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.     

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

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.     

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.     

Polarized light biomicroscopic observations on the pre-corneal tear film. 3. The normal tear film of the cat

Polarized light biomicroscopy was used to examine the pre-corneal tear film in 14 normal cats. Blink rates were also determined. The normal range of surface morphology of the feline tear film was established. Two principal categories of surface patterning of the lipid layer of the tear film were identified. These occurred in all eyes examined and were: (a) a wave-like pattern, and (b) a pattern of variable character resembling the polished surface of granite. Over most of the area of the tear film, the thickness of its lipid layer between blinks was under 0·089 μm in all cats examined. However, narrow streaks of thicker lipid (up to 0·511 μm) were occasionally observed. The mean total blink rate was 2·4/min. Overall, incomplete blinks constituted approximately 50 per cent of the total blink rate. The tear film of the cat is compared with that of man and the dog.     

Qualitative tear film disease

Abnormalities of the lipid and mucin components of the preocular tear film may result from diseases of the eyelid margins and conjunctiva. Chronic keratoconjunctivitis with epithelial edema and superficial corneal neovascularization, with or without ulceration, characterizes qualitative tear diseases. Tear components other than lipid and mucin that carry probable clinical significance include tear proteins, all-trans retinal, cholesterol, glucose, and electrolytes. Although less common than quantitative or aqueous deficiencies, qualitative abnormalities are recognized as primary or secondary causes of ocular surface disease in companion animals.     

Conjunctival effects of canine distemper virus-induced keratoconjunctivitis sicca

Objective  This study compared the histopathology of canine distemper virus (CDV)-induced keratoconjunctivitis sicca (KCS) to non-infectious KCS in conjunctival tissues.
Animals studied  Forty mongrel dogs were assigned to three distinct groups: (i) non-infectious KCS (G1, n  = 10), (ii) CDV-induced KCS (G2, n  = 20), and (iii) healthy animals without any ocular alterations (G3, n  = 10).
Procedure  IgG titers and physical and ophthalmic examinations (e.g. Schirmer tear test [STT], tonometry, biomicroscopy, indirect biomicroscopy, and fluorescein test) were performed on all dogs. Conjunctival biopsies were collected and examined microscopically.
Results  Non-infectious and CDV-induced KCS demonstrated similar histopathological changes. Both types of KCS correlated with low STT, conjunctival hyperemia, mucopurulent ocular discharge, predominant lymphoplasmacytic infiltration, and acantholysis and keratinization of the ocular surface. G1 had lower conjunctival goblet cell counts than G3. Inclusion bodies were sporadically found in conjunctival samples of dogs from G2. The severity of ocular lesions in G1 and G2 did not correlate with the histopathological findings.
Conclusions  Dogs with non-infectious and CDV-induced KCS had very similar conjunctival histopathology. Our findings suggest that the pathophysiology of CDV-induced KCS is likely to be the same as non-infectious KCS, that is, a result of lacrimal deficiency and inflammation of the ocular surface.     

Immunopathogenesis of keratoconjunctivitis sicca in the dog.

Keratoconjunctivitis sicca (KCS), more commonly known as dry eye, is an inflammatory condition of the ocular surface caused by a pathologic reduction in the aqueous component of the tear film. It is seen commonly in the dog and defined as a Schirmer tear test with a reading of less than 10 mm in one minute. While KCS may be caused by neurological disease or drug toxicity, most cases are immune-mediated. Whereas the immunological basis of autoimmune KCS has been extensively investigated in humans and experimental rodent models, little research has been undertaken in the dog. It is hoped that this review spurs further research into the etiopathogenic factors in canine KCS.     

