Mydriasis in eastern box turtles (Terrapene carolina carolina) following topical administration of proparacaine, 10% phenylephrine, and rocuronium bromide

OBJECTIVE

To determine the mydriatic effect of topical 10% phenylephrine with 10 mg/mL rocuronium bromide and compare this protocol with and without pretreatment with proparacaine.

ANIMALS STUDIED

Ten client-owned pet adult eastern box turtles (Terrapene carolina carolina).

PROCEDURES

All turtles were sedated with 8 mg/kg alfaxalone intramuscularly. One group of four turtles received four 20 μL drops of 10% phenylephrine and four 20 μL drops of rocuronium bromide in the right eye. Another group of four turtles received one standard drop of proparacaine followed by four 20 μL drops of 10% phenylephrine and four 20 μL drops of rocuronium bromide in the right eye. Two control group turtles received four 20 μL drops of saline in the right eye. The left eye was untreated in all turtles. Drops of the same type were separated by 2 min while drops of different types were separated by 5 min. Pupil size was recorded at 0, 15, 30, 60, 90, 120, 180, 240, and 360 min after administration of the final drop.

RESULTS

Treatment with 10% phenylephrine and rocuronium bromide resulted in pupil diameter changes from baseline that were statistically significant from zero at 60, 90, and 120 min in the non-proparacaine group and 90 min in the proparacaine group. The time to peak effect was 90 min in the proparacaine group and 75 min in the non-proparacaine group. Saline-treated pupils in the control group decreased in diameter over the study period. Overall, the treated eyes of the proparacaine group and non-proparacaine group were not different from each other, but both dilated more than the control group.

CONCLUSIONS

Rocuronium bromide and 10% phenylephrine can produce effective and safe mydriasis in eastern box turtles, but there was wide interindividual variation in effectiveness. Proparacaine did not improve the mydriatic effect.

Ophthalmic findings and parameters in Western tiger salamanders (Ambystoma mavortium) from northern Colorado

OBJECTIVE

The aim of this study was to document ophthalmic examination findings and provide reference values for ocular examinations and diagnostics in clinically normal Western tiger salamanders (Ambystoma mavortium) and to evaluate the mydriatic effect of a topical rocuronium bromide and identify any adverse effects.

ANIMALS STUDIED

Sixteen Western tiger salamanders.

PROCEDURE

A complete ophthalmic examination, including intraocular pressure via rebound tonometry [iCare® TonoVet (dog-setting) or iCare® TonoVet Plus (dog-setting)], and fluorescein and Rose Bengal stains, was performed. Ocular surface flora culture swabs were collected for microbiology in four salamanders. Rocuronium bromide (50 μL; 0.01 mg) was administered into each eye in three salamanders. Pupil size and constriction ability were evaluated up to 60 min following administration of rocuronium bromide. Distant visual examination and Doppler heart rate were used to monitor for potential adverse effects of rocuronium bromide.

RESULTS

Observed ocular abnormalities included lipid keratopathy/keratitis (19%; 3/16), parasitic ophthalmitis (19%; 3/16), and cataracts (6.3%; 1/16). A significant difference was found between tonometry with iCare® TonoVet (11.5 ± 2.7 mmHg) versus TonoVet Plus (15.4 ± 3.7 mmHg) (p = .025). Fluorescein and Rose Bengal stains were negative in all salamanders. Ocular surface microbiology revealed a high incidence of contamination from environmental flora, with the most common isolate being unidentified as Gram-negative nonfermenters (75%; 3/4). No significant change in pupil size or constriction ability was observed with rocuronium bromide.

CONCLUSION

This is the first study to document ocular examination findings and diagnostics in captive and wild urodeles and may serve as a reference for clinical assessment and future studies of the Western tiger salamander.

Application of topical rocuronium bromide dosing by ocular size in four species of wild birds

BACKGROUND

Rocuronium bromide has been evaluated as a mydriatic agent in birds, but the species applied were limited and the dose and effect were variable.

OBJECTIVE

This study aims to evaluate the efficacy of topical rocuronium bromide as mydriatics in 4 species according to horizontal palpebral fissure length: Feral pigeon (Columba livia), Common kestrel (Falco tinnunculus), Northern boobook (Ninox japonica), and Eurasian eagle owl (Bubo bubo).

METHODS

A total of 32 birds (8 for each species) were included as pre-releasing examination. Rocuronium bromide was instilled in one randomly selected eye of each bird based on palpebral fissure length criteria (0.5 mg/50 µL for pigeons, 1 mg/100 µL for kestrels and boobook owls, and 2 mg/200 µL for eagle owls). The contralateral eye was used as control and treated with normal saline. After instillation of the drug, pupil diameter, pupillary light reflex, intraocular pressure, heart rate, and respiratory rate were evaluated at 10 min intervals up to 180 min and at 30 min intervals up to 360 min.

