Effects of ketamine, diazepam, and their combination on intraocular pressures in clinically normal dogs

Comparison of the effects of intranasal and intramuscular midazolam-butorphanol-ketamine on intraocular pressure, tear production and sedation in New Zealand White rabbits

OBJECTIVE

To compare the effects of intranasal (IN) and intramuscular (IM) midazolam-butorphanol-ketamine on intraocular pressure (IOP), tear production (TP) and sedation in rabbits.

STUDY DESIGN

Prospective, randomized, crossover experimental study.

ANIMALS

Fourteen male New Zealand White rabbits, aged 1-2 years, body mass 3.1 ± 0.8 kg (mean ± standard deviation).

METHODS

Rabbits were administered midazolam (1 mg kg-1), butorphanol (1.5 mg kg-1) and ketamine (5 mg kg-1) via IN and IM routes. IOP, TP and sedation scores were assessed at 0 (before drug administration), 5, 15, 30, 45 and 60 minutes after drug administration. Heart rate (HR), respiratory rate (fR), rectal temperature (RT), noninvasive mean arterial blood pressure (MAP) and peripheral hemoglobin oxygen saturation (SpO2) were simultaneously recorded until 45 minutes after drug administration. The onset and duration of sedation and sedation scores were recorded.

RESULTS

Drug delivery route had no significant impact on mean IOP (p = 0.271) or TP (p = 0.062), and there were no significant changes over time for IOP (p = 0.711) or TP (p = 0.372). Similarly, delivery route had no significant impact on HR (p = 0.747), fR (p = 0.872), RT (p = 0.379), MAP (p = 0.217) and SpO2 (p = 0.254). Sedation onset was faster with IN (3.0 ± 1.0 minutes) than with IM administration (4.9 ± 0.7 minutes) (p = 0.011), but sedation duration was significantly longer with IM (52.6 ± 7.2 minutes) than with IN delivery (30.7 ± 6.8 minutes) (p = 0.004). There was no significant difference in sedation scores between the two delivery routes at any of the recorded time points.

CONCLUSIONS AND CLINICAL RELEVANCE

The combination of midazolam-butorphanol-ketamine had minimal impact on physiological and ocular variables regardless of the route of administration, whereas IN drug administration led to a shorter onset and duration of action than IM administration.

Ocular examination findings and selected ophthalmic diagnostic tests in African green monkeys (Chlorocebus aethiops sabaeus)

OBJECTIVE

To document ocular lesions and establish ophthalmic diagnostic test reference values in a colony of African green monkeys (Chlorocebus aethiops sabaeus).

ANIMALS STUDIED

Fifty one geriatric (GAGM, 19-30 years old), 10 adult (AAGM, 5-9 years old) and 10 juvenile (JAGM, <2 years old) African green monkeys housed in a single Caribbean research colony.

PROCEDURES

Ocular biomicroscopy, indirect fundoscopy, Schirmer tear test (STT), rebound tonometry (TonoVet®) and corneal fluorescein staining were performed. Mixed ANCOVA tests were performed to compare STT and IOP between groups.

RESULTS

Common ocular lesions in GAGM included vitreal degeneration (27/51, 51/102 eyes) and cataracts (21/51, 32/102 eyes). Vitreal degeneration was also common in AAGM (8/10, 16/20 eyes) and infrequent in JAGM (3/10, 6/20 eyes). Cataracts were not present in any JAGM or AAGM. All eyes in all three groups had perilimbal corneal pigmentation and faint lace-like anterior corneal stromal opacification. Median (range) STT values were 16.0 (18) mm/min in GAGM. Mean (SD) STT values were 14.2 (4.6) mm/min in AAGM, and 8.9 (3.4) mm/min in JAGM. Median (range) IOP values were 16.5 (27) mmHg in GAGM. Mean (SD) IOP values were 18.0 (2.8) mmHg in AAGM, and 14.1 (2.2) mmHg in JAGM. JAGM had significantly lower STT and IOP values compared to AAGM (p = .0449, .0057, respectively) and GAGM (p = .0002, .0130, respectively).

CONCLUSIONS

Spontaneous ocular lesions were common in geriatric monkeys in this research colony. IOP and STT values were lower in juvenile African green monkeys relative to adult or geriatric animals.

Influence of ketamine, propofol or isoflurane on intraocular pressure, heart rate and blood pressure in healthy dogs premedicated with medetomidine and midazolam

BACKGROUND

According to the findings of several studies, sedatives and anaesthetics have different effects on the functioning of the cardiovascular system and intraocular pressure (IOP). For accurate diagnosis, treatment and surgery with minimal complications, it is necessary to be aware of the effects of sedatives and anaesthetics on the cardiovascular system and IOP.

OBJECTIVES

The aim of this study was to evaluate the effects of sedatives (medetomidine and midazolam) and anaesthetics (ketamine, propofol and isoflurane) on IOP, heart rate (HR) and blood pressure in dogs.

METHODS

In this study, 10 dogs participated in three treatments using a randomised cross-over design, with a 1-week washout period between each treatment. Dogs in all treatments were premedicated with medetomidine and midazolam. Anaesthesia was induced using ketamine, propofol, or isoflurane and maintained for 60 min with the appropriate doses of each drug. The cardiovascular variables (heart rate, and systolic, diastolic and mean arterial pressures) and IOP were measured at different timepoints: before premedication (baseline values, T-Bas), 15 min after medetomidine administration (T-Med), 20 min after midazolam administration (T-Mid) and at 15 (T-15), 30 (T-30), 45 (T-45) and 60 (T-60) min after anaesthesia induction.

RESULTS

Medetomidine significantly reduced the IOP and HR and did not significantly change the mean arterial pressure (MAP). Midazolam significantly reduced the IOP while did not significantly change the HR and MAP. Ketamine and isoflurane significantly increased the IOP and HR while did not significantly change the MAP. Propofol significantly increased the HR, but did not cause significant changes in IOP and MAP.

