Effect of topical 1% cyclopentolate hydrochloride on tear production, pupil size, and intraocular pressure in healthy Beagles

Optical Coherence Tomography: A Review of Current Applications in Veterinary Ophthalmology

Normative standards for healthy animal structures have been established by optical coherence tomography (OCT). OCT has been used in animal studies to characterize more precisely ocular lesions, identify the origin of the affected layer, and eventually provide a curative treatment. To acquire a high image resolution, several challenges must be overcome when performing an OCT scan on animals. Sedation or general anesthesia is usually necessary in OCT image acquisition to alleviate motion during image acquisition. Mydriasis, eye position and movements, head position, and corneal hydration must also be managed during the OCT analysis.

Topical Ocular Therapeutics in Small Animals

This article reviews the administration of common topical ophthalmic medications, in relation to factors influencing absorption including composition of topical ophthalmic preparations, and potential systemic effects. Commonly prescribed, commercially available topical ophthalmic medications are discussed with respect to pharmacology, their indications for use, and adverse effects. Knowledge of topical ocular pharmacokinetics is essential for the management of veterinary ophthalmic disease.

Comparative effects of latanoprost and latanoprostene bunod on intraocular pressure and pupil size in ophthalmologically normal Beagle dogs

OBJECTIVE

To compare effects of latanoprost, a topical prostaglandin analogue (PGA) commonly used to treat glaucoma and lens instability in dogs, and latanoprostene bunod, a novel PGA with a nitric oxide-donating moiety, on intraocular pressure (IOP) and pupil diameter (PD).

ANIMALS STUDIED

Ten ophthalmologically normal Beagle dogs.

PROCEDURES

Dogs were treated twice a day for 5 days in a randomly selected eye with either latanoprost or latanoprostene bunod. After a 6-week washout period, dogs were treated with the opposite drug. IOP and PD were measured at treatment times, at midday on days 1 and 5, and for 6 days post-treatment.

RESULTS

Both drugs significantly decreased IOP and PD. At midday on day 5 of treatment, mean IOP in eyes treated with latanoprost was 4.5 mmHg lower than the fellow eye and 3.0 mmHg lower than the same eye at baseline, while mean IOP in eyes treated with latanoprostene bunod was 5.5 mmHg lower than the fellow eye and 3.6 mmHg lower than baseline. Mean PD was 0.94 mm in eyes treated with latanoprost and 0.76 mmHg in eyes treated with latanoprostene bunod. There was no significant difference between the two drugs for either parameter at that time point (p = .372 and .619, respectively, for IOP relative to control and to baseline; p = .076 for PD) or when analyzed longitudinally. Significant diurnal variation in PD was noted and may have implications for treatment of lens' instability.

CONCLUSIONS

Latanoprost and latanoprostene bunod produce similar IOP reduction and miosis in normal canine eyes.

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.

Effect of Topical Cyclopentolate 1% on Ocular Ultrasonographic Features, Intraocular Pressure, Tear Production, and Pupil Size in Normal Donkeys (Equus Asinus)

This study was performed to investigate the effects of cyclopentolate on ultrasonographic parameters of eye structures, intraocular pressure (IOP), tear production, and pupil size in normal donkeys. Sixteen eyes of eight clinically healthy adult donkeys (2-2.5 years old) weighing 295 ± 34 kg (mean ± standard deviation) were used in this study. Cyclopentolate hydrochloride 1% was instilled in a randomly selected eye and the other eye received normal saline drops as a control. The effect of cyclopentolate was evaluated by ultrasonography. Additionally, changes in IOP and tear production were evaluated for 2 hours post-instillation by tonometry and Schirmer tear test (STT), respectively. Vertical and horizontal pupil diameters were recorded pre-instillation (0), and 15, 30-, 45-, 60-, and 120-minutes post-instillation. After cyclopentolate 1% instillation, iridocorneal angle and width of the entry of ciliary cleft were significantly increased as observed by ultrasonography. IOP was significantly increased starting from 30 minutes till 60 minutes post-instillation of cyclopentolate 1%. Non-significant alteration in the STT was observed in the cyclopentolate-treated eyes compared to the control eyes. Both vertical and horizontal pupil diameters began to significantly increase 30 minutes after cyclopentolate 1% instillation compared to the control saline group. In conclusion, cyclopentolate 1% could be used as a potent cycloplegic drug in donkeys without systemic or ocular side effects.

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.

Effects of orally administered gabapentin, tramadol, and meloxicam on ocular variables in healthy dogs

OBJECTIVE

To determine the effects of gabapentin, tramadol, and meloxicam on tear production, intraocular pressure (IOP), pupillary diameter, tear break-up time, and corneal touch threshold in healthy dogs when given orally for 3 days.

ANIMALS

9 healthy research Beagles.

PROCEDURES

A randomized, blinded, case-crossover study with a 6-sequence, 3-treatment, and 3-period design was performed. A 7-day acclimation period was followed by 3 treatment phases, each with a 3-day treatment period followed by a 7-day washout period for 3 different drugs. Block randomization was used to group dogs for treatments with drug A (gabapentin), B (tramadol), or C (meloxicam). Measurements of tear production, IOP, pupillary diameter, tear break-up time, and corneal touch threshold were performed on a schedule. A generalized mixed-effects linear regression model was created for each ocular variable, accounting for repeated measures within individuals.

RESULTS

Intraocular pressure was the only variable to have differed substantially between the first 5 and last 2 days of the acclimation period. When treatment phase, day, time of day, dog identification, baseline value, and eye were accounted for, the mean IOP was lower for dogs during treatment phases with gabapentin or tramadol, compared with meloxicam, but this difference was not considered clinically meaningful.