RESULTS

Statistically significant mydriasis was obtained in all birds (p < 0.001). However, in boobook and eagle owls, marked mydriasis persisted until 360 min. Side effects including corneal erosion and lower eyelid paralysis were common, which was observed in 26/32 birds. Blepharospasm was also noted during this study. No systemic adverse signs were observed.

CONCLUSIONS

Rocuronium bromide could be a good mydriatics option for 4 species of birds, however, further studies are needed to find lowest effective dose to reduce drug-related side effects.

Use of a Smartphone-Based Device for Fundus Examination in Birds: A Pilot Study

Simple Summary

Eye examination is crucial for therapeutic plans and rehabilitation of birds in wildlife rehabilitation centers. However, fundus examination using classical direct or indirect ophthalmoscopy techniques can be challenging in those species. The aim of the study was to assess the use of a smartphone-based retinal imaging system in birds. Fundus examination was feasible in most bird species examined in this study. The difficulties of carrying out the examination seem to be related to the form of the globe, the color of the iris, and the quality of pupil dilation. Further investigations are necessary to confirm these findings.

Abstract

Ophthalmic examination is essential in the avian triage process in order to apply prompt therapeutic plans and evaluate rehabilitation potential. Fundoscopy is traditionally performed by direct or indirect ophthalmoscopy. Recent technological developments have enabled the design of a small-sized and affordable retinal imaging system to examine the fundus. We investigate the use of a smartphone-based device to realize fundus examination through a prospective cross-sectional observational study. Seventy-seven eyes of 39 birds of 15 different species were evaluated using the smartphone-based device in a rescue wildlife center. Pupil dilation was achieved prior to examination via rocuronium topical application. Assessment of fundus by the smartphone was classified as satisfactory, moderately satisfactory, and unsatisfactory. Fundus examination was also performed with a 20D, 30D, or 78D lens for comparison. Pupillary dilation was satisfactory, moderately satisfactory, or absent in 17, 32, and 28 eyes, respectively. Fundus examination with the smartphone-based device was satisfactory, moderately satisfactory, or unsatisfactory in 44, 15, and 18 eyes, respectively. The feasibility of the fundus examination was affected by the form of the globe; by the quality of pupil dilation; by the color of the iris (images could not be obtained from species with an orange, bright iris); and by the species, with owls (Strigiformes) being the easiest to observe. Based on these findings, fundus examination was feasible in most bird species examined in this study.

Pupillary behavior during wakefulness, non-REM sleep, and REM sleep in birds is opposite that of mammals

Mammalian pupils respond to light^1,2 and dilate with arousal, attention, cognitive workload, and emotions,³ thus reflecting the state of the brain. Pupil size also varies during sleep, constricting during deep non-REM sleep^4-7 and dilating slightly during REM sleep.^4-6 Anecdotal reports suggest that, unlike mammals, birds constrict their pupils during aroused states, such as courtship and aggression,^8-10 raising the possibility that pupillary behavior also differs between mammals and birds during sleep. Here, we measured pupil size in awake pigeons and used their translucent eyelid to investigate sleep-state-dependent changes in pupil size. Male pigeons constricted their pupils during courtship and other male-female interactions but not while engaging in other waking behaviors. Unlike mouse pupils, the pigeons' pupils were dilated during non-REM sleep, while over 1,000 bursts of constriction and relaxation, which we call rapid iris movements (RIMs), occurred primarily during REM sleep. Consistent with the avian iris being composed largely of striated muscles,^11-15 rather than smooth muscles, as in mammals, pharmacological experiments revealed that RIMs are mediated by nicotinic cholinergic receptors in the iris muscles. Despite receiving input from a parasympathetic nucleus, but consistent with its striated nature, the avian iris sphincter muscle behaves like skeletal muscles controlled by the somatic nervous system, constricting during courtship displays, relaxing during non-REM sleep, and twitching during REM sleep. We speculate that during wakefulness, pupillary constrictions are involved in social communication, whereas RIMs occurring during REM sleep might maintain the efficacy of this motor system and/or reflect the processing of associated memories.

Assessment of the pigeon (Columba livia) retina with spectral domain optical coherence tomography

BACKGROUND

To assess the normal retina of the pigeon eye using spectral domain optical coherence tomography (SD-OCT) and establish a normative reference.

