Objective—To assess the effect of treatment with a topical ophthalmic preparation of 1.2% nalbuphine solution on corneal sensitivity in clinically normal horses.
Procedures—Baseline corneal touch threshold (CTT) was measured (defined as the mean filament length [mm] at which a consistent blink response was elicited) for both eyes of each horse by use of a Cochet-Bonnet aesthesiometer. Subsequently, 0.2 mL of 1.2% nalbuphine solution was instilled in 1 randomly selected eye of each horse, and 0.2 mL of artificial tears solution was instilled in the contralateral eye (control treatment). For all 8 horses, CTT of each eye was measured within 1 minute following nalbuphine or artificial tears administration and every 15 minutes thereafter for 60 minutes. For 5 of the 8 horses, CTT was also measured in both eyes at 120 minutes. Changes in CTT values from baseline over time were assessed, as were differences between treated and control eyes.
Results—At any time point, corneal sensitivity following nalbuphine treatment did not differ significantly from control treatment findings. Mean CTTs for nalbuphine-treated and control eyes were 38.8 and 37.9 mm, respectively. In both groups, CTT was significantly lower than baseline value at 15, 45, 60, and 120 minutes. No tearing or redness developed in any eye treated with nalbuphine.
Conclusions and Clinical Relevance—Topical administration of ophthalmic 1% nalbuphine solution had no effect on corneal sensitivity in clinically normal horses. The topical ocular treatment was not associated with local irritation.
Objective—To measure duration of corneal anesthesia and time and degree of maximal anesthetic effect of 0.5% proparacaine hydrochloride by use of a Cochet-Bonnet aesthesiometer in horses.
Animals—10 clinically normal adult horses.
Procedures—Baseline corneal touch threshold (CTT) was measured in millimeters for 1 randomly selected eye of each horse by use of the aesthesiometer by applying the filament to the cornea at maximum length (60 mm) and decreasing in 5-mm increments until a consistent blink response was elicited. Following baseline CTT measurement, 0.2 mL of 0.5% proparacaine hydrochloride was instilled in the selected eye. The CTT was measured within 1 minute following proparacaine administration and every 5 minutes thereafter for 60 minutes. A mixed-model ANOVA with tested eye varying between subjects and measurement time varying within subject was used to test for main effects and any interaction between these factors. A contrast between means of baseline and each subsequent CTT identified the duration of corneal anesthesia as the time at which there was no difference from baseline. Maximal anesthetic effect occurred at the time with the lowest mean CTT.
Results—Duration of corneal anesthesia achieved by use of proparacaine was 25 minutes, and maximal anesthetic effect occurred within 5 minutes, although CTT never went to 0 in any horse at any time.
Conclusions and Clinical Relevance—Duration of corneal anesthesia in horses was shorter than in dogs, and degree of maximal effect was less than in cats and dogs, most likely because of increased sensitivity of the equine cornea, compared with corneal sensitivity in those species.