Topical eye drops are fundamental to ophthalmic diagnostics and therapy, yet conventional delivery is inefficient because commercial droppers dispense volumes that exceed the retention capacity of the canine ocular surface. This randomized, prospective crossover study compared the pharmacodynamic effects of small-volume delivery using a Nanodropper adaptor versus conventional delivery in eight healthy dogs. In three separate experimental sessions, one randomly selected eye received a single small-volume drop via the adaptor, while the fellow eye received a standard-volume drop of 0.5% tropicamide, 0.005% latanoprost, or 1% brinzolamide-0.5% timolol. Pupil diameter (PD) and intraocular pressure (IOP) were measured at baseline and at predetermined intervals for eight hours post-instillation. Mean dispensed volume was reduced by approximately 70% with the adaptor compared with standard bottles (8.6-11.8 µL vs. 27.7-38.2 µL; P<0.001). Following tropicamide administration, both delivery methods induced significant mydriasis, with no between-group differences at individual time points (P=0.486) and only a small reduction in overall PD exposure with microdrops. Latanoprost induced rapid, marked miosis and significant IOP lowering in both groups (P≤0.037); however, small-volume delivery resulted in a slightly shorter duration of miosis, with larger PD values between five and eight hours (P≤0.041), while maintaining equivalent IOP control (P=0.278). Brinzolamide-timolol produced comparable miosis and IOP reduction with both delivery methods, without significant differences in PD or IOP over time (P≥0.067). Small-volume delivery preserved clinically relevant pharmacodynamic effects across pharmacologic classes in dogs. These findings support more rational, volume-conscious dosing in dogs, potentially minimizing both local and systemic drug toxicity without compromising clinical efficacy.
Fruchter et al. (Fri,) studied this question.