Effect of four local anesthetics (tetracaine, proparacaine, lidocaine, and bupivacaine) on intraocular pressure in dogs

Evaluation of lidocaine for auriculopalpebral nerve block in dogs: Onset, duration, and effects on intraocular pressure and eye examination

OBJECTIVES

Accurate intraocular pressure (IOP) measurement is essential for managing glaucoma, requiring tonometry. Local anesthesia is typically used, but nerve blocks may be needed for blepharospasm. This study investigated the efficacy of auriculopalpebral nerve block with lidocaine in achieving eyelid akinesia and its influence on IOP in dogs.

ANIMALS AND PROCEDURES

In a randomized, blinded trial, 12 healthy adult mixed-breed dogs (24 eyes) received either auriculopalpebral nerve block with 2% lidocaine (n = 12 eyes) or no block (n = 12 eyes). Tetracaine drops were used for topical anesthesia in half of blocked/non-blocked eyes, and the rest of the eyes got artificial tears as control. The impact of nerve block was evaluated through assessments of menace response, palpebral reflex, and IOP before the block, after drop instillation, and at 15-min intervals until block dissipation.

RESULTS

Auriculopalpebral nerve block provided effective eyelid akinesia in 58.5% (7/12 eyes) at 15 min, reaching 91.7% (11/12 eyes) at 30 min, indicating peak efficacy. Subsequently, the block gradually diminished, with 66.7% (8/12 eyes) and 33.3% (4/12 eyes) maintaining akinesia at 45 and 60 min, respectively. Importantly, neither auriculopalpebral nerve block nor tetracaine administration significantly affected IOP measurements (p > .05).

CONCLUSIONS

Auriculopalpebral nerve block using lidocaine demonstrated efficient eyelid akinesia, peaking at 30 min postinjection. This technique proved to be safe with no notable alterations in IOP, suggesting its potential utility in canine ophthalmology for procedures requiring eyelid akinesia, particularly in the management of glaucoma where maintaining accurate IOP measurements is crucial for diagnosis, treatment, and monitoring the disease.

Effects of intramuscular alfaxalone and dexmedetomidine alone and combined on ocular, electroretinographic, and cardiorespiratory parameters in normal cats

Background

This study aimed to determine the effects of intramuscular (IM) administration of alfaxalone with or without dexmedetomidine on short electroretinography (ERG), ocular parameters and cardiorespiratory in healthy cats.

Methods

Eight healthy female spayed cats were treated with three sedation protocols: IM administration of 5 μg/kg dexmedetomidine (DEX), 5 mg/kg alfaxalone (ALF), and 5 μg/kg dexmedetomidine plus 5 mg/kg alfaxalone (DEX + ALF). The washout period after each treatment was 2 weeks. Physiological parameters, time metrics, intraocular pressure (IOP), Schirmer tear test 1 (STT-1) and a short ERG protocol were recorded. For age data, weight data, time metrics and ERG data, one-way ANOVA with Bonferroni posterior comparisons were performed. For physiological parameters, IOP and STT-1 data, two-way repeated measures ANOVA with Bonferroni posterior comparisons were performed. Statistical significance was set at a p-value <0.05.

Results

IOPs were increased in all three groups compared to baseline and showed no significant differences among three groups at any time point. STT-1 values were decreased significantly during the process. Significant differences were noticed between a-wave amplitude in the dark-adapted response between DEX and ALF, and a-wave amplitude in light-adapted response between ALF and DEX + ALF.

Conclusion

This study demonstrates the feasibility of three sedation protocols for short ERG recording in cats. All these treatments resulted in increased IOP values and reduced STT-1 values. But baseline data of ERG was not obtained as a blank control in cats.