CONCLUSIONS

Considering that anaesthetics are typically administered in conjunction with pre-anaesthetic drugs, the increases in IOP induced by ketamine and isoflurane are not important, as the IOP did not exceed the baseline values. However, further studies are required to investigate these effects in patients with elevated IOP.

Ketamine versus midazolam as an adjuvant to peribulbar block using a single inferonasal injection in patients undergoing vitreoretinal surgery: A randomized controlled trial

INTRODUCTION AND OBJECTIVES

This study aimed to assess the safety and efficacy of midazolam and ketamine as adjuvants to the peribulbar block in vitreoretinal surgeries.

PATIENTS AND METHODS

This randomized controlled trial included 93 adult patients undergoing vitreoretinal surgeries performed with peribulbar anaesthesia. Patients were randomly allocated to 3 groups (31 participants each): control (standard anaesthetic mixture), midazolam (standard mixture + midazolam), and ketamine (standard mixture + ketamine). The primary outcomes were onset of globe akinesia and duration of analgesia. Secondary outcomes were duration of motor blockade, onset of corneal anaesthesia and lid akinesia, and changes in vital data (blood pressure, oxygen saturation, and pulse rate).

RESULTS

The ketamine group vs. the control and midazolam groups showed the most rapid onset of lid and globe akinesia (p < 0.001) and corneal anaesthesia (0.7 ± 0.2 vs. 1.5 ± 0.5 and 1.2 ± 0.4, respectively; p < 0.001) and the longest duration of both analgesia (3.7 ± 0.6 vs. 2.3 ± 0.4 and 3.1 ± 0.6, respectively; p < 0.001) and akinesia (3.8 ± 0.5 vs. 3.0 ± 0.4, and 3.7 ± 0.5, respectively; p < 0.001). The midazolam group showed better outcomes than controls, but the drug was less effective than ketamine. There were no significant differences in vital data among groups (p > 0.05).

CONCLUSIONS

Ketamine is an effective adjuvant for peribulbar blockade. It enhances both motor and sensory blockade by hastening onset and prolonging duration. These effects are desirable in lengthier ophthalmic procedures such as vitreoretinal surgeries. The effects of ketamine were superior to those of midazolam.

Diurnal Variation and Effects of Dilation and Sedation on Intraocular Pressure in Infant Rhesus Monkeys

PURPOSE

Intraocular pressure (IOP) is an important factor in numerous ocular conditions and research areas, including eye growth and myopia. In infant monkeys, IOP is typically measured under anesthesia. This study aimed to establish a method for awake IOP measurement in infant rhesus monkeys, determine diurnal variation, and assess the effects of dilation and sedation.

METHODS

Awake IOP (iCare TonoVet) was measured every 2 h from 7:30 am to 5:30 pm to assess potential diurnal variations in infant rhesus monkeys (age 3 weeks, n = 11). The following day, and every 2 weeks to age 15 weeks, IOP was measured under three conditions: (1) awake, (2) awake and dilated (tropicamide 0.5%), and (3) sedated (ketamine and acepromazine) and dilated. Intraclass correlation coefficient (ICC) was used to determine intersession repeatability, and repeated measures. ANOVA was used to determine effects of age and condition.

RESULTS

At age 3 weeks, mean (±SEM) awake IOP was 15.4 ± 0.6 and 15.2 ± 0.7 mmHg for right and left eyes, respectively (p=.59). The ICC between sessions was 0.63[-0.5 to 0.9], with a mean difference of 2.2 ± 0.3 mmHg. Diurnal IOP from 7:30 am to 5:30 pm showed no significant variation (p=.65). From 3 to 15 weeks of age, there was a significant effect of age (p=.01) and condition (p<.001). Across ages, IOP was 17.8 ± 0.7 mmHg while awake and undilated, 18.4 ± 0.2 mmHg awake and dilated, and 11.0 ± 0.3 mmHg after sedation and dilation.

CONCLUSIONS

Awake IOP measurement was feasible in young rhesus monkeys. No significant diurnal variations in IOP were observed between 7:30 am and 5:30 pm at age 3 weeks. In awake monkeys, IOP was slightly higher after mydriasis and considerably lower after sedation. Findings show that IOP under ketamine/acepromazine anesthesia is significantly different than awake IOP in young rhesus monkeys.

Effect of anesthetic induction with propofol, alfaxalone or ketamine on intraocular pressure in cats: a randomized masked clinical investigation

OBJECTIVE

To compare the effect of propofol, alfaxalone and ketamine on intraocular pressure (IOP) in cats.

STUDY DESIGN

Prospective, masked, randomized clinical trial.

ANIMALS

A total of 43 ophthalmologically normal cats scheduled to undergo general anesthesia for various procedures.

METHODS

Following baseline IOP measurements using applanation tonometry, anesthesia was induced with propofol (n = 15), alfaxalone (n = 14) or ketamine (n = 14) administered intravenously to effect. Then, midazolam (0.3 mg kg^-1) was administered intravenously and endotracheal intubation was performed without application of topical anesthesia. The IOP was measured following each intervention. Data was analyzed using one-way anova and repeated-measures mixed design with post hoc analysis. A p-value <0.05 was considered significant.

RESULTS

Mean ± standard error IOP at baseline was not different among groups (propofol, 18 ± 0.6; alfaxalone, 18 ± 0.7; ketamine, 17 ± 0.5 mmHg). Following induction of anesthesia, IOP increased significantly compared with baseline in the propofol (20 ± 0.7 mmHg), but not in the alfaxalone (19 ± 0.8 mmHg) or ketamine (16 ± 0.7 mmHg) groups. Midazolam administration resulted in significant decrease from the previous measurement in the alfaxalone group (16 ± 0.7 mmHg), but not in the propofol group (19 ± 0.7 mmHg) or the ketamine (16 ± 0.8 mmHg) group. A further decrease was measured after intubation in the alfaxalone group (15 ± 0.9 mmHg).

