Proliferation of Streptococcus zooepidemicus and Pseudomonas aeruginosa within a simulated subpalpebral lavage flushed with equine serum

Objective  To evaluate whether equine serum administered via a simulated subpalpebral lavage system (SPL) supports proliferation of Streptococcus zooepidemicus or Pseudomonas aeruginosa within the tubing.
Procedures  A sterile i.v. catheter with injection cap was inserted into sterilized silicone tubing (Mila^®). To mimic an SPL within the dorsal conjunctival fornix, the tubing was secured to an elevated platform. The tip of the tubing extended from the platform into a vial containing culture medium just inoculated with approximately 1.5 × 10⁸ CFU/mL P. aeruginosa or S. zooepidemicus . To mimic administration of medication, the tubing was infused twice daily with equine serum, sterile saline (negative control), or culture medium (positive control) followed by air. Incubation was at 25 or 37 °C. At 24, 48, and 72 h postinoculation, samples were obtained for bacterial culture from one simulated SPL for each experimental variant. The following sections were cultured: (i) tubing tip previously submerged in the inoculated culture medium, (ii) tubing mid-section, and (iii) tip of the i.v. catheter. The experiment was performed in triplicate.
Results  Streptococcus zooepidemicus or P. aeruginosa were isolated from 100% of the tubing tips. Streptococcus zooepidemicus was isolated from one mid-section flushed with culture medium incubated at 37 °C. All other samples were negative for growth of the inoculated agents.
Conclusions  Streptococcus zooepidemicus and P. aeruginosa did not proliferate within silicone tubing infused with equine serum. These data suggest that topical serum can be safely administered through a superiorly placed SPL in clinical cases.     

Subpalpebral lavage placement for remote topical administration of ocular medications in 12 dogs: A retrospective review and assessment of owner perception

Objective

The aim of this study was to describe the placement of subpalpebral lavage (SPL) systems in 12 dogs (15 eyes) intolerant of topical ocular medications to assess the suitability, complications encountered and owner perception of use.

Animals Studied

Retrospective review of dogs that underwent SPL placement for treatment of ocular disease at the Ophthalmology Department, University of Bristol Small Animal Hospital between 2017 and 2021.

Procedure(s)

Data recorded included signalment, history, diagnosis, treatment, reason for SPL placement, uni- or bilateral placement, duration of placement, complications, and outcome. Owner perception was assessed using an online questionnaire. Statistical analysis included McNemar and Wilcoxon signed-ranks tests.

Results

Twelve dogs (15 eyes) underwent SPL placement. Eleven owners completed the online questionnaire. Corneal ulceration was the most common disease requiring SPL placement (n = 13/15 eyes, 86.7%). Most cases received multimodal topical therapy (n = 9/15 eyes, 60.0%) via SPL. Owners administered medication 6.63 times daily via SPL (range 1–16 applications/day). All dogs requiring ongoing topical medication (n = 8/12, 66.7%) were trained to accept direct administration during SPL treatment. Statistically significant improvements in medication compliance, ease of application, and reduced perceived risk of iatrogenic ocular injury were reported by owners (p-value = .001, .004, and .031 respectively). Minor complications were infrequently reported but an excellent outcome was achieved for all eyes.

Conclusion

Subpalpebral lavage placement provides a practical and safe solution for the provision of frequent multimodal ocular medication when treating patients with a challenging temperament.     

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.     

Phacoemulsification and +14 diopter intraocular lens placement in a Saddlebred foal

A 2‐month‐old, 110‐kg Saddlebred filly presented for evaluation of bilateral cataracts. A hypermature cataract in the left eye (OS) and an incipient nuclear cataract in the right eye (OD) were diagnosed. Electroretinography and ocular ultrasound revealed no contraindications for surgical removal of the cataractous lens OS. Phacoemulsification and implantation of a +14 diopter (D) intraocular lens (IOL) OS were performed at 4 months of age without complication, with the exception of a partial iridectomy performed on a small iris section that prolapsed through the corneal incision. Complete ophthalmic examinations, including ocular ultrasound and streak retinoscopy, were performed 1, 2, 6 weeks, 4 months, 1, and 2 years postoperatively. Diffuse corneal edema and a superficial corneal ulcer developed OS during the early postoperative period and resolved without complication. Dyscoria was identified owing to anterior synechia of the dorsomedial iris at the incision site. Two years after surgery, menace response, palpebral reflex, dazzle reflex, and pupillary light reflexes were present in both eyes (OU). The IOL remained centrally positioned within the capsule, with mild anterior tilting of the superior portion of the IOL and mild fibrosis of the lens capsule. The postoperative net refractive error was +0.31 D OS. Based on this report, a +14 D IOL may be the appropriate choice following lens extraction in a foal to achieve refraction near emmetropia at maturity. To our knowledge, this is the first report of phacoemulsification and IOL implantation in a foal with long‐term follow‐up.     