Effect of isoflurane anaesthetic time on ocular a-scan ultrasonography measures and their relationship to age and OCT measures in the Guinea pig

A-scan ultrasonography enables precise measurement of internal ocular structures. Historically, its use has underpinned fundamental studies of eye development and aberrant eye growth in animal models of myopia; however, the procedure typically requires anaesthesia. Since anaesthesia affects intra-ocular pressure (IOP), we investigated changes in internal ocular structures with isoflurane exposure and compared measurements with those taken in awake animals using optical coherence tomography (OCT). Continuous A-scan ultrasonography was undertaken in tri-coloured guinea pigs aged 21 (n = 5), 90 (n = 5) or 160 (n = 5) days while anaesthetised (up to 36 min) with isoflurane (5% in 1.5L/min O2). Peaks were selected from ultrasound traces corresponding to the boundaries of the cornea, crystalline lens, retina, choroid and sclera. OCT scans (Zeiss Cirrus Photo 800) of the posterior eye layers were taken in 28-day-old animals (n = 19) and compared with ultrasound traces, with choroid and scleral thickness adjusted for the duration of anaesthesia based on the changes modelled in 21-day-old animals. Ultrasound traces recorded sequentially in left and right eyes in 14-day-old animals (n = 30) were compared, with each adjusted for anaesthesia duration. The thickness of the cornea was measured in enucleated eyes (n = 5) using OCT following the application of ultrasound gel (up to 20 min). Retinal thickness was the only ultrasound internal measure unaffected by anaesthesia. All other internal distances rapidly changed and were well fitted by exponential functions (either rise-to-max or decay). After 10 and 20 min of anaesthesia, the thickness of the cornea, crystalline lens and sclera increased by 17.1% and 23.3%, 0.4% and 0.6%, and 5.2% and 6.5% respectively, whilst the anterior chamber, vitreous chamber and choroid decreased by 4.4% and 6.1%, 0.7% and 1.1%, and 10.7% and 11.8% respectively. In enucleated eyes, prolonged contact of the cornea with ultrasound gel resulted in an increase in thickness of 9.3% after 10 min, accounting for approximately half of the expansion observed in live animals. At the back of the eye, ultrasound measurements of the thickness of the retina, choroid and sclera were highly correlated with those from posterior segment OCT images (R2 = 0.92, p = 1.2 × 10-13, R2 = 0.55, p = 4.0 × 10-4, R2 = 0.72, p = 5.0 × 10-6 respectively). Furthermore, ultrasound measures for all ocular components were highly correlated in left and right eyes measured sequentially, when each was adjusted for anaesthetic depth. This study shows that the depth of ocular components can change dramatically with anaesthesia. Researchers should therefore be wary of these concomitant effects and should employ adjustments to better render 'true' values.

Determination of intraocular pressure and Schirmer tear test and the comparison between the applanation tonometer (Tono-Pen AVIA®) and the rebound tonometer (TonoVet Plus®) in mini lionhead rabbits

OBJECTIVE

To determine intraocular pressure (IOP) and tear production, as well as to compare the IOP obtained with the TonoVet Plus® (rebound) with the Tono-Pen Avia® (applanation) tonometers.

ANIMALS

Twenty-five Mini Lionhead rabbits (n = 50 eyes).

PROCEDURE

Tear production was measured at 6:00 a.m. and 6:00 p.m. by using the STT. The IOP reading was performed with the rebound tonometer, followed by the applanation tonometer, at 6:00 a.m., 9:00 a.m., 12:00 p.m., 3:00 p.m., and 6:00 p.m. Regression analysis, analysis of variance (anova) and Bland-Altman statistics were used.

RESULTS

Daily tear production was 10.25 ± 3.75 mm/min, with no differences among the moments evaluated. Average daily IOP was 17.7 ± 3.08 mmHg with the TonoVet Plus® and 11.5 ± 4.56 mmHg with the Tono-Pen Avia®. IOP values were higher at the beginning and end of the day with both tonometers.

CONCLUSION

The IOP values are higher with the TonoVet Plus® tonometer. The reference values of IOP and tear production obtained in this work may support the diagnosis, treatment, and monitoring of ocular disorders in pet Mini Lionhead rabbits.