Characterization of ocular gland morphology and tear composition of pinnipeds

Objective The importance of tear film integrity to ocular health in terrestrial mammals is well established, however, in marine mammals, the role of the tear film in protection of the ocular surface is not known. In an effort to better understand the function of tears in maintaining health of the marine mammal eye surface, we examined ocular glands of the California sea lion and began to characterize the biochemical nature of the tear film of pinnipeds. Procedures Glands dissected from California sea lion eyelids and adnexa were examined for gross morphology, sectioned for microscopic analysis, and stained with hematoxylin and eosin. The tear film was examined using interferometry. Tears were collected from humans and pinnipeds for the analysis of protein and carbohydrate content. Results The sea lion has sebaceous glands in the lid, but these glands are different in size and orientation compared with typical meibomian glands of terrestrial mammals. Two other accessory ocular glands located dorsotemporally and medially appeared to be identical in morphology, with tubulo‐acinar morphology. An outer lipid layer on the ocular surface of the sea lion was not detected using interferometry, consistent with the absence of typical meibomian glands. Similar to human tears, the tears of pinnipeds contain several proteins but the ratio of carbohydrate to protein was greater than that in human tears. Conclusions Our findings indicate that the ocular gland architecture and biochemical nature of the tear film of pinnipeds have evolved to adapt to the challenges of an aquatic environment.     

Qualitative tear film and conjunctival goblet cell assessment of cats with corneal sequestra

OBJECTIVES: To evaluate the tear film qualitatively and conjunctival goblet cell numbers in cats with and without corneal sequestra. ANIMALS STUDIED AND PROCEDURES: This was a prospective evaluation of 11 cats with corneal sequestra and 14 control eyes that were either the contralateral normal eye when the sequestrum was unilateral or from control cats of similar age with no ocular disease. All cats in this study were examined by a veterinary ophthalmologist. The ophthalmic examinations included a neuro-ophthalmic evaluation, Schirmer tear tests, fluorescein staining, tear film break-up times, applanation tonometry, biomicroscopy, and indirect ophthalmoscopy. The palpebral conjunctiva at the dorsal nasal, ventral nasal, dorsal temporal and ventral temporal fornices were biopsied after topical anesthetic was applied to the cornea and conjunctiva. The conjunctival biopsies were fixed in formalin and sectioned routinely and stained with hematoxylin and eosin, and periodic acid-Schiff. These slides were examined by light microscopy by a blinded examiner. Goblet cell numbers were compared to conjunctival basal epithelial cell numbers by region. The goblet cell numbers by region from the eyes with sequestra was statistically compared to those from eyes without sequestra, with a student's paired t-test. Conjunctival swabs were collected from the cats with corneal sequestra and submitted for polymerase chain reaction for Herpes felis, Chlamydia psiitticia, and Mycoplasma felis. The corneal sequestra were removed by surgical keratectomy and fixed and stained routinely, and examined by light microscopy. RESULTS: No neurologic abnormalities were detected in any of the cats. The Schirmer tear tests (eyes with sequestra 14+/-5.1 mm/min; normal eyes 15+/-6.8 mm/min) and intraocular pressures (eyes with sequestra 21+/-6.6; normal eyes 22+/-5.8) were within normal reference ranges for cats. Biomicroscopic examinations revealed varied sizes and depths of brown- and amber-colored corneal sequestra. No abnormalities were noted on indirect ophthalmoscopic examinations. The tear film break-up time was 21 s (+/-12) for the normal eyes (n=14) and 14 s (+/-13) in eyes with corneal sequestra (n=11). The average goblet/epithelial cell ratios by region for the normal eyes and the eyes with sequestra respectively were 0.66, 0.56 for the dorsal nasal fornix, 0.68, 0.57 for the ventral nasal fornix, 0.63, 0.48 for the temporal dorsal fornix, and 0.55, 0.49 for the temporal ventral fornix. There were no significant differences in tear film break-up times and goblet cell numbers in eyes with corneal sequestra and those without sequestra. Three conjunctival swabs from two of 11 cats with sequestra were positive with PCR for Herpes felis virus. These included one cat with bilateral sequestra and one cat with unilateral corneal sequestrum. CONCLUSIONS: The pathogenesis of feline corneal sequestra does not appear to be linked primarily to abnormal goblet cell numbers, qualitative tear film abnormalities, and accelerated tear film break-up time.     

