Retrobulbar vs peribulbar regional anesthesia techniques using bupivacaine in dogs.

OBJECTIVE: To compare the effectiveness of retrobulbar anesthesia (RBA) and peribulbar anesthesia (PBA) in dogs. ANIMAL STUDIED: Six adult mixed-breed dogs (18-24 kg). PROCEDURES: In a randomized, masked, crossover trial with a 10-day washout period, each dog was sedated with intravenously administered dexmedetomidine and administered 0.5% bupivacaine:iopamidol (4:1) as RBA (2 mL via a ventrolateral site) or PBA (5 mL divided equally between ventrolateral and dorsomedial sites). The contralateral eye acted as control. Injectate distribution was evaluated by computed tomography. Following intramuscularly administered atipamezole, corneal and periocular skin sensation, intraocular pressure (IOP), and ocular reflexes, and appearance were evaluated for 24 hours. Comparisons were performed with mixed-effects linear regression (IOP) or the exact Wilcoxon signed rank test (scores). Significance was set at P ≤ .05. RESULTS: Injectate distribution was intraconal in 2/6 RBA- and 4/6 PBA-injected eyes. Eyes undergoing PBA had significantly reduced lateral, ventral, and dorsal periocular skin sensation for 2-3 hours, and significantly reduced corneal sensitivity for 4 hours, relative to control eyes. Chemosis and exophthalmos occurred in 33%-40% of eyes undergoing RBA and 83%-100% eyes undergoing PBA but resolved within 14 hours. Anterior uveitis developed in 2/6 and 1/6 eyes of RBA and PBA, respectively, of them corneal ulcer developed in one eye of each treatment. Both resolved 1-3 days following medical treatment. CONCLUSIONS: Peribulbar injection produced notable anesthesia more reliably than did retrobulbar injection. Both techniques may produce adverse effects, although the uveitis/ulcer could have resulted from the contrast agent used.

The impact of vaccination route on Mycoplasma gallisepticum vaccine efficacy.

Mycoplasma gallisepticum infection can lead to major financial losses for poultry producers. Control of M. gallisepticum infection in the layer industry is generally obtained through vaccination due to the nature of the multi-aged flocks in the facilities. Live vaccines can provide significant protection from the pathogenic effects of M. gallisepticum infection. However, differing management practices, including vaccination procedures, can lead to significant variations in the efficacy of the same vaccine. The site of vaccine deposition has been shown to be one important factor significantly influencing the vaccination outcome. Previous research has shown that vaccine applied to the eyes or sprayed on the head is significantly more effective than when sprayed on the body. Vaccine application to the eyes, through the nares (nasal), and 2 routes through the oral cavity were studied to further characterize the most efficient route for delivery. Results of this work demonstrate that eye drop vaccination is significantly more effective than nasal vaccination, and vaccine delivered through the oral cavity has a negligible contribution to overall vaccination outcome.

Bimatoprost sustained-release intracameral implant reduces episcleral venous pressure in dogs.

OBJECTIVE: To determine the effect of a bimatoprost sustained-release intracameral implant (Bimatoprost SR) on episcleral venous pressure (EVP) in normal dogs. METHODS: Normotensive beagle dogs were randomized to receive Bimatoprost SR 30 µg (n = 7) or sham injection (needle insertion only, n = 7) in one eye on day 1. EVP was measured with an episcleral venomanometer through day 65. Episcleral aqueous outflow vessels were identified using fluorescence imaging following intracameral injection of indocyanine green in one additional animal. A separate cohort of dogs that had been trained for conscious intraocular pressure (IOP) measurements received Bimatoprost SR 30 µg (n = 8) in one eye; IOP was evaluated through day 66. RESULTS: Baseline mean EVP was 10.0 mmHg in the Bimatoprost SR group and 10.4 mmHg in the sham group. Eyes treated with Bimatoprost SR exhibited a transient increase in mean EVP that peaked at day 8, followed by a decrease to levels below baseline. From day 29 to day 65, the change in mean EVP from baseline ranged from -2.4 to -3.9 mmHg (P < 0.05 vs. sham). Baseline mean IOP in eyes treated with Bimatoprost SR was 14.9 mmHg, and a steady IOP reduction was maintained through day 66. Bimatoprost SR-treated eyes exhibited a selective, sustained dilation of aqueous outflow vessels that was not observed in sham-treated eyes. CONCLUSIONS: In normal dogs, Bimatoprost SR was associated with a transient increase in EVP followed by a sustained decrease. Changes in EVP were accompanied by a sustained dilation of aqueous outflow vessels.

