Abstract
AIM: To document the efficacy of five commercially available mydriatics for their potential for diagnostic and therapeutic use in Angora goats.
METHODS: Over 8 weeks, the mydriatic effects of 1% tropicamide, 2% homatropine, 1% cyclopentolate, 1% atropine and 0.25% hyoscine were evaluated. Given as block treatments, drugs were applied randomly to one eye of 10 Angora goats, and the contralateral eye served as a control. Vertical and horizontal pupil diameters were measured to document onset ofeffect, time to reach a difference of 5 mm in the vertical/horizontal pupil diameter between eyes, time to maximum pupillary dilation, and duration of mydriatic action.
RESULTS: Onset of mydriasis for all drugs occurred within 15 minutes. Time to reach a difference of 5 mm in the vertical pupil diameter between eyes was shortest for 1% tropicamide and 0.25% hyoscine (0.5 h), then 2% homatropine and 1% atropine (0.75 h), and longest for 1% cyclopentolate (1.5 h). The maximum vertical pupillary dilation occurred earliest with 1% tropicamide and 1% atropine (2 h), followed by 0.25% hyoscine (3 h), 2% homatropine (4 h), and latest with 1% cyclopentolate (8 h). The duration of vertical dilation of the pupil was shortest with 1% tropicamide (6 h), then 2% homatropine (12 h), 1% cyclopentolate (12 h), 1% atropine (24 h), and longest for 0.25% hyoscine (96 h).
The time to reach maximum horizontal dilation of the pupil in treated eyes was shortest with 1% cyclopentolate (1 h), followed by 1% tropicamide (1.5 h), 0.25% hyoscine (3 h), 2% homatropine (3.5 h), and 1% atropine (4 h). The duration of horizontal pupil dilation was shortest with 1% tropicamide (4.5 h), and longest with 0.25% hyoscine (48 h).
CONCLUSION: All five mydriatics induced clinical dilation. Tropicamide (1%) had the shortest duration of effect, but gave incomplete dilation. Good dilation was achieved with 1% cyclopentolate and 2% homatropine, but took too long to reach maximum dilation for routine mydriasis. The largest vertical dilation of the pupil was achieved with 1% atropine and 0.25% hyoscine, but pupils remained dilated for more than 24 h.
CLINICAL RELEVANCE: For routine mydriasis in goats, it is recommended that 1% tropicamide be used, though there may be incomplete dilation. For a longer duration of mydriasis, such as in the treatment of anterior uveitis, 1% atropine or 0.25% hyoscine would be the drugs of choice.
Acknowledgements
The Institute of Veterinary, Animal and Biomedical Sciences, Massey University, Palmerston North, New Zealand, provided funding assistance. The authors would like to acknowledge Janine Buckleton-Reid of Alcon Laboratories, New Zealand, for provision of the mydriatic drugs; Drs Bill Pomroy, Ian Scott and Keith Thompson for access to the goats; Barbara Adlington and Anne Tunnicliffe for technical assistance and animal care; and Gabrielle Monteith of the Ontario Veterinary College for the statistical analysis.
Notes
*Non-peer-reviewed