CONCLUSIONS AND CLINICAL RELEVANCE

Results indicated that a minimum 5-day acclimation period is necessary for IOP measurements to return to baseline in dogs. The statistically identified effect of gabapentin and tramadol on IOP in dogs of the present study warrants further investigation. It is possible that at higher dosages, or in dogs with glaucoma, this effect may become clinically significant.

Effects of topical 1% cyclopentolate hydrochloride on quantitative pupillometry measurements, tear production and intraocular pressure in healthy horses

OBJECTIVE

To evaluate the effect of topical cyclopentolate hydrochloride (CH) on quantitative pupillometric readings (PR), tear production (TP), and intraocular pressure (IOP) in healthy horses.

ANIMALS STUDIED

Fourteen client-owned horses.

PROCEDURES

In a two-phase design study, each animal received 1% CH ophthalmic solution in the left eye [treated] and 0.9% NaCl in the right eye [control] (0.2 mL each). In the first phase (n = 7), TP, IOP, and PR assessment was performed by Schirmer tear test I, rebound tonometry and static pupillometry, at 1, 8, 24, 48, 72, 96, 120, 148, 172, and 196-hours post-instillation. In the second phase (n = 7), plateau mydriasis was evaluated by assessing PR hourly for 8 hours post-instillation. For PR assessment, pupil area (PA), vertical diameter (VPD), and horizontal diameter (HPD) were recorded. All pupillometries were obtained in a room with fixed light intensity (45-60 lux). Statistical analysis was performed by generalized estimating equations method for the effect on parameters over time.

RESULTS

After topical CH, significant differences in pupil dilation were seen from 1 to 172 hours for VPD and from 8 to 24 hours for PA, without significant differences on HPD over time. In the second phase, plateau PA and VPD were reached at 3 hours, while plateau HPD at 2 hours. No significant effects were detected on TP and IOP in both eyes at any time, nor on PR of the nontreated eyes.

CONCLUSIONS

Topical 1% cyclopentolate hydrochloride could be considered an effective and safe option when a mydriatic/cycloplegic drug is needed in horses.

Changes in intraocular pressure, horizontal pupil diameter, and tear production during the use of topical 1% cyclopentolate in cats and rabbits

Background

Cyclopentolate is not commonly used as mydriatic drug in veterinary medicine because of limited data on the local and systemic effects in animals.

Aim

To determine the effects of topical 1% cyclopentolate hydrochloride on intraocular pressure (IOP), horizontal pupil diameter (HPD) and tear production in the cat and rabbit's eye during the first hour and up to 36 hours after treatment.

Methods

One drop of 1% cyclopentolate hydrochloride was used in the left eye in 10 clinically and ophthalmologically healthy domestic cats and 10 rabbits. IOP and HPD were recorded every 5 minutes during the first hour, then every 2 hours during the following 12-hour period, and at 24 and 36 hours after application. Schirmer tear test (STT) was measured at 30 and 60 minute after treatment, then in same time points as IOP and HPD. Rebound tonometer (TonoVet^®) was used to assess IOP, Jameson calliper to measure HPD and STT to determine the tear production.

Results

1% cyclopentolate increased IOP in cats, reaching a maximum (28.1 ± 5.4 mmHg) at T ₅₀ and in rabbits at T₂₅ (16.7 ± 1.3 mmHg). Maximal mydriasis in cats was observed at T ₄₀ and lasted 24-36 hours, but in rabbits at T ₂₅, and returned to pre-treatment values at T _10h-T _12h. In cats, STT decreased in both eyes 30 minutes after treatment and remained lower throughout the 36-hour period. In rabbits, STT decreased in the treated eye 30 minutes after treatment, but all following STT measurements returned to normal pre-treatment levels.

Conclusion

Study showed novel data about the effects of 1% cyclopentolate to IOP, HPD, STT in cats and rabbits. Cyclopentolate in cats caused mydriasis 20-40 minutes after the treatment by increasing IOP, at the same time, pupil diameter reached pre-treatment values 24-36 hours after treatment. In rabbit's mydriasis occurred faster, 10-25 minutes after treatment without significant IOP increase and mydriasis lasted 10-12 hours. Significant STT decrease was recorded in cats, but more likely were connected to stress factors. This drug could be considered as a therapeutical alternative in rabbit more than in cats.

Effect of Topical 1% Cyclopentolate Hydrochloride on Tear Production, Intraocular Pressure, and Pupil Size in Healthy Turkman Horses

This study was performed to evaluate the effect of topical 1% cyclopentolate hydrochloride on tear production (STT), intraocular pressure (IOP), and vertical pupil diameter (VPD) in healthy Turkman horses. Forty eyes of 20 clinically normal horses were used for this study, which were randomly assigned to two groups. Before instillation of 1% cyclopentolate, the baseline STT, IOP, and VPD of each group were recorded. Then, one drop of cyclopentolate was instilled randomly into one eye of each animal, and the contralateral eye served as control. Measurements were repeated at 20 minutes, 60 minutes, 90 minutes, 120 minutes, 12 hours, and 24 hours, and every 24 hours up to 120 hours post drug instillation in all animals. There was no significant effect on STT over the time course measured in both the treated and untreated eyes of the treatment groups after unilateral instillation of 1% cyclopentolate when compared to baseline values. A significant increase in the IOP was observed after 20 minutes, which persisted for more than 90 minutes; then, the IOP insignificantly decreased below the baseline values after 120 minutes. Maximum VPD was recognized at 12 hours post instillation in treated eyes (15.8 ± 2.3 mm), which was significantly different in comparison to the baseline (P = .07). Cyclopentolate could be considered as a long term and potent cycloplegic drug in horses when taking into account the possible side effect of atropine.