Chitosan-adjuvanted Mycoplasma gallisepticum bacterin via intraocular administration enhances Mycoplasma gallisepticum protection in commercial layers.

Mycoplasma gallisepticum (MG) causes respiratory signs and economic losses in the poultry industry. MG vaccination is one of the effective prevention and control measures that have been used around the world. Our previous study demonstrated that chitosan-adjuvanted MG bacterin could effectively reduce pathological lesions induced by MG and that chitosan could be used as an adjuvant in MG bacterin. The present study determining the efficacy of MG bacterins against the Thai MG strain was based on vaccine programs. Seven groups (25 layers/group) were received MG bacterins containing 0.5% chitosan or a commercial bacterin via intramuscular (IM) or intraocular (IO) route at 6 and 10 wk of age. Sham-negative and sham-positive controls were groups 1 and 2, respectively. Group 3: IM route of chitosan bacterin followed by IM route of chitosan bacterin; group 4: commercial bacterin via IM route followed by chitosan bacterin via IO route; group 5: commercial bacterin via IM route followed by commercial bacterin via IM route; group 6: chitosan bacterin via IM followed by chitosan bacterin via IO route; and group 7: chitosan bacterin via IO route followed by chitosan bacterin via IO route were determined. At 16 wk of age, all groups, excluding group 1, were challenged intratracheally with 0.1 mL containing Thai MG strain 107 colony-forming unit. At 17, 18, and 20 wk of age, 5 birds in each group were bled for serological testing and swabbed at the choanal cleft for the quantitative real-time PCR assay, the euthanized and necropsied. The results showed that birds vaccinated with a commercial intramuscular bacterin followed by an intraocularly chitosan adjuvant bacterin showed the best protection against the MG challenge. The study indicated that chitosan could be the effective mucosal adjuvant and increased the effectiveness of MG bacterin.

A dose-escalation ex vivo study on the effects of intracameral benzalkonium chloride in rabbits.

BACKGROUND: Rabbits are currently not a good model for studying diseases of the corneal endothelium because their corneal endothelial cells (CECs) maintain a high proliferative capacity throughout almost all their life. Addressing this particular feature might allow the use of this species for such a purpose. The aim of this study was to evaluate the corneal endothelial injury after intracameral benzalkonium chloride (BAC) injection into rabbit eyes ex vivo, and to establish the most suitable starting dose for an in vivo study aimed at developing an animal model of corneal endothelial disease. RESULTS: Forty rabbit eyes obtained postmortem by transconjunctival enucleation were divided into 8 groups according to the injected compound: Control (no injection), BSS, and increasing BAC concentrations (0.005%, 0.01%, 0.025%, 0.05%, 0.1% and 0.2%). At 0, 6, 24 and 48 h, ophthalmologic examination of the anterior segment, pachymetry and specular microscopy were performed, and corneas were finally vital-stained and observed under the light microscope to assess the CECs morphology and mortality rate. When compared to BSS, CECs density started to decrease significantly at 0.025% BAC concentration, while mean cell area, corneal edema and corneal thickness began to increase significantly at 0.05%, 0.005% and 0.1% BAC concentrations, respectively. Concentrations of 0.05% BAC and above caused significant increases in CECs pleomorphism (decreased hexagonality) and mortality, compared to control and BSS. CONCLUSIONS: Ex vivo intracameral BAC injection induces corneal endothelial toxicity in rabbits. However, confirmatory in vivo studies are required to develop the desired model, with 0.05% BAC being a suggested starting point.

