Lack of effects of intramuscular medetomidine on intraocular pressure in clinically normal cats

Diagnostic Tests Used During the Ocular Examination

This article provides a review of the required ocular tests during the ophthalmologic examinations of canine and feline patients. Knowledge of medications affecting ocular parameters and awareness of available instrumentation and test materials is essential for accurate diagnoses.

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.

Ophthalmic effects of dexmedetomidine, methadone and dexmedetomidine-methadone in healthy cats and their reversal with atipamezole

OBJECTIVES

The aims of this study were to evaluate and compare the effects that dexmedetomidine and methadone, either alone or in combination, have on the ocular variables of healthy adult cats when administered intramuscularly, as well as their reversal with atipamezole.

METHODS

A randomized crossover blinded study of 10 healthy cats was used to assess the effect of 0.2 mg/kg methadone (MET), 7.5 μg/kg dexmedetomidine (D7), 10 μg/kg dexmedetomidine (D10), 7.5 μg/kg dexmedetomidine and 0.2 mg/kg methadone (DM7) and 10 μg/kg dexmedetomidine and 0.2 mg/kg methadone (DM10) on intraocular pressure (IOP), tear production and pupil diameter (PD). The animals were evaluated for 30 mins. Afterwards, atipamezole was administered and ocular variables were evaluated for 30 mins.

RESULTS

D10, DM7 and DM10 significantly decreased mean IOP but MET or D7 did not. Tear production decreased significantly in all treatments, corresponding to 18%, 59%, 63%, 86% and 98% in MET, D7, D10, DM7 and DM10, respectively. PD increased in all treatments, but MET showed the highest PD. Thirty minutes after atipamezole (RT30), IOP returned to baseline with no difference between groups, and there was a significant increase in tear production, but the means were still different from baseline.

CONCLUSIONS AND RELEVANCE

Dexmedetomidine decreases IOP and tear production but increases PD in healthy cats. Atipamezole can partly reverse those alterations. Low-dose dexmedetomidine (7.5 µg/kg) promotes sedation without changing the IOP. All protocols significantly decrease tear production, and Schirmer tear test after sedation is not representative of non-sedated values. Methadone induces quick onset mydriasis without changing the IOP.

MEASUREMENT OF INTRAOCULAR PRESSURE USING REBOUND TONOMETRY IN ANESTHETIZED PERUVIAN FUR SEALS (ARCTOCEPHALUS AUSTRALIS) FROM PUNTA SAN JUAN, PERU

Ocular disease in pinnipeds under human care is well described, and intraocular pressure (IOP) can be impacted by a variety of ophthalmic conditions. Species-specific reference parameters from clinically normal animals are instrumental for understanding how ophthalmic diseases may impact ocular pressures. IOP measurements were obtained using rebound tonometry from free-ranging Peruvian fur seals (Arctocephalus australis unnamed subspecies) at Punta San Juan, Peru, over a 6-yr period (2010-2016). Retrospective data obtained from 108 (81 adults and 27 neonates comprising 69 females and 39 males) anesthetized fur seals with normal anterior segment ophthalmic examinations was included in the analysis. Differences in IOP from each eye were compared to categorical variables (age, year, sex, restraint) using an independent-samples t test. All univariate results with a significance of P < 0.05 were included in multivariate analysis. Of the 13 general linear models evaluated, the top two for both the right and the left eye included age class when all variables were evaluated simultaneously. Neonates had significantly lower IOP values than adults in both the right eye (17.5 mm Hg; 95% confidence interval [CI]: 14.0-21.1 mm Hg compared to 33.5 mm Hg; 95% CI: 31.0-36.1 mm Hg, respectively) and the left eye (18.4 mm Hg; 95% CI: 14.4-22.5 mm Hg compared to 32.3 mm Hg; 95% CI: 29.3-35.3 mm Hg, respectively). Anesthesia method was not statistically significant (P > 0.05). This is the first report of normal IOP measurements for any fur seal species. Described data can be used to improve diagnosis and management of ocular alterations in pinnipeds.

