Medical Treatment of Primary Canine Glaucoma

Magnesium Hydroxide Nanoparticles Improve the Ocular Hypotensive Effect of Twice Daily Topical Timolol Maleate in Healthy Dogs

Timolol maleate (TM), a beta-adrenergic receptor antagonist, is widely used for canine antiglaucoma eye drops; however, its bioavailability is <5%. Our previous study revealed that magnesium hydroxide nanoparticles (nMH) have potency in improving the bioavailability of fixed-combined TM in rodent models. This study aimed to investigate whether the fixed combination with nMH improves the ocular hypotensive effect of TM and affects pupil size (PS), heart rate (HR), and mean arterial pressure (MAP) in clinically healthy dogs. Five clinically healthy dogs were administered topical saline, commercial 0.5% TM, and a 0.01% or 0.1% nMH–0.5% TM fixed combination (0.01% or 0.1% nMH–TM) twice daily in one eye for 7 days with at least a 28-day interval. The changes from baseline were calculated and were statistically analyzed for each drug. IOP was significantly reduced in both 0.01% and 0.1% nMH–TM-treated-dogs compared with saline- and TM-treated dogs. Meanwhile, 0.01% and 0.1% nMH did not exacerbate the side effects of TM. From these results, nMH improved the ocular hypotensive effect of TM without enhancing side effects. Topical nMH–TM is potentially more effective for canine ocular hypotensive eye drops than TM.

Effects of topical administration of tafluprost and combination of tafluprost and timolol or tafluprost and betaxolol on Schirmer tear test, intraocular pressure, and pupil size in clinically healthy dogs

PURPOSE

The aim of this study was to evaluate the effects of 0.0015% preservative-free (PF) tafluprost alone and in combination with 0.5% timolol maleate or 0.5% betaxolol HCl on Schirmer tear test (STT), intraocular pressure (IOP), and pupil diameter (PD) in clinically normal dogs.

METHODS

Twenty-one healthy adult castrated male cross-bred dogs were used in this study. Dogs were randomly divided into three groups. The first group received one drop of (PF) tafluprost (Taf), in a randomly selected eye. The second group received one drop of (PF) tafluprost plus one drop of timolol maleate (Taf-Tim), and the last group received one drop of (PF) tafluprost plus one drop of betaxolol HCl, (Taf-Bet). In all groups, the fellow eyes were served as control and received one drop of saline as a placebo. IOP, STT, and PD measurements were performed at the baseline and every 30 min for the first 2 h, every 2 h for the next 10 h, and at 24 h and 36 h post-instillation (PI).

RESULTS

In all groups, significant differences in IOP values were observed between treated and untreated eyes (Taf: p < 0.001, Taf-Tim: p = 0.014, Taf-Bet: p = 0.008). The maximum reduction in mean IOP after unilateral administration of Taf, Taf-Tim, and Taf-Bet was 8.3 mmHg, 10.7 mmHg, and 13 mmHg, respectively. No significant differences in STT values were observed between treated and untreated eyes at any time points. In all groups, significant differences in PD values were observed between treated and untreated eyes in all time points except the baseline and 36 h post-drug instillation (p < 0.001).

CONCLUSIONS

Tafluprost alone or in combination with timolol and betaxolol was able to reduce intraocular pressure. The greatest effect of the drugs occurred 6 and 8 h PI. The present study revealed that the combination of tafluprost/betaxolol is more potent in decreasing IOP than tafluprost alone or a combination of tafluprost/timolol in healthy dogs.

Ocular Emergencies in Small Animal Patients

Small animal ocular emergencies vary from relatively benign to potentially vision or life threatening, with significant overlap in clinical signs. Careful ophthalmic examination in dim light conditions with a bright light source and competent patient head restraint are crucial to properly diagnosing ocular disease. Adjunctive ophthalmic diagnostic testing should be performed to rule out corneal ulceration, glaucoma, and dry eye before empiric topical antibiotic or steroid medications are prescribed. Most emergency cases present because of ocular redness, cloudiness, discomfort, apparent bulging, or vision loss; categorizing differential diagnoses on this basis can be helpful to the emergency clinician.