Sub-Tenon's injection in equine cadaver eyes: MRI visualization of anesthetic fluid distribution and comparison of two different volumes.

OBJECTIVE: To compare the localization and distribution of two different anesthetic fluid volumes around equine cadaver eyes to determine an appropriate volume for a single sub-Tenon's injection in horses. PROCEDURE: A single sub-Tenon's injection of 2% lidocaine was performed in 10 equine cadaver heads (20 eyes) using two different volumes (7 mL on one side and 10 mL on the opposite side). The posterior circular distribution of the anesthetic was quantified in sagittal, dorsal, and transverse MRI (T2W-TSE) sequences and evaluated independently by three board-certified radiologists. The distribution of the two fluid volumes was compared via a paired Student's t-test. The interobserver reliability was evaluated via a Kruskal-Wallis test. RESULTS: Extension of the injection fluid was observed along the dorsal and temporal quadrants of the globe within the subconjunctival space, the anterior and posterior sub-Tenon's space, and into the muscle sheaths along the extraocular muscles. Accumulation of anesthetic fluid directly surrounding the optic nerve was detected in three of 20 cadaver eyes. Circular distribution of the 7 and 10 mL anesthetic volumes was not significantly different (P = 0.849). More retrograde leakage of the anesthetic was observed using the 10 mL volume. Evaluation of interobserver reliability revealed no significant differences between observers (P = 0.21-0.92). CONCLUSIONS: Sub-Tenon's anesthesia can have potential as an alternative to retrobulbar anesthesia for ophthalmic surgeries in equines. A 7- to 10-mL injection volume should be appropriate based on the results of this study. The distribution of the anesthetic solution in live tissues, the clinical effects, and the potential for complications will have to be evaluated in vivo.

The effects of lidocaine or a lidocaine-bupivacaine mixture administered into the infraorbital canal in dogs.

OBJECTIVE To determine the onset, duration, and extent of regional nerve blocks performed by administration of lidocaine or lidocaine-bupivacaine into the infraorbital canal in dogs. ANIMALS 6 healthy hound-type dogs. PROCEDURES Under general anesthesia, stimulating needles were inserted into the gingiva dorsolateral to both maxillary canine (MC) teeth and the maxillary fourth premolar (MPM4) and second molar (MM2) teeth on the treatment side. A reflex-evoked muscle potential (REMP) was recorded from the digastricus muscle after noxious electrical stimulation at each site. After baseline measurements, 1 mL of 2% lidocaine solution or a 2% lidocaine-0.5% bupivacaine mixture (0.5 mL each) was injected into the infraorbital canal (at approx two-thirds of the canal length measured rostrocaudally). The REMPs were recorded for up to 7 hours. The REMP data for the contralateral (untreated control) canine tooth were used to normalize results for all stimulation sites. RESULTS With both treatments, nerve block for MC teeth on the treated side was achieved by 5 (n = 5 dogs) or 10 (1) minutes after injection, but nerve block for ipsilateral MPM4 and MM2 teeth was successful for only 3 dogs and 1 dog, respectively. Mean duration of nerve blocks for MC teeth was 120 and 277 minutes following injection of lidocaine and lidocaine-bupivacaine, respectively. CONCLUSIONS AND CLINICAL RELEVANCE Local anesthesia, as performed in this study, successfully blocked innervation of MC teeth, but results for MPM4 and MM2 teeth were inconsistent. This specific technique should not be used during tooth extractions caudal to the MC teeth.

Comparison of two bupivacaine delivery methods to control postoperative pain after enucleation in dogs.