METHODS

Twelve eyes of six ophthalmologically normal pigeons (Columba livia) were included. SD-OCT images were taken with dilated pupils under sedation. Four meridians, including the fovea, optic disc, red field, and yellow field, were obtained in each eye. The layers, including full thickness (FT), ganglion cell complex (GCC), thickness from the retinal pigmented epithelium to the outer nuclear layer (RPE-ONL), and from the retinal pigmented epithelium to the inner nuclear layer (RPE-INL), were manually measured.

RESULTS

The average FT values were significantly different among the four meridians (p < 0.05), with the optic disc meridian being the thickest (294.0 ± 13.9 µm). The average GCC was thickest in the optic disc (105.3 ± 27.1 µm) and thinnest in the fovea meridian (42.8 ± 15.3 µm). The average RPE-INL of the fovea meridian (165.5 ± 18.3 µm) was significantly thicker than that of the other meridians (p < 0.05). The average RPE-ONL of the fovea, optic disc, yellow field, and red field were 91.2 ± 5.2 µm, 87.7 ± 5.3 µm, 87.6 ± 6.5 µm, and 91.4 ± 3.9 µm, respectively. RPE-INL and RPE-ONL thickness of the red field meridian did not change significantly with measurement location (p > 0.05).

CONCLUSIONS

Measured data could be used as normative references for diagnosing pigeon retinopathies and further research on avian fundus structure.

Effect of mydriasis with topical rocuronium bromide on electroretinography in domestic pigeons (Columba livia)

This study aimed to investigate the effect of mydriasis using topical rocuronium bromide on electroretinography (ERG) in domestic pigeons (Columba livia). Scotopic mixed rod and cone, photopic cone, and photopic flicker ERG were performed on nine eyes of nine healthy adult pigeons under sedation. Each pigeon underwent two sets of ERG recordings. First, without the induction of mydriasis (control) and the second time with the induction of mydriasis using topical rocuronium bromide (treatment). The results were compared using either the Student's t-test or Wilcoxon rank-sum test, where a P-value of <0.05 was considered statistically significant. No significant differences were observed in the a- and b-wave implicit times and amplitudes during scotopic ERG between the two groups. The a- and b-wave amplitudes in the photopic cone were significantly higher in the treatment group (63.83 ± 32.33 and 191.75 ± 94.46 µV) compared to the control group (46.15 ± 27.60 and 116.76 ± 70.65 µV; P=0.045 and P=0.032, respectively). The photopic flicker amplitude was also significantly higher in the treatment group (76.23 ± 48.56 µV) than in the control group (42.18 ± 31.18 µV; P=0.044). No statistically significant differences were observed in the photopic cone and flicker implicit times between both groups. In conclusions, mydriasis induced by rocuronium bromide in pigeon resulting in higher amplitudes during the photopic ERG but not scotopic ERG.

Efficacy of topical rocuronium bromide as a mydriatic agent in domestic pigeons (Columba livia)

This study was conducted to investigate the efficacy of rocuronium bromide as mydriatic agent in domestic pigeons (Columba livia). This study was done in two phases. In the first phase, rocuronium bromide (0.20 mg/20 µl) was topically instilled to the right eye (OD) of eight domestic pigeons. Pupil diameter was measured before instillation (T0), and at 5 (T05) and 10 (T10) min after instillation, and every 10 min thereafter until 160 (T160) min. Pupillary light reflex (PLR) was assessed using a scoring system at the same time points. In the second phase, the same dosage was instilled twice in the span of 10 min into both eyes (OU) of four pigeons (eight eyes). Measurements were done accordingly. The iris color in the first phase were: gravel, pearl and bull eye. All irises in the second phase were bull eye. Mydriasis were observed in 6/8 (75%) pigeons in the first phase. Maximal mydriasis was observed at T30 (mean pupil diameter=4.62 ± 0.13 mm). Pupil diameter in the treated eye was significantly different from contralateral eye and from T0 since T05 (P=0.017 and P=0.006, respectively)−T120 (P=0.043 and P=0.044, respectively). PLR was disappeared from T10 (P=0.034) to T90 (P=0.041). In the second phase, mydriasis was only observed in 2/8 eyes. This study suggested that rocuronium bromide was able to produce mydriasis in pigeons other than bull eye iris.

Safety and efficacy of unilateral topical application of rocuronium bromide in healthy scops owls (Otus scops)

OBJECTIVE

To evaluate the safety and efficacy of unilateral topical application of rocuronium bromide in scops owls.

ANIMALS STUDIED

Ten healthy adult scops owls.