CONCLUSIONS AND CLINICAL RELEVANCE

Propofol should be used with caution in cats predisposed to perforation or glaucoma, as any increase in IOP should be avoided.

Effects of tiletamine-zolazepam vs. propofol on peri-induction intraocular pressure in dogs: A randomized, masked crossover study

Introduction

Anesthesia induction agents have the potential to cause severe ocular side effects, resulting in lasting damage to the eye.

Objectives

The purpose of this study is to determine the effects of tiletamine-zolazepam on IOP compared to propofol when they are used as an induction agent in normal healthy dogs.

Methods

Twenty healthy adult client owned dogs weighing 22.2 ± 7.6 kg were selected for the study. In a randomized order, all dogs received tiletamine-zolazepam 5 mg/kg IV or propofol 8 mg/kg IV titrated to effect without premedication. Washout between each treatment was at least seven days. IOP measurements were obtained at four time points: baseline, post-induction, post-intubation, and after recovery using applanation tonometry. No additional procedures were performed. After normality of the data was determined, a linear mixed model was built with time, eye, treatment and all interactions of those variables as fixed effects and subject as a random effect.

Results

There was no significant difference for age, body weight, drug dose, baseline IOP, and recovery IOP between treatments. Average IOP measurements remained within the normal range of 15-25 mmHg at these time points. However, IOP was significantly less elevated by the tiletamine-zolazepam treatment vs. propofol at the post-induction (mean difference: -4.7 ± 4.6 [95%CI -6.8 to -2.5]) and the post-intubation (mean difference: -4.4 ± 4.6 [95%CI -6.5 to -2.2]) time points.

Clinical significance

Dogs receiving tiletamine-zolazepam for anesthetic induction had a significantly less elevated IOP at induction and intubation compared to dogs receiving propofol.

Intraocular pressure and cardiovascular effects of dexmedetomidine premedication and tiletamine-zolazepam for anesthetic induction in dogs

Background and Aim

The effect of anesthetic drugs on intraocular pressure (IOP) is an important concern in ophthalmic surgery. The impact of dexmedetomidine (DEX) combined with tiletamine-zolazepam on IOP is scarcely studied. This study aimed to evaluate IOP and cardiovascular effects in dogs after premedication with 5 μg/kg (DEX5) or 10 μg/kg (DEX10) of intramuscular DEX followed by intravenous tiletamine-zolazepam administration for induction of anesthesia in healthy dogs.

Materials and Methods

Eighteen dogs, American Society of Anesthesiologists I or II, without ocular abnormality were investigated. All dogs were randomly divided into the DEX5 (n = 9) and DEX10 groups (n = 9). The IOP, heart rate (HR), systolic blood pressure (SBP), oxygen saturation, and sedation scale were measured before premedication (baseline), after premedication at 5, 10, 15, and 20 min, after tiletamine-zolazepam administration, after endotracheal intubation, and post-operative.

Results

There were no significant differences between the groups at any time point. The DEX5 and DEX10 groups had significantly decreased HR values at 10 min compared with baseline. The IOP at 20 min was significantly lower compared to the baseline in the DEX10 group. Moreover, the DEX10 group showed increased IOP, HR, SBP, and sedation scale values after induction and intubation compared with 20 min, but these values did not differ significantly from baseline. All parameters of both groups did not change significantly between post-operative and baseline.

Conclusion

Intramuscular DEX (10 μg/kg) is an appropriate premedication in ophthalmic examination or surgical procedures. Moreover, it could be combined with tiletamine-zolazepam for generalized anesthesia in dogs with an ophthalmic problem, as it had no clinically significant effects on IOP or cardiovascular values.

Single instead of triplicate intraocular pressure measurements in dogs do not substantially lower accuracy and precision but do slightly reduce statistical power

OBJECTIVE

To compare single and triplicate applanation tonometry values across previous intraocular pressure (IOP) studies in dogs.

ANIMALS

116 ophthalmologically normal dogs.

PROCEDURES

Triplicate IOP readings (n = 1432) from studies evaluating effect of anesthetic protocols were analyzed to estimate a range of probable differences between averaged triplicate and first, averaged and lowest, and first and lowest IOPs. The decrease in variability with triplicate measurements and the magnitude of effects on statistical power were quantified.

RESULTS

The 2.5th to 97.5th interpercentile range for differences of averaged triplicate values minus first IOP readings was –3 to 2.7 mm Hg; for averaged minus lowest: 0 to 3.7 mm Hg; for first minus lowest: 0 to 5 mm Hg. The 95% prediction interval for differences in study group means (n = 160 groups, n = 5 to 11 eyes per group) based on averaged minus first measurements was –1.0 to 0.9 mm Hg with associated SDs reduced by 4% on average. Analysis of previous studies using averaged instead of first IOP values resulted in minimal decreases in SEs of 3–9% (0.03 to 0.09 mm Hg). Of 11 comparisons found significant with averaged data, 2 (18%) were found nonsignificant with first measurements. Of 96 comparisons found nonsignificant with averaged data, 3 (3%) were found significant with first measurements.

CLINICAL RELEVANCE

With applanation tonometry in ophthalmologically normal dogs, no clinically meaningful difference was found between the first, lowest, or averaged triplicate IOP measurements, but the first reading has a larger variance and hence will result in lower statistical power.

Keratometry, biometry, and prediction of intraocular lens power in adult tigers (Panthera tigris)

OBJECTIVE

To calculate the necessary pseudophakic intraocular lens (IOL) power to approximate emmetropia in adult tigers.

ANIMALS

17 clinically normal adult tigers.

PROCEDURES

33 eyes of 17 clinically normal adult tigers underwent routine ophthalmic examination and B-scan ultrasonography while anesthetized for unrelated procedures. Specific ultrasound data (globe measurements and corneal curvature) and estimated postoperative IOL positions were utilized to calculate predicted IOL power by use of Retzlaff and Binkhorst theoretical formulas. Applanation tonometry and refraction were also performed.