Viruses associated with outbreaks of equine respiratory disease in New Zealand

AIM: To identify viruses associated with respiratory disease in young horses in New Zealand.

METHODS: Nasal swabs and blood samples were collected from 45 foals or horses from five separate outbreaks of respiratory disease that occurred in New Zealand in 1996, and from 37 yearlings at the time of the annual yearling sales in January that same year. Virus isolation from nasal swabs and peripheral blood leukocytes (PBL) was undertaken and serum samples were tested for antibodies against equine herpesviruses (EHV-1, EHV-2, EHV-4 and EHV-5), equine rhinitis-A virus (ERAV), equine rhinitis-B virus (ERBV), equine adenovirus 1 (EAdV-1), equine arteritis virus (EAV), reovirus 3 and parainfluenza virus type 3 (PIV3).

RESULTS: Viruses were isolated from 24/94 (26%) nasal swab samples and from 77/80 (96%) PBL samples collected from both healthy horses and horses showing clinical signs of respiratory disease. All isolates were identified as EHV-2, EHV-4, EHV-5 or untyped EHV. Of the horses and foals tested, 59/82 (72%) were positive for EHV-1 and/or EHV-4 serum neutralising (SN) antibody on at least one sampling occasion, 52/82 (63%) for EHV-1-specific antibody tested by enzyme-linked immunosorbent assay (ELISA), 10/80 (13%) for ERAV SN antibody, 60/80 (75%) for ERBV SN antibody, and 42/80 (53%) for haemagglutination inhibition (HI) antibody to EAdV-1. None of the 64 serum samples tested were positive for antibodies to EAV, reovirus 3 or PIV3. Evidence of infection with all viruses tested was detected in both healthy horses and in horses showing clinical signs of respiratory disease. Recent EHV-2 infection was associated with the development of signs of respiratory disease among yearlings [relative risk (RR)=2.67, 95% CI=1.59-4.47, p=0.017].

CONCLUSIONS: Of the equine respiratory viruses detected in horses in New Zealand during this study, EHV-2 was most likely to be associated with respiratory disease. However, factors other than viral infection are probably important in the development of clinical signs of disease.     

Successful use of topical mitomycin C for the treatment of a putative neoplastic vascular mass on the nictitating membrane of a dog

A nine-year-old female desexed Great Dane presented with a painful, proliferative, soft red putative neoplastic vascular mass on the nictitating membrane. Three 7-day cycles of the topical cytotoxic drug mitomycin C 0.04%, applied four times daily to the lesion using a low-dose alternate-week pulse therapy, brought about rapid remission of the lesion. The lesion was still in remission at time of euthanasia some 13 months later.     

Keratometry, biometry and prediction of intraocular lens power in the equine eye

OBJECTIVE: To determine ocular dimensions (A- and B-scan ultrasound) and corneal curvature (radius of corneal diameter determined in B-scan ultrasound) in the equine eye and to calculate the appropriate dioptric power for a posterior chamber intraocular lens (IOL) necessary to achieve emmetropia in the eyes of horses undergoing lens extraction. ANIMALS: Fourteen clinically normal adult horses of various breeds. Additionally, for comparison, one American Miniature colt foal, and one 2.5-year-old Shire gelding were examined. PROCEDURE: B-scan ultrasound was performed on one eye from each horse. One eye from both the Shire and the American Miniature were examined for comparison. Data from ultrasound (globe measurements and corneal curvature), and the estimated postoperative IOL positions were entered into theoretical IOL formulas (Binkhorst and Retzlaff theoretical formulas) in order to calculate the predicted IOL strength required to achieve emmetropia after lens extraction in horses. Results: Mean axial length of globes was 39.23 mm +/- 1.26 mm, mean preoperative anterior chamber depth (ACD) was 5.63 +/- 0.86 mm, and mean lens thickness was 11.75 +/- 0.80 mm. Predicted postoperative ACD (PACD) was calculated as the ACD plus 50% of the lens thickness. Additionally, PACD 2 mm anterior and 2 mm posterior to the center of the lens were calculated in order to evaluate the effect of IOL position on its required refractive power. Required IOL strength calculated, using the three values for the predicted postoperative ACD, was 29.91 D +/- 2.50, 29 D +/- 2.52 (center of lens); 27.13 D +/- 2.27, 26.33 D +/- 2.20 (2 mm anterior to center of lens); and 33.18 D +/- 2.78, 32.24 D +/- 2.68 (2 mm posterior to center of lens) with the Binkhorst and Retzlaff theoretical formulas, respectively. CONCLUSIONS: An IOL of substantially lower diopter strength than that needed in either dogs or cats is required to achieve emmetropia after lens extraction in adult horses. IOL strength of approximately 30 D, depending on where the IOL ultimately comes to rest, will probably be required.     

