A review of equine rectal tears and current methods of treatment

Rectal tears are a risk of rectal palpation during equine clinical examination and can be life‐threatening; prompt medical and surgical intervention is required to improve patient outcome. Depending on the degree of the tear, conservative treatment or surgical management may be warranted. Surgical management involves either direct suturing or faecal diversion techniques, such as colostomy or a temporary indwelling rectal liner. The prognosis for a horse with a rectal tear depends on size of the tear, grade and location of the tear, and time between occurrence and first aid measures.     

Topical effect of various agents on gelatinase activity in the tear film of normal dogs

OBJECTIVE: To evaluate the topical effect of various agents, currently used in the treatment of melting ulcers, on gelatinase activity present in the tear film of normal dogs. ANIMAL STUDIED: Eight normal adult beagles. PROCEDURES: Each animal received the following agents: cyclosporine A 1%, N-acetylcysteine 10%, ciprofloxacin 0.3%, ethylenediaminetetraacetic acid (EDTA) 1%, doxycycline 0.001%, polysulfated glycosaminoglycans (PSGAG) 5%, autoserum, and artificial tears during a 48-h period following a Latin square design. Tear samples were collected with micro-capillary pipettes following a corneal surface irrigation of each eye with sterile saline on four different occasions. Basal and total gelatinase activities were evaluated by optical density after processing in a commercial gelatinase activity assay. From the optical density ratio, a semi-quantitative measure of gelatinase activity was obtained. Basal and total activities were measured in all samples. RESULTS: The lowest total gelatinase activity, representing a percent decline in the enzyme activity although not significant, was observed 1 h after the last treatment in seven out of the eight ophthalmic agents; EDTA (68%), ciprofloxacin (76%), cyclosporine A (68%), doxycycline (47%), artificial tears (26%), PSGAG (25%), and N-acetylcysteine (20%). However, only the reduction observed with EDTA 6 h after the last treatment was significantly lower compared to the reduction observed with the artificial tears. CONCLUSION: This study indicated that only EDTA was able to significantly reduce the gelatinase activity in a persistent manner in the tear film of normal canine eyes. Further studies will be required to evaluate the effect of EDTA under ulcerative conditions and to more accurately ascertain the potential in vivo effect of the other agents.     

Constant rate infusion for topical ocular delivery in horses: a pilot study

OBJECTIVE: To assess the efficacy and kinetics of a continuous infusion modality for topical ophthalmic drug delivery via subpalpebral lavage in horses. ANIMALS STUDIED: Five ophthalmically normal horses PROCEDURES: A constant-rate continuous delivery pump was used to apply 0.01% fluorescein solution to the eyes of five ophthalmically normal horses via subpalpebral lavage. Fluorescein was applied at a rate of 0.14 mL/h for 72 h. Tear samples were collected from the ventral conjunctival fornix at regular intervals via capillary tube and tear fluorescein concentrations were determined via spectral assay. Laboratory studies to evaluate the procedures used in the study also were performed. RESULTS: Overall mean tear film fluorescein concentration was approximately 20% of the applied concentration of fluorescein. However, tear film fluorescein concentrations varied considerably between horses and over time. Dilution varied from 0.62% to 60% of the applied concentration. Air pockets sporadically appeared in subpalpebral lavage tubing lines, resulting in discontinuous topical application of fluorescein. CONCLUSIONS: Constant-rate delivery of ophthalmic medications using a continuous infusion pump may provide a valuable method of topical drug delivery if tear film dilution of drugs is taken into account.     

Effect of age, gender, weight, and time of day on tear production in normal dogs

OBJECTIVE: To investigate the effects of age, weight, gender, and of time of day on tear production in normal dogs. ANIMALS: studied One hundred ophthalmoscopically and systemically unremarkable dogs. PROCEDURE: Schirmer tear tests (STT) were performed every 2 h during the day on one randomly chosen eye of each of 100 dogs. RESULTS: There was a statistically significant effect of time of day and age on the STT measurement. The mean STT decreased by 0.4 mm for every 1 year that age increased (P=0.007). Mean STT values taken at 10:00 am were 0.7 mm lower than values taken at 4:00 pm (P=0.04). CONCLUSIONS: Tear production decreases with age in the normal dog. In this population of dogs the largest difference was between the 10:00 am and the 4:00 pm STT measurements, but this still only amounted to 0.7 mm. This value is unlikely to be of clinical significance in the diagnosis of keratoconjunctivitis sicca (KCS).     