RESULTS

Mean ± SD axial globe length was 29.36 ± 0.82 mm, preoperative anterior chamber depth was 7.00 ± 0.74 mm, and crystalline lens thickness was 8.72 ± 0.56 mm. Mean net refractive error (n = 33 eyes) was +0.27 ± 0.30 diopters (D). By use of the Retzlaff formula, mean predicted IOL power for the postoperative anterior chamber depth (PACD), PACD - 2 mm, and PACD + 2 mm was 43.72 ± 4.84 D, 37.62 ± 4.19 D, and 51.57 ± 5.72 D, respectively. By use of the Binkhorst equation, these values were 45.11 ± 4.91 D, 38.84 ± 4.25 D, and 53.18 ± 5.81 D, respectively. Mean intraocular pressure for all eyes was 14.7 ± 2.69 mm Hg.

CLINICAL RELEVANCE

The calculated tiger IOL was lower than reported values for adult domestic felids. Further studies evaluating actual PACD and pseudophakic refraction would help determine the appropriate IOL power to achieve emmetropia in this species.

Effects of acute stress, general anesthetics, tonometry, and temperature on intraocular pressure in rats

Intraocular pressure (IOP) is important for eye health as abnormal levels can led to ocular tissue damage. IOP is typically estimated by tonometry, which only provides snapshots of pressure history. Tonometry also requires subject cooperation and corneal contact that may influence IOP readings. The aim of this research was to investigate IOP dynamics of conscious animals in response to stressors, common anesthetics, tonometry, and temperature manipulations. An eye of male Brown-Norway rats was implanted with a fluid-filled cannula connected to a wireless telemetry system that records IOP continuously. Stress effects were examined by restricting animal movements. Anesthetic effects were examined by varying isoflurane concentration or injecting a bolus of ketamine. Tonometry effects were examined using applanation and rebound tonometers. Temperature effects were examined by exposing anesthetized and conscious animals to warm or cool surfaces. Telemetry recordings revealed that IOP fluctuates spontaneously by several mmHg, even in idle and anesthetized animals. Environmental disturbances also caused transient IOP fluctuations that were synchronous in recorded animals and could last over a half hour. Animal immobilization produced a rapid sustained elevation of IOP that was blocked by anesthetics, whereas little-to-no IOP change was detected in isoflurane- or ketamine-anesthetized animals if body temperature (BT) was maintained. IOP and BT decreased precipitously when heat support was not provided and were highly correlated during surface temperature manipulations. Surface temperature had no impact on IOP of conscious animals. IOP increased slightly during applanation tonometry but not rebound tonometry. The results show that IOP is dynamically modulated by internal and external factors that can activate rapidly and last long beyond the initiating event. Wireless telemetry indicates that animal interaction induces startle and stress responses that raise IOP. Anesthesia blocks these responses, which allows for better tonometry estimates of resting IOP provided that BT is controlled.

A comparative study on intraocular pressure under various anesthetics in cynomolgus monkeys (Macaca fascicularis)

Background

Nonhuman primates (NHPs) are superior model for ocular research due to its morphological and physiological similarities with humans. Thus, the effect of four different anesthetic combinations [ketamine (10 mg/kg), ketamine + xylazine (7 + 0.6 mg/kg), zoletil (4 mg/kg), and zoletil + xylazine (4 + 0.2 mg/kg)] on intraocular pressure (IOP) was determined in cynomolgus monkeys.

Results

The administration of ketamine + xylazine or zoletil + xylazine resulted in lower IOP compared to ketamine or zoletil alone. Moreover, the IOP in male monkeys was higher than in females. The difference between the right and left eye was not found.

Conclusions

Anesthetics affected the IOP, and gender differences should be considered when measuring the IOP of nonhuman primates (NHPs).

INTRAOCULAR PRESSURE, TEAR PRODUCTION, AND OCULAR BIOMETRY IN HEALTHY ADULT CHEETAHS (ACINONYX JUBATUS)

Schirmer tear test (STT), intraocular pressure (IOP), and ocular biometry were measured in 58 healthy cheetahs (Acinonyx jubatus) between the ages of 2 and 14 yr in two captive groups. During routine health examination under immobilization, each animal underwent ophthalmic examination including STT, IOP, slit-lamp biomicroscopy, indirect ophthalmoscopy, and ocular ultrasonography. Mean ± SD values for STT and IOP were 13.58 ± 5.29 mm/min and 31.40 ± 5.01 mm Hg, respectively. The time between immobilization and examination significantly influenced both STT and IOP measurements. For IOP measurements, a significant group effect was also demonstrated, possibly due to the different anesthetic drug combinations used. Mean ± SD values for biometry were as follows: globe length (32.73 ± 1.74 mm), lens thickness (7.25 ± 1.09 mm), anterior chamber (8.54 ± 1.21 mm), and posterior segment (16.31 ± 2.06 mm). Surprisingly, all of the biometry measurements differed significantly between the two groups. Establishing STT, IOP, and biometric reference values is important for evaluating the ocular health status of the species. These reference values will assist veterinarians working with cheetahs to perform a full and informed ophthalmic examination.