Protocol for laser-induced chronic ocular hypertension and intracameral injection in nonhuman primates

Laser-induced hypertension in nonhuman primates is used to mimic human glaucoma, the leading cause of irreversible blindness. In this protocol, we detail steps for laser-induced ocular hypertension in nonhuman primates by laser photocoagulation of the trabecular meshwork and subsequent intracameral injection. We further describe recording and evaluation of intraocular pressure changes and peripapillary retinal nerve fiber layer thickness. This protocol can assist researchers improve the success rate and repeatability of the procedure and reduce the number of nonhuman primates needed.

For complete details on the use and execution of this protocol, please refer to Sun et al. (2022).

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Detailed description for general and ophthalmological examination before experiment

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Protocol to generate laser-induced chronic ocular hypertension in rhesus monkeys

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Laser photocoagulation of the trabecular meshwork followed by intracameral injection

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Approach is highly reproducible and offers a tool to test potential treatment strategies

Publisher’s note: Undertaking any experimental protocol requires adherence to local institutional guidelines for laboratory safety and ethics.

Effect of topical 0.5% tetracaine hydrochloride on intraocular pressure in ophthalmologically normal cats

OBJECTIVES

The aim of this study was to assess the effect of topical tetracaine hydrochloride 0.5% on intraocular pressure (IOP) in ophthalmologically normal cats.

METHODS

Twenty domestic shorthair cats (40 eyes) were used in this study. Each cat was randomly allocated to one of two groups (treatment or control). Baseline IOP (T0) was measured in each cat, and then one drop of tetracaine hydrochloride 0.5% or artificial tears was administered into a randomly chosen eye of each cat in the treatment and control groups, respectively. Repeat IOP measurements were performed at 2 mins (T2), 5 mins (T5), 15 mins (T15) and 30 mins (T30) with a rebound tonometer.

RESULTS

Mean baseline IOP in all eyes was 20.6 ± 2.5 mmHg. After the unilateral administration of tetracaine, mean IOP decreased significantly in the treated eye at T2 (P = 0.01). Mean IOP returned to baseline values at T15. The mean IOPs in the treated eyes at T0, T2, T5, T15 and T30 were 20.6 ± 3.3 mmHg, 18.2 ± 2.5 mmHg, 18.2 ± 3.4 mmHg, 20.2 ± 3.2 mmHg and 19.8 ± 2.7 mmHg, respectively. A significant difference in IOP was found at all time points between the tetracaine and control groups (P <0.03).

CONCLUSIONS AND RELEVANCE

The results of the present study showed a statistically significant reduction in mean IOP 2 mins after the administration of tetracaine hydrochloride 0.5% in the treated eyes of the cats.

The effect of central corneal thickness on intraocular pressure values using various tonometers in the dog

OBJECTIVE

To compare intraocular pressure readings from three different tonometers, the Tono-Pen AVIA® (TP), TonoVet® (TV) and TonoVet Plus® (TV+) and to determine how measurements from each tonometer are affected by central corneal thickness (CCT).

ANIMALS

Ninety dogs.

PROCEDURES

Normal dogs and dogs with ocular disease were selected for study inclusion. Central corneal thickness measurements were gathered with the Pachette 4 ultrasonic pachymeter, and IOP measurements were gathered with the three tonometers in random order. ANOVA or Wilcoxon tests were utilized for overall group comparisons. Linear regression analyses were utilized to determine the association between IOP and CCT.

RESULTS

When comparing tonometers to each other, for all dogs, readings from the TV+were significantly different compared to the TV (p = <.0001) and TP (p = <.0001); however, there was no significant difference between the TV and the TP (p = .999). Linear regression did not find any significant correlation between corneal thickness and IOP readings with any tonometer when looking at normal dogs or when including dogs with ocular abnormalities.

DISCUSSION

This study did not find a significant correlation between an increase in CCT and increase in IOP reading in any tonometer comparison amongst normal and dogs with ocular abnormalities. The TV+produced consistently and significantly higher readings, but measurements did not exceed the expected IOP range in normal dogs. For consistency, the same tonometer should be used when monitoring IOP over time.