OBJECTIVE: To compare the efficacy of a preoperative retrobulbar injection of bupivacaine to an intraoperative splash block of bupivacaine in controlling postoperative pain following enucleation in dogs. ANIMALS STUDIED: Prospective, randomized, double-masked clinical study of 31 client owned dogs with end-stage ophthalmic disease requiring enucleation. PROCEDURES: Dogs admitted for unilateral enucleation were randomly assigned to receive bupivacaine 0.5% (1 mL/kg) into the retrobulbar space either via an inferior-temporal palpebral (ITP) injection preoperatively or an intraoperative splash block. Pain was assessed prior to pre-anesthetic sedation and at 0, 0.25, 0.5, 1, 2, 4 6, 8, and 24 hours (H) after extubation by masked observers using a previously described subjective pain scoring system. Rescue analgesia was initiated if overall pain score was >9 or if the score in any category at any time point was >3. RESULTS: There were no adverse reactions. One of 15 dogs that received bupivacaine via a preoperative retrobulbar ITP injection required rescue analgesia. There was no significant difference between groups with regard to the need for rescue analgesia or pain scores at any time point or overall. CONCLUSIONS AND CLINICAL RELEVANCE: Pain control using an intraoperative orbital splash administration of bupivacaine is not significantly different to a preoperative retrobulbar injection of bupivacaine.

Ultrasound-assisted periconal ocular blockade in rabbits.

OBJECTIVE: This study aimed to evaluate the benefit and specifically the feasibility of using ultrasound in ophthalmologic periconal block, and the occurrence of complications. STUDY DESIGN: Prospective experimental study. ANIMALS: Ten healthy New Zealand White rabbits (6-8 months of age), weighing 2.0-3.5 kg. METHODS: Rabbits were anesthetized by intramuscular injection of acepromazine (1 mg kg(-1)), ketamine (30 mg kg(-1)) and xylazine (3 mg kg(-1)). Ultrasound-assisted periconal block with lidocaine was performed on 18 eyes. Intraocular pressure was measured by applanation tonometry whereas corneal sensitivity was assessed using an esthesiometer, before and after each periconal anesthesia. RESULTS: In all 18 eyes, it was possible to adequately visualize the needle shaft within the periconal space, as well as muscular cone, optic nerve and local anesthetic solution spread. Lidocaine 2% without epinephrine (0.79 ± 0.19 mL) was injected into the periconal space. There was no statistical difference between the intraocular pressure (mean ± SD) measured before (10.9 ± 2.9 mmHg) and after (11.9 ± 3.8 mmHg) the periconal anesthesia (p = 0.38). The effectiveness of the ultrasound-assisted technique was shown according to the values for corneal sensitivity, assessed before and after periconal anesthesia (p < 0.0001). Complications were not observed in this study. CONCLUSIONS: Eye ultrasonography allowed visualization of all anatomic structures necessary to perform a periconal block, as well as the needle insertion and anesthetic spread in real time. Further studies are required to prove the real potential of ultrasound for reducing the incidence of complications associated with ophthalmic blocks, especially when anatomic disorders of the eye could potentially increase the risk. CLINICAL RELEVANCE: Ultrasonography is a painless, noninvasive tool that may improve safety of ophthalmic regional blocks, potentially by reducing the prevalence of globe perforation or penetration of the optic nerve associated with the needle-based techniques.

Treatment of six cases of equine corneal stromal abscessation with intracorneal injection of 5% voriconazole solution.