Analysis of tear uptake by the Schirmer tear test strip in the canine eye

OBJECTIVE: To analyze the uptake of tears in a Schirmer tear test (STT) in vitro and in vitro. MATERIALS AND METHODS: Uptake of fluid by Schirmer tear test strips was studied in vitro by examining fluid uptake over time from an unlimited fluid supply as well as with specific fluid volumes applied to the test strip. Uptake of fluid by Schirmer tear test strips was evaluated in a population of 100 ophthalmologically normal dogs together with a group of 40 dogs with tear film abnormalities such as keratoconjunctivitis sicca (KCS) or epiphora. Each animal was given a full ophthalmic examination followed by a standard Schirmer tear test extended over between 3 and 5 min with the STT reading recorded every 5 s and plotted over time. To determine the effect of ocular irritation by the test strip, uptake of tears by test strips was determined before and after topical anesthesia in 20 dogs. RESULTS: In vitro examination of fluid uptake by the STT strips showed an initial rapid uptake followed by a gradual reduction in rate of uptake. Temporal evaluation of STT in vivo showed a similar rapid initial uptake of tear fluid, followed in the majority of cases by a sudden change to a steady state uptake of fluid. The initial gradient was 29.3 +/- 16.9 mm/min followed by a steady state uptake of 5.2 +/- 2.3 mm/min in normal dogs and 1.9 +/- 1.3 mm/min in dogs with KCS. This corresponds to a steady state tear turnover of 7.8 +/- 3.4 microL/min in normal dogs and 2.8 +/- 1.9 microL/min in animals with KCS. Dogs with nasolacrimal blockage and resultant epiphora showed a high initial gradient but final gradients were not statistically different from those of normal dogs. Discussion and conclusions Temporal evaluation of tear uptake by the STT shows substantial differences in rate of tear uptake at different time-points during the period of the test. RESULTS: of this study suggest that the initial rapid rise in STT value represents uptake from the tear lake followed by a slower tear uptake of tears from steady state tear production. Temporal examination of the Schirmer tear test allows a more precise evaluation of tear production than the standard STT measuring tear uptake in 1 min, together with estimation of the contribution to the test strip tear uptake of tears from the residual tear lake volume and those from continual tear production.     

Ocular disease in the guinea pig (Cavia porcellus): a survey of 1000 animals

Objective Anecdotal evidence has suggested that guinea pigs have a high prevalence of ocular lesions. Here we undertook a survey of 1000 guinea pigs from populations of animals kept as laboratory animals, breeding show cavies, animals kept as pets and those from rescue and rehoming centers. Each animal was examined to assess for ocular abnormalities. Procedures A full ophthalmic examination was performed on each animal with direct and indirect ophthalmoscopy and with slit lamp biomicroscopy. Measurement of tear production using the Schirmer tear test 1 and intraocular pressure using the Tonopen applanation tonometer after topical anesthesia was undertaken in selected animals. Results Forty‐five percent of animals examined had some ocular abnormality. The majority were lens lesions including 17% with cataract and 21% with subclinical lens abnormalities such as nuclear sclerosis. Other abnormalities included conjunctivitis in 4.7% and keratitis in 3.6%. Lipid deposition in conjunctiva was observed in 2.3% of guinea pigs and ciliary body heterotopic bone formation in 0.8% of animals. Conclusions This study shows a high proportion of eyes with some degree of abnormality in animals otherwise considered healthy. Information on diseases of the guinea pig eye is important given the use of the species as a laboratory rodent and also the number kept as pets and show animals.     

The tear film and ocular mucins

Abstract The trilaminar tear film, composed of the lipid, aqueous and mucin layers, has many functions including defending the ocular surface. The aqueous layer has several soluble antimicrobial factors that protect the ocular surface. Ocular mucins have recently been studied with regard to their role in the defense of the eye as well as in dry eye syndromes. To date, 15 mucin genes have been identified, and six of these mucin genes are localized to or secreted by ocular glands or epithelia. Understanding the production, secretion and function of ocular mucins will aid in the treatment of dry eye syndromes and ocular surface microbial infections.     