PROCEDURES

Birds weighting between 82-111 g were enrolled. Complete physical and ophthalmic examinations were performed. Each animal received a single dose of 0.15 mg of rocuronium bromide (30 µL) in a randomly selected eye. Static pupillometric evaluations were performed before and after drug instillation at 0, 30, 60, 90, and 120 minutes, in a room with fixed light intensity. Physical and ophthalmic examinations were carried out to evaluate possible adverse effects.

RESULTS

Median pupil (95% CI) size at t₀ was 7.10 mm (5.51-7.41) for placebo eyes and 7.22 mm (6.93-7.48) for treated eyes, showing no statistical differences (P > .05). When compared to the placebo eye, significant mydriasis was achieved at t₃₀ [8.18 mm (7.22-9.00)] (P = .014) and lasting until t₉₀ [7.35 mm (6.20-9.52)] (P = .004). Maximal mydriasis was obtained at t₆₀ [8.63 mm (7.72-9.81)] (P = .001). During this period, the treated eye no longer responded to direct light stimulation. Complete mydriasis was observed in 5/10 birds (mean weight 97.4 g). Pupil size at t₉₀ and t₁₂₀ did not differ from baseline (P > .05) in treated eyes. No adverse effects were seen during the study period.

CONCLUSION

Single-dose topical rocuronium bromide (0.15 mg) is a safe and effective medium duration mydriatic agent in scops owls. Further studies are needed to evaluate bilateral topical application and standardize the mydriatic protocol.

Effect of Three Different Sedatives on Electroretinography Recordings in Domestic Pigeons (Columba livia)

This study was conducted to compare the effects of 3 different sedative agents on electroretinography (ERG) in domestic pigeons (Columba livia). Six pigeons were sedated with alfaxalone, xylazine, and medetomidine at separate times with a 1-week washout period between sedative administration. After sedation with each agent, pigeons underwent the modified ERG protocol adapted from the standardized protocol for dogs. The scotopic mixed rod and cone response was recorded after 20 minutes of dark adaptation, and the photopic cone response and photopic flicker response were recorded after 10 minutes of light adaptation. Either a 1-way analysis of variance or a Kruskall-Wallis test was used to compare the a-wave and b-wave implicit time and amplitude. No significant differences were observed in the scotopic mixed rod and cone response among all 3 sedatives used. Compared with alfaxalone, medetomidine significantly prolonged the a-wave implicit time, depressed the b-wave amplitude of photopic cone response, and prolonged the peak implicit time of the photopic flicker response (P < .05). These results show that medetomidine has a depressant effect on photopic ERG in pigeons at a dosage that produces light sedation.

Effective mydriasis in juvenile loggerhead turtles (Caretta caretta) following topical administration of rocuronium bromide and 10% phenylephrine

OBJECTIVE

To determine the combined mydriatic effects of topical rocuronium bromide and phenylephrine in juvenile loggerhead turtles and identify any adverse effects associated with treatment.

ANIMALS STUDIED

Eleven juvenile loggerhead turtles (Caretta caretta).

PROCEDURES

Four 20 μL drops of rocuronium bromide and four 20 μL drops of 10% phenylephrine were placed into the right eye at 2-minute intervals of 5 turtles, while the same volume of saline was administered to six control turtles. A pupilometer recorded pupil measurements at rest and following a light stimulus at 2, 15, 30, 60, 120, 150, 180, 210, 240, 300, and 360 minutes following delivery of the final drop to the ocular surface. Intraocular pressure (IOP) was also measured at similar time points.

RESULTS

The nonilluminated and light-stimulated pupillary diameter of the right eye of treated turtles was significantly greater than baseline starting at 120 and 15 minutes, respectively. Light-stimulated pupillary diameter of treated eyes was greater than that of control eyes from time 15 minutes until the end of the treatment period. No systemic side effects were noted over a 24 hours period following treatment and all turtles showed normal behavior and appetite. No mydriasis was noted in either eye at 24 hours and the anterior segment was normal.

CONCLUSIONS

A combination of topical ophthalmic rocuronium bromide and 10% phenylephrine is safe and effective for mydriasis in juvenile loggerhead turtles.

Phacoemulsification cataract surgery in the loggerhead turtle (Caretta caretta): surgical technique and outcomes in 10 cases

Cataract removal using phacoemulsification was performed in 10 loggerhead turtles being rehabilitated after stranding. All turtles had significant systemic abnormalities and had cataracts either at the time of rescue or developed them during rehabilitation. Surgical difficulties encountered included an extremely soft globe that did not allow for a partial thickness corneal incision, incomplete topical anesthesia of the ocular surface with proparacaine, inability to dilate the pupil pharmacologically, a markedly shallow anterior chamber, a thick posterior capsular plaque in most cases, and difficulty creating a watertight closure with sutures. Minimal to no intraocular inflammation was seen in all cases following surgery, but all cases in which corneal sutures were used developed a marked inflammatory reaction surrounding the sutures and appeared uncomfortable until sutures were removed or sloughed. All turtles appeared to have improved vision following surgery and were eventually released. Two turtles were re-encountered a year or more after release. Both showed signs of normal growth and the ability to capture prey in the wild. This report documents successful outcomes associated with cataract surgery in loggerhead turtles, but also presents significant surgical challenges that should be taken into account before attempting this procedure in this species.