Effect of Topical 1% Tetracaine Hydrochloride on Intraocular Pressure in Ophthalmologically Normal Horses; a Pilot Study

The aim of this study was to evaluate the effect of topical 1% tetracaine hydrochloride on the intraocular pressure (IOP) in ophthalmologically normal horses. Thirty eyes of 15 clinically normal horses were used for this study. The animals were randomly assigned to two groups (treatment and control). Prior to the instillation of 1% tetracaine or placebo, the baseline IOPs (T0) of each animal were recorded in both groups. Then one drop of tetracaine was instilled randomly into one eye of each horse in the treatment group (8 horses). In the control group (7 horses), one drop of artificial tear was instilled in one randomly selected eye. The measurements were repeated at 2 minutes (T2), 5 minutes (T5), 15 minutes (T15), and 30 minutes (T30) post instillation via a rebound tonometer. There was no significant difference in the treatment group (P = .3). The peak IOP measured at T2 returned to the baseline value at T30. No significant difference was found in the mean IOP values between the treatment and the control groups, or between the males and females on any of the occasions (P > .05). The Results of this study revealed a nonsignificant increase of the IOP 2 minutes post instillation of 1% tetracaine in horses.

Ophthalmology of clinically normal alpacas (Vicugna pacos) in the United Kingdom: a cross-sectional study

Background

Alpacas are being more frequently presented to veterinarians in the UK. It is important to validate whether published normal ocular parameters are consistent with the alpaca population in the UK.

Methods

Ophthalmic examinations were performed on healthy alpacas (Vicugna pacos) from three farms in East Anglia, UK.

Results

On direct ophthalmoscopy of 35 alpacas, there was a 50 per cent prevalence of opacities within the lens in alpacas older than two years old (n=8/16). There was a 36.8 per cent prevalence of persistent hyaloid arteries in alpacas under two years old (n=7/19). The mean Schirmer tear test-1 value was 20.0 ±6 mm/minute (n=40). The mean intraocular pressure measured by rebound tonometry was 17.2 ±5.5 mmHg (n=46), and applanation tonometry resulted in statistically similar values (P=0.30; n=25). There was a significant variation in intraocular pressure throughout a 24-hour period (n=8). Fluorescein dye was not detected at the nostrils of any of the alpacas which underwent a Jones test to assess nasolacrimal duct patency (n=8).

Conclusion

The ophthalmic findings appear largely consistent with previously published values from North America and continental Europe. Variations include the large range of measurements obtained and evidence of diurnal variation in intraocular pressure.

1% Tetracaine hydrochloride injection pure solution aerosol inhalation combined with oral administration of dyclonine hydrochloride mucilage as upper airway anesthesia for bronchoscopy: A randomized controlled trial

BACKGROUND

During the bronchoscopy process, successful passage of the tracheoscope through the glottis can affect the following procedure of bronchoscopy. Therefore, safer, more effective and less painful anesthesia methods are particularly important for the bronchoscopy success rate.

OBJECTIVE

This study aimed to evaluate the efficacy of 1% tetracaine hydrochloride injection pure solution aerosol inhalation combined with oral administration of dyclonine hydrochloride mucilage during bronchoscopy.

METHODS

Patients who need bronchoscopy or bronchoscope treatment were randomly assigned to two groups; group A received pure tetracaine hydrochloride injection solution (3 mL of 1% tetracaine hydrochloride) aerosol inhalation combined with oral 5 mL of dyclonine hydrochloride mucilage and group B received diluted tetracaine hydrochloride injection (3 mL of 1% tetracaine hydrochloride injection + 3 mL of sterile water for injection) aerosol inhalation combined with oral 5 mL of dyclonine hydrochloride mucilage. The anesthetic effect and adverse reactions of these groups were observed and compared.

RESULT

A total of 523 patients were randomized. The results showed that patient's tolerance, cough response, glottis opening during the bronchoscope into the glottis and the time required to the tracheoscope pass through the glottis were obviously significantly better in group A than in group B. Vital signs including blood pressure, heart rate and pulse oxygen saturation were more stable in group A than in group B.

CONCLUSION

The 1% tetracaine hydrochloride injection pure liquid aerosol inhalation combined with oral administration of dyclonine hydrochloride mucilage as upper airway anesthesia is effective and safe for bronchoscopy. This method of local anesthesia is worthy of clinical application.