Hyperbranched Cationic Glycogen Derivative-Mediated IκBα Gene Silencing Regulates the Uveoscleral Outflow Pathway in Rats

The role of the IκB/NF-κB signaling pathway in the uveoscleral outflow pathway was investigated with IκBα gene silencing mediated by the 3-(dimethylamino)-1-propylamine-conjugated glycogen (DMAPA-Glyp) derivative. The IκBα-siRNA-loaded DMAPA-Glyp complex was transfected into the ciliary muscles of rats by intracameral injection (labeled as the DMAPA-Glyp+siRNA group). The Lipofectamine™ 2000 (Lipo)/siRNA complex and the naked siRNA were set as the controls. The mRNA and protein expression of IκBα, NF-κBp65, and MMP-2 were analyzed by real-time PCR, western blotting, and in situ gelatin zymography. Nuclear translocation of NF-κBp65 was analyzed by immunofluorescence. Rat intraocular pressure (IOP) was monitored pre- and postinjection. Gene transfection efficiency and toxicity of the DMAPA-Glyp derivative were also evaluated. After RNA interference (RNAi), IκBα mRNA and protein expression were significantly inhibited. NF-κBp65 mRNA and protein expression showed no significant differences. Nevertheless, nuclear translocation of NF-κBp65 occurred in the DMAPA-Glyp+siRNA group. Both mRNA expression and activity of MMP-2 increased, with the largest increase in the DMAPA-Glyp+siRNA group. IOP in the DMAPA-Glyp+siRNA group fell to the lowest level on day 3 after RNAi. The levels of Cy3-siRNA in the ciliary muscle of the DMAPA-Glyp+siRNA group did not significantly decrease over time. At 7 and 14 d after RNAi, no significant pathological damage was detectable in the eyes injected with the DMAPA-Glyp derivative or the DMAPA-Glyp/siRNA complex. Taken together, our results suggest that downregulation of IκBα expression in the ciliary muscle plays a crucial role in reducing the IOP values of rats. IκBα may become a new molecular target for lowering IOP in glaucoma. The DMAPA-Glyp derivative is safe and feasible as an effective siRNA vector in rat eyes.

Effect of multiple head positions on intraocular pressure in healthy, anesthetized horses during hoisting

OBJECTIVE

To evaluate changes in intraocular pressure (IOP) with variable head position in healthy, anesthetized horses in hoisted inversion and to assess the influence of various cofactors (age, sex, body weight, body condition score, and neck length) on IOP changes during hoisting.

ANIMALS STUDIED

Seventeen healthy adult horses without significant ocular abnormalities.

PROCEDURES

Subjects were administered intravenous xylazine/butorphanol premedication and ketamine/midazolam induction with xylazine/ketamine boluses for anesthetic maintenance. While hoisted, IOP was measured in triplicate for each eye via rebound tonometry (TonoVet) at neutral head position (ie, eyes level with the withers), at multiple 5 cm increments above and below neutral (-20 cm through +20 cm) using foam pads for head support, and with eyes above heart level via manual support.

RESULTS

In hoisted positions, IOP ranged from 18 to 51 mmHg. Intraocular pressure significantly decreased with head position elevated ≥+15 cm from neutral and significantly increased when lowered ≤-5 cm from neutral. Neck length significantly influenced IOP (P = .0328) with linear regression indicating a median (range) increase of 0.244 (0.034-0.425) mmHg in IOP for every 1 cm increase in neck length. Age, sex, breed, body weight, body condition score, and eye (OD vs OS) did not significantly influence IOP. Intraocular pressure only varied significantly between eyes at +10 cm above neutral (OS > OD, 1.7 ± 0.6 mm Hg, P = .0044).

CONCLUSIONS

Intraocular pressure in healthy, anesthetized horses varies with head position during hoisting; increased neck length may be associated with larger changes in IOP during hoisting.

Ophthalmic contributions to assessing eyes of two neotropical canids: Cerdocyon thous and Chrysocyon brachyurus

OBJECTIVE

To describe selected ophthalmic tests and anatomical features of eyes of crab-eating foxes (Cerdocyon thous) and maned wolves (Chrysocyon brachyurus).

ANIMALS STUDIED

Six crab-eating foxes (12 eyes), eight maned wolves (16 eyes).

PROCEDURES

Intramuscular and/or inhalatory anesthesia, ophthalmic evaluation with portable slit-lamp biomicroscope, Schirmer tear test (STT), intraocular pressure measurement with rebound and applanation (crab-eating fox only) tonometers, measurement of palpebral fissure length (PFL), gonioscopy, and fundoscopy. Data were analyzed with ANOVA and Tukey's tests.

RESULTS

Both species presented upper and lower eyelids, both with eyelashes and Meibomian glands openings. A third eyelid was also present. In partial miosis, pigmented projections were observed along the edge of the pupil. The draining angle was open, with thin pectinate ligaments. The retina was holangiotic. For crab-eating foxes, mean ± standard deviation values were as follows: STT: 4.33 ± 2.96 mm/min; PFL: 17.45 ± 1.55 mm; rebound tonometry: 10.70 ± 3.43 mm Hg (TonoVet^® calibration D),5.66 ± 3.44 mm Hg (TonoVet^® calibration P), 17.00 ± 4.64 mm Hg (TonoVet^® Plus calibration dog); and applanation tonometry: 11.70 ± 5.70 mm Hg(TonoPen^® XL). For maned wolves, the mean ± standard deviation values were as follows: STT: 9.31 ± 7.40 mm/min; PFL: 22.79 ± 1.63 mm; rebound tonometry: 11.00 ± 2.77 mm Hg (TonoVet^® calibration D), 6.78 ± 2.58 mm Hg (TonoVet^® calibration P), and 18.29 ± 3.47 mm Hg(TonoVet^® Plus calibration dog).

CONCLUSIONS

This study contributes with knowledge that can help the clinical assessment regarding eyes of crab-eating foxes and maned wolves. The data herein presented for rebound tonometry are new for both species.

A systematic review of the effects of injectable sedative and anesthetic drugs and inhalant anesthetics on intraocular pressure in the dog

OBJECTIVE

The purpose of this systematic review was to summarize the results of studies that have determined the effect of injectable and inhalant drugs used in anesthesia on intraocular pressure (IOP) in dogs.

DATABASES USED

A comprehensive search of research literature was performed without language restriction. The search utilized the PubMed, CAB Abstracts and the University of Georgia's Galileo electronic databases using a combination of free text terms 'Ophthalmology', 'Intraocular Pressure', 'Anesthetic', 'Anesthesia', 'Canine' or 'Dog'. The time frame searched was from 1970 to October 2018. Any published research paper that dealt with sedatives or anesthetics administered systemically and the canine eye was evaluated.