The pupillary light responses of animals; a review of their distribution, dynamics, mechanisms and functions

The timecourse and extent of changes in pupil area in response to light are reviewed in all classes of vertebrate and cephalopods. Although the speed and extent of these responses vary, most species, except the majority of teleost fish, show extensive changes in pupil area related to light exposure. The neuromuscular pathways underlying light-evoked pupil constriction are described and found to be relatively conserved, although the precise autonomic mechanisms differ somewhat between species. In mammals, illumination of only one eye is known to cause constriction in the unilluminated pupil. Such consensual responses occur widely in other animals too, and their function and relation to decussation of the visual pathway is considered. Intrinsic photosensitivity of the iris muscles has long been known in amphibia, but is in fact widespread in other animals. The functions of changes in pupil area are considered. In the majority of species, changes in pupil area serve to balance the conflicting demands of high spatial acuity and increased sensitivity in different light levels. In the few teleosts in which pupil movements occur they do not serve a visual function but play a role in camouflaging the eye of bottom-dwelling species. The occurrence and functions of the light-independent changes in pupil size displayed by many animals are also considered. Finally, the significance of the variations in pupil shape, ranging from circular to various orientations of slits, ovals, and other shapes, is discussed.

Technique, postoperative complications, and visual outcomes of phacoemulsification cataract surgery in 21 penguins (27 eyes): 2011-2015

OBJECTIVE

To describe surgical technique, postoperative complications, and visual outcome in penguins after phacoemulsification lens extraction surgery.

ANIMALS STUDIED

Twenty-one penguins (27 eyes) that had phacoemulsification from 2011 to 2015 at Animal Eye Associates. Species included are as follows: 14 southern Rockhopper (18 eyes, 66.6%), 4 Gentoo (4 eyes, 19%), 2 King (3 eyes, 9.5%), and 1 Chinstrap penguin (2 eyes, 4.8%). Eleven of the penguins were females, and 10 were males with average age at the time of surgery being 27.5 years (range of 22-31 years).

PROCEDURE

This is a retrospective study of phacoemulsification cataract surgery patients from 2011 to 2015. Visual outcome was evaluated by veterinary ophthalmologists at postoperative recheck examinations and subjectively by penguin keepers using individual bird surveys and paired t tests for statistical analysis.

RESULTS

All eyes were functionally visual after surgery and at the time of last follow-up. Based on keeper surveys, 81% (17/21) of penguins showed immediate improvements in overall quality of life and 90% (19/21) of penguins exhibited improvement in mobility and behavior within their exhibit following cataract removal. Of the 14 penguins that received 1:5 intracameral atracurium during surgery, 10 (71.4%) had moderate mydriasis, 1 (7.1%) had minimal mydriasis, and 3 (21.4%) showed no effect to the pupil. Seventy percent of the cases had phacoemulsification times less than 60 seconds/eye; the mean time was 72 seconds. Sixteen eyes (59.3%) underwent anterior capsulotomy only, planned anterior and posterior capsulotomies were performed in 3 eyes (11.1%), and the entire lens capsule was removed due to capsular fibrosis and wrinkling in 8 eyes (29.6%). The most common short-term postoperative complication was temporary mild blepharospasm and/or epiphora, reported in 8 eyes (29.6%) from 7 penguins (33.3%). Long-term complications, 2-6 years postoperatively, included posterior synechiation resulting in dyscoria (10 of 24 eyes, 41.7%) and capsular fibrosis in all penguins with residual lens capsule (19/19, 100%).

CONCLUSION

The prognosis for vision and behavioral improvement after phacoemulsification surgery in penguins is good, with low incidence of vision-threatening complications.

Evidence-Based Advances in Avian Medicine

This article presents relevant advances in avian medicine and surgery over the past 5 years. New information has been published to improve clinical diagnosis in avian diseases. This article also describes new pharmacokinetic studies. Advances in the understanding and treatment of common avian disorders are presented in this article, as well. Although important progress has been made over the past years, there is still much research that needs to be done regarding the etiology, pathophysiology, diagnosis, and treatment of avian diseases and evidence-based information is still sparse in the literature.