Long-term effect on the equine eye of an intravitreal device used for sustained release of cyclosporine A

OBJECTIVE: To determine the long-term toxicity of an intravitreal device releasing continuous cyclosporinee A (CsA) in normal eyes of horses by evaluating clinical signs, electroretinography, and histopathology. Animals Studied Ten adult horses with normal ophthalmic examinations were used in this study Procedure(s) Four horses had one eye implanted with a CsA device, and six horses had the right eye implanted with a CsA-containing device (10 eyes with CsA in total) and the left eye (six eyes in total) with the device without drug (control). The implants were placed in the vitreous of the eyes through a sclerotomy 1 cm posterior to the limbus in the dorso-temporal quadrant of the eye. Scotopic electroretinograms were performed prior to implantation and at 1 week, and at 1, 3, 6, 9, and 12 months postimplantation. Two of the unilaterally implanted horses were euthanized at 1 weeks postimplantation, and two at 6 weeks postimplantation. Two of the bilaterally implanted horses were euthanized at 6 months, two at 9 months, and two at 12 months postimplantation. At euthanasia, the eyes were removed, aqueous and vitreous humor aspirated, and tissues fixed in 10% buffered formalin and processed for histopathology. CsA concentrations were measured by high pressure liquid chromatography in the aqueous and vitreous humors, and in peripheral blood. RESULTS: The devices were tolerated well in 14 of 16 eyes. There was minimal postoperative inflammation in most eyes, with a normal appearance within 7 days. In two eyes implanted with the CsA device, severe inflammation resulted in phthisis bulbi by 28 days. One of these eyes exhibited suspected bacterial endophthalmitis, and one had a sterile endophthalmitis and cataract presumably from trauma to the lens during implantation. In the other 14 eyes, no change was observed in the scotopic electroretinograms (ERG) from preoperative results, and no significant differences between the right (CsA) and left (control device) eyes were observed. CsA levels in the aqueous and vitreous humor, and peripheral blood were below the detection limit of the HPLC. Histologic findings revealed only a mild lymphoplasmacytic cellular infiltrate in the ciliary body and pars plana near the implantation site. CONCLUSIONS: The CsA devices were well tolerated with no long-term complications from the implants themselves. However, complications may occur from inadvertent implantation trauma or contamination during surgery. The long-term safety of the device may make it useful for delivery of CsA in the control of equine recurrent uveitis.     

Histologic effect of semiconductor diode laser transscleral cyclophotocoagulation on the normal equine eye

Abstract Objective To determine the acute histologic effects of semiconductor diode laser transscleral cyclophotocoagulation (TSCP) on the normal equine eye. Animal studied Part 1: eight eyes of four horses. Part 2: 10 eyes of five horses. Materials and methods Part 1: TSCP was performed on four eyes at 4 mm and four eyes at 6 mm posterior to the limbus with 15 sites treated in four quadrants at 1800 mW for 1500 ms. The globes were sectioned transversely or sagitally to examine all quadrants and histologic sections were taken every 1 mm for the entire globe. Part 2: Based on the results from Part 1, TSCP was performed at 20 sites 4 mm posterior to the dorsotemporal limbus with a constant energy varying from 0.75 to 4 J/site. Histologic sections were taken every 1 mm for a total of 10 sections per eye and 20 sections per energy level group. Results Part 1: At 4 mm posterior to the limbus, coagulation of the nonpigmented epithelium (NPE) of the pars plicata was observed in the temporal (14%) and dorsal quadrants (12%). Retinal detachment was observed in the nasal quadrant (12%). Hemorrhage was common in the nasal (19%) and temporal (12%) quadrants. At 6 mm posterior to the limbus, coagulation of the NPE of the pars plicata was observed in the dorsal (14%), ventral (16%), nasal (2%), and temporal (2%) quadrants. Retinal detachment was observed in the dorsal (8%), ventral (18%), nasal (20%) and temporal (2%) quadrants. Part 2: Settings of 0.75 J/site were ineffective; 1.5, 2.25 and 3 J/site damaged the pars plicata without disruption of anatomy; and 4 J/site caused disruption of normal architecture. Conclusions The most appropriate site for equine TSCP appears to be 4 mm posterior to the dorso‐ and ventrotemporal limbus avoiding the 3 and 9 o’clock positions and using an initial energy setting of 2.25 J/site. This results in effective damage to the pars plicata while minimizing surgical complications such as retinal detachment and hemorrhage.     