CONCLUSIONS

The effects of many anesthetic drugs in dogs with ocular pathology are largely unknown. Many anesthetic drugs do not induce clinically relevant changes in IOP in dogs with normal eyes, although some studies demonstrated results with statistically significant changes. The dose, route of administration, experimental conditions, drug combinations, timing of measurements, measurement technology and setting or individual animal characteristics may all produce some heterogeneity in results from multiple studies.

Treatment of canine postoperative ocular hypertension with combined latanoprost 0.005% and atropine 1% ophthalmic solutions

OBJECTIVE

To compare the effects of topical 0.005% latanoprost (L) vs combined 0.005% latanoprost and 1% atropine (LA) on control of postoperative ocular hypertension (POH), development of posterior synechiae formation, pupil size, and blindness after phacoemulsification surgery in dogs.

ANIMAL STUDIED

Dogs with postoperative ocular hypertension were included in the study: L-group, latanoprost (eight dogs, 14 eyes) and LA-group, latanoprost and atropine (nine dogs, 15 eyes).

PROCEDURES

Complete ophthalmic examinations including tonometry were performed at 1, 7, and 21 days following phacoemulsification.

RESULTS

No significant differences were found between the measured intraocular pressure (IOP) at days 1 and 7 postphacoemulsification surgery in the L-group and the LA-group (P = 0.26 [14.12 ± 1.76 mmHg vs 16.96 ± 1.68 mmHg] and P = 0.71 [15.45 ± 1.43 mmHg vs 16.20 ± 1.36 mmHg], respectively). No significant differences were found between pupil sizes at day 7 for the two groups (P = 0.25 [13.83% vs 24.77%]). No significant differences were found between odds of posterior synechiae formation at day 21 (P = 0.92) with a probability ± SE for L-group vs LA-group at 0.27 ± 0.14 vs 0.25 ± 0.13. No significant differences were found in odds of postoperative blindness between groups (P = 0.58) with a probability ± SE of 0.21 ± 0.11 vs 0.13 ± 0.09, respectively for L and LA.

CONCLUSIONS

Combined topical latanoprost and atropine in dogs maintains normal postoperative IOPs but does not seem to cause increased mydriasis compared to latanoprost alone.

Measurement of tear production and intraocular pressure in conscious captive European fallow deer (DAMA dama)

Normal values for intraocular pressure (IOP) and tear production in conscious cervids have not been reported to date. Based on trends in zoological institutions to perform non-anaesthetized health exams, it is applicable to establish normal values in conscious animals, as anaesthesia and sedation can alter these parameters. The goal of this study was to estimate intraocular pressures using rebound tonometry and measure tear production values in a group of healthy, conscious, European fallow deer utilizing chute restraint. Evaluation of these values with regards to instrumentation and restraint variables will be assessed. Complete ophthalmic examinations, including estimation of IOP with rebound tonometry and measurement of tear production with Schirmer tear tests (STT) were performed on nine conscious European fallow deer (Dama dama) restrained in a chute. Correlations between IOP on the unspecified (P) and the equine (H) settings, as well as IOP and STT differences between left (OS) and right (OD) eyes were evaluated, in addition to assessment of correlations between right and left lateral recumbency on IOP and STT. Tear production measurements were 18.7 ± 5.1 mm min-1 with a 95% confidence interval (CI) range of 16.4-21.1 mm min-1 . Intraocular pressure measurements for the P setting were 16.1 ± 4.5 mmHg with a 95% CI range of 14.1-18.2 mmHg, and for the H setting were 21.5 ± 5.1 mmHg with a 95% CI range of 19.1-23.9 mmHg. No statistically significant difference (P > 0.05) was found between OS and OD in any test. Neither left nor right lateral recumbency was found to have a statistically significant effect on IOP or STT. This study represents the first assessment of ophthalmic parameters in conscious fallow deer with rebound tonometry and STT.

Effects of propofol on intraocular pressure in premedicated and nonpremedicated dogs with and without glaucoma

OBJECTIVE To establish a study cutoff for evidence of glaucoma on the basis of IOP measurements from a large population of healthy dogs and to assess the effects of IV propofol administration on IOPs in premedicated and nonpremedicated dogs with and without glaucoma defined by this method. DESIGN Prospective, descriptive study. ANIMALS 234 client-owned dogs. PROCEDURES IOPs measured in 113 healthy dogs (226 eyes) were used to calculate an IOP value indicative of glaucoma. The IOPs were measured in an additional 121 dogs (237 eyes) undergoing ophthalmic surgery. Midazolam-butorphanol was administered IV as preanesthetic medication to 15 and 87 dogs with and without glaucoma, respectively. A placebo (lactated Ringer solution) was administered IV to 8 and 11 dogs with and without glaucoma, respectively. Anesthesia of surgical patients was induced with propofol IV to effect. The IOPs and physiologic variables of interest were recorded before (baseline) and after preanesthetic medication or placebo administration and after propofol administration. RESULTS An IOP > 25 mm Hg was deemed indicative of glaucoma. Compared with baseline measurements, mean IOP was increased after propofol administration in nonpremedicated dogs without glaucoma and unchanged in nonpremedicated dogs with glaucoma. Propofol-associated increases in IOP were blunted in premedicated dogs without glaucoma; IOP in affected eyes of premedicated dogs with glaucoma was decreased after preanesthetic medication and after propofol administration. CONCLUSIONS AND CLINICAL RELEVANCE Results indicated that preexisting IOP influences the response to anesthetic drugs, and administration of preanesthetic medication with muscle-relaxing properties may blunt or reduce propofol-induced increases in IOP. Further research with a larger number of dogs is needed to confirm our results in dogs with glaucoma.