Intraocular pressure and pupil diameter in healthy cats anesthetized with isoflurane and pre-medicated with isolated acepromazine or in combination with tramadol

ABSTRACT The objective of this study was to determine changes on intraocular pressure (IOP) and pupil diameter (PD) in healthy cats anesthetized with isoflurane, and premedicated with acepromazine alone or in combination with tramadol. Thirty cats were allocated in two groups (n=15/each) and were treated with acepromazine (AG) or acepromazine/tramadol (ATG). PD and IOP were assessed before and following 30 (PM1), and 40 minutes (PM2) of treatments. Anesthesia was induced with propofol, and IOP and DP were recorded (A10) at 10 minute intervals until the end of anesthesia (A40). IOP decreased in AG and ATG, when comparing baseline with PM1. IOP decreased only in AG, in comparisons between baseline and PM2. During anesthesia, IOP did not change within and between groups. Comparisons between baseline with those recorded at PM1 and 2 showed that PD increased in the ATG. During anesthesia, PD decreased significantly in AG and ATG. Both protocols maintained the IOP within the reference range to perform corneal or intraocular surgery in healthy cats but did not sustain pre-anesthetic pupil dilation observed in ATG.

Comparison of two eyelid speculums and their effect on intraocular pressure in clinically normal cats

OBJECTIVES

The present study was undertaken to determine the possible effects of the placement two different types of eyelid speculum on intraocular pressure (IOP) measurement in clinically normal cats.

METHODS

Thirty healthy cats were divided randomly into two groups of 15, group B (Barraquer wire speculum) and group W (Williams eye speculum). All cats were sedated with intramuscular medetomidine (Dorbene vet; 100 μg/kg) then placed in right lateral recumbency, and IOP was recorded in the left eye using a Tono-Pen Vet tonometer without and with an eyelid speculum in place in both groups.

RESULTS

The without-speculum IOPs for cats in group B and group W were 13.8 ± 3.0 mmHg and 13.2 ± 3.6 mmHg, respectively, and did not differ significantly. A significant increase in IOP (19.8 ± 3.7 mmHg) was observed in group W in with-speculum measurements in comparison to the without-speculum values (P <0.001).There was no significant difference between with- and without-speculum IOP values (13.8 ± 2.7 mmHg) in group B (P = 1.0).

CONCLUSIONS AND RELEVANCE

The Barraquer wire speculum has no effect on IOP compared with the Williams eye speculum in normal cats, and may be an appropriate choice in cats for intraocular surgeries that cannot tolerate acute increases in IOP.

Measurement of Intraocular Pressure Using Rebound Tonometry in Anesthetized Free-ranging South American Sea Lions (Otaria byronia)

Intraocular pressures (IOPs) were measured using a rebound tonometer in 56 free-ranging adult South American sea lions (Otaria byronia) from Punta San Juan, Peru. All animals were anesthetized using medetomidine, midazolam, and butorphanol and determined to be in good health. No ocular abnormalities were observed affecting the cornea or ocular adnexa. Field conditions precluded evaluation of the lens and posterior segment of the eye. Mean (SD) IOP values for males (n=37) were 31±11 mmHg (right eye) and 31±9 mmHg (left eye). The same values for females (n=19) were 24±9 mmHg in the left eye and 27±10 mmHg in the right eye. These values are similar to those previously reported for pinnipeds under professional care and higher than those generally reported for terrestrial mammals.

Effect of body position on intraocular pressure in clinically normal cats

Objectives The objective of this study was to investigate the effect of body position on intraocular pressure in clinically normal cats. Methods Sixteen clinically normal cats without any ocular abnormalities were used in this study. Cats were sequentially placed in three different recumbency positions (sternal recumbency, right lateral recumbency and dorsal position). For each of the three body positions, intraocular pressure (IOP) was recorded in the left eye using a Tono-Pen Vet tonometer (Reichert). Results Mean IOP readings in cats in the sternal recumbency, right lateral recumbency and dorsal positions were 15.6 ± 4.1, 16.6 ± 6.4 and 18.6 ± 6.8 mmHg, respectively. A significant increase was observed in IOP in cats in the dorsal position compared with the IOP observed in cats in sternal recumbency ( P = 0.01) and right lateral recumbency ( P = 0.04). There was no significant difference between the IOP recorded in the lateral recumbency and sternal recumbency ( P = 0.17) positions. Conclusions and relevance Body position has a significant effect on the IOP of cats. IOP increases when cats are placed in dorsal recumbency.