OBJECTIVE: To describe a reproducible technique for intrastromal injection in the standing horse for treatment of corneal stromal abscessation. ANIMAL STUDIED: A retrospective clinical study addressing the history, treatment, and outcome of six equids (six eyes) that received intrastromal voriconazole injection. PROCEDURE: Equids having a deep stromal abscess suspected to be of fungal origin were administered intrastromal injection of 5% voriconazole solution under standing sedation in an effort to bring about enhanced resolution of clinical disease. RESULTS: Intracorneal administration of 5% voriconazole solution resulted in resolution of clinical disease, specifically stromal abscessation and secondary uveitis. All animals displayed decreased blepharospasm and no significant complications in the immediate postinjection period. Convalescent periods were subjectively shorter than anticipated with traditional medical therapy. All animals developed mild to moderate stromal fibrosis relative to the initial severity and depth of abscessation. CONCLUSIONS: Intrastromal injection of 5% voriconazole solution may provide a safe and effective treatment option for corneal stromal abscessation in horses. In all reported cases, administration of injection early in the treatment period appeared to contribute to rapid resolution of clinical disease without significant complications. The authors present this technique as an alternative to traditional surgical intervention, being more economical, having shorter treatment duration, and potentially resulting in less scar formation.

Comparison of systemic atracurium, retrobulbar lidocaine, and sub-Tenon's lidocaine injections in akinesia and mydriasis in dogs.

OBJECTIVE: To compare the effect of sub-Tenon's lidocaine injections (ST) on akinesia and mydriasis to those of systemic atracurium (AT) and retrobulbar lidocaine injections in dogs. ANIMAL STUDIED: Ten healthy beagle dogs without apparent ocular disease. PROCEDURES: Three treatments were performed on 10 beagle dogs with a minimum 7-day washout period: intravenous injection of AT (0.2 mg/kg, AT group); retrobulbar (RB) injection of 2% lidocaine (2.0 mL, RB group) in one eye; and sub-Tenon's injection of 2% lidocaine (2.0 mL, ST group) in the opposite eye. When the akinesia was not obtained within 10 min, an additional 1 mL of lidocaine was administered in the RB and the ST groups. RESULTS: Onset of akinesia in the AT (1.5 ± 0.9 min) and the ST (3.8 ± 5.8 min) groups was significantly shorter than that in the RB group (9.0 ± 6.5 min). Duration of akinesia in the ST group (116.2 ± 32.8 min) was longer compared to the AT (60.6 ± 23.6 min) and the RB (89.0 ± 52.8 min) groups, even though there was only a significant difference between the AT and the ST groups. Mydriasis was achieved in five eyes in the RB group and nine eyes in the ST group. There was no significant difference in onset (3.6 ± 3.1 and 2.9 ± 2.3 min, respectively) or duration (91.4 ± 31.9 and 102.1 ± 35.8 min, respectively) of mydriasis between the groups. CONCLUSIONS: Sub-Tenon's lidocaine injections provide excellent akinesia and mydriasis compared to systemic AT and retrobulbar lidocaine injections. Therefore, sub-Tenon's anesthesia could be an alternative to the systemic administration of neuromuscular blockers and retrobulbar anesthesia for ophthalmic surgery in dogs.

A sub-Tenon's capsule injection of lidocaine induces extraocular muscle akinesia and mydriasis in dogs.

The effect of local anaesthetic on the extraocular muscles was investigated in dogs by injecting lidocaine into the space between Tenon's capsule and the sclera. A cross-over design was used with both eyes from five Beagle dogs randomly injected, under general anaesthesia, with 1 mL of 2% lidocaine (1 mL-lidocaine group), 2 mL of 2% lidocaine (2 mL-lidocaine group) or 2 mL of normal saline (control group). Each eye was assigned to all treatments with a minimum 14 day interval between injections. Changes in eye position, pupil diameter, and intraocular pressure (IOP) were evaluated during the procedure. All eyes in the 2 mL-lidocaine group exhibited akinesia and mydriasis (pupil diameter >10mm) with an onset time of 6.5 ± 4.9 and 4.2 ± 4.3 min, respectively. In the 1 mL-lidocaine group, akinesia was induced in nine eyes and mydriasis occurred in seven eyes at 10.7 ± 5.8 and 5.4 ± 2.4 min after the injection, respectively. No changes in eye position or pupil diameter were observed in the control group. Akinesia was maintained for 44.3 ± 26.7 min in the 1 mL-lidocaine group and for 88.5 ± 17.2 min in the 2 mL-lidocaine group. Duration of mydriasis was 51.7 ± 28.9 min in the 1 mL-lidocaine group and 82.9 ± 15.6 min in the 2 mL-lidocaine group. Marked chemosis and sub-conjunctival haemorrhage occurred in 16/30 and 15/30 eyes, respectively. No significant change in IOP was observed between the mean pre- and post-injection values in all groups. These results suggest that a sub-Tenon's injection of 2 mL of 2% lidocaine provided effective extraocular muscle akinesia and mydriasis in dogs.

