Field use of N-butylscopolammonium bromide to facilitate thorough ophthalmic examination in horses.

The research article investigated the use of N-butylscopolammonium bromide (NBB), a type of muscle relaxant, as a means to dilate the pupils for a comprehensive eye examination in horses. The test compared NBB against different controls and measured its effectiveness based on changes in pupil size and the ability to carry out a complete examination of the horse’s eye.

Study Design and Approach

• The experiment involved six adult horses. These horses were randomly selected to participate in one of four treatments. There was a two-week washout period cleared between each treatment to prevent overlap and cross-effects.
• The treatments included: (1) topical saline combined with intravenous (IV) saline as the negative control; (2) topical tropicamide combined with IV saline as the positive control; (3) topical NBB alongside IV saline; and (4) topical saline paired with IV NBB.
• Several variables were recorded for each horse post-treatment, including horizontal and vertical pupil diameters, body temperature, heart rate, breathing rate, pupillary light reflexes (PLRs – the change in pupil size in response to light), and whether the horse’s pupil dilation (mydriasis) was sufficient for a complete examination of the fundus (back of the horse’s eye).

Results of the Experiment

• The results showed that the topical application of tropicamide, which was the positive control, led to pupil dilation in all horses. This outcome was expected, as this effect is known to be caused by tropicamide.
• When topical NBB was applied, mydriasis was observed in one horse. This suggested that NBB, when applied topically, may not be consistently effective in facilitating comprehensive eye examination in horses.
• By contrast, when NBB was administered intravenously, two horses had sufficient pupil dilation to enable a thorough fundic examination. However, two horses only showed delayed PLRs and weren’t conducive to a complete examination. In the remaining two horses, there seemed to be no noticeable effect of the IV NBB administration, indicating that its effectiveness may vary among individuals.

Conclusions of the Research

• The research provided mixed results regarding the use of N-butylscopolammonium bromide in either topical or intravenous application method to dilate horse pupils significantly enough to perform a complete eye examination.
• While NBB showed potential to produce mydriasis (pupil dilation), enabling full eye examination in some horses, it was not universally effective and its outcomes varied among the test subjects.
• The study suggests a need for further investigation into the use of NBB for ophthalmic use in horses before it can be conclusively decided if it’s a reliable and consistent method for pupils dilation in equine eye examinations.