a reduced number of arteries. The light-stimulated pupillary reflex was weak and became considerably weaker with age. Histopathological examination revealed a decreased number of nerve fibers, an increased amount of collagen fibers and gliosis in the right optic nerve, and also vacuolation in the nerve fiber layer, a decreased number of ganglion cells and thinning of the inner plexiform layer of the retina in the right eye. Based on the above findings, we confirmed that the lesion was situated along the right descending optic nerve somewhere between the retina and the optic chiasm. We concluded the lesion was the result from a circulatory disturbance.

Cystic opacity of the lens was found in 11 out of 88 stroke prone spontaneously hypertensive rats (SHRSP) at 11 weeks of age. Ophthalmoscopically, a semitransparent, oval or irregular-shaped cyst with or without opaque foci was observed in the posterior or posterior-equatorial portion of the lens. The eyeballs with the cystic lens opacity in all cases were affected with persistent hyaloid artery. In addition, vitreous hemorrhage was detected in 4 affected eyeballs. Histopathological observations confirmed that the cystic lens lesions developed in the posterior or posterior-equatorial subcapsular portion of the lens. The cysts contained eosinophilic serous fluid and the lens fibers in the surface region of the cysts were degenerative. The residual segments of the hyaloid arteries were degenerative or necrotic and were adherent to the cystic lens lesions. Cellular infiltration and hemorrhage were observed in the affected vitreous. These results disclosed that the cystic lesion of the lens was closely associated with degenerative changes of the hyaloid arteries in SHRSP at 11 weeks of age, when hypertension developed.