Refractive state following retinal reattachment and silicone oil tamponade in dogs.

OBJECTIVE: To evaluate the refractive error induced by intraocular administration of silicone oil (SiO) in dogs. ANIMALS: 47 client-owned dogs evaluated for blindness secondary to retinal detachment. PROCEDURES: -3-port pars plana vitrectomy with perfluoro-octane and SiO exchange (1,000- or 5,000-centistoke SiO) was performed in 1 or both eyes for all dogs (n = 63 eyes), depending on which eye or eyes were affected. Dogs were normotensive, had complete oil filling of the eyes, and were examined in a standing position for retinoscopic examination of both eyes (including healthy eyes). RESULTS: The mean refractive error for SiO-filled phakic and pseudophakic eyes was 2.67 and 3.24 D, respectively. The mean refractive error for SiO-filled aphakic eyes was 6.50 D. Dogs in which 5,000-centistoke SiO was used had consistently greater positive refractive errors (mean, 3.45 D), compared with dogs in which 1,000-centistoke SiO was used (mean, 2.10 D); however, the difference was nonsignificant. There was no significant linear relationship between refractive error and the number of days between surgery and retinoscopy. CONCLUSIONS AND CLINICAL RELEVANCE: Hyperopia was observed in all dogs that underwent SiO tamponade, regardless of lens status (phakic, pseudophakic, or aphakic). Aphakic eyes underwent a myopic shift when filled with SiO. Pseudophakic eyes appeared to be more hyperopic than phakic eyes when filled with SiO; however, additional investigation is needed to confirm the study findings.

Retro-orbital injection in adult zebrafish.

Drug treatment of whole animals is an essential tool in any model system for pharmacological and chemical genetic studies. Intravenous (IV) injection is often the most effective and noninvasive form of delivery of an agent of interest. In the zebrafish (Danio rerio), IV injection of drugs has long been a challenge because of the small vessel diameter. This has also proved a significant hurdle for the injection of cells during hematopoeitic stem cell transplantation. Historically, injections into the bloodstream were done directly through the heart. However, this intra-cardiac procedure has a very high mortality rate as the heart is often punctured during injection leaving the fish prone to infection, massive blood loss or fatal organ damage. Drawing on our experience with the mouse, we have developed a new injection procedure in the zebrafish in which the injection site is behind the eye and into the retro-orbital venous sinus. This retro-orbital (RO) injection technique has been successfully employed in both the injection of drugs in the adult fish as well as transplantation of whole kidney marrow cells. RO injection has a much lower mortality rate than traditional intra-cardiac injection. Fish that are injected retro-orbitally tend to bleed less following injection and are at a much lower risk of injury to a major organ like the heart. Further, when performed properly, injected cells and/or drugs quickly enter the bloodstream allowing compounds to exert their effect on the whole fish and kidney cells to easily home to their niche. Thus, this new injection technique minimizes mortality while allowing efficient delivery of material into the bloodstream of adult fish. Here we exemplify this technique by retro-orbital injection of Tg(globin:GFP) cells into adult casper fish as well as injection of a red fluorescent dye (dextran, Texas Red ) into adult casper fish. We then visualize successful injections by whole animal fluorescence microscopy.