Reduced tear production in three canine endocrinopathies

OBJECTIVES: Previous reports have suggested that hypothyroid and diabetic patients can be predisposed to keratoconjunctivitis sicca. This study aimed to measure tear production in dogs with diabetes, hypothyroidism and hyperadrenocorticism using the Schirmer tear test and to compare these results with Schirmer tear test values for a group of normal dogs. METHODS: Schirmer tear tests were performed on 16 dogs with hyperadrenocorticism, 18 with diabetes and 12 with hypothyroidism together with 100 control dogs. Corneal sensitivity was also measured in 12 of the 18 diabetic dogs with a Cochet Bonnet aesthesiometer and compared with age- and breed-matched normal dogs. RESULTS: Schirmer tear test values in dogs with hypothyroidism, hyperadrenocorticism and diabetes were 12.3+/-3.2, 14.0+/-4.0 and 12.3+/-5.3 mm/minutes, respectively. Schirmer tear test values were significantly lower than that for the control group (19.6+/-4.2 mm/minutes) in all dogs with an endocrinopathy. Only in two hypothyroid dogs and three diabetics, this was manifested as profound keratoconjunctivitis sicca with Schirmer tear test value lower than 5 mm/minutes. Diabetic dogs had significantly reduced corneal sensitivity compared with a matched set of control dogs. CLINICAL SIGNIFICANCE: This study shows a significant reduction in tear production in animals with diabetes mellitus, hypothyroidism and hyperadrenocorticism. Further research is needed to elucidate the mechanisms by which this reduction in tear production occurs. Assessment of tear production should be undertaken in animals diagnosed with these endocrinopathies, as these animals may progress to clinical keratoconjunctivitis sicca.     

Canine meibometry: establishing baseline values for meibomian gland secretions in dogs

Meibomian lipid secretions are essential in preventing tear evaporation. Disorders of the meibomian glands may therefore play an important role in the pathogenesis of some forms of keratoconjunctivitis sicca (KCS). Until now, meibomian lipid secretions have never been quantitatively evaluated in dogs. With the aim of establishing baseline values of canine meibomian lipid secretions, meibometry was conducted in 42 healthy dogs, 16 of which were Miniature Schnauzers. The mean meibomium level in 84 eyes of the 42 dogs was 179+/-60 Meibometer units. Age, gender and side did not affect the results. However, meibomium levels were significantly lower in the Miniature Schnauzers, a breed that is susceptible to KCS, compared to other breeds. This report demonstrates that meibometry is a simple and minimally invasive technique that may be readily used in conscious dogs to quantify meibomian gland secretions and explicate tear film dynamics in normal and dry canine eyes.     

Evaluation of the Schirmer tear test in clinically normal rabbits

Mean (+/- SD) value for results of the Schirmer tear test without use of topical anesthesia on 142 rabbit eyes was 5.30 (+/- 2.96) mm/min; range was 15 mm/min, with low value of 0 and high value of 15 mm/min. Two SD from the mean provided a normal clinical range of 0 to 11.2 mm/min for inclusion of 95% of the population. Significant differences were not evident between eye (right vs left) or gender or among breeds; interaction among eye, gender, and breed also was not observed. Although mean values for 2 breeds were significantly different from values in the other 10 breeds and from each other, they were still within the proposed normal range of 2 SD. The Schirmer tear test without topical anesthesia may be useful in rabbits for evaluation of increased values correlated with ocular irritation, rather than for determination of decreased values associated with keratoconjunctivitis sicca.     

Use of punctal occlusion in the treatment of canine keratoconjunctivitis sicca

Twenty eyes of 10 dogs with keratoconjunctivitis sicca (KCS) were treated by occlusion of the ventral nasolacrimal punctum with a silicone punctal plug in order to increase the volume of the remaining tear lake. Punctal size was measured using a commercially available punctal gauge and the appropriate sized plug was inserted under local anaesthesia. Seven dogs showed an increase in Schirmer tear test I (STT) value. STT values immediately prior to plug placement were 2.3 +/- 1.7 mm/minute. STT values with punctal occlusion were 6.1 +/- 4.1 mm/minute, giving a mean increase of 3.8 +/- 2.7 mm/minute (P<0.001). In 14 eyes of eight dogs, the increase in STT values was accompanied by a clinical improvement in the appearance of the ocular surface. In the three dogs with no increase in STT values, the use of punctal plugs reduced the frequency of artificial tear replacement therapy required to maintain a healthy ocular surface. These results show that use of punctal plugs in dogs with KCS may be appropriate where other lacrimomimetic medications have been unsuccessful.     