Effects of premedication with oral gabapentin on intraocular pressure changes following tracheal intubation in clinically normal dogs

Background

Gabapentin is an antiepileptic drug widely approved as an add-on therapy for epilepsy treatment in human and dogs. There is a clinical impression that gabapentin is a suitable drug which attenuates the IOP elevation associated with tracheal intubation in humans. The present study performed to determine the effects of oral gabapentin on intraocular pressure (IOP) changes following tracheal intubation in dogs.

Results

Twenty adult healthy dogs were randomly assigned to treatment (n = 10) and control (n = 10) groups. Dogs in the treatment group received oral gabapentin (50 mg/kg) 2 h before induction of anesthesia and dogs in the control group received oral gelatin capsule placebo at the same time. The dogs were anesthetized with propofol 6 mg/kg, and anesthesia was maintained with a constant infusion of 0.2 mg/kg/min of propofol for 20 min. IOP were measured immediately before induction and then repeated immediately after induction, as well as 5 min, 10 min and 15 min following tracheal intubation in both groups. IOP was significantly higher immediately after induction, and 5 min after tracheal intubation when compared with IOP reading before induction in the control group. There was no statistically significant change in IOPs immediately after induction, and 5 min after tracheal intubation in comparison to the values before induction in the treatment group.

Conclusions

Based on the findings of this study, preanesthetic oral administration of gabapentin significantly prevents an increase in the IOP associated with tracheal intubation in dogs anesthetized with propofol.

Effect of tiletamine-zolazepam on the intraocular pressure of the dog

OBJECTIVE

To determine the effect of tiletamine-zolazepam (TZ) on canine intraocular pressure (IOP).

ANIMALS STUDIED

Six healthy dogs without ocular abnormalities were used in this study.

PROCEDURES

The study was carried out as a crossover experimental trial with a 7-day interval between treatments. TZ combination was administered intravenously (IV) at a dose of 5, 10, and 20 mg/kg (TZ5, TZ10, and TZ20, respectively). Following preanesthetic baseline readings of IOP, each dog received IV TZ and then the IOP values were measured every 10 min for 40 min in all treatments.

RESULTS

The baseline IOP values (mean ± standard deviation) for TZ5, TZ10, and TZ20 were 12.7 ± 0.8, 14.4 ± 1.2, and 15.3 ± 1.7 mmHg, and each IOP changed to 11.1 ± 1.1, 13.1 ± 1.4 and 13.5 ± 1.7 mmHg after intravenous administration of each TZ treatment, respectively. However, there were no statistical differences between baseline and post-treatment values.

CONCLUSIONS

The TZ combination had no clinically significant effect on IOP of the dog. This could be an option for induction or surgical procedures in dogs with ophthalmic problems when an increase in IOP is undesirable.

Effects of ketamine, propofol, or thiopental administration on intraocular pressure and qualities of induction of and recovery from anesthesia in horses

OBJECTIVE

To assess the effects of ketamine hydrochloride, propofol, or compounded thiopental sodium administration on intraocular pressure (IOP) and qualities of induction of and recovery from anesthesia in horses.

ANIMALS

6 healthy adult horses.

PROCEDURES

Horses were sedated with xylazine hydrochloride (0.5 mg/kg), and anesthesia was induced with guaifenesin followed by ketamine (2 mg/kg), propofol (3 mg/kg), or thiopental (4 mg/kg) in a crossover study with ≥ 1 week between treatments. For each horse, IOP in the right eye was measured with a handheld applanation tonometer before and after xylazine administration, at the time of recumbency, and every 3 minutes after induction of anesthesia until spontaneous movement was observed. Cardiorespiratory responses and venous blood measurements were recorded during anesthesia. Induction of and recovery from anesthesia were subjectively evaluated by investigators who were unaware of the anesthetic treatment of each horse. Data were analyzed via a repeated-measures ANOVA with Holm-Ŝidák post hoc comparisons.

RESULTS

Compared with findings after xylazine administration (mean ± SD, 17 ± 3 mm Hg), thiopental decreased IOP by 4 ± 23%, whereas propofol and ketamine increased IOP by 8 ± 11% and 37 ± 16%, respectively. Compared with the effects of ketamine, propofol and thiopental resulted in significantly lower IOP at the time of recumbency and higher heart rates at 3 minutes after induction of anesthesia. No other significant differences among treatments were found.

CONCLUSIONS AND CLINICAL RELEVANCE

These findings support the use of thiopental or propofol in preference to ketamine for horses in which increases in IOP should be minimized.

The effect of ketamine on intraocular pressure in pediatric patients during procedural sedation

OBJECTIVES

Ketamine is one of the most commonly used procedural sedation and analgesia (PSA) agents in pediatric emergency departments (PEDs). It is considered a very safe and reliable agent, with limited respiratory suppression, hemodynamic effects, and adverse outcomes. However, physicians are often reluctant to use ketamine for patients with eye injuries due to a concern that ketamine might increase intraocular pressure (IOP). The objective was to measure IOP in previously healthy children receiving ketamine for PSA for a reason other than eye injury.

METHODS

This was a prospective noninferiority study of patients seen in an academic tertiary care children's hospital emergency department (ED) who required ketamine for PSA. The authors measured IOP in the right eye as soon as possible after ketamine had been administered and then at 2.5, 5, and 10 minutes after ketamine had been administered.

RESULTS

Eighty patients were enrolled (28 between 1 and 5 years of age, 26 between 6 and 10 years, 26 between 11 and 15 years); 49 (61%) were male. Procedures requiring PSA included fracture/dislocation reduction (63%), abscess incision and drainage (16%), laceration repair (11%), dental abscess incision and drainage (6%), and other (4%). The mean total ketamine dosage was 1.6 mg/kg (95% confidence interval [CI] = 1.4 to 1.7). The mean initial IOP was 17.5 mm Hg (95% CI = 16.4 to 18.6 mm Hg) and at 2.5 minutes was 18.9 mm Hg (95% CI = 17.9 to 19.9 mm Hg). The mean difference was 1.4 mm Hg (95% CI = 0.4 to 2.4 mm Hg). Using a noninferiority margin of 2.6 mm Hg (15%), noninferiority (no significant elevation in IOP) was demonstrated with 95% confidence between the first and second readings.