Efficacy of a portable oxygen concentrator with pulsed delivery for treatment of hypoxemia during equine field anesthesia

ObjectiveHypoxemia is common during equine field anesthesia. Our hypothesis was that oxygen therapy from a portable oxygen concentrator would increase PaO₂ during field anesthesia compared with the breathing of ambient air.Study designProspective clinical study.AnimalsFifteen yearling (250 – 400 kg) horses during field castration.MethodsHorses were maintained in dorsal recumbency during anesthesia with an intravenous infusion of 2000 mg ketamine and 500 mg xylazine in 1 L of 5% guaifenesin. Arterial samples for blood gas analysis were collected immediately post-induction (PI), and at 15 and 30 minutes PI. The control group (n = 6) breathed ambient air. The treatment group (n = 9) were administered pulsed-flow oxygen (192 mL per bolus) by nasal insufflation during inspiration for 15 minutes PI, then breathed ambient air. The study was performed at 1300 m above sea level. One-way and two-way repeated-measures anova with post-hoc Bonferroni tests were used for within and between-group comparisons, respectively. Significance was set at p ≤ 0.05.ResultsMean ± SD PaO₂ in controls at 0, 15 and 30 minutes PI were 46 ± 7 mmHg (6.1 ± 0.9 kPa), 42 ± 9 mmHg (5.6 ± 1.1 kPa), and 48 ± 7 mmHg (6.4 ± 0.1 kPa), respectively (p = 0.4). In treatment animals, oxygen administration significantly increased PaO₂ at 15 minutes PI to 60 ± 13 mmHg (8.0 ± 1.7 kPa), compared with baseline values of 46 ± 8 mmHg (6.1 ± 1 kPa) (p = 0.007), and 30 minute PI values of 48 ± 7 mmHg (6.5 ± 0.9 kPa) (p = 0.003).ConclusionsThese data show that a pulsed-flow delivery of oxygen can increase PaO₂ in dorsally recumbent horses during field anesthesia with ketamine-xylazine-guaifenesin.Clinical relevanceThe portable oxygen concentrator may help combat hypoxemia during field anesthesia in horses.     

Establishing a reproducible method for the culture of primary equine corneal cells

Objective  To establish a reproducible method for the culture of primary equine corneal epithelial cells, keratocytes, and endothelial cells and to describe each cell's morphologic characteristics, immunocytochemical staining properties and conditions required for cryopreservation.
Procedures  Corneas from eight horses recently euthanized for reasons unrelated to this study were collected aseptically and enzymatically separated into three individual layers for cell isolation. The cells were plated, grown in culture, and continued for several passages. Each cell type was characterized by morphology and immunocytochemical staining.
Results  All three equine corneal cell types were successfully grown in culture. Cultured corneal endothelial cells were large, hexagonal cells with a moderate growth rate. Keratocytes were small, spindloid cells that grew rapidly. Epithelial cells had heterogenous morphology and grew slowly. The endothelial cells and keratocytes stained positive for vimentin and were morphologically distinguishable from one another. The epithelial cells stained positive for cytokeratin. Keratocytes and endothelial cells were able to be cryopreserved and recovered. The cryopreserved cells maintained their morphological and immunocytochemical features after cryopreservation and recovery.
Discussion  This work establishes reproducible methods for isolation and culture of equine corneal keratocytes and endothelial cells. Cell morphology and cytoskeletal element expression for equine corneal epithelial cells, keratocytes, and endothelial cells are also described. This has not previously been reported for equine corneal cells. This report also demonstrates the ability to preserve equine keratocytes and endothelial cells for extended periods of time and utilize them long after the primary-cell collection, a feature that has not been reported for veterinary corneal cell culture.