Scanning electron microscopy of experimental keratoconjunctivitis sicca in dogs: cornea and bulbar conjunctiva

Keratoconjunctivitis sicca was produced experimentally in 16 beagles by bilateral surgical removal of the lacrimal and nictitans glands; four dogs were not treated, and 12 received tear-replacement therapy on post-operative days 7 through 28. Keratoconjunctivitis sicca was verified by reduction in Schirmer tear test values by post-operative day 6, and there was no response on day 28 to tear-replacement therapy. Corneas of both normal and tear-deficient dogs had polygonal squamous epithelial cells of light and dark electron density by scanning electron microscopy. Light cells had more microvilli and microplicae than dark cells. Conjunctivae were similar to corneas, except for numerous goblet cells on the surface. Corneal dark-cell density and goblet cell density were not different between groups. Goblet cells most often occurred singly in normal dogs, while they were in clusters in tear-deficient dogs. A hypothesis that petrolatum/mineral oil ointment should provide more effective artificial tear replacement than hydroxymethylcellulose drops for tear-deficient dogs could not be confirmed by objective analysis of corneal dark-cell density or conjunctival goblet cell density.     

Tear-film osmolarity in normal cats and cats with conjunctivitis

Objective To compare the tear‐film osmolarity of normal cats and cats with conjunctivitis. Animal studied The population consisted of shelter, research, and privately owned cats. Procedures Cats were classified as normal or having conjunctivitis. An ophthalmic examination including Schirmer tear test (STT), fluorescein staining, tear‐film break‐up time (TFBUT), intraocular pressure (IOP), and slit‐lamp biomicroscopy of the anterior segment was performed. The severity of conjunctivitis was graded and assigned a numerical score. The Tear Lab^TM Osmolarity System was utilized to determine the tear‐film osmolarity. Unpaired t‐tests were used to compare tear‐film osmolarity, TFBUT, IOP, and STT of the two groups. Results A total of 93 cats (186 eyes) were examined. There were 37 normal cats (74 eyes) and 39 conjunctivitis cats (78 eyes). The mean age was 2.34 years. There was no statistical difference (P = 0.2065) between the median tear‐film osmolarity of normal cats (328.5 ± 17.94 mOsms/L) and conjunctivitis cats (325.0 ± 24.84 mOsms/L). Cats with conjunctivitis had an accelerated TFBUT (P < 0.0001) and lower IOPs (P < 0.0001) as compared to normal cats. No statistical difference was found between STT values (P = 0.1304). Conclusions The median tear‐film osmolarity of normal cats was 328.5 mOsms/L. Despite the accelerated TFBUT, conjunctivitis did not cause a statistically significant change in tear‐film osmolarity. The Tear Lab^TM Osmolarity System was easily used and well tolerated by the cats in the study.     

Tear-deficient and evaporative dry eye syndromes of the horse

Tear-deficient dry eye (keratoconjunctivitis sicca), and evaporative dry eye, with some overlap between these two categories, are two major categories of dry eye recognized in the horse. Careful examination of the eyelid margins, the inner and outer surfaces of the upper and lower eyelids, assessment of blink and third eyelid movement, specific testing of tear production, assessment of corneal sensitivity, and slit-lamp examination of the ocular surface before and after fluorescein dye application is recommended to detect dry eye problems. Rose Bengal dye application is also recommended in many cases. Facial nerve paresis is a possible complicating factor in some instances. Evaporative dry eye deserves closer scrutiny for it may be a contributory factor when ocular surface disease such as keratomycosis is present. Factors which influence ocular surface health need more close examination in horses.     

Ophthalmic complications following megavoltage irradiation of the nasal and paranasal cavities in dogs

Megavoltage x-radiation was used to treat orbital nasal, and paranasal cavity malignant neoplasia in 29 dogs. In each instance, the globe and adnexal tissues were within the treatment portals (entry and/or exit). Doses administered to tumors ranged from 3,680 to 5,000 cGy. Ocular reactions after irradiation were classified as mild in 5 of 29 cases (17.2%) and severe in 17 of 29 cases (58.6%). No ocular complications were noticed in 7 of 29 cases (24.1%). Complications frequently noticed included severe keratitis (41%), mild conjunctivitis (34%), severe conjunctivitis (28%), cataract (28%), and keratoconjunctivitis sicca (24%). Ocular complications that developed were not life threatening, but posed a threat to visual function and patient quality of life. Treatment for the complications included control of bacterial infection, reduction of tissue inflammation, and ocular surface protection when tear film deficiencies were noticed. Mild complications represented acute effects of irradiation, and typically resolved. Severe complications developed both acutely and as late irradiation effects. Those attributed to late irradiation effects were more vision threatening and altered the quality of life more than did the early effects.