CONCLUSIONS

 Ketamine does not significantly increase IOP in pediatric patients without eye injuries receiving typical PSA dosages in the PED. Further study should assess its safety in patients with ocular injury.

Reference intervals for intraocular pressure measured by rebound tonometry in ten raptor species and factors affecting the intraocular pressure

Intraocular pressure (IOP) was measured with the TonoVet rebound tonometer in 10 raptor species, and possible factors affecting IOP were investigated. A complete ophthalmic examination was performed, and IOP was assessed in 2 positions, upright and dorsal recumbency, in 237 birds belonging to the families Accipitridae, Falconidae, Strigidae, and Tytonidae. Mean IOP values of healthy eyes were calculated for each species, and differences between families, species, age, sex, left and right eye, as well as the 2 body positions were evaluated. Physiologic fluctuations of IOP were assessed by measuring IOP serially for 5 days at the same time of day in 15 birds of 3 species. Results showed IOP values varied by family and species, with the following mean IOP values (mm Hg +/- SD) determined: white-tailed sea eagle (Haliaeetus albicilla), 26.9 +/- 5.8; red kite (Milvus milvus), 13.0 +/- 5.5; northern goshawk (Accipiter gentilis), 18.3 +/- 3.8; Eurasian sparrowhawk (Accipiter nisus), 15.5 +/- 2.5; common buzzard (Buteo buteo), 26.9 +/- 7.0; common kestrel (Falco tinnunculus), 9.8 +/- 2.5; peregrine falcon, (Falco peregrinus), 12.7 +/- 5.8; tawny owl (Strix aluco), 9.4 +/- 4.1; long-eared owl (Asio otus), 7.8 +/- 3.2; and barn owl (Tyto alba), 10.8 +/- 3.8. No significant differences were found between sexes or between left and right eyes. In goshawks, common buzzards, and common kestrels, mean IOP was significantly lower in juvenile birds than it was in adult birds. Mean IOP differed significantly by body position in tawny owls (P = .01) and common buzzards (P = .04). By measuring IOP over several days, mean physiologic variations of +/- 2 mm Hg were detected. Differences in IOP between species and age groups should be considered when interpreting tonometric results. Physiologic fluctuations of IOP may occur and should not be misinterpreted. These results show that rebound tonometry is a useful diagnostic tool in measuring IOP in birds of prey because it provides rapid results and is well tolerated by birds.

Intraocular pressure and Schirmer tear test results in clinically normal Long-Eared Hedgehogs (Hemiechinus auritus): reference values

OBJECTIVE

The present study was undertaken to establish reference values for Schirmer tear test (STT) and intraocular pressure (IOP) in the long-eared hedgehog (Hemiechinus auritus).

ANIMALS

Fourteen healthy long-eared hedgehogs (H. auritus) of either sex were studied.

PROCEDURES

The hedgehogs were individually immobilized with an intramuscular injection of combined Ketamine (20 mg/kg) and Diazepam (0.5 mg/kg), and each animal underwent ophthalmic examinations including: STT, tonometry, biomicroscopy, and indirect ophthalmoscopy.

RESULTS

No significant effects of animal gender, weight, side (right vs. left eye) were found in this study. Mean (SD) STT values for all eyes (n = 28) were 1.7 ± 1.2 mm/1 min with a range of 0-4 mm/1 min. Mean STT in male animals was 2.2 ± 1.2. Mean STT in female Hedgehogs was 1.3 ± 1.1. Mean (SD) IOP values by applanation tonometry were 20.1 ± 4.0 mmHg (range 11.5-26.5 mmHg). Mean (SD) IOP values by applanation tonometry were 18.2 ± 4.0 and 22.0 ± 3.2 mmHg for males and females, respectively.

CONCLUSIONS

This study reports STT and IOP findings in long-eared hedgehogs (H. auritus).

Effect of daily prolonged ketamine anesthesia on intraocular pressure in monkeys

PURPOSE

To determine if repeated intramuscular ketamine in monkeys on consecutive days affects intraocular pressure (IOP) and if the ketamine-induced IOP change has any relationship to systemic dehydration and/or changes in mean arterial pressure (MAP) of the animals.

METHODS

Nine monkeys were studied per four protocols. IOP was determined hourly for 6 hr by Goldmann tonometry under ketamine anesthesia on 3 (protocol 1) or 5 (protocols 2 and 3) consecutive days, or on alternating days 1, 3, and 5 (protocol 4). Monkeys in protocols 3 and 4, but not in protocols 1 and 2, received subcutaneous Ringer's fluids at the end of each 6-hr session on days 1-4 or days 1, 3, and 5; monkeys in protocols 2 and 3 received intravenous fluid infusion throughout the experiment on day 5. In protocols 2-4, MAP was measured hourly following each IOP measurement.

RESULTS

Monkeys receiving ketamine but no Ringer's fluids in protocol 1 or 2 showed significant IOP declines on days 2-3 or 2-4. The IOP declines were greater in magnitude in protocol 1 than in protocol 2. Daily subcutaneous Ringer's fluids appeared to delay IOP declines in protocol 3. Continuous intravenous fluid infusion on day 5 variably prevented IOP declines in protocols 2 and 3. Monkeys receiving ketamine and subcutaneous fluids on alternate days in protocol 4 showed no decline in IOP. No significant relationship between IOP and MAP was observed.

CONCLUSIONS

Anesthesia induced by repeated intramuscular ketamine on consecutive days may produce significant IOP declines. Systemic dehydration during the anesthesia seems to be the predominant factor contributing to the IOP reduction. However, inter-individual differences in monkeys indicate that multiple factors may be involved. This study also suggests that fluid supplementation plus alternating anesthesia with recovery days may prevent IOP reduction in monkeys resulting from daily prolonged ketamine anesthesia.