Effects of Intravenous Detomidine on Schirmer Tear Test Results in Clinically Normal Horses

This study was conducted to determine the effects of intravenous detomidine on Schirmer tear test (STT) results in clinically normal horses. Eighteen adult horses were randomly divided into two groups of nine horses each. The treatment group was sedated with intravenous detomidine alone (20 μg/kg), and the control group received only intravenous saline (0.2 mL/100 kg). Schirmer tear test was performed just before intravenous administration of detomidine or saline in treatment and control groups, respectively. Schirmer tear tests were repeated 5, 20, 60, and 120 minutes later. Horses enrolled in this study consisted of nine males and nine females. Breeds were Arabian and Hanoverian, ranging from 3 to 6 years in age. In the treatment group, the pretreatment and subsequent posttreatment mean ± standard deviation values were 17.0 ± 6.9 (0 minutes), 11.8 ± 2.9 (5 minutes), 12.1 ± 2.0 (20 minutes), 12.1 ± 3.1 (60 minutes), and 15.0 ± 2.8 (120 minutes) mm wetting/min. In this group of horses, a significant reduction was observed in STT values at 5, 20, and 60 minutes after treatment with detomidine hydrochloride in comparison to the pretreatment values (analysis of variance with post hoc testing; P₅ = 0.004, P₂₀ = 0.007, P₆₀ = 0.006). There was no significant difference between baseline values and posttreatment values in the control saline group (P ≥ .08). We conclude that intravenous detomidine causes a significant reduction in STT values in clinically normal horses. In horses, practitioners should measure STT values before intravenous administration of detomidine to accurately assess the results.     

Tear production in normal juvenile dogs

Objective To establish a baseline range or average for tear production in normal juvenile dogs and evaluate the effects of age, weight, and gender on Schirmer tear test (STT) in juvenile dogs. Materials and methods Healthy puppies of various breeds <6 months of age. STT1 and STT2 were performed in both eyes of each subject. Statistical analysis was performed using a backwards stepwise regression model with repeated measures. Using continuous variables of STT1 and STT2 as the dependent variables separately, the independent variables were age (days), eye (left or right), gender (male or female), ocular disease processes in eyes or not, and weight (kg). Results Eighty‐six eyes from 27 males and 16 females were included in this study. Ages ranged from 25 to 133 (mean ± SEM: 61.74 ± 24.15) days and weights ranged from 0.88 to 8.86 (3.27 ± 2.22) kg. STT1 results ranged from 0 to 26 (15.76 ± 5.79) mm/min. STT2 results ranged from 0 to 24 (8.79 ± 5.01) mm/min. Age, weight, and gender significantly affected STT1 results. Weight and gender significantly affected STT2 results. STT1 values increased by 0.15 mm/min for each 1 day increase in age and by 0.84 mm/min for each 1 kg increase in body weight. STT2 values increased by 0.57 mm/min for each 1 kg increase in body weight. Conclusions Age, weight, and gender significantly affect tear production in normal juvenile dogs. STT1 increases to adult values at approximately 9–10 weeks of age.     

Profiles of matrix metalloproteinase activity in equine tear fluid during corneal healing in 10 horses with ulcerative keratitis

OBJECTIVE: Levels of tear film matrix metalloproteinases (MMPs) activity are significantly elevated in horses with ulcerative keratitis and contribute to the excessive breakdown of stromal collagen. Changes in the amount of proteolytic activity in horse tear film during corneal healing and stromal remodeling have not yet been reported, but we hypothesize they should decrease. In the present study we analyzed serial tear fluid from horses with ulcerative keratitis to identify any changes in MMP activity during corneal healing and stromal remodeling. PROCEDURES: Samples of tear fluid were obtained from both eyes of 10 horses with ulcerative keratitis on the day of admission (day 1) at the hospital and then at various time points until complete healing of the cornea. Tear film MMP2 and MMP9 activity was determined by quantitative gelatin zymography. In all cases medical treatment included topical applications of equine serum, antibiotics, atropine and systemic administration of anti-inflammatory drugs. Surgical procedures were performed in several cases on day 2 in addition to the medical treatment. RESULTS: The mean total MMP activity (+/- SD) measured in relative standard units (RSU) in the tear fluid of the ulcerated eye (2.44 +/- 1.44) of the 10 horses was significantly higher than the mean in the contralateral eye (0.81 +/- 0.68) (P = 0.006), on the day of admission at the VMTH. The mean MMP activity in these ulcerated eyes significantly decreased (-82.4%) between the first day of admission and the day when the ulcer had completely healed (P = 0.0002). The activity level in the healed eye (0.43 +/- 0.17) was not significantly different to the one in the contralateral eye (0.36 +/- 0.18) on the day of complete corneal healing (P = 0.374). The level of MMP activity in the contralateral eye also decreased from 0.81 +/- 0.68-0.36 +/- 0.18 but this decrease (56%) was not significant (P = 0.069). CONCLUSIONS: Ulcerative keratitis in horses is associated with initially high levels of tear film proteolytic activity that decrease as the ulcers heal. The success of medical and surgical treatment of the corneal ulcers is reflected by the enzyme activity in tears. In horses successful treatment does lead to a rapid reduction in tear film proteolytic activity that corresponded with the improvement in the clinical signs of corneal ulceration. Measurement of MMP activity in the tear film might represent a way to monitor the progression of corneal healing in horses with ulcerative keratitis.